Diurnal Patterns and Microclimatological Controls on Stomatal Conductance and Transpiration at    High Creek Fen, Park Cou...
This Master Thesis has been defended before the following committee:                                    ii
AcknowledgementsThis research was funded in part by The Nature Conservancy. Additional    support was granted by the Germa...
TABLE OF CONTENTSSIGNATURE PAGE........................................................................... iiACKNOWLEDGEME...
2.4.     AGROMETEOROLOGY AND CROPS……………...... 212.5.     RECENT PUBLICATIONS…………………………....... 262.5.1.   JOHN L. MONTEITH…...
CHAPTER 4. METHODS4.1.              INTRODUCTION……..........……………………………. 654.2.              ON-SITE CLIMATE STATION………………...
LIST OF TABLESTable 5.1. Minima, maxima, and means of transpiration [E] in mmolm-2 s–1 and stomatal conductance [g] in mol...
LIST OF FIGURESFigure 3.1. Map shows the northwestern part of the Garoquadrangle topographic map; the study site located n...
Figure 5.3.b. Leaf temperature [TL] of S. monticola and quantumflux [Q] measured at a leaf of 70 cm height.Figure 5.3.c. L...
Figure 5.9. Stomatal conductance [g] in dependence upon leaftemperature [TL] of all six species investigated at High Creek...
Figure 5.15. Transpiration [E] and stomatal conductance [g] fromSalix candida on DOY 191; compared to the previously seen ...
LIST OF PHOTOGRAPHSTitle page         Sunrise over High Creek Fen in Summer 2001.Photograph 3.1. Cumulus Cloud over High C...
LIST OF SYMBOLSSymbol   Definition                        UnitsD        Atmospheric Water Vapor Deficit   kPaE        Tran...
CHAPTER 1. INTRODUCTION1.1.   OBJECTIVES OF THIS RESEARCH       While broad-scale climates of the Earth‘s major vegetative...
water vapor to the atmosphere. Results from measuring and modelingthe E over such surfaces can aid researchers in improvi...
variables on stomatal conductance [g]. First, g and E rates from oneindividual of Salix monticola at three different heigh...
1.2.   THE SCALE OF THE DISCIPLINE       This research defines the microenvironment as the area thatsurrounds an animate o...
1.3.   EVAPORATION AND EVAPOTRANSPIRATION       Evaporation and, in the presence of transpiring plants,evapotranspiration ...
leaves of plants over the past 1000 years is evidence that plants aregetting more efficient at photosynthesis as atmospher...
necessary to acquire information about the hydrogeological features ofthe ground beneath it. The potential amount of water...
saturation vapor pressure deficit [D], may lower the rate of transpiration.                                 8
CHAPTER 2. LITERATURE2.1.   LITERATURE REVIEW OF EARLY WORKS       Questions that explore the role of evapotranspiration i...
themselves with energy fluxes (e.g., Blanken and Rouse 1994, Burba etal. 1999, Takagi 1998). Such values tell a knowledgea...
restricted to [considering processes] after thorough wetting of the soilby rain or irrigation, when soil type, crop type a...
circling its prey (i.e. the research question). It is a slow, yet useful wayof approaching the solution to a hypothesis.  ...
velocity, and switch between inches per month and mm/day forevaporation, but fortunately the scientific community today is...
of its omnipresence on Earth, bioclimatology‘s ―scope is tremendous‖.The authors see the field in its early stage, where ―...
for a plant to reach maturity. The index was acquired by summing thedegrees of mean daily air temperatures during certain ...
Thornthwaite and Mather (1953) develop a list of concerns aboutthe current needs of the field of bioclimatology, and later...
proven very successful. This success could be attributed to the firstecological principle, that all things are interrelate...
value is ―independent of soil type, kind of crop, or mode of cultivationand is, thus, a function of climate alone.‖       ...
with their surrounding climatic situations. Incentives to tackle thecomplexity of these relationships have been given by t...
altitudes, predictability of asthma attacks, and the influence ofmeteorological fronts on the general wellness of people. ...
rhythm and that rhythm may then modify the response in eitherdirection.       This little excursion proves quite interesti...
maximize crop yield has primarily been researched in those areas,where dry conditions called for water resource management...
moisture patterns down to four feet depth. Detailed observations,including height and age of trees, root development and t...
differentiation of the terrain, whereas the microclimate comprises areaswhich are far too small.‖ 2 One can only guess, fo...
soil temperature and humidity, and wind intensity values, to come to theconclusion that the phytoclimate must be considere...
forest strip every 500 meters. However, he does not go into potentialsoil water competition between trees and crops.2.5.  ...
importance of considering the distribution of sources and sinks of heat,mass, and momentum in the canopy, mechanisms that ...
the environment, the state of the plant, and the nature of the relevantphysical and physiological mechanisms.‖ Monteith ex...
essentials: development of instruments and recording systems,interpretation of measurements, construction of mathematical ...
covariance technique that simultaneously measures large-scale fluxesof certain entities, e.g. CO2 concentration and vertic...
approach deems especially interesting, since the loss of wetlands dueto development has been rapid. While many states have...
different times throughout the growing season and to assess generalpatterns of leaf area index (LAI) over a "nearly comple...
the fen habitat. With such a significant change in the water balance offens like this, the decrease in species richness is...
research should be placed. In 1969s "Geography and Public Policy",Gilbert White emphasized the importance of "translating ...
goals, engaging all sources of creativity. Heres to Gilbert White: "Wemust work with all our heart and mind".             ...
CHAPTER 3. BACKGROUND3.1. INTRODUCTION    The role of E in the water and energy balance of high latitudewetlands is well ...
to satisfy their physiological demands at such sites. Plant diversity ofsuch areas is often remarkable; therefore, varying...
of this knowledge gap, and lays the groundwork for the formation ofsuccessful management strategies to be implemented by T...
leaf area (Monson 2000). Increased density of chlorophyll pigments,roughly translatable into the ―greenness‖ of the leaf, ...
for C3 plants usually range between 30 and 40 C, but plants can alsoalter their optimum to match their typical environmen...
Energy at the surface can be expressed in Watts per square meter(W m-2), or in micromol per square meter per second (mol ...
atmospheric water vapor deficit [D]. D exerts another strong controlover plant transpiration. As stated above, water vapor...
at the surface. Hence, the large E above the fen is combined with dryair (D max = 5 kPa).       Due to physiological cons...
minimum  of 93 %, which is to be considered saturated soil. Incontrast, investigating soil moisture control in non-satura...
3.3. STUDY SITE DESCRIPTION       In the following paragraphs, the research site is described frompersonal observation and...
Geologically, (visible from a geologic map of the area) HighCreek Fen is underlain by easterly dipping Cambrian throughPen...
layer, or (2) ground water is recharged from one formation only, (e.g., alayer of shale forms an aquifer) topped again by ...
values between 8% outside the fen and 60% within the fen with soiltexture ranging from clay to silt with varying organic m...
60                                           Tow er                                50 Volumetric Soil Moisture [%]        ...
Photograph 3.2. View across the fen from NW (transect survey pole) toSE shows approximate transect location; the location ...
bison, elk and antelope (Brand and Carpenter 1999). Apart from theabove, High Creek Fen has remained undeveloped and large...
Reservoir and Fairplay was measured to be 234 mm and 352 mmrespectively (Brand and Carpenter 1999). Those long-term record...
Maximum D was measured by the porometer over S. monticola at 5kPa with a TL = 36 C and Q = 1800 mol m-2 s-1 and  = 40 %...
Wetland habitats include hummock communities, meadowcommunities, spring fen communities, and a sodic flat community(Cooper...
Photograph 3.3.     Dense ground-cover of willow, birch, and sedge atHigh Creek Fen, Summer 2001. Blue spruce in the backg...
The research sites were chosen to control for , plant compositionand accessibility. Measurements of leaf conductance, tra...
Photograph 3.4. Betula glandulosa (Swamp Birch) in a drier locationat High Creek Fen, Summer 2001. This species occurs in ...
Photograph 3.5. Close view of the thick, dark-green leaves of Salixcandida (silver willow). Although not measured, leaf ap...
willow of the South Park region (Sanderson, pers. comm. 2001), andcomparing its environmental constraints with those of th...
3.5.   STUDY HYPOTHESES       The research presented here investigates interactions of theenvironmental factors explained ...
3.5.1. PROBLEM STATEMENT 1: DOES HEIGHT ABOVE GROUNDINFLUENCE PHYSIOLOGICAL RESPONSES WITHIN ANINDIVIDUAL SPECIES?       S...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
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Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
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Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
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Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County,...
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Diurnal Patterns and Microclimatological Controls on Stomata Conductance and Transpiration at High Creek Fen, Park County, Colorado.

  1. 1. Diurnal Patterns and Microclimatological Controls on Stomatal Conductance and Transpiration at High Creek Fen, Park County, Colorado. Heide Maria Baden, Department of Geography, University of Colorado, Boulder.
