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Do Geologic Refugia Influence Perennial
Grass Survival During Extreme Drought
       on the Edwards Plateau?
 Perennial Gr...
Introduction
► Grazing & variable precipitation two primary
 drivers of temporal shifts in herbaceous
 species composition...
Introduction
► Grazing & variable precipitation two primary
 drivers of temporal shifts in herbaceous
 species composition...
Justification & Objectives
► Opportunity  to examine interaction of these two
  variables on perennial grass community
  ...
Justification & Objectives
► Opportunity  to examine interaction of these two
  variables on perennial grass community
  ...
Justification & Objectives
► Opportunity  to examine interaction of these two
  variables on perennial grass community
  ...
Study Area: Sonora Experiment Station

► Southwest  Edwards
  Plateau MLRA
► Station established in
  1916
   Early empha...
Vegetation & Topo-Edaphic Features
► Juniper-oak   savanna (Kuchler 1964, Smeins and Merrill
 1988)
   Mid- or short-gras...
Vegetation & Topo-Edaphic Features
► Juniper-oak   savanna (Kuchler 1964, Smeins and Merrill
 1988)
   Mid- or short-gras...
Climatic Environment
► Annual
 precipitation
                                    Sonora Experiment Station                ...
Comparison of two severe drought events
► Period   of Interest
   Drought of 1951 to 1956
    ►Most  intense continuous d...
Comparison of two severe drought events
► Period   of Interest
   Drought of 1951 to 1956
    ►Most  intense continuous d...
Comparison of two severe drought events
► Period   of Interest
   Drought of 1951 to 1956
    ►Most   intense continuous ...
Comparison of two severe drought events

► Palmer    Drought Severity Index (Palmer 1965)
     Pattern, intensity & durat...
Vegetation Analysis
► Eightgrazing treatment units: 2 heavy
 grazing, 4 moderate grazing and 2 no
 grazing
   Treatments ...
Community structure between
          droughts
►Permanent   vegetation quadrats
  Established in 1949
  23 years of vege...
Community structure & topo-edaphic
            variation
►Paired quadrats based on the presence
 or absence of large or ab...
Cumulative Annual Precipitation
                               Sonora Experiment Station
                                 ...
► Palmer Drought
  Severity Index
► Quarterly values for
  1949 to 1959 &
  1992 to 2002                                  ...
► Palmer Drought
  Severity Index
► Quarterly values for
  1949 to 1959 &
  1992 to 2002                                  ...
► Palmer Drought




                                                              Palmer Dorught Severity Index
         ...
►   Palmer Drought




                                                                  Palmer Dorught Severity Index
   ...
►   Palmer Drought




                                                                  Palmer Dorught Severity Index
   ...
Mean Weekly High Temperatures
                                                                       Sonora Experiment Sta...
Mean Weekly High Temperatures
                                                                       Sonora Experiment Sta...
Perennial Grass Basal Area
                              Drought Years 1953 & 2002

                               Wilcoxo...
Perennial Grass Density
                       1953 vs. 2002

               Wilcoxon Signed Rank Test, Error Bar = Standa...
Perennial Grass Density                                                      Perennial Grass BA per Plant
                ...
Perennial Grass Density                                                      Perennial Grass BA per Plant
                ...
Topo-Edaphic Variation & Drought Response
Perennial grass basal area
                   Rock and non-rock sites across heavy, moderate, and no
                     ...
Perennial grass basal area
                   Rock and non-rock sites across heavy, moderate, and no
                     ...
Perennial Grass Density

                       70.00


                               Split Plot ANOVA, Error Bar = Stand...
Perennial Grass Basal
                         Perennial Grass Density                                                    ...
Perennial Grass Density & Basal Area
              per Plant
► Significant
           differences between both grazing
 tr...
Gradient of Perennial Grass Basal Area,
                          Rock Cover & Size
                                      ...
Perennial Grass Basal Area
                                                       Response to Rock Site Variation

