Campbell_Leslie_A_201203_MSc_thesis

Biophysical Drivers of Tree Crop Performance in Shade
Agroforestry Systems: The Case of Coffee in Costa Rica
by
Leslie Campbell
A thesis submitted in conformity with the requirements
for the degree of Master of Science
Department of Geography
University of Toronto
© Copyright by Leslie Campbell, 2012

ii
Biophysical Drivers of Tree Crop Performance in Shade
Agroforestry Systems: The Case of Coffee in Costa Rica
Leslie Campbell
Master of Science
Department of Geography
University of Toronto
2012
Abstract
Agroforestry production methods present one option for addressing growing concerns about the long
term sustainability of intensive coffee production techniques. A study was designed to compare the
effects of fertilization and shading from two leguminous species, Erythrina poeppigiana and
Chloroleucon eurycyclum, on coffee grown at a Costa Rican research site. Coffee below biannually
pruned, conventionally fertilized Erythrina exhibited the highest photosynthetic performance under
both low and high light levels as well as greater biomass and higher N concentration. Soil P did not
affect coffee performance, although shade trees on sites with higher soil P fixed more N compared to
trees grown on low P sites, most of which were not found to be fixing. Results suggest shade
mechanisms are the most important drivers of coffee adaptation in coffee agroforestry systems,
though proper soil nutrient management and legume species pairing also appear to augment coffee
response to microclimate conditions.

iii
Acknowledgements
I am deeply grateful to my thesis supervisor, Professor Marney Isaac, whose patience and
direction were an incredible help in guiding me through this process. Your encouragement,
suggestions and insight were invaluable in helping this come together. I would also like to thank
Christian Abizaid and Nathan Basiliko for their useful revision suggestions and for agreeing to sit on
my defense committee.
Thank you also to Gabriella Soto for her logistical assistance with setting up and carrying out
my fieldwork as well as for helping me to better appreciate the contextual significance of coffee
agroforestry in Costa Rica. I would also like to thank Dr. Olivier Roupsard (CIRAD) for his
assistance and advice on CO2 gas chamber analysis field techniques. Thank you also to Fabien
Charbonnier, Pablo Siles, Patricia Leandro and to all of the other researchers and staff members at
CATIE for your suggestions and support with fieldwork planning, sample collection and preparation
and during my time in Costa Rica.
I would also like to thank my tireless lab assistants at the University of Toronto for all of
their help processing my seemingly endless bags of samples. Thank you also to all those at the
University of Guelph and the University of Waterloo who lent their equipment and expertise to the
sample analysis process and to the Natural Science and Engineering Research Council of Canada
(NSERC) for providing the funding that made this research possible.
Lastly, my deep thanks also to my friends and family here in Canada for their constant
support and encouragement both during my field research and throughout the thesis-writing process.

iv
Table of Contents
Abstract .........................................................................................................................ii
Acknowledgements.......................................................................................................iii
List of Tables................................................................................................................iv
List of Figures.............................................................................................................viii
Chapter 1: Introduction................................................................................................1
1.1 Introduction ...........................................................................................................1
1.2 Research questions and objectives..........................................................................3
1.3 Research significance.............................................................................................6
Chapter 2: Coffee and Agrarian Development in Costa Rica: A review of the
literature........................................................................................................................7
2.1 Introduction ...........................................................................................................7
2.2 Pre-Coffee Costa Rica and the rise of industrial capitalism.....................................8
2.2.1 The rural egalitarianism perspective.................................................................9
2.3 The interventionist/reform era ..............................................................................13
2.4 The era of neoliberal transnationalism..................................................................16
Chapter 3: Costa Rican Coffee Agroforestry System Structure and Function: A
review of the literature................................................................................................20
3.1 Introduction .........................................................................................................20
3.2 Agroforestry systems ...........................................................................................21
3.3 Species competition .............................................................................................22
3.4 Non-nutrient dynamics in agroforestry systems ....................................................26
3.4.1 Light effects...................................................................................................26
3.5 Soil and nutrient dynamics in coffee agroforestry systems....................................29
3.5.1 Nitrogen dynamics .........................................................................................30
3.5.2 Phosphorus limitation.....................................................................................34
3.5.3 Photosynthetic nitrogen and phosphorus use efficiency ..................................36
Chapter 4: Site Description and Methodology...........................................................38
4.1 Site layout and experimental design .....................................................................38
4.1.1 Site layout......................................................................................................38

v
4.1.2 Shade tree species ..........................................................................................39
4.1.3 Experimental site design ................................................................................40
4.1.4 Sample specimen selection.............................................................................43
4.2 Treatment evaluation............................................................................................43
4.2.1 Measurement of whole plant coffee characteristics.........................................43
4.2.2 Measurement of coffee leaf characteristics .....................................................44
4.2.3 Chemical analysis ..........................................................................................45
4.2.4 Measurement of shade tree characteristics......................................................46
4.2.5 Measurement of nitrogen fixation...................................................................47
4.2.6 Vector analysis...............................................................................................48
4.2.7 Statistical analysis..........................................................................................49
Chapter 5: Results.......................................................................................................50
5.1 Effects of shade management on coffee growth....................................................50
5.1.1 Shade characteristics ......................................................................................50
5.1.2 Plant level adaptations to shade ......................................................................50
5.1.3 Leaf level adaptations to shade.......................................................................50
5.1.4 Foliar physiology ...........................................................................................54
5.1.5 Foliar function ...............................................................................................57
5.2 Effects of nutrient management on coffee growth.................................................60
5.2.1 Foliar nutrient content....................................................................................60
5.3 Correlates of leaf level traits.................................................................................63
5.4 Effects of nutrient management on coffee performance ........................................63
5.4.1 Soil status.......................................................................................................63
5.5 Soil nutrient availability and N2 fixation...............................................................68
Chapter 6: Discussion: Intercropping and Fertilization Effects on Shade Coffee
Function and Physiology.............................................................................................74
6.1 Shading effects on coffee physiology ...................................................................74
6.1.1 Whole plant effects ........................................................................................74
6.1.2 Leaf level effects............................................................................................77
6.2 Shading effects on coffee function .......................................................................80
6.3 Nutrition effects ...................................................................................................84
6.4 Fertilization effects on coffee physiology and function.........................................87
6.4.1 Leaf nutrient use efficiency............................................................................89
6.4.2 Leaf nutrient diagnosis...................................................................................90
6.5 Nitrogen fixation in coffee agroforestry................................................................92
Chapter 7: Conclusions and Future Prospects...........................................................98
7.1 Conclusions .........................................................................................................98
7.2 Areas for future research .................................................................................... 100
Bibliography.............................................................................................................. 102

vi
List of Tables
Table 1. Management and fertilizer applied since 2006 in organic and conventional
fertilization treatments at the study site in Turrialba, Costa Rica....................................41
Table 2. Photosynthetically Active Radiation (PAR) (μmol m-2
s-1
) in full sun and under
shade of Chloroleucon and Erythrina at conventional and organic sites and corresponding
shade levels (%) as compared to full sun .......................................................................51
Table 3. Plant level physiological parameters (Height, Above ground biomass (ABG)) of
coffee grown in full sun and under shade of Erythrina and Chloroleucon at conventional
and organic sites (n=9, all treatments compared to conventional Full Sun using Dunnet’s
test of significance) .......................................................................................................52
Table 4. Analysis of variance table for coffee physiological (leaf area, water content,
mass/area) and functional (photosynthesis, dark respiration, stomatal conductance) traits
as whole plot effects of fertilization (fert), and subplot effects of shade treatment (shade)
and their interaction (P x Trt) (n=9, excludes full sun treatment). Significant effects are
in bold...........................................................................................................................53
Table 5. Leaf level parameters (leaf area, leaf water content, leaf dry mass) of coffee
grown in full sun and under shade of Erythrina and Chloroleucon at conventional and
organic sites (n=9, all treatments compared to Full Sun MC using Dunnet’s test of
significance...................................................................................................................55
Table 6. Leaf mass per area of coffee grown in full sun and under shade of Erythrina and
Chloroleucon at conventional and organic sites (n=9, all treatments compared using
Tukey’s test of significance).......................................................................................... 56
Table 7. Light saturation photosynthesis rate (Amax) of shaded Erythrina and
Chloroleucon compared with full sun under conventional treatment (n=9) .................... 58
Table 8. Coffee under Erythrina and Chloroleucon average photosynthetic N use
efficiency (PNUE) and leaf P content compared to coffee in full sun with conventional
fertilizer treatment (N=3, treatments compared using Tukey’s test of significance........ 61

vii
Table 9. Analysis of variance table for coffee leaf nutrient traits (photosynthetic N use
efficiency (PNUE), photosynthetic P use efficiency (PPUE) as whole plot effects of
fertilization (Fert), and subplot effects of shade treatment (Shade) and their interaction
(Fert x Shade) (n=3, excludes full sun treatment) Significant effects are in bold ...........62
Table 10. Correlations between leaf nutrient parameters and averaged (avg) leaf physical
parameters. Significant effects are in bold .................................................................... 64
Table 11. Correlations between leaf physiological parameters. Significant effects are in
bold............................................................................................................................... 65
Table 12. Comparison of available soil P in the top 10cm of soil between organic and
conventionally fertilized plots. (N=6)............................................................................ 67
Table 13. Tree height of Erythrina and Chloroleucon under organic with conventional
fertilizer treatment......................................................................................................... 70
Table 14. Comparison of average N derived from atmosphere (%Ndfa) at the whole plot
level (conventional to organic) ...................................................................................... 71
Table 15. Comparison of average N derived from atmosphere by organically and
conventionally fertilized Erythrina and Chloroleucon shade trees ................................. 73