  2. 2. This Master Thesis has been defended before the following committee: ii
  3. 3. AcknowledgementsThis research was funded in part by The Nature Conservancy. Additional support was granted by the Germanistic Society of America and the Graduate School of this University. I thank Terri Schulz of The NatureConservancy for her support in the field and on the defense committee. I especially thank Peter Blanken for outstanding and persistent advice. Ifurther thank Karen Weingarten, our graduate secretary for immeasurable patience and support. Last but not least I thank my parents for their everlasting love. Fuer die Regenbogenkinder iii
  4. 4. TABLE OF CONTENTSSIGNATURE PAGE........................................................................... iiACKNOWLEDGEMENTS AND DEDICATION.............................. iiiTABLE OF CONTENTS.................................................................... ivLIST OF TABLES.............................................................................. viiLIST OF FIGURES............................................................................ viiiLIST OF PHOTOGRAPHS................................................................ xiiLIST OF SYMBOLS........................................................................... xiii CHAPTER 1. INTRODUCTION1.1. OBJECTIVES OF THIS RESEARCH……………......... 11.2. THE SCALE OF THE DISCIPLINE………………......... 41.3. EVAPORATION AND EVAPOTRANSPIRATION......... 5 CHAPTER 2. LITERATURE REVIEW2.1. LITERATURE REVIEW OF EARLY WORKS..……...... 92.1.1. I.S. BOWEN AND THE BOWEN RATIO…………........ 92.1.2. H.L. PENMAN AND POTENTIAL EVAPORATION…. 102.1.3. C. WARREN THORNTHWAITE ……………………… 132.2. THE FIELDS OF AGRO-AND BIOMETEOROLOGY.. 182.3. BIOCLIMATOLOGY AND HUMAN HEALTH……….... 19 iv
  5. 5. 2.4. AGROMETEOROLOGY AND CROPS……………...... 212.5. RECENT PUBLICATIONS…………………………....... 262.5.1. JOHN L. MONTEITH…………………………………..... 262.5.2. BIOMETEOROLOGICAL MODELING……………….... 292.6. CONCLUSION………………………………..………….. 33 CHAPTER 3. BACKGROUND3.1. INTRODUCTION…………..…………………………….. 363.2. PHOTOSYNTHESIS AND ENERGY BALANCE ..…... 383.3. STUDY SITE DESCRIPTION ………………………….. 453.3.1. TOPOGRAPHY, HYDROGEOLOGY, AND HISTORY………………………………………………..... 453.3.2. CLIMATE AND ENERGY BALANCE AT HIGH CREEK FEN……..………………………………... 513.3.3. VEGETATION AT HIGH CREEK FEN……………….... 533.4. THE FOUR SITES AND THEIR INHABITANTS…….... 553.5. STUDY HYPOTHESES……......................................... 603.5.1. PROBLEM STATEMENT 1: DOES HEIGHT ABOVE GROUND INFLUENCE PHYSIOLOGICAL RESPONSES WITHIN AN INDIVIDUAL SPECIES?.... 613.5.2. PROBLEM STATEMENT 2: DOES SOIL MOISTURE CONTROL RATES OF STOMATAL CONDUCTANCE AND TRANSPIRATION FROM SAME SPECIES IN DIFFERING LOCATIONS?........................................... 623.5.3. PROBLEM STATEMENT 3: WHEN EXPOSED TO THE SAME MICROCLIMATE, DO DIFFERENT SPECIES VARY IN STOMATAL CONDUCTANCE AND TRANSPIRATION?....................................................... 63 v
  6. 6. CHAPTER 4. METHODS4.1. INTRODUCTION……..........……………………………. 654.2. ON-SITE CLIMATE STATION………………………...... 654. 3. METHODS OF DATA COLLECTION AT THE FOUR SITES.......................…………………………………….. 674.4. THE DATA SET………………………………………….. 714.4.1. DATA SET PREPARATION…………………………….. 74 CHAPTER 5. RESULTS5.1. INTRODUCTION……………………………………....... 775.2. METEOROLOGICAL DATA OBSERVED BY THE TOWER……………………………………….... 775.3. RESULTS FOR PROBLEM STATEMENT 1………….. 785.4.1. RESULTS FOR PROBLEM STATEMENT 2.a……….. 905.4.2. RESULTS FOR PROBLEM STATEMENT 2.b……….1015.5. RESULTS FOR PROBLEM STATEMENT 3………....105 CHAPTER 6. DISCUSSION.....................................131 CHAPTER 7. CONCLUSION.....................................137REFERENCES.................................................................................142APPENDIX A....................................................................................147APPENDIX B....................................................................................148 vi
  7. 7. LIST OF TABLESTable 5.1. Minima, maxima, and means of transpiration [E] in mmolm-2 s–1 and stomatal conductance [g] in mol m-2 s–1 for S. monticola atz = 40, 70, 100 cm.Table 5.2. Transpiration [E] measured from three distinct heights ofS. monticola measured on DOY 188 (July 7th), 2001 expressed inmmol m-2 h–1 and g H2O m-2 h-1.Table 5.3. Minima, maxima, means, and standard deviations of  inthe wet [ (w)] and dry [ (d)] location. Ranges were 8 and 6% for thewet and dry location, respectively.Table 5.4. Comparing the means of transpiration [E] and stomatalconductance [g] for the two populations (d) and (w) via a pairedsamples t-test, results show paired samples correlations for E and g ofS.candida in dry and wet location as highly significant.Table 5.5. Comparing paired samples differences of transpiration[E] and stomatal conductance [g] show a higher predictability of thedifferences in g (80.2 % confidence) than differences in E (35 %confidence).Table 5.6.a. Transpiration [E], expressed in mmol m-2 h-1 and g m-2h-1, on DOY 174 (June 23rd), 2001, from S. candida (d) in soil moisture[ ] ~45 % and S. candida (w) in  ~50 %.Table 5.6.b. Transpiration in the wet location [E (w)] exceedstranspiration in the dry location [E (d)] by 30.0 %. Hence, S.candida(w) in  ~50% transpired one third more than S.candida (d) in  ~45%.Table 5.7 Transpiration [E] from all six species on DOY 191 (July10th), 2001 expressed in mmol and grams H2O m-2 s-1 as well as h-1.Fluxes are listed in decreasing order from top to bottom.Table 5.8. Mean daily stomatal conductance [g] from all six specieson DOY 191 (July 10th), 2001 expressed in mol m-2 s-1 as well as h-1. vii
  8. 8. LIST OF FIGURESFigure 3.1. Map shows the northwestern part of the Garoquadrangle topographic map; the study site located near High Creekis circled; the Colorado index map shows the location of Park County.Figure 3.2. Soil moisture transect from southeast (0) to northwest(1000 m) taken across the fen on July 1st, 2001. With distanceincrements of 33 m, 31 data points were recorded. Low  valuesrepresent areas outside the fen.Figure 4.1. Wetting and Drying Curve of 1500 cm3 High Creek FenSoil determined in the laboratory. Wetting: 20x75 ml of H2O wereadded to the oven-dried soil in increments of 5 minutes; through thisprocess, actual soil moisture was continuously increased by 5 %, andHydroSense delay times were recorded. Drying: soil was repeatedlyplaced in oven, weighed, and delay times were recorded, until nofurther weight was lost. The following fit was created for all datapoints:  = - 55.36 + 62.74 ms +13.97 ms2.Figure 4.2. HydroSense Calibration Curve from both wetting anddrying curve data; to view the fit from this new calibration, this figureshows how the originally reported delay time increasinglyoverestimates increasing actual volumetric water content [ ] by afactor of up to 2 at saturation.Figure 5.1. Vapor pressure deficit [VPD] and air temperature [TA] asobserved by the tower for DOY 188 as decimal time, where 188 =00:00:00 hours on July 7th, and 188.5 = noon. Graph shows that VPDis a function of TA.Figure 5.2.a. Stomatal conductance [g] for S. monticola from leavesat heights of z = 40 cm, z = 70 cm, and z = 100 cm.Figure 5.2.b. Transpiration [E] and from leaves of S. monticola atheights of z = 40, z = 70, and z = 100 cm.Figure 5.3.a. Leaf temperature [TL] of S.monticola and quantum flux[Q] measured at a leaf at 40 cm height show that the plant’s TL doesnot react to Q. Also, compared to the incident radiation at z = 100,this height of z = 40 catches a larger amount more quickly in themorning (e.g., from 06:30 until 07:00, the leaf receives 100 to 850mol m-2 s-1). viii
  9. 9. Figure 5.3.b. Leaf temperature [TL] of S. monticola and quantumflux [Q] measured at a leaf of 70 cm height.Figure 5.3.c. Leaf temperature [TL] of S. monticola and quantumflux [Q] measured at a leaf located at 100 cm tree height. Comparedto the other heights, this part of the plant reacts with TL mostaggressively to a change in Q.Figure 5.4.a. Regression of transpiration rates (E) of S. candida inthe dry location against E from S. candida in the wet location as mmolH2O transpired m-2 s-1.Figure 5.4. b. Regression of stomatal conductances (g) of S.candida in the dry location against g of S. candida in the wet locationexpressed as molar flux through stomatal magnitude m -2 s-1.Figure 5.5.a. Transpiration [E] for S. candida on DOY 174 in a dry(d) and wet (w) location show a visible, although not statisticallysignificant difference in mmol of E released m-2 s-1 throughout the day;the mid-day data gap is due to temporary system failure.Figure 5.5.b. Stomatal conductance [g] for S.candida in the dry (d)and wet (w) location again show a visible, however, not statisticallysignificant difference in the flux of mol m –2 s-1 of g on DOY 174(summer solstice).Figure 5.6. The scatter plot shows mean daily transpiration [E] independence upon soil moisture []. Plant locations 1 – 3 weregrouped as the drier locations, 4 – 6 as the mesic, and 7 – 9 as thewet, close to saturated locations. E from case 3 with av = 20.8 % didnot differ from the average E values produced by cases 7 and 9.Figure 5.7. The scatter plot shows mean daily stomatalconductance [g] in dependence upon soil moisture []. Again, cases 1– 3 were grouped as the drier locations, 4 – 6 as the mesic, and 7 – 9as the wet, close to saturated locations.Figure 5.8. Stomatal conductance [g] plotted against quantum flux[Q] for all six species investigated at High Creek Fen. Data may becompared with general statements made about C3 plants in Nobel(1999). ix
  10. 10. Figure 5.9. Stomatal conductance [g] in dependence upon leaftemperature [TL] of all six species investigated at High Creek Fen. Datamay be compared with general statements made about C3 plants in Nobel(1999), where photosynthetic rate doubles between 20 and 30 C, andmaximizes between 30 and 40 C.Figure 5.10. Stomatal conductance [g] as controlled by vaporpressure deficit [D] surrounding all six plant species investigated atHigh Creek Fen. Usually, g can be expected to decreaseexponentially with increasing D. Since D is highly correlated with TL,most data points are expected to fall into the same quadrant from boththis, and the previous figure (5.11.).Figure 5.11. Stomatal conductance[g] regressed with soil moisture[] measured in the separate locations of the six plants researched inthe fen; this graph should not be interpreted as revealing soil moisturetolerance ranges – respective plants may grow in areas notrepresented here. However, all  spectra of B. glandulosa as well asmost  spectra of S. candida should be found in this graph; theresearcher searched the fen for locations of these species thatencompassed the complete  range in this fen. Generally, all plantunderlying soils were saturated between 50 and 55 %.Figure 5.12. Transpiration [E] and stomatal conductance [g] fromBetula glandulosa on DOY 191 (July 10th), 2001. This speciesreaches gmax around 10:00 a.m., and then gradually decreases g overthe afternoon, when TL and D become limiting. As seen from Table5.7., B. glandulosa ranks highest in E compared to the other fivespecies.Figure 5.13. Transpiration [E] and stomatal conductance [g] fromCarex aquatilis on DOY 191; here, mid-day stomatal depressioneffecting necessary reduction of the quantity of water vapor demandby the atmosphere is evident. Compared to gmax from B. glandulosaand S. brachycarpa, gmax from C. aquatilis is a third, and half as largeas that of S. monticola. S. candida exceeds it by a factor of 2.5.Figure 5.14. Transpiration [E] and stomatal conductance [g] fromSalix brachycarpa on DOY 191. Again, mid-day stomatal depressionto reduce water stress is evident. Morning conductance allows thisspecies to still rank third in E compared to the other five species. x