       ...
Conclusions
► Drought   events structurally different
   Differences in intensity, duration & temp
► Community   structur...
Conclusions
► Rock  cover & topo-edaphic features
 facilitate the survival of perennial grasses
     Function of rock siz...
Conclusions
► Grazing
       intensity primary modifier of
 community structure over time
   Den & BA / plant differences...
Questions?
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Geologic Refugia and Herbaceous Community Survival During Extreme Drought

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A presentation on a portion of my graduate research examining the influence of grazing and drought on herbaceous community structure and persistance.

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Transcript of "Geologic Refugia and Herbaceous Community Survival During Extreme Drought"

  1. 1. Do Geologic Refugia Influence Perennial Grass Survival During Extreme Drought on the Edwards Plateau? Perennial Grass Community Response to Drought, Topo- Edaphic Variation & Herbivory
  2. 2. Introduction ► Grazing & variable precipitation two primary drivers of temporal shifts in herbaceous species composition & community structure (O'Connor 1995, Fuhlendorf et al. 2001)
  3. 3. Introduction ► Grazing & variable precipitation two primary drivers of temporal shifts in herbaceous species composition & community structure (O'Connor 1995, Fuhlendorf et al. 2001) ► Sonora Experiment Station  Three major & several minor drought events  Long term vegetation records across different grazing regimes  Onset of drought upon my arrival at Texas A&M
  4. 4. Justification & Objectives ► Opportunity to examine interaction of these two variables on perennial grass community  Impact of drought on plant survival  Response of plant community to variable grazing intensity and drought
  5. 5. Justification & Objectives ► Opportunity to examine interaction of these two variables on perennial grass community  Impact of drought on plant survival  Response of plant community to variable grazing intensity and drought ► Perennial grass community structure  Basal area, density, and basal area per plant
  6. 6. Justification & Objectives ► Opportunity to examine interaction of these two variables on perennial grass community  Impact of drought on plant survival  Response of plant community to variable grazing intensity and drought ► Perennial grass community structure  Basal area, density, and basal area per plant ► Examination of three areas  Comparison of drought intensity and pattern between two severe drought events  Response of perennial grass community structure to these two drought events across grazing intensity gradient  Response of perennial grass community structure to topo-edaphic variation during severe drought across a grazing gradient
  7. 7. Study Area: Sonora Experiment Station ► Southwest Edwards Plateau MLRA ► Station established in 1916  Early emphasis on Sonora animal science Experiment Station  Research shifted to grazing management in 1948
  8. 8. Vegetation & Topo-Edaphic Features ► Juniper-oak savanna (Kuchler 1964, Smeins and Merrill 1988)  Mid- or short-grass matrix  Variable woody vegetation composition and cover (Fuhlendorf et al. 1996) ►topo-edaphic features, fire, grazing history
  9. 9. Vegetation & Topo-Edaphic Features ► Juniper-oak savanna (Kuchler 1964, Smeins and Merrill 1988)  Mid- or short-grass matrix  Variable woody vegetation composition and cover (Fuhlendorf et al. 1996) ►topo-edaphic features, fire, grazing history ► Heterogeneous mix of soil depths, rock outcrops and topographic position  Tarrant stony clays ►5 – 30 cm deep ►30 – 60% stone fragments ►Thermic family of Lithic Haplustolls