viii
List of Figures
Figure 1. Model of the Turrialba study site indicating the location of the trees and
adjacent coffee plants. Note, coffee plants not sampled as part of this study are not
shown. .................................................................................................................................................42
Figure 2. Conventionally fertilized C. arabica leaf photosynthesis values (Amax) as a
function of photosynthetically active radiation density (PAR) under full sun (a),
Erythrina (b) and Chloroleucon (c). Best fit line was fitted to average Amax data limited
by PAR.................................................................................................................................................59
Figure 3. Coffea arabica photosynthesis (Amax) at 1500μmol m-2
s-1
as a function of
stomatal conductance (gs) across all shade and fertilizer treatments......................................66
Figure 4. Soil concentration of Phosphorus (a), Nitrogen (b) and Carbon (c) for
conventional and organic soil fertilizer treatments sampled at a soil depths of 10, 20 and
40cm.....................................................................................................................................................69
Figure 5. Average Amax values for conventionally fertilized coffee plants grown under
Chloroleucon (a), Erythrina (b), and full sun (c) compared with measured light levels
(PAR) within each treatment...........................................................................................................83
Figure 6. Directional changes in relative leaf biomass, nutrient content and concentration
(N, P) of organically fertilized coffee plants growing under Erythrina (EO) and
Chloroleucon (CO) as well as conventionally fertilized Erythrina (EF) and Chloroleucon
(CF), relative to conventionally fertilized full sun coffee (R). The reference condition (R)
is normalized to 100. Circled vector (a) represents significant P accumulation response
of organically fertilized coffee under Erythrina, (b) represents N accumulation at
sufficiency of conventionally fertilized coffee under Erythrina, (c) represents a dilution
effect for P with increasing coffee leaf biomass in both organic and conventionally
fertilized Chloroleucon and (d) represents a dilution effect for N in organically and
conventionally fertilized Chloroleucon.......................................................................... 91
Figure 7. Percent N derived from atmosphere (%Ndfa) as a function of soil P availability
for Erythrina (a) and Chloroleucon (b).......................................................................... 96

1
Chapter 1: Introduction
1.1 Introduction
Since the green revolution of the 1950s and 60s, it has been widely documented that the rate
of agricultural production has been on the rise (Matson, et al., 1997; Evenson & Gollin, 2003).
Advances in agricultural technology combined with their increased accessability meant that
agriculturalists could increase their production efficiency by employing techniques that were
increasingly reliant on external inputs. This led to the advent of what is now known as “intensive”
or “conventional” agriculture (Evenson & Gollin, 2003).
Typically, conventional agriculture refers to a large scale, capital intensive, highly
mechanized form of agriculture involving the extensive use of artificial fertilizers, pesticides and
crop monocultures with the sole aim of maximizing yields (Pimentel, et al., 2005). Over time, the
use of these techniques has led to regional pollution, erosion and soil fertility losses. Given its
negative impacts, conventional agriculture does not present an ecologically sustainable option in
many regions. As a result, there are currently growing concerns about the long-term sustainability of
these techniques given the context of increasing global populations especially within a tropical
context where soils tend to be weathered and nutrient poor (Matson, et al., 1997; Magdoff & van Es,
2009). These factors and others are placing pressure on agronomists to develop processes that will
allow for greater agricultural productivity and reduced reliance on external resources, while
conserving biodiversity and harnessing ecosystem services. These issues are especially important
within developing countries, where lack of access to external inputs for production is a major force
pushing farmers to look beyond conventional agriculture and explore alternative practices in their

2
attempts to improve food security and maintain their livelihoods, particularly in the tropics for
highly significant economic cash crops such as coffee.
Agroforestry systems present one such alternative. The ability of tree species to improve the
input and cycling of nutrients when incorporated into annual or perennial agricultural systems has
been well documented (Schroth, et al., 2001; Garcia-Barrios & Ong, 2004). Consequently the use of
low-input multispecies agroecosystems has moved to the forefront of best management practices.
Costa Rica provides an excellent example case in which shade coffee agroforestry systems
are widely utilized as one response to environmental and socioeconomic constraints. The tree
species in these coffee systems are used for their valuable ecosystem functions or to provide
supplementary income from the sale of their fruit and or timber when coffee prices are low (Beer, et
al., 1998). Within the unique ecological and socioeconomic contexts of Costa Rica, informed design
and management for optimal functioning of these systems is imperative to ensure farmer access to a
steady source of income while minimizing the environmental impacts of agricultural practices.
On November 21, 2011, the New Yorker magazine published an article on the importance
recent trends in the contemporary coffee movement in Central America. The article discusses the
increasingly centralized nature of coffee production and its worrying implications for farmers who
are finding it more and more difficult to secure a fair price for their beans (Kelefa, 2011). Shifts in
consumer demand in the West have led to the rise of the lucrative specialty coffee market and more
recently to an increasingly farmer-focused, socially and environmentally conscious consumer.
These shifts appear to embody the beginnings of a movement towards more coffee production that is
more socially and environmentally sustainable than current methods. The fact that a prominent
magazine such as The New Yorker would publish an article solely focused on coffee and coffee
culture is a powerful indication of its increasing relevance as a global commodity.

3
Due to their increased complexity relative to industrial monocultures, effective design of
agroforestry systems requires a detailed understanding of the biogeochemical cycles and species
interactions that govern resource availability (Swift, et al., 2004). While much research has
examined crop resource requirements and interspecific interactions in multispecies agroecosystems,
little is yet understood about the subsequent effects of these interactions on plant nutrient and non-
nutrient resource acquisition strategies, key factors in determining whether competition or
facilitation takes place. The need for greater understanding of the effects of light availability and
soil conditions on biogeochemical processes is increasingly being recognized as important to
agriculturalists, particularly within the context of the growing popularity of intercropping, a common
agroforestry practice (Beer, et al., 1998; Isaac, et al., 2007a). Despite this increasing recognition,
research into the effects of above and below ground resource availability on specific crop nutrient
acquisition strategies remains relatively scarce. This study directly addresses a number of these gaps
in current understandings of tropical shade coffee agroecosystem function, building on existing
knowledge of interspecific resource competition by examining how crop nutrient acquisition
strategies adapt to above and below ground resource availability.
1.2 Research Questions and Objectives
This research project has two main goals. The first is to examine the ecophysiological response
of a target coffee crop species to the presence of two varieties of nitrogen-fixing tree species and
under two fertilization regimes associated with conventional and organic management practices. I
do this by linking nutrient and light conditions to plant performance metrics such as functional leaf
traits, foliar nutrient content and biomass allocation. The second goal of my research is to examine
how fertilization regimes affect coffee performance as well as biological nitrogen (N) fixation of the

4
two agroforestry shade trees. These two goals can be broken down further into four key questions,
for which hypotheses have been developed.
1) To what extent do ecophysiological adaptations play a role in minimizing interspecific
competition in shade coffee agroforestry systems?
Plasticity has been well documented in coffee species, especially in response to different light
conditions (Araujo, et al., 2008; Chaves, et al., 2008; Matos, et al., 2009). As such, I am expecting
that my findings will indicate both physiological and functional differences between coffee growing
in shade systems versus non-shade systems, or soil with elevated P levels (organic management)
versus low P soil (conventional management). These functional differences are expected to
highlight both complementary and competitive relationships between the species growing in these
systems.
2) What are the effects of shade on overall plant health, photosynthetic efficiency and leaf level
nutrient balance in tropical coffee agroforestry systems?
I expect to find significant differences between shade and sun grown coffee leaves. Under shade
conditions I anticipate coffee plants will generally exhibit higher photosynthetic efficiencies,
higher specific leaf areas, lower light compensation points, lower stomatal conductance and
lower dark respiration rates than sun grown coffee. I also expect that the light saturation points
of sun leaves will be higher than those of shade leaves due to their acclimatization to strongly lit
conditions. The extent of these differences is expected to become more pronounced under higher
shade levels.

5
3) What are the effects of soil nutrients, specifically soil phosphorus, on overall plant health,
photosynthetic efficiency and leaf level nutrient balance?
Due to the fact that P has been strongly linked to N2 fixation in legume species, it is expected that
increased P levels in the soil will increase soil N availability and thus N uptake by plants. Under the
organic treatment I expect to find that coffee plants have a higher leaf nutrient content. Furthermore,
the majority of plant P acquisition from the soil has been attributed to mycorrhizal fungi and P-
solubilizing soil microbes (Van Der Heijden, et al., 2008). This being the case, I expect that that the
intensive organic soil treatment will contain higher soil microbial populations and thus provide
plants with greater access to soil P, manifesting in higher levels of P in intensive organic coffee leaf
tissue. Higher photosynthesis rates are also expected to be observed in coffee grown in a higher P
environment due to the fact that the main energy molecule driving this process, ATP, contains
phosphorus.
4) What is the extent of N2 fixation taking place in these systems and is there evidence to
suggest that N is being transferred from the overstory species to the associated coffee plants?
I expect to find evidence of that both legume and shade tree species are fixing atmospheric N2 via
the natural abundance method. Furthermore, I expect there to be differences in the δ 15
N of coffee
roots grown under an N2 fixing over-story crop and those of the reference species, chosen from the
full sun plot where N is only available via uptake from soil N pools. I also hypothesize that the δ 15
N
ratio found in sample tissue from the tree species will be more similar to the coffee plants they shade
than to the reference coffee plants, grown in the absence of N2 fixers.