  11. 11. Figure 5.15. Transpiration [E] and stomatal conductance [g] fromSalix candida on DOY 191; compared to the previously seen (5.12 –5.14) flux developments over time, the silver willow shows a highmorning, toward evening gradually decreasing g. Nevertheless, mid-day stomatal depression is visible, as well as a second depressionstarting after 14 hours solar time (15:10 MDT), when the towershowed a solar flux of 1008 W m-2. Stomatal conductance increasedafter 15 hours (16:10 MDT), when intensity of radiation dropped again.Figure 5.16. Transpiration [E] and Stomatal conductance [g] fromSalix monticola on DOY 191. As also seen from Table 5.7., thisspecies seems best adapted to its environment, since it has thestrongest E of all compared plants. Clouds were over the area whenthe steep drop in stomatal conductance occurred around 13:30 hourssolar time. Possible explanation for the drop in g may be a TL of 32.8C at this time, which may have caused the partial stomatal closure.Figure 5.17. Transpiration [E] and Stomatal conductance [g] fromSalix planifolia on DOY 191 show the typical behavior of anunstressed plant with no mid-day stomatal depression. Ranking 5th inE and g (Tab. 5.7.) might allow a stress-free life in this environment.Figure 5.18. Stomatal conductance [g] from B. glandulosa, S.candida, C. aquatilis, S. monticola, S. brachycarpa, and S. planifoliaon DOY 191. On this daily basis, C. aquatilis conducted least, S.monticola most. See Tables 5.7. and 5.8. for numeric details.Figure 5.19. Transpiration [E] from B. glandulosa, S. candida, C.aquatilis, S. monticola, S. brachycarpa, and S. planifolia on DOY 191.On this daily basis, S. planifolia conducted least, B. glandulosa mostamounts of H2O. S. planifolia was also the least stressed (no mid-daystomatal depression). See Table 5.7. and 5.8. for numeric details. xi
  12. 12. LIST OF PHOTOGRAPHSTitle page Sunrise over High Creek Fen in Summer 2001.Photograph 3.1. Cumulus Cloud over High Creek Fen (view to NE)in Summer 2001.Photograph 3.2. View across the fen from NW (transect surveypole) to SE shows approximate transect location; the location of themeteorological tower is included on transect.Photograph 3.3. Dense ground-cover of willow, birch, and sedge atHigh Creek Fen, Summer 2001. Blue Spruce in the backgroundgreatly influence turbulence at the site.Photograph 3.4. Betula glandulosa (Swamp Birch) in a drier locationat High Creek Fen. Summer 2001. This species occurs in a range oflocations where 15 % <  < 60 %.Photograph 3.5. Close view of the thick, dark-green leaves of Salixcandida (Silver Willow). Although not measured, S.candida’sphysiology suggests multi-storied, dense chlorophyll pigmentation.Photograph 3.6. Salix monticolaPhotograph 3.7. Salix brachycarpaPhotograph 4.1. On-site climate station in Summer 2001Photograph 4.2. Porometer measurements by Researcher; machinestrapped on via belt, storage module attached to belt on the back,cuvette in right hand.Photograph 7.1. High Creek Fen looking west toward the MosquitoRange. xii
  13. 13. LIST OF SYMBOLSSymbol Definition UnitsD Atmospheric Water Vapor Deficit kPaE Transpiration mmol m-2s-1g Stomatal conductance mol m-2s-1gmax Maximum stomatal conductance mol m-2s-1E Latent heat flux W m-2K Incoming shortwave radiation W m-2K Reflected shortwave radiation W m-2L Incoming longwave radiation W m-2L Reflected longwave radiation W m-2 Volumetric soil moisture %Q Quantum flux mol m-2s-1RH Relative humidity %Rn Net radiation W m-2TA Air temperature CTdew Dew point temperature CTL Leaf temperature CTS Soil temperature C xiii
  14. 14. CHAPTER 1. INTRODUCTION1.1. OBJECTIVES OF THIS RESEARCH While broad-scale climates of the Earth‘s major vegetativeregions have been well studied, a fine-scale investigation of localenvironments is required to understand the influence of bothatmosphere and soil on local vegetation dynamics. An area‘smicroclimate often distinguishes itself from the regional climate bypeculiarities such as soil texture, topography, or biomass (Rouse 2000).As functions of microclimate, water and solar energy are among themain lifelines for plants, and their abundance and availability aretherefore a question of precise locality. Assessing the sensitivity ofplants from different regions to soil moisture and microclimate allowsresearchers to establish a gauge for these plants‘ susceptibility todisturbances such as drainage and climate change. Net all-wave radiation and its partitioned sensible andevaporative heat flux are extremely important components of both theenergy and water balances of an area, especially those of high- latitudeand alpine wetlands, which partition up to 80% of their net radiation intothe evaporative, or latent heat flux [E] (Rouse 2000). Plants thatinhabit these areas therefore constitute a considerable local source of
  15. 15. water vapor to the atmosphere. Results from measuring and modelingthe E over such surfaces can aid researchers in improving currentclimate models (Beringer et al. 2001). This research focuses on fine-scale exchange of both water andenergy between the soil, the plant, and the atmosphere in a 750-acrefen in central Colorado. In particular, the combined effects of theatmospheric vapor pressure deficit, solar energy flux, leaf temperature,and soil moisture availability on plant stomatal conductance andtranspiration of water vapor during the photosynthetically active part ofthe day were examined. While a complete list of resources controllingplant physiological responses includes N and CO2 (Kazda 1995), thisresearch investigates water and energy resources. Understanding theirrole, their spatial and temporal distribution at certain locations, and theiravailability and use in relationship to particular plant species was thegoal of this research. Salicaceae (willow), Betulaceae (birch), and Cyperaceae(sedges) are typical examples of wetland species of the arctic, alpine,and boreal tundra regions. As meteorological and soil moistureconditions exert limitations and affect the magnitude of planttranspiration [E], this research focused on analyzing the effect ofvariation in the spatial and temporal magnitudes of these environmental 2
  16. 16. variables on stomatal conductance [g]. First, g and E rates from oneindividual of Salix monticola at three different heights (40 cm, 70 cm,and 100 cm above ground) were compared. This was to assesswhether there was a significant difference in the magnitudes in g andthe plant‘s stomatal responses at different heights. Second, g and E oftwo specimens of Salix candida situated in a dry (40-45 % volumetricsoil moisture,  ) and a wet (50-55 %) location were compared. Third, gand E of nine Betula glandulosa situated in dry (with an average  of18 %), mesic (35 %), and wet (51 %) locations were compared. Parttwo and three of the study analyzed this soil moisture variability towhich plants in different microclimatological locations were exposed,and evaluated intraspecific variation in g and E based upon soilmoisture abundance. Lasty, differences in g and E between sixdifferent species exposed to the same environmental conditions wereexamined. Species included were Salix monticola, S. brachycarpa, S.planifolia, S. candida, Carex aquatilis and Betula glandulosa. Thisfourth part of the study determined whether different species havediffering adaptations to the same microclimatological conditions.Results of all four studies enhanced the understanding of localvegetation dynamics in this high altitude wetland. 3
  17. 17. 1.2. THE SCALE OF THE DISCIPLINE This research defines the microenvironment as the area thatsurrounds an animate object, e.g. a plant, an animal, or a human being.The scale beyond which neither the object, nor its environment have adirect or indirect influence on each other shall be the limit to the microscale. Micrometeorology concerns itself with the processes that occurwithin or closely above the atmospheric boundary layer, beyond whichthe Earth‘s surface has little influence on the atmospheric processes.The height of the boundary layer varies constantly with wind andtemperature. On a calm day with a large sensible heat flux, the heightof the boundary layer reaches its maximum. Correspondingly, ―areasexperiencing greater wind speeds tend to have shorter vegetation, suchas cushion plants in alpine tundra or the procumbent forms on coastaldunes‖ (Nobel 1999). Inside the atmospheric boundary layer, turbulent(wind-driven) transport is the predominant motion of the gas moleculesthat make up the air. This research investigates the lower boundary ofthe atmospheric boundary layer ending where the plant roots do notreach any further. This soil-plant-atmosphere is the region of directhydrogeologic influence on the plant and its atmospheric environment.However, potential upwelling of water from even deeper regions in theground must be considered. 4
  18. 18. 1.3. EVAPORATION AND EVAPOTRANSPIRATION Evaporation and, in the presence of transpiring plants,evapotranspiration are of the few basic climatic factors that scientistsare neither able to estimate easily, nor extrapolate from remotelysensed data. They are important variables, because their values areneeded to assess the water, and the energy budget of all organisms. Measurements taken on the ground are highly dependent onnumerous physical factors that include temperature, radiation, humidity,soil moisture, and ground heat flux. As a mandatory agent to thephotosynthetic process, water is needed to dissolve carbon and keepleaf surfaces cool. If a plant‘s water supply is at its end, i.e. the rootscannot draw up any more water from the ground, the plant will dry upcompletely. Plants have evolved physiological features to acclimatethemselves to their microclimate, and the physiology and phenology ofa plant tell a lot about the climate of the area. As Lieth (1997) mentions in his abstract on phenologicalmonitoring, the "data on vegetation development provided by thephenologists during the last two centuries are about the most reliableinformation available for the evaluation of global trends ofenvironmental parameters." As an example of this, Blanken(pers.comm. 2000) stated that the decrease in stomatal density on the 5
  19. 19. leaves of plants over the past 1000 years is evidence that plants aregetting more efficient at photosynthesis as atmospheric CO2concentrations have increased. Evaporation has been and still is especially important in aridclimates such as the Southwestern United States, where this study hasbeen conducted. Here, the water supply for E depends on the relativelysmall amount of precipitation that is received (often in the form of snow)as well as underground aquifers that occasionally allow their water tosurface in streams. In these arid regions, the usually dry air constantlydemands water vapor from the surface of the earth, and its inhabitants. Stream and ground water flow may be an important contributorto the water supply of vegetated surfaces. As in the case of High CreekFen in Park County, Colorado, evapotranspiration exceeds precipitationby a factor of 3 (Blanken, pers. comm. 2002). This fact ponders thequestion where the additional water may be added to the system. Thehydrogeological processes seem to provide moisture to themicroenvironment through lateral in- and outputs of water from surfaceand subsurface flow systems, such as those Rouse (1998) observed insimilar ecosystems. This goes to show that evaporation is not at allstrictly a function of infiltrated water just through precipitation. Toexplain the amount of water evaporated by a surface, it is therefore 6
  20. 20. necessary to acquire information about the hydrogeological features ofthe ground beneath it. The potential amount of water available to theplants at High Creek Fen is yet to be estimated through local research. The prime factor that drives evapotranspiration, radiation, mustbe investigated. Incident solar radiation is measured at the site by apermanently installed pyranometer. If a cloud passes over the area, theincident radiation is diminished, leading to several feedback processes,which will be discussed in the later sections. The second factor thataccounts for the amount of E, the saturation vapor pressure deficit ofthe air, gives an estimate of the evaporative demand at the surface. The presence of plants on the surface greatly modifies theenergy balance and the partitioning between evaporation andtranspiration. Evaporation from the non-vegetated part of the surface,as well as the amount of water transpired by the plant [E] yieldevapotranspiration [E]. The plants‘ transpiration rates are influencedby the same physical factors as the rates of evaporation, however, theirneed to conserve water will induce stomatal resistances that lower therate of transpiration. Stomata are the physiological means of plants toregulate water loss and CO2 uptake throughout the photosyntheticprocess. Biochemical triggers like hormones regulate stomatalresistance, i.e. the partial closure of stomata, which, depending on the 7
  21. 21. saturation vapor pressure deficit [D], may lower the rate of transpiration. 8