  10. 10. Climatic Environment ► Annual precipitation Sonora Experiment Station Mean 569 mm Annual Mean 24.950 C Median 426 mm 50 100 variable Mean Temp Mean Precip Median Precip  High of 1055 40 80 mm in 1935  Low of 156 Precipitation mm 30 60 Temp 0 C mm in 1951 ► Tempannual 20 40 mean 24.90 C 10 20  July mean 340 C 0 0  January mean Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec 160 C
  11. 11. Comparison of two severe drought events ► Period of Interest  Drought of 1951 to 1956 ►Most intense continuous drought event in Texas since 1698 (Stahle & Cleaveland 1988).
  12. 12. Comparison of two severe drought events ► Period of Interest  Drought of 1951 to 1956 ►Most intense continuous drought event in Texas since 1698 (Stahle & Cleaveland 1988).  Alternating drought & abundant rainfall beginning around 1994
  13. 13. Comparison of two severe drought events ► Period of Interest  Drought of 1951 to 1956 ►Most intense continuous drought event in Texas since 1698 (Stahle & Cleaveland 1988)  Alternating drought & abundant rainfall beginning around 1994  Individual years of interest: 1953 & 2001 ►Look at prior three year pattern of weather ►Relationship of perennial grass basal area to three year running averages of precipitation (Fuhlendorf & Smeins 1997, Herbel et al 1972)
  14. 14. Comparison of two severe drought events ► Palmer Drought Severity Index (Palmer 1965)  Pattern, intensity & duration of drought events  Widely used as an index of drought severity (Alley 1984)  Models accumulated effect of deficit or surplus rainfall relative to the soil water needs of plants ► Temperature for the periods of interest
  15. 15. Vegetation Analysis ► Eightgrazing treatment units: 2 heavy grazing, 4 moderate grazing and 2 no grazing  Treatments began in 1948  Decreasing intensity over time  Grazing intensities shifted in 1983 ►Grazed versus no grazing treatments ► Perennial grass community structure  Basal area, density, basal area per plant
  16. 16. Community structure between droughts ►Permanent vegetation quadrats  Established in 1949  23 years of vegetation history across 54 years ►Comparisons between the drought years 1953 and 2002 across three grazing intensities  1953 & 2002 lowest basal area for each drought, most complete record
  17. 17. Community structure & topo-edaphic variation ►Paired quadrats based on the presence or absence of large or abundant surface rock features ►One heavy grazing treatment unit not included  Rainfall event between sampling periods  Hilaria belangeri production, 2.5 times the basal area measurements of other treatment units
  18. 18. Cumulative Annual Precipitation Sonora Experiment Station 1919 to 2002 1200 1000 Precipitation mm 800 600 400 200 0 1920 1940 1960 1980 2000 Year
  19. 19. ► Palmer Drought Severity Index ► Quarterly values for 1949 to 1959 & 1992 to 2002 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S 6 1992-2002 1949-1959 4 Palmer Drought Severity Index 2 0 -2 -4 -6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959
  20. 20. ► Palmer Drought Severity Index ► Quarterly values for 1949 to 1959 & 1992 to 2002 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ► Monthly values 1949 6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S to 1953 1992-2002 1949-1959 4 Palmer Drought Severity Index 2 0 -2 -4 -6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 Palmer Dorught Severity Index 4 2 0 -2 -4 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1949 1950 1951 1952 1953
  21. 21. ► Palmer Drought Palmer Dorught Severity Index 4 Severity Index 2 ► Quarterly values for 0 -2 1949 to 1959 & -4 1992 to 2002 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1998 1999 2000 2001 2002 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ► Monthly values 1949 6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S to 1953 1992-2002 1949-1959 4 ► Monthly values 1998 Palmer Drought Severity Index 2 to 2002 0 -2 -4 -6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 Palmer Dorught Severity Index 4 2 0 -2 -4 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1949 1950 1951 1952 1953