6
1.3 Research Significance
In quantifying these crucial but poorly understood agroecosystem dynamics, my research
aims to inform the establishment of guidelines for optimum species pairing and soil amendment
regimes which minimize species competition and maximize beneficial interactions by using
plants with complementary resource capture techniques. Within the Costa Rican context, coffee
makes up a significant portion of the export market so management prescriptions derived from
this study have the potential to improve management efficiency and reduce resource use within
low-input systems. In the broader agroecological context, by quantifying the physical
manifestations of interspecific resource competition, this research, advances the knowledge base
needed to design effective agroecological systems, and secondly, has the potential to reduce the
need for costly and environmentally damaging external inputs.

7
Chapter 2: Coffee and agrarian development in Costa
Rica: A review of the literature
2.1 Introduction
In an attempt to place this study of coffee systems in its proper geopolitical and historical
context, what follows is an attempt to reconstruct a cohesive picture of Costa Rica’s agrarian history
since the introduction of coffee as a crop species. Relying on the writings of prominent Latin
American agricultural historians, I will examine of coffee’s impact on Costa Rican class relations
and socioeconomic development. The analysis will focus on the changes in technologies and forms
of production that took place as the coffee industry evolved, and on major changes in land and
labour as they relate to the formation of contemporary Costa Rican class structure. It should be
noted that this section is not key to understanding the technical aspects of this experiment, but is
meant to help the reader understand the broader importance of coffee as an export crop in Costa
Rica, and to appreciate the importance of its study.
Inegalitarian land and income distribution resulting in the extraordinary concentration of
ownership and entrenched position of the elite class in Latin America has been widely regarded as a
primary cause of the marginalization and impoverishment of the rural majority in this region. This
shifting distribution has profoundly affected the trajectory of regional development since the colonial
era. It has been argued that within this context, Costa Rica represents somewhat of an exception to
this rule.
Precapitalist Costa Rica has been characterized as largely egalitarian, with a low population
density and uniform patterns of poverty punctuated by occasional fluctuations in local economic
prospects. It has been argued that this is what prevented the establishment of colonial economic
institutions such as encomiendas and repartimientos found in much of the rest of Latin America

8
during the colonial era, setting the stage for Costa Rica’s unique postcolonial development path
(Seligson, 1980). In this context, the introduction of coffee as an export crop species in the early
1800s significantly altered the trajectory of Costa Rican development. Coffee and its development
as an export industry can be linked to major changes in land distribution, labour patterns, and social
class relations, changes that continue today despite coffee’s decreasing importance as a percentage
of Costa Rica’s national GDP.
2.2 Pre-coffee Costa Rica and the rise of Industrial Capitalism
Before the introduction of coffee, it has been argued that Costa Rican society was largely
egalitarian, characterized by a large class of self sufficient yeomen and that it was not until the
introduction of agrarian capitalism that major economic differences began to manifest themselves
(Seligson, 1980). It is evident that the impacts of colonization were not felt as strongly in Costa Rica
as elsewhere in Latin America. Seligson attributes this to Costa Rica’s small, widely dispersed, rural
indigenous population and lack of readily exploitable resources or transport infrastructure. These
qualities made resource extraction from the newly acquired colony quite difficult and meant that
Costa Rican colonists tended to be self sufficient, independent and relatively poor. Even following
colonization, differentiation within Costa Rican society was said to be largely social and not
economic. This precapitalist rural egalitarianism is seen as an enduring basis for the Costa Rican
way of life by both coffee growers and social scientists, but authors such as Gudmundson have also
argued that this view is more myth than reality. First, let us examine in greater detail Seligson’s
interpretation of the changes to class structure and land tenure that occurred during the advent of
agrarian capitalism in Costa Rica.

9
2.2.1 The Rural Egalitarianism Perspective
Aside from a limited number of haciendas, Seligson asserts that the general pattern of land
tenure during the colonial period in Costa Rica was that of the small farm. The supply of indigenous
labour simply was not large enough to support large scale hacienda agriculture (Seligson, 1980).
This did not prevent colonists from obtaining title to land, though due to a policy of taxation on
unused land, gaining larger tracts than could be worked by a small labour force was discouraged
keeping landholdings small and dominated by subsistence livelihoods. This was the case within the
both the indigenous and Spanish colonist populations. Slowly, a subsistence and barter village
economy emerged over the course of the 17th
and 18th
centuries, based on village exchange and
moderate levels of extraction of labour by the colonists. There was little direct control over
indigenous landed property rights or smallholder production and most wealth was garnered through
taxes and tithes (Gudmundson, 1986).
Stone (1973) also highlights the fact that the existence of general poverty did not preclude
some class distinctions in colonial Costa Rica. The society is said to have been divided in two,
between the small elite nobility and the rest of the population which lived in extreme poverty. It was
this elite class that Seligson argues formed the basis for the eventual development of more
differentiated social classes within Costa Rica.
Seligson believes that this unique class structure and subsistence mode of production
continued through much of the rest of the colonial period, up to and including the initial introduction
of coffee to Costa Rica in 1806. Initial adoption of the new crop was quite slow for a number of
reasons. At this point, peasants made up the majority of the landowning class in Costa Rica. The
risk of converting to coffee as a means of subsistence did not outweigh the potential returns to
production, so production levels remained low (Seligson, 1975). This also meant that the few who

10
could afford to switch to growing coffee were those with enough capital afford the risk. In 1821,
Costa Rica received its independence from Spain. It first moved to exploit its moderate stores of
gold which was the primary source of capital in the initial post-independence period. By the mid
1820s, the newly established state began to take the first steps to encourage the growth of coffee by
providing incentives to growers. Tax exemptions and land titles were given to those who cultivated
coffee in a successful campaign to increase production. By 1832, coffee production had increased to
the point where it was available for major export. This signalled a significant transition in terms of
production in Costa Rica as it began a slow but steady shift from a domestic, subsistence mode of
agriculture to a more export oriented one.
Supported by government incentives, coffee exports in Costa Rica increased steadily from 1
million tons/year in the 1840s, to 4 million in the 1850s, 11 million by 1870 and 20 million by the
end of the century (Seligson, 1980). Initial coffee exports were to Chile, which signalled the first
opening of Costa Rican markets to foreign consumer goods. A few years later, Britain also became
a trading partner and export revenues increased rapidly. Despite this increase, profits by coffee
exporters tended to be significantly higher than the profits made by producers, who had to pay for
the costs of planting, weeding, picking, washing, drying and transporting the beans to the exporters,
which cut deeply into their revenues (Seligson, 1980). Once established, this profit structure
continued to be reinforced as the development of the coffee industry took place.
Early revenues from the sale of coffee were invested mainly in transport infrastructure which
sped Costa Rica’s development in a number of areas. New products and agricultural technologies
were also introduced, leading to improvements in both living standards and agricultural efficiency,
the majority of which were enjoyed by the slowly growing middle and upper classes (Seligson,
1980). The economy became more and more monetized as the cacao bean, which had been heavily

11
used as a medium of exchange in a barter system prior to coffee’s introduction, was replaced.
Seligson also highlights the fact that barter systems, unlike capitalist systems, are immune to large
scale inflation and are far less susceptible to external economic shocks. Costa Rica was now
exposed to the risk of fluctuations in the global economy in ways it had never been before,
fluctuations that were most likely to disadvantage the poor.
As the economy shifted to rely more heavily monetary exchange, an increasing number of
peasants found they needed to plant coffee. Despite their supposed progress towards the optimal
productivity model promised by capitalist development, peasants were being simultaneously
divested of control over what they produced on their lands and found they needed to grow coffee
even if only to obtain the currency to purchase supplies. Both land and labour were diverted away
from more traditional forms of subsistence production in favour of coffee production which in turn
decreased domestic food production and availability. By 1854, domestic production of subsistence
crops such as wheat had dropped to the point that flour had to be imported despite a history of self
sufficient production in Costa Rica. Other staples were to follow causing food prices to rise, the
effects of which were disproportionately felt by the poor who spend the largest percentage of their
earnings on food (Seligson, 1975). Seligson argues that this in combination with fluctuations in
world market prices for coffee prevented peasants from taking full advantage of Costa Rica’s
newfound wealth.
The growing export industry also led to a technological revolution in coffee production in
Costa Rica. From the first years of production, through the 1930s, coffee production was a low
technology, labour intensive process. This limited family production capacity and placed intrinsic
limits on the maximum level of production because the process was so labour intensive. (Seligson,
1975). The intensive nature of the process also meant many beans were damaged which lowered the