  22. 22. CHAPTER 2. LITERATURE2.1. LITERATURE REVIEW OF EARLY WORKS Questions that explore the role of evapotranspiration in the waterbudget and bioclimate have quite a long history, as well as an extendedfield of origin. Scientific articles can be found since before the turn ofthe 20th century, many of the early ones published in the U.S.Department of Agriculture Bulletin; many articles on evaporation andevapotranspiration came from several different scientific fields,including physics and meteorology, agro-ecology, as well as hydrology,soil science, botany and plant physiology. Having mentioned theinterconnectedness of micrometeorology to almost all physicalsciences, the first part of this chapter is focused on several earlierpublications that brought new thoughts and findings into the field.2.1.1. I. S. BOWEN AND THE BOWEN RATIO Bowen (1926) experimented with evaporation as a measurementof latent heat loss in comparison to sensible heat loss. With his paperon the Bowen Ratio, he introduced the ratio of the sensible heat flux [H]to E, which typically ranges from 0.1 for an irrigated crop to 5 fordesert environments. The Bowen Ratio when combined with theenergy balance, is used in a great number of papers that concern 9
  23. 23. themselves with energy fluxes (e.g., Blanken and Rouse 1994, Burba etal. 1999, Takagi 1998). Such values tell a knowledgeable climatologista lot about the place where it was measured, even if she has not beenthere personally – much like the morphology of a plant gives away thenature of its surrounding microclimate.2.1.2. H.L. PENMAN AND POTENTIAL EVAPORATION In 1947, the British meteorologist H.L. Penman modeledevaporation in his well-known paper titled ―Natural evaporation fromopen water, bare soil, and grass‖ published in the Proceedings of theRoyal Society of London, describing pan evaporation experiments, aswell as evaporation from soil and vegetation. His experiments onlylooked at potential evapotranspiration, i.e. from water-saturatedsurfaces. Although this did not account for stomatal conductance as aresistance to the magnitude of plant transpiration, he laid thegroundwork for the still widely used Penman-Monteith combinationequation which models E as controlled by plant physiologicalparameters. In his introduction, Penman states, that ―a complete survey ofevaporation from bare soil and transpiration from crops should take intoaccount all relevant factors [but that his current] account will be largely 10
  24. 24. restricted to [considering processes] after thorough wetting of the soilby rain or irrigation, when soil type, crop type and root range are of littleimportance.‖ Penman goes into the physical requirements for theoccurrence of evaporation, which are ―a supply of energy to provide thelatent heat of vaporization [i.e. solar radiation] and some mechanism forremoving the vapor, i.e. there must be a sink for vapor.‖ His argumentsconsider the laminar boundary layer in which non-turbulent, butdiffusive movement of air takes place. This is an important concept inthe aerodynamic considerations made when calculating fluxes at theleaf level. Penman‘s discussion on the energy balance introduces theimportant concept of assumptions. In bioclimatological modeling,assumptions must be made in order to translate the reality intomathematical formulae. While the assumption of horizontalhomogeneity, for example, works well for oceans and lakes, it is anassumption also made in most canopy flux models, so that x and ycoordinates are negligible, and all statistical moments (mean, variance,skewness, kurtosis) are forced into the vertical z coordinates. Oftenunrealistic to natural environments, assumptions allow scientists to ruleout possibilities by making reliable estimates, much like a predator 11
  25. 25. circling its prey (i.e. the research question). It is a slow, yet useful wayof approaching the solution to a hypothesis. The assumption Penman makes is that the factor of heat storageis negligible, a factor that indeed can be assumed zero formeasurements at the leaf level, however not at the canopy level(Monson 2000). Penman admits that ―obtaining a reliable daily meanvalue of the dew point temperature remains one of the mainexperimental problems to be solved‖—data that with nowadays‘technology is easily obtained (for example a chilled-mirror hygrometer).Penman gives a detailed description of the instruments used. However,to be meticulous about the description of the exact type or make of aninstrument, gives experienced micrometeorologists and other scientistsappropriate insight into potential errors of a measurement. It is alsomentioned that the accuracy of the cloudiness factor is a hard one toobtain. The reason may be that although pyranometers had beeninvented, measurements for 24 hours a day were taxing, whereasnowadays, data loggers take the place of a measurement-readingscientist (let‘s invent an automatic porometer). The article is a cornerstone work in micrometeorology. Itsterminology is still used in today‘s lectures. The use of units isconfusing to metric scale users, since they are miles per day for wind 12
  26. 26. velocity, and switch between inches per month and mm/day forevaporation, but fortunately the scientific community today is in theprocess of collectively changing to the (more sensible) metric system.2.1.3. C. WARREN THORNTHWAITE Thornthwaite incorporated evaporation into his global climateclassification model (1951). His quantitative method distinguishedaridity from humidity in climates of the Low-Latitudes, Mid-Latitudes,and High-Latitudes as a function of potential evaporation and soil-waterstorage capacity reflected in the plants‘ need for water, which generallyincreases from the poles toward the equator. His climate classificationis still used in geographic education. However, for themicroclimatologist, this kind of classification is of lesser interest. Moreimportant here were Thornthwaite‘s contributions to bioclimatology onthe micro scale. The following paragraphs will explore some thoughtsof Thornthwaite and his group of scientists at Johns Hopkins Universityin New Jersey. A monograph on bioclimatology, compiled in 1954 byThornthwaite, May, and Mather, consists of several articles on theeffects of the physical environment on life, including human issues likehealth and housing. In the book‘s preface, May points out that in light 13
  27. 27. of its omnipresence on Earth, bioclimatology‘s ―scope is tremendous‖.The authors see the field in its early stage, where ―various niches ofignorance will be filled as more […] data becomes available‖(Thornthwaite et al. 1954). According to May, and not surprisingly, thefirst man to concern himself with the field was the Greek Hippocrates.His work that May refers to is Airs, Waters, and Places, a treatise thatdeals with ―the action of climate on living things‖. Another interestingpart in the preface explains May‘s view on the variation of climate. ―Climates vary not only between the poles and the equator, between the level sea and the tops of the mountains, but between a hollow as big as the palm of one‘s hand in a field and a similar depression several feet away. All these variations occur according to natural laws, some of which man has discovered and learned to understand, some of which remain mysterious and represent the field of research for tomorrow.‖May describes the processes between climate and physicalenvironment, which are constantly modifying each other, as in ―a racetowards a state of equilibrium that will never be reached‖. From this same compilation, an article by Thornthwaite andMather (1953) titled ―Climate in Relation to Crops‖ gives interestinghistorical facts about the first developments of bioclimatology, includinginformation on the 17th century French scientist Réaumur, whodeveloped an index in 1735 that attempts to quantify the heat required 14
  28. 28. for a plant to reach maturity. The index was acquired by summing thedegrees of mean daily air temperatures during certain stages ofdevelopment of a plant. Réaumur called this sum the ―thermalconstant‖ for the particular plant (Thornthwaite et al.1954), based on hisobservations. Thornthwaite later explains how Réaumur was wrongsince ―his thermal constants were not constant,‖ but showed that oneplant in higher latitudes yielded a smaller constant than the same plantin lower latitudes. Thus, ―less heat was required in cold climates than inwarm to bring about a given amount of development‖ and a cold yearhad a smaller thermal constant than a warm year. Thornthwaite et al.conclude their paragraph about Réaumur‘s heat index that ―the manychanges and refinements that have been introduced in recent yearshave not removed the basic deficiencies of the heat unit theory.‖ Although this method did not render successful for cropscheduling, its theory seems quite interesting. Keeping in mind that itwas developed 265 years ago, the ideas show scientific ingenuity andexpertise. Also, its findings harmonize with the zonal idea of climaticregions, and with some climatic imagination, show May‘s idea that life ismodified by the environment, while at the same time the environment ismodified by life in a ―race for equilibrium‖. 15
  29. 29. Thornthwaite and Mather (1953) develop a list of concerns aboutthe current needs of the field of bioclimatology, and later describe theirmethod that stems from research with their group of bioclimatologists inNew Jersey. This approach will be outlined later. According to them,the needs of the discipline in 1953 were a collection of observationaldata, since the Federal Weather Service was obviously not able todeliver anything but regional data, thus giving information on―observations […] inadequate to the solution of most problems.‖ Theyargue ―the climate of a region as determined by means of thestandardized observations is more or less of an abstraction‖ and ―theregion is a composite of innumerable local climates‖ including ravines,south-facing slopes, hill tops, meadows, corn fields and woods. Theygo on to say that ―the climates of areas of very limited extent are calledmicroclimates. They are clearly the ones that concern the farmer, theagronomist and the biologist‖ (Thornthwaite et al. 1954). The authors point out the importance of approaching theproblems, of, e.g., the effects of frost, drought or extremely hightemperatures on plants, from both the climatological as well as thebiological side through the cooperation of scientists from the respectivegroups. This call for synthesis has, as far as I am concerned, beenincreasingly heard, maybe because most attempts at integration have 16
  30. 30. proven very successful. This success could be attributed to the firstecological principle, that all things are interrelated. As with synthesis, another suggestion from the authors is thedevelopment of a climatic calendar that organizes the observationaldata according to the relationship between climate and plants. Thedevelopment of such a device could help ―schedule successiveplantings of vegetable crop to yield uniform harvest.‖ The Laboratory ofClimatology at Seabrook devised a method to control soil moisture,targeting the ―twin problems of crop and irrigation scheduling.‖ Theirgoal was not to just observe peas and corn, but to devise a morecomprehensive method that links the ―water used by plants intranspiration and growth [to] the rate of plant development.‖ A well-developed discussion on the water budget of plants isgiven, that introduces the term evapotranspiration. The ―return flow ofwater from the ground to the atmosphere‖ is a ―climatic factor asimportant as precipitation‖ that is not only dependent on climate, butalso ―related to certain vegetation and soil factors [such as] type andstage of development of the vegetation, the method of cultivation, thesoil type, and above all the moisture content of the soil.‖ Thediscussion goes on to distinguish the actual from the potentialevapotranspiration; the latter is reached only in a well-hydrated soil. Its 17