  22. 22. ► Palmer Drought Palmer Dorught Severity Index 4 Severity Index 2 ► Quarterly values for 0 1949 to 1959 & -2 -4 1992 to 2002 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1998 1999 2000 2001 2002 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ► Monthly values 1949 6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S to 1953 1992-2002 1949-1959 Monthly values 1998 4 ► to 2002 Palmer Drought Severity Index 2 ► Unprecedented 0 pattern of alternating -2 abundant precip & drought -4 -6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 Palmer Dorught Severity Index 4 2 0 -2 -4 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1949 1950 1951 1952 1953
  23. 23. ► Palmer Drought Palmer Dorught Severity Index 4 Severity Index 2 ► Quarterly values for 0 1949 to 1959 & -2 -4 1992 to 2002 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1998 1999 2000 2001 2002 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 ► Monthly values 1949 6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S to 1953 1992-2002 1949-1959 Monthly values 1998 4 ► to 2002 Palmer Drought Severity Index 2 ► Unprecedented 0 pattern of alternating -2 abundant precip & drought -4 ► Aug 1999 to Sep 2000 -6 D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S D M J S lowest 12 month PDSI 1949 1950 1951 1952 1953 1954 1955 1956 1957 1958 1959 values outside of Palmer Dorught Severity Index 4 1950’s drought & dust 2 bowl drought of 1934 0 -2 -4 J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D J F M A M J J A S O N D 1949 1950 1951 1952 1953
  24. 24. Mean Weekly High Temperatures Sonora Experiment Station 1951 to 1953 & 1999 to 2001 Weekly Mean High Temperature C 40 35 o 30 25 20 15 Mean Weekly High Temp 10 Long Term Mean High Temp 5 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1951 1952 1953 Weekly Mean High Temperature C 40 35 o 30 25 20 15 10 5 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1999 2000 2001
  25. 25. Mean Weekly High Temperatures Sonora Experiment Station 1951 to 1953 & 1999 to 2001 Weekly Mean High Temperature C 40 35 •Higher temperatures during drought o 30 25 event of 1999 to 2000 compared to 1950’s drought 20 15 Mean Weekly High Temp 10 Long Term Mean High Temp 5 0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1951 1952 1953 Weekly Mean High Temperature C 40 35 o 30 •Longest & largest continuous difference between weekly high 25 20 temperature & long term weekly 15 10 5 0 mean in 83 year history Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 1999 2000 2001
  26. 26. Perennial Grass Basal Area Drought Years 1953 & 2002 Wilcoxon Signed Rank Test, Error Bar = Standard Error 100 80 A CM / M Basal Area 60 A 2 40 2 20 0 1953 2002 Basal area during both droughts was at least 5X less than non-drought years
  27. 27. Perennial Grass Density 1953 vs. 2002 Wilcoxon Signed Rank Test, Error Bar = Standard Error 100 A 80 2 60 Plants / M 40 20 B 0 1953 2002
  28. 28. Perennial Grass Density Perennial Grass BA per Plant 1953 vs. 2002 1953 vs. 2002 Wilcoxon Signed Rank Test, Error Bar = Standard Error Wilcoxon Signed Rank Test, Error Bar = Standard Error 3.5 100 A B 3.0 80 2.5 CM2 Basal Area / Plant 2 2.0 60 Plants / M 1.5 40 1.0 B 20 A 0.5 0 0.0 1953 2002 1953 2002
  29. 29. Perennial Grass Density Perennial Grass BA per Plant 1953 vs. 2002 1953 vs. 2002 Wilcoxon Signed Rank Test, Error Bar = Standard Error Wilcoxon Signed Rank Test, Error Bar = Standard Error 3.5 100 A B 3.0 80 2.5 CM2 Basal Area / Plant 2 2.0 60 Plants / M 1.5 40 1.0 B 20 A 0.5 0 0.0 1953 2002 1953 2002 ► Inverse relationship between perennial grass density and basal area per plant between years ► High density of low BA plants vs. low density of high BA plants
  30. 30. Topo-Edaphic Variation & Drought Response