12
value of the final product. According to Seligson, this also placed limits on the aspiring aristocracy
because Costa Rica lacked the surplus labour force to tend large coffee estates.
As coffee processing equipment became more readily available, larger growers who could
afford it began opening mechanical processing plants called beneficios using imported equipment to
process coffee from numerous local farmers. This also established the separation of the growth and
processing stages of coffee production characteristic of a more agrarian capitalist mode of
production (Sick, 2008). Beneficios significantly improved the efficiency of the coffee production
process causing the spike in both production and export quantities observed between the mid 1830s
and the end of the 19th
century. (Seligson, 1980).
Technological change in the early 1900s also impacted land use by allowing for the further
growth of beneficios, growth that resulted in a reduced number of much larger scale beneficio
operations. Originally, a small beneficio had to be close to the farmers’ fields to allow for rapid
transport between field and transfer station. With the advent of cars and trucks, fresh coffee berries
could be transported long distances without danger of spoilage. As a result, beneficio operations
expanded to include recibidores, regional collection stations that would collect coffee from a number
of different farmers before shipping it all to a central beneficio elsewhere. Larger beneficios were
now able to outcompete smaller ones, squeezing them out of the market, a trend that was accelerated
following World War 2. Before this period, the majority of Costa Rican coffee sold on the world
market was sold based on its distinctive appearance and flavour. Recibidores were much less
common and beneficio size was limited by the fact that producers were careful not to mix high
quality coffee berries with lower quality ones because it decreased the price of the final product
(May, et al., 1952). As the war neared, the USA began to purchase a larger share of Costa Rican
coffee in an attempt to secure their position as an ally. American consumers were accustomed to

13
pre-ground blended coffee, which made the appearance and flavour much less relevant to pricing.
This was in line with the trend towards larger coffee production operations (Sick, 2008)
To summarize Seligson’s interpretation, precapitalist peasant society in Costa Rica was a
dispersed, relatively uniform population without significant exchange or exploitation by any sort of
ruling class. Seligson sees these peasants as rational individuals who are able to operate relatively
independently, unfettered by the potentially exploitative relationships associated with capitalist
modernization. This ‘rural egalitarian’ mode of production was irreversibly changed with the
introduction of coffee and its associated modes of production, ultimately resulting in the
proletarization of the lower class.
2.3 The Interventionist/Reform Era
In the early years of the 1900s, an increasingly agitated lower and middle class began to
voice its discontent with labour and market conditions to the Costa Rican government. This was
likely due in part to the fact that up until 1893, coffee had been largely untaxed to encourage
growers to adopt the export species. Producers were unhappy to face the new tax, which was
followed by a series of other taxes levied through the 1920s making coffee a somewhat less lucrative
option for producers (Sick, 2008). This was the first stage in the reestablishment of a number of
other crops in a market that had previously been growing increasingly dominated by coffee.
In 1933 in the midst of the falling global coffee prices of the Great Depression, the Costa
Rican government relented to mounting pressure from discontented coffee growers by establishing
the Instituto de Defensa del Café de Costa Rica (ICAFE), a public organization that established the
prices that each beneficio was required to pay producers based on the quality of their coffee. These
reforms also placed a limit on the maximum profit that a beneficio owner could make from

14
processing (Seligson, 1975). Although these regulations were initially met with resistance by
beneficio owners who evaded minimum wage laws and profit regulations, these reforms marked the
beginning of an era of more interventionist policies by the government in an attempt to both promote
the coffee industry as a whole but also to improve the position of smallholder farmers (Seligson,
1975).
Agricultural development in Costa Rica following the end of World War 2 generally
concentrated on the continued expansion of the agricultural sector, initially with a much greater
focus on smallholder agriculture. The introduction of other crops into the export market and
movement of agricultural population into frontier areas outside of central Costa Rica was another
major shift during this period (Jacobstein, 1987). Prewar industry in Costa Rica was oriented to
export almost exclusively to Britain. By 1940 as a result of the war, demand for goods by Britain
had shrunk considerably, so production costs had to be financed by the domestic banking system
rather than foreign interests (Seligson, 1980). Costa Rica’s government began to shift its focus
more towards domestic production, attempting to improve the position of smallholder producers
through social reforms, which by then were badly needed.
By the 1950s, land in Costa Rica was more unequally distributed than any of the other four
countries in Latin America (Alker, et al., 1966). Population growth was increasing land pressure on
the rapidly shrinking Costa Rican frontier. Government investments of the 1950s had been
concentrated mainly in the relatively heavily settled Meseta Central region and outlying settlers
suffered as a result. A lack of legal land titles in many cases also reduced incentives for working to
improve tilled land as many poor would deplete the soil before moving on in a pattern consistent
with shifting cultivation (Jacobstein, 1987). Increasing land concentration was also complemented
by a growing tendency towards minifundia, farms too small to support subsistence or profitable

15
management without some sort of supplementary income source such as seasonal labour elsewhere.
A 1963 census found 43% of farms were considered too small to be independently economically
viable (Jacobstein, 1987) Most large landowners were by this point engaged in modern, capitalist-
type operations making it even more difficult for poor farmers to enter the highly competitive
market.
It was this increasingly difficult environment that co-operative action also began playing an
increased role for small scale producers, as farmers began to band together for the first time. Peasant
organization had been relatively low up to this point. Part of the reason for this may be that Costa
Rica’s rural standard of living was historically better than that of other countries in the region, and it
did not experience the same large scale colonial land dispossession that might have inspired the
formation of violent opposition movements via peasant co-operation seen in other areas of Latin
America (Brockett, 1988). Despite the formation of ICAFE, in the 1930s, many farmers still felt
they were being taken advantage of by the processors, who were favoured by the agrarian capitalist
system. To address this issue, processing co-operatives were promoted within the 1940s, to allow
small farmers to compete with larger producers while maintaining egalitarian structure. By
removing the intermediaries between farmers and consumers, farmers were able to increase their
share of the sale price (Sick, 2008). The first official co-op was formed in 1943 with government
support. Participants already owned their own land, and simply wanted to take control of the
processing operations.

16
2.4 The era of Neoliberal Transnationalism
Despite increasing reforms post-war shifts in policy to give greater support to small and
medium sized farmers and to promote co-operatives through protectionist policies, the Costa Rican
government also supported the growth of capital intensive industrial development to increase export
revenues in both the agricultural and industrial sectors (Jacobstein, 1987). These supports were
remarkably successful, tripling coffee yields between 1950 and 1980 and increasing national
production six-fold, but were accompanied by increasing competitive pressure on marginal private
producers and further ownership concentration within the production industry (Paige, 1997).
Throughout the 1970s, income disparity in Costa Rica was also the worst in Latin America. In
response, smallholders began migrating from failing rural minifundia to urban areas (Brockett,
1988). Many traditional aristocratic coffee producers and processors abandoned the domestic
industry, creating industrial scale processing operations, referred to as mega-processors and aligned
with the interests of foreign capital. Even large producers that did not make this transition were
often pushed aside by this agro-industrial transformation. Slowly, a new class of mega-processors
was beginning to dominate the export industry in Costa Rica (Paige, 1997).
The consequences of this newly expanded production and technical superiority created new
problems for coffee producers (Paige, 1997). These producers found that their interests were in
conflict with the International Coffee Agreement (ICA), which had controlled world coffee prices
and production between 1962 and 1989. It was felt that these mega-processors could be more
lucrative within a free market system with unregulated enterprises than they could under the ICA.
They complained that the quotas they were receiving reflected Costa Rica’s historical position in the
global coffee economy, and not the current reality, lobbying for changes to the agreement. Some
producers also took matters into their own hands, beginning to operate independently of the

17
agreement and by 1989 when the ICA collapsed, 40% of Costa Rican coffee was being sold
independently, outside of the ICA because production had far exceeded the set quotas (Paige, 1997).
By the time the ICA collapsed, shifts in consumer demand were making higher quality coffee
more valuable, while generic brands did poorly. Confident in their ability to produce high quality
coffee with low production costs, many Costa Rican producers entered the international coffee
market independently, in direct competition with traditional production leaders such as Brazil and
Columbia. Unfortunately, the disappearance of the ICA and coffee quotas caused a drastic decrease
in coffee prices, which fell by 50% and remained low through the mid 90s.
By the mid 1990s, the Government policy had shifted again, this time setting “sustainable
development” policy objectives, which is still an area of focus today. Agricultural policies were
once again focussed on rural areas, laid out to achieve continuous rural income rise. Most
importantly, the focus was on increasing smallholder and medium scale production, and on
participation in agricultural policy development (Roebeling, et al., 2000). It is hoped that these
policies will be more effective than those of the past in improving conditions for the rural poor.
As we have seen, the transformation of the coffee economy in Costa Rica had a profound
effect on both its social and economic development as the result of the ongoing adoption of new
technologies and forms of production within the coffee industry. Despite its slow initial reception,
coffee was able to rise to a position of economic dominance still seen today, causing major shifts in
land and labour relationships as Costa Rica was penetrated by capitalist relations of production in the
process. Costa Rica moved from an isolated, predominantly smallholder agricultural society to
much larger scale production and processing as technology and capital availability increased and
ownership became concentrated largely in the hands of the elite.