  31. 31. value is ―independent of soil type, kind of crop, or mode of cultivationand is, thus, a function of climate alone.‖ The abstract explains further facts about plant processes. Thewording ―green plants manufacture food within their leaves by aprocess called photosynthesis, using water from the soil and carbondioxide from the air as raw materials‖ may bring a smile to today‘sreader‘s faces; it seems amazing that this article is not even 50 yearsold, yet goes to show that Thornthwaite can truly be counted as one ofthe forefathers of bioclimatology. It should seem viable that young, beginning scientists owe muchgratitude to people like Thornthwaite‘s group, who explain these earlydevelopments of bioclimatology with such patiently detailed vocabularyand well-chosen examples that make understanding of the subjecteasily possible. The words used are free of scientific vanity and theirsole purpose is straightforward communication.2.2. THE FIELDS OF AGRO--AND BIOMETEOROLOGY Agro- and biometeorology have made it their goal to elucidatethe relationships between organisms and their physical environment.Both fields take the science of pure micrometeorology a step further, astheir questions concern themselves with the interactions of life forms 18
  32. 32. with their surrounding climatic situations. Incentives to tackle thecomplexity of these relationships have been given by the potentialadvantages of understanding these interactions, from maximizing theyield of a crop to healing human diseases. The first issue of the International Journal of Bioclimatology andBiometeorology (this name later changed to International Journal ofBioclimatology) was published in 1957. It featured four parts. Oneconcerned general bioclimatology, the second dealt with plant –microclimate interactions. The third and fourth parts explored effects ofclimate on animals and humans. The plant-related topics include apaper on the influence of soil preparation on the microclimate of weedyclear-cut fields before reforestation. Also, topics discussed guidelinesfor bioclimatological measurements and whether microclimate can bepredicted (Pascale 1957).2.3. BIOCLIMATOLOGY AND HUMAN HEALTH The fourth section in the first edition of the above journal showsthat early concerns of bioclimatology stemmed not only from agriculturalincentives, but also from questions regarding climates direct effects onhuman beings. Those questions were, for example, acclimation to high 19
  33. 33. altitudes, predictability of asthma attacks, and the influence ofmeteorological fronts on the general wellness of people. Just one year later, in 1958, the medicinal journal Fundamentabalneo-bioklimatologica was established, which deals with theatmospheric influences on living organisms. According to Jordan(1981), balneo-bioclimatology is both a subsection of bioclimatologyand balneology, i.e. therapy through baths, and it stands for appliedtherapy through climate. I cite Jordan here not to go into detail aboutbalneo-bioclimatology, but because his thoughts are a valuablecontribution to understanding the development of bioclimatology. Hebegins by citing Alexander von Humboldts definition of climate as "allchanges in the atmosphere that noticeably affect our organs," therebyspeaking of the dialectic system of humans and their physicalsurroundings. Jordan goes on to explain the difference betweenlooking at stimulus and response versus stimulus and responsibility.Stimulibility, or the readiness to be stimulated by outside processes,modifies the reaction, and therefore the responsibility of an organism.Changes occur along rhythmic or periodic processes. Jordan shares afurther thought by proposing that reactions can initiate either positive ornegative feedback mechanisms, since the stimulus may modify one 20
  34. 34. rhythm and that rhythm may then modify the response in eitherdirection. This little excursion proves quite interesting, especially whenrelating it to the mass and energy balances of vegetated surfaces. Ona sunny day, the balance of energy loss and gain at the surface can bedisturbed by the passage of a thick cloud. This occurs because thecloud intercepts the path of the radiation, which again results in a netheat loss at the surface of the earth. The now cooling surface willdiminish the water vapor concentration gradient between the surfaceand the air (warmer air can hold more moisture), as well as cause alower temperature gradient, the results being less evapotranspirationand a lower rate of sensible heat transfer. When the new gradientshave caused their respective responses to be adjusted, a new energybalance has been established (Monson 2000).2.4. AGROMETEOROLOGY AND CROPS After this intermezzo of how bioclimatology affects humansdirectly, this part of the chapter offers to look at literature that deals withthe climates effects on human food, i.e. crops as an indirect relation tohumans. As mentioned above, evaporation and evapotranspiration arevery important processes especially in arid regions. Irrigation to 21
  35. 35. maximize crop yield has primarily been researched in those areas,where dry conditions called for water resource management. Duringthe 1930s (in the late 1940s together with Criddle), Blaney researchedevaporation as well as evapotranspiration especially in theSouthwestern U.S. Their work, published primarily through the U.S.Soil Conservation Service, developed ways of estimating ―consumptiveuse and irrigation water requirements (Blaney and Criddle 1949).‖ Anumber of other scientists also explored optimized timing of irrigation(Van Bavel and Wilson 1952) in the pursuit of water resourceconservation (Veihmeyer 1951). A study from the College of Agriculture at Berkeley, Californiashows approaches taken toward irrigation methods in the late 1920s.The authors Beckett, Blaney, and Taylor (1930) research the amount ofwater required for irrigation to produce a successful crop of Avocadoand Citrus trees in San Diego County. The goal of the study was notjust crop maximization, but finding optimal irrigation efficiency, sincewater resources were scarce and expensive even in the 1920s."Efficiency of irrigation is defined as the percentage of the water appliedthat is shown in soil-moisture increase in the soil mass occupied by theprincipal rooting system of the crop." The authors describe thewatersheds, classify soils and climate, and map the rainfall and soil 22
  36. 36. moisture patterns down to four feet depth. Detailed observations,including height and age of trees, root development and the intervalbetween irrigation lead the authors to an "estimated seasonalrequirement [of water] at maturity." The study finds an average waterresource efficiency of 60% "under good irrigation practice." Finally, theauthors make several predictions about certain crops and theirparticular irrigation needs during, e.g. a period of drought of "more than6 weeks". An important result of the study was that, "as long as the soilmoisture is above the wilting point, the moisture content has nomeasurable effect on the rate of moisture extraction," a warning to notwaste water through excessive irrigation.1 From the Commission for Agrometeorology (CAgM) of the WorldMeteorological Organization (WMO), four agrometeorologists(Seemann et al. 1979) chose to compile a book titled"Agrometeorology," since students of this young discipline had nocomplete reference book to study by. In this book, J. Seemann, who isobviously an advocate of the meso-scale, or topoclimatology, defendsthe topic of his choice with this abruptly ending sentence"macroclimatology is based on a wide network of measurements anddoes not register the special features resulting from topographical1 I just recently visited Riverside County in CA, and was amazed by the amount ofavocado and citrus trees. I am sure that Blaney and his fellow scholars laid thegroundwork for this intensive use of irrigation in agriculture. 23
  37. 37. differentiation of the terrain, whereas the microclimate comprises areaswhich are far too small.‖ 2 One can only guess, for what purposes hisstatement would make sense, but maybe he was talking about a mid- tolarge-size farm. And indeed, the microclimate can vary between twoareas just a few meters apart, yielding a problem with the accuracy oflarger scale prediction of e.g., highly accurate crop cycles. However, Chirkov, the second author of the book"Agrometeorology" is more precise when giving his ideas aboutmicroclimate. He explains, "microclimate of meadows, fields, forestfringes, glades, and lakes is produced by the disparity in the radiativeheating of the subjacent surface." Chirkov facilitates the agriculturalpoint of view toward microclimate by asking where to expect frost, whento expect frost-free periods, and what the differences are betweensouth-facing versus north-facing slopes in respect to optimal time ofsowing. He coins the term "phytoclimate" as the "meteorologicalconditions produced amongst plants" and therefore as a modifiedmicroclimate that is "controlled by the structure of the plant cover [i.e.height, density] and the width of inter-row spaces." Chirkov relatesspecies, habitus, age of plant community, density of stand (plantation),as well as the sowing or planting method, illumination intensity, air and 2 I did not explore Seemanns article any further, but found his statement ratherfunny and therefore worthy of being shared here. 24
  38. 38. soil temperature and humidity, and wind intensity values, to come to theconclusion that the phytoclimate must be considered closely in order tomake predictions of any sort. He gives the example that a vegetatedsoil can have a temperature difference of up to 25 C compared to asoil in an open location. For accurate information on planting, sowing, or irrigating, hesuggests that vertical measurements must be taken (an approachfundamental to current-day research) and the fields‘ distances to areservoir or a forest strip are to be assessed. The data shall then becompared to that of the nearest weather station. Maps shall be madethat mirror the practical importance of data for the plant developmentand crop formation, an idea that resembles Thornthwaites cropcalendar. Finally, Chirkov suggests that for agricultural purposes, themicroclimate can be improved, e.g. in cold or humid climates by ridgingthe surface to reduce overhumidification, or in arid regions by thinningout timber to preserve moisture. Another strategy to reduce wind andturbulence, and therefore soil erosion, according to Chirkov, is to plantforest strips in between fields that are 25 times their height apart. If thetrees of the forest strips were 20 meters tall, Chirkov suggests one 25
  39. 39. forest strip every 500 meters. However, he does not go into potentialsoil water competition between trees and crops.2.5. RECENT PUBLICATIONS After the groundwork of biometeorology has been highlighted, itis worthy to now explore several paragraphs on contemporary work,especially focusing on John L. Monteith, since he still plays a large rolein today‘s cutting edge of synthesizing science. Several otherresearchers and their attempts to model mass and energy balances willalso be outlined. In the conclusion, the researcher‘s own view andfuture goals about her place in the discipline will be mentioned.2.5.1. JOHN L. MONTEITH In ―Vegetation and the Atmosphere‖ (1975), one of Monteith‘smany books, he states that ―micrometeorology is the measurement andanalysis of the state of the atmosphere near the surface of the earthwhether life is present or not. His main objective was to ―provide aquantitative framework‖ for describing processes such as heat andmass transfer in terms of the prevalent mechanisms that operatethrough radiative heat exchange, turbulent diffusion, or conduction ofheat in the soil. Like his fellow Penman, Monteith stresses the 26
  40. 40. importance of considering the distribution of sources and sinks of heat,mass, and momentum in the canopy, mechanisms that are currently stillbeing explored by biometeorologists, and that are hard to quantifydirectly. Interestingly, Monteith mentions the dialectic that―micrometeorologists have tended to regard vegetation as a steadystate system [which it is not, whereas] plant physiologists have tendedto overlook the significance of the state of the system [i.e. theatmosphere].‖ With this comment, he stresses the importance ofsharing insights amongst scientists from seemingly separate fields. Hepraises the recent contributions biochemists have made to ―our (i.e. themeteorologists‘) understanding of physiological mechanisms elucidatingbiochemical pathways, interactions, and feedback.‖ Monteith‘s thought on biometeorologic models ― [which] linkadjacent levels of organization from cell to leaf, leaf to plant, plant tocommunity‖ is that ―the input to such models is a set of equations(received by assumptions) relating the rates of processes to the stateswhich govern these rates.‖ An example has been outlined in the lastparagraph of the section on human health. The processes Monteith istalking about are physical and chemical, and his following elaborationsstress the intricate and complex interrelationships between the ―state of 27