  31. 31. Perennial grass basal area Rock and non-rock sites across heavy, moderate, and no grazing treatments 450.00 cm2 of Basal Area/ m2 of Total Area 400.00 cm2 of Basal Area /m2 of Plant Available Area Split Plot ANOVA, Error Bar = Standard Error 350.00 A A 300.00 cm of Basal Area 250.00 A 200.00 2 150.00 100.00 B 50.00 B B 0.00 Rock Non-Rock Rock Non-Rock Rock Non-Rock Heavy Grazing Moderate Grazing No Grazing
  32. 32. Perennial grass basal area Rock and non-rock sites across heavy, moderate, and no grazing treatments 450.00 cm2 of Basal Area/ m2 of Total Area 400.00 cm2 of Basal Area /m2 of Plant Available Area Split Plot ANOVA, Error Bar = Standard Error •No difference between grazing 350.00 A treatments A 300.00 cm of Basal Area 250.00 A •Significant differences between rock & non-rock sites – 10X greater BA in rock 200.00 2 150.00 •Accounting for rock cover in a heterogeneous environment gives better 100.00 picture of true plant community structure B 50.00 B B 0.00 Rock Non-Rock Rock Non-Rock Rock Non-Rock Heavy Grazing Moderate Grazing No Grazing
  33. 33. Perennial Grass Density 70.00 Split Plot ANOVA, Error Bar = Standard Error 60.00 A B 50.00 Plant Available Area 40.00 30.00 2 Plants / M A 20.00 C C 10.00 C 0.00 Rock Non-Rock Rock Non-Rock Rock Non-Rock Heavy Grazing Moderate Grazing No Grazing
  34. 34. Perennial Grass Basal Perennial Grass Density Area per Plant 70.00 Split Plot ANOVA, Error Bar = Standard Error 14.00 Kruskal-Wallis, Error Bar = Standard Error 60.00 A 12.00 A B 50.00 10.00 Plant Available Area of Basal Area / Plant 8.00 40.00 C 6.00 30.00 2 B B 2 Plants / M CM A 4.00 20.00 D D C 2.00 C 10.00 C 0.00 Rock Non-Rock Rock Non-Rock Rock Non-Rock 0.00 Heavy Grazing Moderate Grazing No Grazing Rock Non-Rock Rock Non-Rock Rock Non-Rock Heavy Grazing Moderate Grazing No Grazing
  35. 35. Perennial Grass Density & Basal Area per Plant ► Significant differences between both grazing treatments & rock & non-rock sites  Rock sites 5X greater density  Grazed treatments 2X greater density ► Inverse relationship between perennial grass density and basal area per plant between grazing treatments ► Difference in BA per plant holds true for both rock and non-rock sites for grazed vs. no grazing treatments
  36. 36. Gradient of Perennial Grass Basal Area, Rock Cover & Size Limestone Blockfield High Slab Limestone Bench Basal Area Debris Slope Non-Rock Site Low Low Rock Cover & Size High
  37. 37. Perennial Grass Basal Area Response to Rock Site Variation 500 cm basal area / m of plant available area Kruskal-Wallis, Error Bar = Standard Error C 400 300 2 B 200 A 100 2 0 Debris Slope Slab Limestone Limestone Blockfield Bench
  38. 38. Conclusions ► Drought events structurally different  Differences in intensity, duration & temp ► Community structure during each drought a function of the long term grazing history of the Sonora Experiment Station  Shift from high density of small BA plants to low density of high BA plants reflection of grazing history across time  Reflected in year to year comparison of each drought event
  39. 39. Conclusions ► Rock cover & topo-edaphic features facilitate the survival of perennial grasses  Function of rock size & cover  Resource conserving system  Modify soil micro-environment ► Driving parameter behind the persistence of perennial grass during periods of extreme drought on the Edwards Plateau  Geologic refugia of biotic resources for recovery  Meta-population dynamics & recovery
  40. 40. Conclusions ► Grazing intensity primary modifier of community structure over time  Den & BA / plant differences between drought events  Den & BA / plant differences between grazing treatments within drought refugia ► Drought primary driver of abundance  No BA differences between drought events  BA differences between rock & non-rock sites
  41. 41. Questions?

×