18
As part of this process, the aristocratic producer-processor has for the most part disappeared
as the capitalization of agriculture separated the steps of the coffee production process leaving
smaller farmers more vulnerable to exploitation by market forces. Transnational agro-industrial
mega-processors have now risen to play a dominant role in the private sector, crowding out other
producers unable to compete with their economies of scale. To secure their seat in power, these
organizations continue to push for greater market deregulation and free competition while small
producers struggle to remain profitable.
To counter this increasing dominance, government policies targeting both individual
producers and producer co-operatives have been moderately effective, especially those that actively
restrict the profit margins of processors. While generally organized by government and operating
with a top-down structure, co-operatives were also seen as being effective in improving the ability of
smallholders to access both land and resources for coffee production, and to defend their position
against larger operations.
These large producers are driving the growing shift towards more intensive forms of coffee
production for both large and small farms. These shifts often involve a change in management
practises to focus more on the use of external inputs such as chemical pesticides and fertilizers which
facilitate the production of coffee grown in full sun, as opposed to shaded coffee which has
traditionally been the more popular mode of production. Due to the fact that coffee has evolved to
grow in the shade, boosting and maintaining productivity full sun production requires the high levels
of soil fertility which, in tropical resource-poor environments means increasing levels of fertilizer
application. Growing exposure to the increasingly volatile international coffee market is also
increasing the vulnerability of coffee producers who are finding that they must struggle to receive
fair prices in return for their crops (Sick, 2008).

19
In understanding how coffee came to occupy a place of dominance in the Costa Rican
economy, it becomes clear why studies like this one are of crucial importance. In order to remain
competitive in the face of increasing competition from large scale conventional agricultural
operations, farmers lacking resource access cannot purchase the inputs needed to engage in high
intensity coffee production and therefore need a viable alternative. Agroforestry systems present one
such alternative, but in order to maintain system productivity, design for functional efficiency is key.
This requires a thorough understanding of how these systems function and how the species within
them interact with each other. With the sociohistorical context now well established, the following
section will shift to focus more on literature specific to the various unique characteristics of coffee
agroforestry systems and will explore the system mechanisms and interactions upon which the rest
of this study will centre.

20
Chapter 3: Costa Rican coffee agroforestry system
structure and function: A review of the literature
3.1 Introduction
Adding or removing a plant species from an agroforestry system changes the structure and
function of the system in a number of ways by altering the nature of the interactions between species
therein (Chapin, et al., 1997; Chapin, et al., 2000; Hooper, et al., 2005). One of the most important
of these changes involves the ability of agroforestry species to adapt their physiological and
functional traits to a range of microclimate conditions, a characteristic which has been well
documented (Vance, et al., 2003; Matos, et al., 2009). However, due to energy and nutrient
limitations within agroforestry systems, tradeoffs must be made between available adaptive
strategies by plants. Understanding these tradeoffs is of crucial importance in optimizing the
functionality of multispecies systems as these tradeoffs are what determine which adaptive strategies
are the most adventageous in a given environment. Beginning with a brief discussion of key
studies of structural and functional diversity , this section will review the broader academic litearture
on agroforestry system structure and function. This will be followed by an in depth examination of
strategic trade-offs associated with plant adaptation under nutrient and non-nutrient resource
limitations. This section concludes by focusing the examination of resource limitation to look
specifically at Costa Rican shade coffee agroforestry systems and the the inter-species dynamics
which drive them.

21
3.2 Agroforestry systems
Throughout the world, the simultaneous cultivation of tree species and agricultural crops now
known as agroforestry has been practiced at one period or another throughout history and is a
common in traditional land use systems (King, 1987). This being the case, when agroforestry rose to
prominence in the world of academia in the late 1970s, it was considered to be less of a discovery
and more of a process of institutionalization of historical practices. Since then many attempts have
been made to develop a common definition for the practise. (Huxley, 1999). One of the first widely
accepted definitions of agroforestry was developed in the 1980s by the World Agroforestry Centre
which stated that
“Agroforestry is a collective name for all land use systems and practices in which
woody perennials are deliberately grown on the same management unit as crops
and/or animals…To qualify as agroforestry, a given land use system or practice must
permit significant economic and ecological interactions between the woody and non-
woody components.” (Lundgren, 1982)
This definition attempted to summarize all of the defining characteristics of agroforestry
systems, but was later criticized for neglecting to address the ultimate potential of agroforestry as a
method for reducing the deforestation associated with conventional agricultural production. Leakey
(1996) suggested that agroforestry methods should be seen more specifically as facilitating the
transition of less complex land use systems towards a mature agroforest composed of many
ecological niches occupied by a wide variety of organisms to satisfy both human and ecological
needs. This broadened the definition to include the need for increased biodiversity and ecosystem
stability while also providing social benefits (Leakey, 1996). Agroforestry is now widely defined as
“…a dynamic, ecologically based, natural resources management system that, through the
integration of trees in farmland and rangeland, diversifies and sustains production for increased

22
social, economic and environmental benefits for land-users at all levels .” (Leakey, 1996). This
broad based classification accentuates the fact that agroforestry is at its core a resource management
system, distinct from conventional industrial production based systems which tend to be capital
intensive, and highly mechanized involving the extensive use of crop monocultures with the sole aim
of maximizing yields (Knorr & Watkins, 1984). This narrow definition of system functionality often
views the environmental impacts of this form of agriculture as externalities which explains why
industrial monoculture practises often lead to soil erosion, fertility losses and regional pollution
(Pimentel, et al., 2005). Agroforestry practises consider overall agroecosystem health alongside
system yields and inherently balances both human and ecological needs.
The inclusion of trees is another key distinguishing characteristic in agroforestry systems
(Schroth, et al., 2001). Trees add another dimension to system function by adding a secondary
canopy layer within the system. Above ground, this can provide increased light capture efficiency as
well as a wealth of microclimate benefits to associated crops (Huxley P. , 1999). Belowground, this
also leads to increased nutrient capture efficiency due to the ability of many trees to utilize nutrient
pools deeper in the soils than crops would normally be able to access. These nutrients are
assimilated into the biomass of the trees and are returned to the soil surface over time through
literfall, decomposition and mineralization processes thus making them available to crop species
(Nair, et al., 1999).
3.3 Species competition
As previously alluded to, species interactions within multispecies agro-ecosystems are driven
by the structural and functional characteristics of the species involved. While now well established,
the roots of our understandings of interspecies relationships can be traced to two independent but

23
pivotal studies in the mid 1920s which subsequently established the Lotka-Voltera model of
predator-prey interaction (Lotka, 1925; Voltera, 1926). These papers introduced the idea of
competitive exclusion which states that if the resource requirements of two associated species
overlap beyond a certain point, they are unable to both persist indefinitely in the same environment.
This theory has gone on to become one of the central organizing principles in the study of
community ecology. Subsequent papers built on this model of species competition, which was
eventually expanded to include the parameter that n species are unable to coexist if there are fewer
than n resources at their disposal, or in fewer than n niches (MacArthur & Levins, 1964; Rescigno &
Richardson, 1965). In 1960, Garret Hardin dubbed this the “competitive exclusion principle”, which
is the term now used to summarize these theories (Hardin, 1960). Subsequently, a number of other
scholars have also attempted to increase the complexity of the Lotka-Volterra model, thereby
extending its range to include more than one resource or limiting factor (Levin, 1970; Haigh &
Smith, 1972; Haussman, 1972). This continued until 1977, when an important study by McGehee
and Armstrong proved mathetmatically that two species reliant on the same resource could exist
indefinitely (Armstrong, 1980). The model they developed looks at a single resource, R, which is
required by both species A and species B. The two species exhibit different growth rates in response
to increasing resource density. In an environment where only one of the species (either species A or
B) and the resource were present, equilibrium would be reached at the point when population growth
was equal to 0. In a competitive, limited resource environment, the species with the lowest resource
requirements to maintain equilibrium would outcompete the other, winning the competition.
Conversely, if the resource pool is large enough, both species will be able to coexist over a range of
different resource densities . This variation on the Lotka-Volterra model was important in that it
provided a more accurate model of coexistence and competition than had previously existed.

24
Although these early works tended to focused mainly on predator-prey species relationships,
they could also be applied to abiotic resource competition, which are far more useful in
understanding interactions between plant species in agricultural systems. In his 1994 publication on
forest ecosystems, Perry closely examines these relationships, classifying them as one of six types of
interaction: mutualism, commensalism, neutralism, parasitism, predation, amensalism and
competition, (Perry, 1994). Mutualistic relationships benefit both species involved, whereas
commensalism benefits one species without affecting the other. Neutralistic relationships affect
neither species while both predation and parasitism benefit one species at the expense of the other.
Amensalism harms one species while leaving the other unaffected and in competitive relationships,
both species suffer from reduced resource access.
While other studies have expanded further on this definition of species interactions and
resource trade-offs, many focussed more on faunal communities as they represented a simpler model
for species interaction. A seminal paper presenting an alternative hypothesis relating specifically to
complex plant communities was published in 1985 by Tilman. This study attempts to explain
common patterns in plant succession due to competition for limited resources and heterogeneity
within habitats, developing what Tilman refers to as the resource-ratio hypothesis (Tilman, 1985).
This hypothesis can be broken down into two main elements. First, there is the dynamic nature of
competition between species as limiting resource supply patterns change over time. These are
referred to as resource supply trajectories and are key to predicting the outcomes of species
competition over time. The paper goes on to argue that one of the driving forces behind terrestrial
plant evolution and differentiation has been the gradient from nutrient rich low-light habitats to
nutrient poor habitats with high light availability.