  41. 41. the environment, the state of the plant, and the nature of the relevantphysical and physiological mechanisms.‖ Monteith expandedPenman‘s energy balance equation to the Penman-Monteithcombination equation, in which he considers the effects of physiologyon aerodynamic and stomatal resistances. His modification allowsscientists to predict processes much more accurately. In a later section, he mentions micrometeorology‘s contributionsto ecology, which include such application of physical principles to the―relationship of states to processes.‖ Such principles are Newton‘s Lawof Motion explaining the transfer of momentum; the First Law ofThermodynamics elucidating the radiation balance; the Conservation ofMass for water balance; Ohm‘s Law for understanding resistance, andFick‘s Law to explain diffusion. Conclusively, Monteith suggests the importance of applyingmicrometeorologic knowledge to ameliorate crop successes, tounderstand the relationship between weather and disease, or even theparasite susceptibility of a host, that is often related to ―certain physicalstates like temperature and humidity.‖ To achieve this, Monteith callsfor ecological records to be ―interpreted by interdisciplinary teams ofphysicists and biologists‖ while keeping in mind that progress in thisfield can only be maintained with a ―sensible balance between all these 28
  42. 42. essentials: development of instruments and recording systems,interpretation of measurements, construction of mathematical models,and most of all, the collaboration of micrometeorologists and ecologistsprepared to learn from each other.‖ Monteith has followed this vision. In 1995s "Accomodationbetween Transpiring Vegetation and the Convective Boundary Layer",outlines the interactions of meteorology and vegetation, giving specialregard to feedback mechanisms in the relationships of soil-plant, plant-surface layer, and surface layer-planetary boundary layer. Theseinclude the crucial balancing role of stomata in the physicaldependencies of fluxes and resistances to fluxes. Monteiths paper isan extraordinary example of recent synthesis, as it combines the latestfindings of biochemistry, physiology, and environmental physics.2.5.2. BIOMETEOROLOGICAL MODELING Current research on the microclimatological boundary-layerscale is extremely active. The field has been influenced by many of thephysical sciences, as each field‘s advances of knowledge contribute tothe understanding of the whole complex web of complicated processes.With technological innovations, intricate measurements of biosphere—atmosphere interactions have been made possible, e.g. the eddy- 29
  43. 43. covariance technique that simultaneously measures large-scale fluxesof certain entities, e.g. CO2 concentration and vertical wind speed(Monteith and Unsworth 1990) using highly accurate (and expensive)sonic anemometers. The Penman-Monteith combination equation isused in several papers that have been referenced (Blanken and Rouse1994, Chen et al. 1997, Takagi 1998, Burba et al. 1999) to modelevapotranspiration at the leaf- and the canopy level, taking into accountthe boundary layer conductance as meteorological conditions change,i.e. stormy versus calm weather, or dry versus moist air. Generally,measurements can be recorded with minimal time constraints, andcomputer software allows for statistical modeling and plotting of thedata. Biometeorologic modeling is important in the attempt to makepredictions of future events. In an era where the conservation ofspecies richness has become a general concern, the modeling ofnutrient and surface water cycles becomes a helpful tool inunderstanding multidimensional interactions between the many agentsof a biome. Rey Benayas et al. (1999) approach the quantification of speciesrichness by modeling the relationship of "- and -diversity" of speciesto "moisture status and environmental variation". In their study,"environmental status is measured as actual evapotranspiration." This 30
  44. 44. approach deems especially interesting, since the loss of wetlands dueto development has been rapid. While many states have adevelopment prohibition of wetlands intended for their generalprotection as densely populated, species rich areas, money still seemsto have the last word too often, and development of wetland areas isstill a possible threat to their inhabitants (refer to MaryPIRGS, 1999,when The University of Maryland wanted to build a new stadium on awetland and succeeded). A large amount of current research focuses on exploringbiometeorological processes in forests, wetlands, and grasslandvegetation. Some papers are part of a joint effort of exploring majorregions of the earth, and those regions‘ importance on a global level.An example of such a project is the Boreal Ecosystem-AtmosphereStudy (BOREAS), which according to Chen et al. (1997) "has the goalof understanding the contribution of boreal ecosystems to the globalcarbon budget and their response to global change". He goes on toexplain that "solar energy is the driving force for biological activitiesresulting in the observed energy and gas fluxes". He further elaboratesthat the canopy structure, i.e. over- and understory features "requiresspecial attention in the radiation modeling". Overall goals of Chen etal.‘s study were to compare the radiation balance inside the canopy" at 31
  45. 45. different times throughout the growing season and to assess generalpatterns of leaf area index (LAI) over a "nearly complete seasonalcycle." LAI is an important variable that needs to be measured tomodel canopy stomatal conductance. Measured in square meters ofleaf area over square meters of ground, this index quantifies themagnitude of photosynthetic potential, i.e. the leaf area above groundthrough which gas exchange can occur, best pictured in the comparisonbetween a tropical forest (LAI~12) and a desert with sparse vegetation(LAI~0.2). In his concluding discussion, Chen et al. state that LAI isimportant not only because it "defines the photosynthetically active leafsurface area responsible for plant growth and CO2 uptake", but alsosince it delivers an estimate of rainfall that is intercepted by the leaves.Lastly, he includes how the latest efforts to estimate LAI have improvedthe applicability of remotely sensed data on canopy structure. Rouse (1998) uses a water balance model to generate data forGeneral Circulation Models (GCMs) that attempt to predict futureclimatic scenarios. As Rouse determined in his study on a subarcticsedge fen, the increase in air temperature over the next decades willlead to a drier environment of the present day fen, unless precipitationincreases by more than 20%. He goes on to predict several scenarios,including extremely wet and extremely dry years, and their effects on 32
  46. 46. the fen habitat. With such a significant change in the water balance offens like this, the decrease in species richness is almost certain. Acritique of GCMs however, was made by Blanken (pers. comm. 2001).According to him, "GCMs still fall apart today", because the missingdata about soil make-up and moisture is not measurable throughsatellite observations. The application of models contains multiple sources for potentialerror, because their derivations rely on assumptions that are only barelytrue in certain scenarios. If the research area in question deviates fromthe scenario described in the model, e.g. a crop field could qualify forthe assumption of horizontal homogeneity, not though a forest, thescientist will have to correct for these deviations, or chose a differentmodel altogether. It is the responsibility of the scientist to usestatistical models in a sensible way, and to refrain from tasks that aretoo complex for the human mind to explain.2.6. CONCLUSION The field of biometeorology has made invaluable progress overthe last decades, and much of this success stems from the continuingeffort of scientists to synthesize their specialized research. The readermay ask where the discipline is headed, and where the goals for future 33
  47. 47. research should be placed. In 1969s "Geography and Public Policy",Gilbert White emphasized the importance of "translating findings intochanged public policy". The pursuit of a profession should undoubtedlybe linked with the incentive to make a change for the better. For whyshould geography "fabricate a nifty discipline about the world while thatworld and the human spirit are degraded?" In tune with Gilbert Whitesspirit, one has to ask, what are the "truly urgent questions" of today,and whether researchers are able to tackle research questions "in thelight of possible social implications?" as there are bountiful problems tobe solved, both on the local and the global scale. A change for the better to which everyone can contribute throughpersonal input and research reaches out toward reestablishinginalienable rights not only for human beings, but also for every speciesthat inhabits this planet. Also, other geographical fields like urbangeography are developing proposals that increase sustainability incities, ideas that may decrease peoples needs to migrate further andfurther into other species habitats. Interdisciplinary, physical researchin biometeorology will be a necessary and powerful tool in changingpublic policy. Understanding ecosystems and all agents that steerthem, as well as potential changes in biomes through anthropogenicimpact may enable inspired researchers to succeed in reaching their 34
  48. 48. goals, engaging all sources of creativity. Heres to Gilbert White: "Wemust work with all our heart and mind". 35
  49. 49. CHAPTER 3. BACKGROUND3.1. INTRODUCTION The role of E in the water and energy balance of high latitudewetlands is well documented (e.g., Blanken and Rouse 1994, Rouse2000). Further, studies quantifying this flux have been conducted onfairly homogenous areas like forest canopies or sedge meadows (e.g.,Blanken and Rouse 1995), and stomatal conductance has been scaled-up to the canopy level using a leaf area index (e.g., Chen et al. 1997,De Pury and Farquhar 1997). Additionally, habitat loss and decreasingbiodiversity have recently found increasing attention in both public andacademic spheres. Whereas Ehrlich (1994), Pimm et al. (1995), andMyers et al. (2000) focused on biodiversity hotspots and conservationpriorities, Blanken and Rouse (1996) investigated fine-scale processesin specific habitats and assessed the ecological and meteorologicalcharacteristics that explain the existence of particular plantcommunities. Lastly, Rey Benayas et al. (1999) developed an indexthat correlates E of an area to its biodiversity. Wetlands in particular are known for both their exceptionalproperties to filter water and to provide habitat for species that dependon a unique combination of environmental factors, forming an oasis forexample, for waterfowl that often travel several thousands of kilometers 36
  50. 50. to satisfy their physiological demands at such sites. Plant diversity ofsuch areas is often remarkable; therefore, varying spatial and temporaldistributions of limiting or controlling factors deserve special attention. Recent data indicate a 53% loss of U.S. wetlands between 1780and 1980 (Moser et al. 1996), and data for Colorado estimate an annualloss of 60 acres in the state alone (Denver Post, Dec 8, 2000). Thisloss is mainly due to Colorado‘s population increase and concurrentgrowth of development and water demand. Colorado ranks eighth inthe list of states with the largest net population gains recorded from1995 to 2000 (U.S. Census Bureau 2000). Working to keep biodiversityloss minimal, The Nature Conservancy (TNC), a global organizationdedicated to the preservation of endemic species and naturalcommunities, has purchased over 50,000 acres of land in Colorado withthe objective to preserve and restore native species and biologicalcommunities. Brand and Carpenter (1999) have stated that TNCstrives for ecologically intelligent decisions through collaboration withscientists to characterize future site management strategies. High Creek Fen, a 750-acre extreme rich fen 2850 meters abovesea level (a.s.l.) near Fairplay, CO, is part of TNC‘s preserve system.TNC, as well as the scientific community in general, is lacking accuratedata for this type of ecosystem in the Rockies. This research fills part 37