25
Tilman’s hypothesis states that plant species tend towards specialization in the capture of
different proportions of limiting resource pools and that the makeup of these communities will
change in sync with changes to the availability of these factors. Subsequent research has gone on to
use the resource ratio hypothesis to explain competitive exclusion and coexistense in the context of
agroforestry. Jose et al (2004) argue that within an agroforestry context, this hypothesis is useful for
explaining persistent species partnerships, which take place as a result of differing resource
requirements between associated species. Greater overall capture of these different limiting
resources (relative to competing for the same limiting resources) also increases overall uptake of
previously underused non-limiting resources. The argument follows that the interaction between
species within multispecies agroforestry systems can increase overall capture of limiting resources to
levels greater than if the species were each grown separately (Jose, et al., 2004). In this way species
interactions provide an opportunity to increase the efficiency of nutrient capture in agroforestry
systems.
This concept highlights one of the key advantages of agroforestry systems. Increased
nutrient capture. Canell et al summarized this idea well in their 1996 paper examining the simple yet
powerful agroforestry system tree-crop interaction equation first proposed in a paper by Ong in 1995
(Ong, 1995; Cannell, et al., 1996) . The equation is as follows:
I = F – C
Where:
I = The net increase in crop yield due to the presence of trees as estimated for a land area occupied
by both crops and trees as compared with the same area occupied by just crops
F = Crop yield increses due to the beneficial effect of trees on agroecosystem microclimate and soil
fertility

26
C = the crop yield decrease attributable to tree-crop competition for limited nutrient and non-nutrient
resources
If the value for ‘I’ is positive for a given species combination in a given system, agroforestry
practises will allow for higher yields than monocropping in that environment. Jose, Gillespie and
Pallardy (2004) also discuss this relationship, and also highlight the importance management as a
key factor in determining the outcome of agroforestry species interactions. Management to mitigate
competitive species interactions within these systems is key to ensuring continued system
productivity and soil fertility. The following section will address the function management and
function of specific nutrient and non-nutrient resource dynamics within coffee agroforestry systems.
3.4 Non-nutrient dynamics in agroforestry systems
3.4.1 Light effects
Light dynamics are one of the most important drivers of plant growth in agroforestry systems
so it is unsurprising that it is also one of the most studied aspects of system function. Beer et al
(1998) wrote a key review of the management of interactions within coffee and cocoa agroforestry
systems, in which they explore the specifics of light availability. The authors highlight important
considerations concerning the potential negative impacts of shading resulting from improper
management such as increased pest or disease problems and yield suppression due to competition.
They also note that crop yields on a per area basis have been measured to be higher without shade in
environments where intensive chemical and fertilizer application are feasible if one discounts the
environmental impacts associated with their use. In examining coffee systems, the impacts of
shading on coffee production have been found to depend heavily on environmental conditions. In
suboptimal environments with nutrient or non-nutrient limitations, trees are able to mitigate

27
microclimatic fluctuations and increase coffee production compared to unshaded sites (Beer, et al,
1998). Conversely, studies of coffee growing under optimal conditions have been found to outyield
shaded ones in the same environments. Building on this idea, the general relationship has been
summarized by DaMatta (2004), as the idea that generally the benefits of shade in coffee
agroforestry systems are inversely related to the favorability of the environment in which the coffee
is grown (DaMatta, 2004).
These findings were well supported by a 2011 study of Nicaraguan and Costa Rican coffee
agroforestry systems, partially conducted at the same site where my research took place which
compared the effects of fertilization and shading on coffee grown both in full sun and under a
canopy (Haggar, et al., 2011). Benefits to crop yields from shading were not observed on highly
fertilized plots. These benefits were confined to sites with medium and low levels of fertilizer
inputs, reinforcing the idea that the beneficial effects of shade in coffee agroforestry systems are
more pronounced in resource restricted environments, and that these benefits are dependent on
management techniques.
Specific studies have quantified this shading effect in coffee systems, examining how coffee
responds to differing light environments. A Costa Rican study conducted in 2009 examined how
coffee adapts to different shade levels by taking spot measurements of coffee grown under four
different levels of solar irradiance (Franck & Vaast, 2009). Performance was evaluated at a range of
light levels from darkness to full sun and coffee function was evaluated using photosynthetic rates
and stomatal conductance to quantify coffee performance. They observed a negative relationship
between the average leaf light exposure and quantum use efficiency and a positive one between
average leaf light exposure and maximum photosynthesis rates. This study concluded that coffee

28
leaves adapt to shade by reducing photon flux density light saturation points and increasing quantum
use efficiency.
These physiological responses to shading effect are the key to agroforestry system
performance, and the feature of coffee that allows it to perform well within these systems. Matos et
al (2009) conducted a study documenting these light responses in coffee by sampling leaves from
both sun exposed and self shaded leaves on coffee plants under full sun (Matos, et al., 2009). This
allowed for observation of differences between leaves on the same plant growing at different light
levels. The researchers observed adaptations under shaded conditions include increased leaf area,
improved light capture, lower respiration rates and light compensation points and lower stomatal
densities (Matos, et al., 2009). This study suggests that physiological and biochemical adaptations
play an important role in coffee adaptation to shaded conditions, and that morphological or
anatomical plasticity may play a secondary role. Although this study was of shade effects on coffee
grown under full sun conditions, many of the observed adaptations to self-shading also apply to
coffee grown under a shade canopy.
When used as a strategy within these unfavorable conditions, shading management can
provide a number of important benefits to coffee. It has been found to reduce air temperature
fluctuations, buffer wind and humidity and improve and maintain soil fertility (Beer, et al., 1998).
This maintenance of long term soil fertility is a key aspect of shade coffee agroforestry systems, one
that has been documented and studied since the nineteenth century (Lock, 1888). Unfortunately, a
more thorough examination of the effects of these other non-nutrient factors on shade coffee systems
falls outside the scope of my study. The other major benefit of shading is the actual reduction in
light transmission to coffee crops which prevents over-yielding and excessive vegetative growth
(Beer, et al., 1998).

29
3.5 Soil and nutrient dynamics in coffee agroforestry systems
Tropical regions contain some of the oldest soils in the world. These soils are especially
susceptible to nutrient leaching, and rapid decomposition and mineralization and plant uptake mean
that nutrient pools within the soil tend to be small, making them low fertility and resource poor
(Chapin, et al, 2002). As a result, nutrient limitations play an important role in determining tropical
agroforestry system function. Although any number of different nutrients may be limiting these
systems, Nitrogen (N) and phosphorus (P) are the nutrients most commonly found to restrict the
productive capacity in terrestrial ecosystems (Elser, et al., 2007).
With multiple species competing for the same limited pools of nutrients, species interactions
are inevitable and must be understood to ensure system productivity. Due to soil’s central
importance in maintaining overall fertility, studies of the major physical changes to soils within
tropical agroforestry system have identified a number of key interactions. In their 1998 review of
studies examining biophysical interactions that occur in tropical agroforestry systems, Rao et al
(1998) summarize a number of key improvements to soil’s physical characteristics that have been
linked to agroforestry practices. Increased soil organic matter levels due to litterfall and pruning
decomposition, improved soil porosity and aggregation, reduced soil density, and increased soil
macrofauna and microbial populations have all been highlighted, as well as reduced soil
temperature. They emphasize the fact that many of these interactions occur together and are
interdependent, interacting with other chemical, physical and biological processes taking place in the
system (Rao, et al., 1998).

30
3.5.1 Nitrogen dynamics
Nitrogen (N) cycling in conventional agricultural systems is driven largely by management
activity such as the application of synthetic N containing fertilizer. Synthetic N fixation requires
high heat and pressure and is performed using what is known as the Haber process (Chapin, et al.,
2002). Synthetic N is normally applied to agricultural soil in the form of fertilizer which can
significantly increase NO3 levels in the soil but also increases soil leaching and runoff if over-
applied. Once released, this runoff leads to pollution and eutrophication, both of which are highly
damaging to natural systems (Matson, et al., 1997).
Although N cycling is an active and dynamic soil process, it should be noted that 95-99% of
N in soils is found in organic compounds that prevent N loss from the soil but are largely
inaccessible to higher plants (Brady & Weil, 2002). Agroforestry systems have been suggested as a
management response to N limitations in agricultural environments. The inclusion of tree species
known to perform specific functions or “ecosystem services” within the system allows for the
mitigation of various resource defficiencies. (Swift, et al., 2004). Nitrogen fixation is one such
function. This process of N addition can also take place through N fixation, a biological process
driven by certain N-fixing plant species (Chapin, et al., 2002). Certain species of trees (eg
Leguminosae, Alnus) are incredibly valuable in agroforestry systems due to their ability to fix
atmospheric nitrogen and add it to the soil. Due to the fact that nitrogen is so often the limiting
nutrient in terrestrial environments, these species can significantly increase the productivity of
agroforestry systems (Dommergues, 1987).
These plant species have evolved the unique ability to form symbiotic relationship with N
fixing bacteria in the soil. Rhizobia are the most common types of bacteria to associate with legume
trees, though other bacteria such as those of the genus Frankia can associate with other plant