  51. 51. of this knowledge gap, and lays the groundwork for the formation ofsuccessful management strategies to be implemented by TNC over thenext several years.3.2. PHOTOSYNTHESIS AND ENERGY BALANCE Through photosynthesis, plants use the sun‘s photosyntheticallyactive radiation (PAR), referred to in this work by quantum flux [Q], toproduce the energy required for the synthesis of carbohydrates. Q,which represents the flux of PAR in the visible spectrum, is included inthe sun‘s electromagnetic field between 0.4 and 0.7 m. Cell waternecessary for photosynthesis evaporates through the stomata at ratesthat are determined by the magnitude of stomatal conductance inaddition to other factors. Inevitable while stomata are opened, the lossof water due to a water vapor deficit of the ambient air surrounding theleaf additionally offers evaporative cooling to the leaf‘s surfaces. Up tothe point where physiological constraints or N availability limit theturnover rate of the Calvin cycle, Q is a strong driving force in thephotosynthetic process (Monson 2000). The maximization of photosynthetic potential is accounted for byphysiological differences in plants, differences such as density ofchlorophyll pigments, leaf thickness, LAI, and density of stomata per 38
  52. 52. leaf area (Monson 2000). Increased density of chlorophyll pigments,roughly translatable into the ―greenness‖ of the leaf, allows the plant toabsorb energy faster than lighter-colored leaves that have a lesseramount of chlorophyll per leaf area. Thicker leaves allow the plant tocapture more Q. These details strongly influence the plants‘ ability tomake maximum use of the photon energy. Furthermore, the overallbudget of potential CO2 assimilation of a plant depends on its LAI.Additionally, distribution of stomata takes different densities accordingto the urgency to minimize water loss. For example, tropical leavescompared to xerophytic leaves have dense versus sparseconcentrations of stomata, respectively. Because leaf surfaces are theinterfaces of plant correspondence and mass and energy exchangeswith the overlying boundary layer, investigating all leaf processes isimportant. For a plant, the visible wavelengths are not the only solar energyspectrum of interest. All wavelengths outside the visible range areimportant to the plant, because they culminate in the total amount ofenergy available at the surface of the plant‘s habitat. Thermal energy,which partially translates into air temperature, is another factor thatdetermines the rate of photosynthesis. Optimal leaf temperatures [TL] 39
  53. 53. for C3 plants usually range between 30 and 40 C, but plants can alsoalter their optimum to match their typical environment (Nobel 1999). The overall intensity of solar radiation that reaches the plantdepends on the solar angle, which is a function of the time of day andyear, latitudinal position, and leaf orientation. Additionally, depth anddensity of the atmosphere above the plant determine the amount ofenergy (and actual CO2 concentration, which depends on atmosphericpressure, and may therefore be considered lower at High Creek Fenthan at sea level) that arrives at the surface of the earth. Intuitively, thesun‘s intensity will lessen with cloud cover. A thin atmosphere, presentover high elevation sites, allows for less absorption of solar radiationduring its way through the atmosphere, and thus has a more intenseimpact on the surface compared to thicker cloud cover, or anenvironment at sea level. The net radiation (Rn) consists of the incident short-waveradiation that strikes an area (K) minus the amount that is reflected offthat surface (K), plus the incoming long-wave radiation (L) minus theamount that is radiated from that same area (L), the latter is a functionof the surface temperature and emissivity at a particular location.Hence, we have the equation Rn = (K- K) + (L - L) (1). 40
  54. 54. Energy at the surface can be expressed in Watts per square meter(W m-2), or in micromol per square meter per second (mol m-2 s–1).The energy available for absorption (transmittance, and reflectance) bythe leaf is a strong determining factor in the photosynthetic process andthe energy balance over an area. Micrometeorologists like to follow the fate of the net radiation inits distribution at the impacted surface, because it is a distinct way oflooking at the environmental dynamics of an area. The net radiation ispartitioned into three main terms, i.e. the energy is distributed into theheating of air (H), the transformation from water into water vapor,(evaporation or E), and into the heating of the ground (soil heat flux[G]). It follows that Rn = H + E + G (2). Usually, due to the dense ground cover at High Creek Fen, thelesser part of the net radiation goes into the heating of the ground.(Over areas with bare soil, however, the partitioning changes.) Thedistribution of Rn between H and E is often expressed as the Bowenratio (), where  = H/ E. Generally, the Bowen ratio takes onnumbers between 0 and 5, where the latter would typify an extremelyxeric, and the former an intensely humid environment. Another effect ofRn at the surface is upon Tair and the temperature dependent 41
  55. 55. atmospheric water vapor deficit [D]. D exerts another strong controlover plant transpiration. As stated above, water vapor diffuses fromintercellular air spaces and the stomata into the atmosphere. The fluxrate is subject to the differences in water vapor concentration betweenthe inside of the leaf (assumed to be 100 %) and the surrounding air;the steepness of the gradient determines the flow rate. Diffusion ofwater vapor from the plant into the atmosphere, based on the secondlaw of thermodynamics, or the law of entropy, can thereforemathematically be expressed as follows: E = -K cH2O / z, (3)where K is the molecular diffusion coefficient for water vapor (fromhigher to lower concentration), and cH2O / z is the difference in watervapor concentration over the height of the leaf boundary layer, whichagain is a function of wind speed. Strong winds will thin the boundarylayer over the leaf, increasing the gradient. A low relative humidity,usually present at the daily peak of Q, forces water out of the plantfaster than a high relative humidity, which is generally common for themorning hours. Hypothetically, the relatively constant wind at HighCreek Fen delivered warm, dry air from the arid Mosquito Range andPark area in the west, and therefore increased the evaporative demand 42
  56. 56. at the surface. Hence, the large E above the fen is combined with dryair (D max = 5 kPa). Due to physiological constraints, a strong demand for watervapor out of the leaf will likely lead to stomatal depression or fullstomatal closure. This adaptation allows a plant to control the amountof water vapor leaving its stomata, since too great of a demand forwater vapor out of the leaf would result in cautation of water inside thexylem and death of the plant. Soil moisture [ ] at the fen was plentifulduring the whole growing season, assuring the plants in their respectivelocations a generally lesser stressed summer than may be expectedfrom plants located in semi-arid environments. The daily pattern of  varied considerably between sites; soilmoisture recharge occurred either through atmospheric deposition, e.g.,rain or dewfall (surface recharge) or through groundwater movement(subsurface recharge). Intuitively, soil moisture can be expected togradually decrease during a day where photosynthesis occurs, reachinga minimum at the photosynthetic peak, both due to root water extractionand evaporation from the bare soil surface. At the densely vegetatedfen, however,  stayed high throughout the day, and was only slightlyinfluenced to a downward direction throughout a period of little rain atthe end of July 2001, when  measured at the tower showed a 43
  57. 57. minimum  of 93 %, which is to be considered saturated soil. Incontrast, investigating soil moisture control in non-saturated locationsallowed for testing of differences in intra-specific stomatal responses toliving in drier versus wetter areas of the fen. Summer 2001‘s studies onB. glandulosa and S. candida both showed soil moisture control on gand E. Attention to such physical and physiological factors as detailedabove is paramount in assessing the processes that govern plantprocesses. These observations will now be communicated in light ofthe above.Photograph 3.1. Cumulus cloud (Cu) over High Creek Fen (view toNE) in Summer 2001. Although never again in this exact shape, Cucommonly form in areas adjacent to the fen during the summer seasonin early or late afternoon. 44
  58. 58. 3.3. STUDY SITE DESCRIPTION In the following paragraphs, the research site is described frompersonal observation and as communicated through the literature.First, a general description of the site‘s topography, hydrogeology, andhistory, and last a focus on the environmental factors given by itsgeographical location and local dynamics, including the energy balance,microclimate, and soil moisture will be given. High Creek Fen (Photograph 3.1.) is the largest remainingnatural fen in the South Park region of Colorado (Brand and Carpenter1999). It is currently a nature preserve that has been managed by TNCsince 1990. The 750- acre wetland is located at 3906‘00‖N,10557‘30‖W at an elevation of 2850 m, between the towns of Fairplayand Buena Vista Figure 3.1.).3.3.1. TOPOGRAPHY, HYDROGEOLOGY, AND HISTORY Topographically, South Park lies in a flat valley surrounded bythe Mosquito Range to the west, the Kenosha and Taryall Ranges tothe north, and the Rampart Range to the east. The wetland, locatedjust east of Black Mountain (igneous remnant), shows a gentle changein elevation from its highest (2850 m a.s.l.) northwest corner to itslowest (2810 m a.s.l.) southeast corner. 45
  59. 59. Geologically, (visible from a geologic map of the area) HighCreek Fen is underlain by easterly dipping Cambrian throughPennsylvanian sedimentary rocks (quartzite, shale, and dolomite)deposited on a Precambrian basement complex of gneiss and schist(the Idaho Springs Formation). These easterly dipping sedimentaryrocks represent the eastern limb of the Sawatch Anticline to the west.The bedrock geology is obscured at High Creek Fen by surficialdeposits of Quarternary gravels and alluvium, and the underlyinggeology has been inferred by projecting the geology of the adjacentMosquito Range to the east (Misantoni 2002). Hydrogeologically, the fen is subject to complex variables. Theground water pattern is influenced by both the Creek as well as themake up of the material described above. Following the gentle slope,High Creek supplies the fen grounds with fresh (and relatively warm)spring water from the northwest, and leaves the area to the southeast.Additionally, the underlying formations contain several aquifers, e.g.,the Leadville and Quarternary aquifers. Several scenarios concerningthe delivery of ground water into the alluvial substrate and fen soil areviable: (1) ground water is recharged from aquifers through severalPaleozoic strata by ways of faults and fractures (Shawe 1995, Appel1995) that reach into the alluvium through its semi-permeable bottom 46
  60. 60. layer, or (2) ground water is recharged from one formation only, (e.g., alayer of shale forms an aquifer) topped again by a semi-permeablelayer reaching into the alluvium, or (3) the alluvium is itself an aquiferwith an impermeable bottom layer, and recharge is either not yetnecessary (last glacial period only ended 10,000 years ago), or ispartially achieved from surface water. While the shallow ground waterlevel at High Creek Fen may be due to any, all of, or additions to theabove scenarios, the ground water level was relatively constantthroughout the years 1995 – 1998 (Johnson 1998) and 2000/ 2001(tower data). The water supply to the fen, however, may be threatenedby water-use projects such as the ―South Park Conjunctive Use Project‖(now fallen through), in which the city of Arvada would have beensupplied with water from this region. While it is unknown whether adrop in the water table at the fen would likely occur after one or 100years, such projects present a definite threat to sufficient supply of  forthe already dry environments surrounding the fen, including severalranches, i.e. livelihoods of the locals. The high E during the summer months as well as relativelyconstant  even after atmospherically dry days both mandate aperpetually active groundwater recharge. A transect of  takendiagonally across the fen with a water content reflectometer revealed 47