31
families (Taiz & Zeiger, 2002). These bacteria produce the enzyme nitrogenase, which is able to
reduce atmospheric dinitrogenase (N2) forming ammonium (NH3). The N2 fixation process must
take place in anaerobic conditions, so colonies of these bacteria form inside nodules found on the
roots of N2-fixing plants. In return for a providing a safe environment and certain plant carbon
exudates, plants are able to use the ammonium to help satisfy their N requirements. This N can also
be transferred to associated plant species, which is the process that makes N2 fixers so valuable
within the context of tropical agroforestry. This transfer can take place in a number of different
ways and has been researched extensively in tropical systems.
The first is through decomposition and mineralization. When N2 fixing plants die or drop
their leaves, their high N content biomass decomposes releasing dissolved organic nitrogen (DON),
which is used both by plants and soil microbes. Both mineral nitrogen (NO3 and NH4) and dissolved
organic nitrogen (DON) in can be assimilated by plants and used for growth processes. N2 fixing
plants have also been found to release N rich root exudates which allow for N transfer to associated
crops through the soil (Paynel, et al., 2001). Soil fungi called micchorizae have also been found to
facilitate the transfer of fixed N from trees to crops, by acting as pathways linking the roots of the
two species (He, et al, 2009).
Determining the amount and rate of transfer due to N2 fixation between tree and crop species
involves the use of stable isotopes. It is known that the heavy isotope 15
N is present in atmospheric
N at a constant 0.3663%, but can be found at many different abundances in the soil (Dawson, et al.,
2002). By comparing the 15
N abundance within plant tissues with that of the soil and the
atmosphere, estimates of the relative proportion of atmosphere to soil derived N can be estimated.
This method is complicated by the fact that fractionation of 15
N has been found to occur within both
plants and soil within the system which greatly complicates calculations of N transfer. Also, it has

32
been found that 15
N signatures differ between different plant tissues, further complicating 15
N
signature comparison (Nygren & Leblanc, 2009). As a result, the majority of studies rely on a
different method, the N enrichment technique. This method involves enriching a quantity of
nitrogen with higher levels of 15
N than naturally occur in an environment and attempting to track that
N as it moves through the studied environment (Dawson, et al., 2002). One of the major benefits of
this method is that it reduces the effects of fractionation making the labeled N easier to track
(Dawsonet al., 2002).
In a 2000 study, Snoeck et al. attempted to quantify the amount of N transfer between
associated legume and coffee species using the 15
N natural abundance method. Although they were
able to prove that all but one of the 9 legume species sampled were fixing N2 from the atmosphere, 2
of those found to be fixing did not exhibit any transfer to associated crop species. One of these two
species was Erythrina abyssinica, a close relative of Erythrina poeppigiana, one of the legume
species used in my study. Ultimately, they were able to show that approximately 30% of the N fixed
by the legume species was being transferred to the coffee plants within the system (Snoeck et al.,
2000).
A slightly different method was employed by Jalonen et al in their 2009 study which
examined the extent to which root exudates facilitated the transfer of N from Gliricidia sepium, a
common legume tree species in agroforestry systems to a grass species. This study used the isotope
labeling technique, whereby tree leaves were painted with 15
N-enriched KNO3 which was absorbed
by the leaves, over the course of 10 weeks (Jalonen, et al., 2008). Root exudates were then collected
and analyzed for N content and 15
N enrichment to quantify N transfer. This study found that G.
sepium exuded approximately 1.7% of their total N over the course of the experiment, which was
calculated to satisfy 16% of associated grass N requirements. The majority of these exudates were

33
not absorbed by the grass, which was found to take up between 3.8 and 7.5% of the 15
N from the
exudates, the equivalent of 0.8-1.1% of its N requirements. These low values for transfer via root
exudates suggests that direct root contact between the donor and recipient species.
Another study by Kurppa, et al (2010) of N transfer used a slightly different isotopic
enrichment technique to examine N transfer from G. sepium and Inga edulis, two N2 fixing species
to a woody perennial species specifically Theobroma cacao. In this study, the researchers marked
soil as opposed to leaves with enriched 15
N over the course of eight months in Costa Rica. Leaf litter
accumulation over the source of the experiment was unsubstantial, thus all observed N transfer was
assumed to be occurring belowground. Both tree species were found to be acquiring more than 75%
of their total N from the atmosphere, but evidence that fixed N was then being transferred to
associated crops was weak as transfer was only detected in two out of ten cases. It should be noted
that despite the fact that these trees were found to be fixing significant amounts of N2, competition
was still observed between T. cacao and the N2 fixing overstory for soil N pools. Shade trees were
found to accumulate more soil N than cacao, regardless of whether or not they were found to be
fixing N2 (Kurppa, et al., 2010). This suggests that although N2 fixing trees are a potential solution
to N limitations within tropical agroforestry systems, competitive effects must still be taken into
account and managed accordingly.
The processes by which nitrogen fixing bacteria convert atmospheric N2 is highly energy
intensive and requires large quantities the energy molecule of adenosine triphosphate (ATP) to break
the triple bond holding together the nitrogen atoms (Brady & Weil, 2002). Since each molecule of
ATP contains 3 phosphorus molecules, its production requires significant amounts of P and as a
result the growth and function of N2 fixing plant species is significantly limited by the availability of
P in the soil. Factors determining the rates at which trees are fixing N are also important Laboratory

34
studies have shown that both N and P availability can regulate rates of Nﬁxation: increased N
availability often suppresses rates, while increased P availability frequently stimulates rates
(Madigan, et al., 2003). To fully understand how these limitations arise, the following section will
explore the how P limitations affect these systems.
3.5.2 Phosphorus limitation
Phosphorus (P) concentrations in soils tend to be very low relative to other macronutrients. It
is readily taken up from the soil solution as either phosphate ions released by soil humic material and
plant residues during decomposition or less commonly as soluble organic P compounds (Horst, et
al., 2001). These ions tend to have a low motility in the soil which further reduces their availability
but this is compensated for somewhat by movement of plants roots to zones of high P ion
concentration. Mycorrhizal hyphae in the soil can also facilitate P uptake through their association
with plant roots and are thought to be able to access certain bonded forms of P (Brady & Weil,
2002). Following uptake, plants assimilate P into their tissues, and return it to the soil through plant
residues which are broken down and released back to the soil by soil microorganisms. These
microorganisms absorb part of the P in the process, tying it up until they too die and are
decomposed. Some soil P is also held in the active and passive fractions of soil organic matter
which can store it for future release (Brady & Weil, 2010).
The amount of P actually available to plants from the soil solution is very low tropical most
soils, often less than 0.01% of the total soil P content (Brady & Weil, 2010). This is because of the
high concentrations of iron and aluminum oxides often found in tropical soils, both of which bind
tightly with P forming secondary compounds which plants are unable to access (Chapin, et al., 2002;
Vance, et al., 2003). The majority of this P can be classified into one of three broad groups of

35
compounds: organic phosphorus, calcium-bound inorganic phosphorus or aluminum/iron bound
inorganic phosphorus. Although all of these compounds contribute small amounts phosphorus to the
soil solution slowly over time, the vast majority of the P in each group is unavailable to plants due to
its low solubility (Brady & Weil, 2010).
Due to the fact that the majority of soil P is tightly bonded to soil minerals, loss of P from
tropical soils via leaching is quite low, though like N, artificial additions of P fertilizer to the soil can
significantly increase leaching and stimulate downstream eutrophication. Natural P additions to the
soil occur through rock weathering, but this slow process does not readily replenish losses from the
soil (Vitousek et al., 2010), the majority of which take place through plant uptake, erosion of P-
bonded particles and through dissolution in runoff water (Brady & Weil, 2010).
As previously mentioned, plants in agroforestry systems able to carry out N2 fixation are
reliant on P availability to complete the process. The P they require is needed to provide energy in
the form of ATP, used for the development of functional nodules to house N-fixing bacteria and for
membrane biosynthesis and signal transduction (Graham & Vance, 2003). As a result, soil P
limitations can hinder the ability of N fixing plants to address N limitations in tropical soils, further
compounding existing issues of soil infertility.
Numerous studies provide evidence in support of this phenomenon. One such study by
Binkley et al (2003) looked at the effects of P limitations on N2 fixation in Facaltaria moluccana
and Eucalyptus saligna. Using the pool dilution method, researchers found that the addition of soil P
caused a doubling of the amount of N fixed by Facaltaria seedlings (Binkley, et al., 2003).
Thissuggested that P was a significantly limiting factor on N2 fixation in these systems. Similarly, a
2011 study by Isaac et al yielded similar results in Acacia senegal species in agroforestry systems,
finding that N2 fixation rates increased with increasing soil P which they link to increased N

36
mineralization rates within the soil (Isaac, et al., 2011). While this study does not directly look at N
uptake, it does provide evidence for increased potential N mineralization which suggests the
possibility of higher soil N availability as the result of increased P levels
3.5.3 Photosynthetic nitrogen and phosphorus use efficiency
Both N and P are also closely tied to carbon assimilation through photosynthesis in coffee
agroforestry systems. The use of these nutrients efficiently has been linked to overall plant fitness
and is believed to have a heavy influence on productivity and nutrient cycling in these environments
(Aerts & Chapin, 2000; Vitousek et al., 2004). Photosynthetic N use efficiency (PNUE) and
Photosynthetic P use efficiency (PPUE) are defined as the ratios of the rate of photosynthetic carbon
(C) assimilation to foliar N and P use, respectively.
Similar to N2-fixation processes, leaf photosynthesis requires the energy molecule ATP. As
a result, leaf P deficiency has been linked to reduced maximum photosynthetic rates (Amax) (Lauer,
et al., 1989). Therefore, efficient use of P via a high PPUE is key to maintaining high rates of
carbon assimilation in agroforestry systems. Nitrogen use efficiency is also important from a
photosynthetic perspective. This nutrient is a key component the photosynthetic components within
the coffee leaf and studies have shown N to be especially important to the production of the enzyme
Rubisco (ribulose-1,5-bisphosphate carboxylase oxygenase) (Poorter & and Evans, 1998).
A 2009 study of the response of PNUE and PPUE to soil fertility gradients found that PNUE
tended to decrease as average leaf mass per area increased with decreasing soil N and P availability
(Hidaka & Kitayama, 2009). Similar results have been found in other studies and it has been
suggested that this negative relationship between mass per area and PNUE was due to the fact that as
leaf mass per area increases, a greater percentage of foliar N must be invested in cell walls and as a

37
result is no longer available for the production of photosynthetic enzymes (Onada, et al., 2004;
Takashima & Hikosaka, 2004). With less photosynthetic enzyme available, leaf photosynthetic
ability is also reduced.