  61. 61. values between 8% outside the fen and 60% within the fen with soiltexture ranging from clay to silt with varying organic matter contents.This transect of  taken throughout the fen in summer 2001 (Figure3.1.) and an accompanying photograph to gain perspective on thetransect (Photograph 3.2.) can be viewed below.Photograph 3.2. View across the fen from NW (transect survey pole)to SE shows approximate transect location; the location of themeteorological tower is included on transect. Note: this picture wastaken in Winter 2001/ 2002, while the transect data graphed below(Figure 3.1.) was collected July 1st 2001. 48
  62. 62. 60 Tow er 50 Volumetric Soil Moisture [%] 40 30 20 10 0 0 200 400 600 800 1000 1200 Dist ance [m]Figure 3.1. Soil moisture transect from southeast (0) to northwest(1000 m) taken across the fen on July 1st, 2001. With distanceincrements of 33 m, 31 data points were recorded. Low  valuesrepresent areas outside the fen. 49
  63. 63. Photograph 3.2. View across the fen from NW (transect survey pole) toSE shows approximate transect location; the location of the meteorologicaltower is included on transect. Note: this picture was taken in Winter 2001/2002, while the transect data graphed above (Figure 3.1.) was collectedJuly 1st 2001. Historically, small portions of High Creek Fen were disturbed during a short period of peat mining from the 1970s until the mid- 1980s (Schulz 1998), when 22 of the 750 acres were mined. Since 1992, attempts have been made to restore plant communities (Sanderson, pers.comm. 2001). Disturbance also occurred while High Creek Fen was open to grazing by cattle and sheep since 1860 and prior to that by 50
  64. 64. bison, elk and antelope (Brand and Carpenter 1999). Apart from theabove, High Creek Fen has remained undeveloped and largelyundisturbed.3.3.2. CLIMATE AND ENERGY BALANCE AT HIGH CREEK FEN The harsh climate of High Creek Fen is characterized by intensesolar radiation, strong winds, and little precipitation. Due to its highelevation, on cloudless days, High Creek Fen is exposed to a solarpeak of 2500 mol m-2 s -1 during 10:00 and 15:00 hours mountaindaylight time (MDT) throughout the height of the growing season; thisamount is 1.25 times higher than the average sea-level peak of 2000mol m-2 s –1. Winds typically originate from the northwest; peakobservations of up to 150 km per hour have been made on the ridges tothe N and W, e.g., Boreas Pass and Windy Ridge (Cusack, personalcommunication 2001). While the Mosquito Range to the west of the fenfunctions as a rain shadow most of the time, convective clouds(Photograph 3.1.) are common in the summer time; they supply most ofthe precipitation recorded throughout the year. As stated above,  isgenerally recharged by the ground water of High Creek Fen and barelyinfluenced by local precipitation. The mean total annual precipitationbetween 1961 and 1997 at the nearby weather stations Antero 51
  65. 65. Reservoir and Fairplay was measured to be 234 mm and 352 mmrespectively (Brand and Carpenter 1999). Those long-term recordingsalso show that 40% of this precipitation falls in July and August. On-site measurements, while on a different scale, indicate that 121 mmprecipitated onto the fen in the summer of 2001. Thus, High CreekFen‘s location exhibits extreme conditions of little precipitation and highsolar radiation; high soil moisture (Figure 3.1.) and special soilchemistry and nutrients are conditional for the relatively dense and lushvegetation present throughout the site (Blanken, pers. comm. 2001). While High Creek Fen is exposed to the above-mentionedregional meteorology, its microclimate differs from those of thesurrounding areas. During the photosynthetically active hours of thedays of this study, TS ranges were small, e.g., 2.5 or 3.5 C; such smalldifference between minimum and maximum TS during daylight hours ismainly due to the high volumetric moisture content of the soil,perpetuated by an insulating, dense ground cover. Further, the diurnaltrend of D over the fen has a distinct shape and large amplitude. In themorning, D has been measured as low as 0.2 kPa (in this case, 80 %relative humidity). At the warmest part of the day, D can be as high 2.3kPa (in this case, 25% relative humidity), both due to the solar heatingof the air, and the increasing, dry winds typically from the northwest. 52
  66. 66. Maximum D was measured by the porometer over S. monticola at 5kPa with a TL = 36 C and Q = 1800 mol m-2 s-1 and  = 40 %. Due to its high elevation, the vegetation of High Creek Fen iscomparable to that of high-latitude wetlands of the boreal and tundraregions (with exception of the perma-frost layer), where, as mentionedabove, E can comprise close to 80% of the net radiation. At HighCreek Fen, preliminary measurements of E using the Bowen Ratiosuggest that E is an important component of the wetland‘s water cycle,and also, that the source of the water that is available for planttranspiration cannot solely be local precipitation, but must primarily besupplied by deeper rock units, or adjacent uplands.3.3.3. VEGETATION AT HIGH CREEK FEN The growing season lasts from early June until mid- September;the ground is thawed from May throughout October. The vegetationpattern can broadly be divided into upland and wetland types (Brandand Carpenter 1999). The vegetation of the wetland exhibits greatvariety in comparison with the adjacent upland areas (Cooper 1996,Sanderson and March 1996). A description of both upland and wetlandspecies can be found in Cooper (1996) and Brand and Carpenter(1999). 53
  67. 67. Wetland habitats include hummock communities, meadowcommunities, spring fen communities, and a sodic flat community(Cooper 1996). Dominant shrubs of the wetland are several willowspecies, including silver willow (Salix candida), myrtleleaf willow (Salixmyrtillifolia), planeleaf willow (Salix planifolia), mountain willow (Salixmonticola) and barren-ground willow (Salix brachycarpa). Alsoabundant are dwarf birch (Betula glandulosa), which inhabit mostly thehummock and meadow communities, but also border the drier sodic flatcommunities, as well as the moist spring fen areas. While kobresia isthe dominant grass throughout the fen, abundant especially at thewetland‘s platform are sedges, mainly water sedge (Carex aquatilis)(Photograph 3.3.). Furthermore, the existence of several state-rare andglobally-rare plants at High Creek Fen, including porter feathergrass(Ptilagrostis porterii) and pale blue-eyed grass (Sisyrinchium pallidum)supports TNC‘s recent suggestion that the fen is a globally significantsite. The species diversity at High Creek Fen is exceptional, deservesscientific attention, and may be dependent upon protection fromanthropogenic disturbance such as a lowering of the water table. 54
  68. 68. Photograph 3.3. Dense ground-cover of willow, birch, and sedge atHigh Creek Fen, Summer 2001. Blue spruce in the background greatlyinfluence turbulence at the site.3.4. THE FOUR SITES AND THEIR INHABITANTS All sites served as environments to investigate the importance ofsoil moisture, water vapor deficit of the atmosphere, leaf temperature,and solar radiation on stomatal conductance and plant transpiration.Spatially,  is highly variable, and while some plants, e.g., B.glandulosa seem to be tolerant of a wide spectrum, others, such as S.candida are restricted to a narrower range. 55
  69. 69. The research sites were chosen to control for , plant compositionand accessibility. Measurements of leaf conductance, transpiration,vapor pressure deficit, leaf temperature, and solar radiation were takenon several randomly chosen days dispersed throughout the growingseason from early June until late August 2001. Additionally, soilmoisture measurements were taken at each plant. Data were collectedfrom sunrise until sunset, weather permitting. This study focused on sixplant species abundant in the fen: Betula glandulosa, Salix candida,Carex aquatilis, Salix monticola, Salix brachycarpa, and Salix planifolia. B. glandulosa (Photograph 3.4.) grows on sites varying in  from15% to 60%, constituting a good indicator for potential soil moisturecontrol on its stomatal conductance and transpiration. 56
  70. 70. Photograph 3.4. Betula glandulosa (Swamp Birch) in a drier locationat High Creek Fen, Summer 2001. This species occurs in a range oflocations where 15 % <  < 60 %. In contrast, S. candida (Photograph 3.5.) was not found in areaswith less than 35% average volumetric soil moisture. However, it waschosen as a study organism since these plants are state-rare glacialrelicts, which are not found anywhere else in the Southern RockyMountain region but at the South Park fens. Assessing theirenvironmental constraints is of great interest to the botanicalcommunity, and existing work on this plant species in Manitoba,Canada (Blanken and Rouse 1996) allowed a general comparisonbetween the plant‘s behavior on a latitudinal gradient. 57
  71. 71. Photograph 3.5. Close view of the thick, dark-green leaves of Salixcandida (silver willow). Although not measured, leaf appearancesuggests a multi-storied photosynthetic apparatus and densechlorophyll pigmentation. C. aquatilis is the most abundant sedge in portions of High CreekFen, offering necessary data for future mapping of transpirationthroughout the fen. A sample of one specimen can be seen inAppendix A. S. monticola (Photograph 3.6.) is the most abundant 58
  72. 72. willow of the South Park region (Sanderson, pers. comm. 2001), andcomparing its environmental constraints with those of the rare S.candida was an integral part of this project, as this allowed a look forpotential constraints to S. candida’s occurrence in these latitudes. S.brachycarpa (Photograph 3.7.) and S. planifolia were chosen to furtherthe investigation of on-site willows for comparison of stomatal responseof different willow species to varying environmental factors.Photograph 3.6. S. monticola Photograph 3.7. S. brachycarpa 59
  73. 73. 3.5. STUDY HYPOTHESES The research presented here investigates interactions of theenvironmental factors explained above. It explains the nature of thecorrelations between stomatal conductance [g] and transpiration [E]from the leaf with the meteorological and soil moisture conditions thatexert limitations and affect the magnitude of transpiration. Thisresearch is expected to explain several processes and therefore toenhance the understanding of the interrelationships betweenmeteorological and plant physiological processes. In particular, itshows a spatial variability of E corresponding to the heterogeneity ofthe vegetative surfaces. It strives to explain the nature of thecorrelation of g and E from the leaf with the meteorological conditionsthat exert limitations on the plant physiological processes. Thisresearch expands former analyses to include the effects of  on themagnitude of E;  is expected to be also highly variable throughout thefen. This research focused on testing three specific hypotheses, whichare outlined below. 60
  74. 74. 3.5.1. PROBLEM STATEMENT 1: DOES HEIGHT ABOVE GROUNDINFLUENCE PHYSIOLOGICAL RESPONSES WITHIN ANINDIVIDUAL SPECIES? Stomatal conductance and E from distinct heights in anindividual plant above ground may vary because light absorption in theleaf depends on the magnitude and partition between direct and diffuseradiation that reaches to the vertical leaf layers of a plant, and becausethe plant itself creates its own microclimate that may, for example, alterthe vapor pressure deficit of the air surrounding the leaf [D] so that aleaf at the top of the plant may experience a higher D than a leaf in themiddle of the plant. Such differences would lead to diverging values ofg and E from different heights above ground, and if sufficiently large,would have to be considered when extrapolating from the leaf to thecanopy level. Hence, the magnitudes of g and E from three leaves ofthe same plant (S. monticola) at heights of z = 40, 70, and 100 cmabove ground were compared. It was hypothesized that no significant differences in both g andE from the three leaf levels of the same plant would be found. 61

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