38
Chapter 4: Site description and methodology
4.1 Site layout and experimental design
4.1.1 Site layout
This study was conducted at the experimental farm site associated with the Centro
Agronomica Tropical de Investigación y Enseñanza (CATIE), 1.5km Northwest of the central
campus in Turrialba, Costa Rica. The site itself is located at 9°53´44´´ North Latitude and 83°40´7´´
West Latitude. Average temperature is 21.8 °C, average annual precipitation is 2700mm yr-1
and
average relative humidity is 88%. This region is considered a low altitude (685 m above sea level)
and has no distinct dry season. Soils are mixed alluvial and have medium or poor fertility with a
water table that fluctuates between 40 and 120m. Previous assessments of soils in this region have
characterized them as Eutric Cambisols due to the fact that this area occupies an old alluvial terrace
of the Reventazon river which flooded regularly prior to the installation of a drainage system (Kass,
et al., 1995). The structure is characterized as moderate with fine subangular blocks with relatively
high levels or organic matter. Previous characterizations of soil pH have found the reaction be acid
in the surface horizons but nueutral at depth due to increases in base saturation (Kass, et al., 1995).
Sloping on the research site was negligible (<1%) though drainage was poor, necessitating the use of
drainage channels of 1m in depth. The site was planted with Coffea arabica L. var “Caturra” at a
density of 8000 plants per hectare by planting two plants per planting hole, in keeping with local
practices. Three species of shade tree (Chloroleucon eurycyclum, Erythrina poeppigiana and
Terminalia amazonia, henceforth referred to as Chloroleucon, Erythrina and Terminalia,
respectively) were paired with the coffee on the site both in single and double mixes. Prior to the
establishment of this trial in November 2000, the site was used for commercial sugar cane
(Saccharum officinarum) production.

39
The management of each plot was divided into two subplot fertilization treatments: moderate
conventional and intensive organic (henceforth referred to as “conventional” and “organic”,
respectively) These treatments were altered over time in accordance with coffee life stages,
beginning with a 2 year growth phase followed by a productive phase. Subsequent adjustments to
treatments were made based on soil fertility analysis until coffee was established and soil conditions
had improved at which point the treatment regimes were stabilized. These treatments have not been
changed since 2006. The description of the subplot management treatments can be found in Table 1.
Management of the conventionally fertilized subplots was designed to mimic standard levels of input
and management used by local farmers. These treatments were divided into three blocks.
4.1.2 Shade tree species
Two N2-fixing species of shade tree grown in association with coffee were chosen for study:
Erythrina, an evergreen low compact service tree and Chloroleucon, a high spreading evergreen
timber species. Trees were selected for their contrasting physical characteristics (crown architecture,
phenotype).
Physical species management was specific to each plant species. Coffee bushes were stump
pruned following each harvest, depending on each plant’s estimated productive potential for the
following year. Erythrina management involved two prunings per year leaving a minimum of three
branches to provide partial shade cover. These prunings were left to decompose on site. The lower
branches of Chloroleucon were removed each year to improve growth structure and also left to
decompose on site.

40
4.1.3 Experimental site design
The study site was set up with three replicates forming a randomized block design. Shade
level was used as the main treatment, with fertilizer regime as a subtreatment within shade plots.
Subplots were between 500 and 600m2
in size, each with a minimum of 24 shade trees and 100
coffee plants, spread over an area of 6 hectares. In the various plots, shade trees were planted in rows
with a spacing of 4m x 6m, which shaded rows of the C. arabica (henceforth referred to as

41
Table 1. Management and fertilizer applied since 2006 in organic and conventional fertilization
treatments at the study site in Turrialba, Costa Rica.
Management input Type Conventional Organic
Soil fertilization Nitrogen 150 kg ha-1
287 kg ha-1
Phosphorus 10 kg ha-1
205 kg ha-1
Potassium 75 kg ha-1
326 kg ha-1
(10 t ha-1
composted chicken
manure, 100kg ha-1
K-
mag)
Pest Control Fungicide (2.4g L-1
H2O)
Atemi or Copper sulfate
(CuSO4), applied once
annually
No fungicide application
Weed Control Round-up® (10ml L-1
)
application to weed
species
No herbicide application,
manual removal of weeds
by hand and mechanical
management using a
string trimmer
Supplementary
Treatment
Foliar applications of
botanical and biological
compost, annual prunings
left to decompose on plot.

42
Figure 1. Model of the Turrialba study site indicating the location of the trees and adjacent coffee
plants. Note, coffee plants not sampled as part of this study are not shown.

43
“coffee”), which was spaced at 1m x 2m. The total area of shade treatment plots containing
Erythrina and Chloroleucon were 4000 and 3200m2
, respectively. Each replication also contained a
full sun treatment where coffee grown without shade with the identical management techniques to
the conventionally fertilized shade plots. No organically fertilized subplot was included in the
original site design, because organic management techniques are normally not practiced in the
growing of full sun coffee. These plots were designed to replicate management techniques
embodied in the recent shift towards more industrial methods of full sun coffee production.
4.1.4 Sample specimen selection
In each shaded subplot, three shade trees thought to accurately represent average height and
canopy characteristics for their species were selected for study. Three coffee plants with
representative characteristics growing within 2 m of the base of each tree were also selected. This
resulted in a total selection of 6 trees and 18 coffee plants per single species shade plot, with 3 trees
and 9 coffee plants in each of the two fertilized subplots. Within the full sun plots, a random 5m x
5m area of the plot was selected and within this area, three coffee plants were randomly selected for
sampling.
4.2 Treatment evaluation
4.2.1 Measurement of whole plant coffee characteristics
Coffee plant height (using a clinometer) and diameter at breast height were manually
measured and recorded. These measurements were used to calculate aboveground biomass. Coffee
aboveground biomass was calculated using the equation outlined by Segura and Kanninen (2006) for

44
estimating total aboveground biomass (BT) (kg/plant) for coffee plants growing in agroforestry
systems (Segura & Kanninen, 2006). The equation is as follows:
Log10(BT) = a + b * Log10(h)
Whereby:
a = a calculated constant parameter (-1.113)
b = a calculated constant parameter (1.578)
h = coffee plant height
4.2.2 Measurement of coffee leaf characteristics
Measured leaves were taken from near to the top of each chosen coffee plant from a level
that was equivalent to approximately 75% of the total plant height. If possible, the leaf was selected
from one of the first set of fully open leaves closest to the branch tip. Photosynthesis rates for these
leaves were measured and collected. Measurements of instantaneous CO2 assimilation rates (Amax)
and stomatal conductance to H2O were taken using a CO2 infrared gas analyzer (LI-COR 6400 XT,
LI-COR Biosciences, Nebraska, USA) connected to a broadleaf chamber under ambient
microclimate conditions. For each leaf, gas exchange measurements were made at 9 light levels: 0,
50, 100, 200, 400, 600, 800, 1000 and 1500 μmol m-1
s-2
. Measurements were not taken until the leaf
was fully induced at that irradiance level; often a single light response curve took over 45 minutes to
complete due to slow induction. Readings taken in darkness were considered to represent dark
respiration rates, whereas readings in 1500 μmol m-1
s-2
represented the full sun photosynthesis rate
(Amax). These measurements were taken over the course of 14 days at the end of May ending June 1,
2011. Leaf measurements took place in the morning between 6:00 AM and 12:00 PM, in
coordination with times of peak gas exchange. Cuvette conditions were maintained at 388p.p.m.

45
CO2. Photon flux density (PFD), light level outside the chamber, air temperature and humidity were
also recorded during each gas exchange measurement. Humidity was monitored during
measurement to ensure it was high enough (above 50%) to provide accurate measurements.
Following data collection, for each subplot treatment, photosynthesis data were averaged and plotted
as a function of photon flux density, and a curve was fitted to these plots using Sigmaplot 9.2
software (SPSS Inc, Chicago, USA).
After photosynthesis rates were measured, each leaf was collected and weighed to find wet
mass. Leaves were then traced to record leaf area and perimeter, dried for 72 hours at 65°C, and
immediately weighed again to find dry mass. These values were used to calculate water content and
leaf mass per area. Leaves were scanned and areas measured with ImageJ 1.45 software (Wayne
Rasband, National Institutes of Health, USA).
4.2.3 Chemical Analysis
Plants
Leaf tissue from dried gas exchange leaves was finely ground and then analyzed for nutrient content.
To assess P concentration in leaf and root tissues, ground samples were assessed using the Kjeldahl
method of wet digestion. The digest was then analyzed using a spectrophotometer with wavelength
set to 410nm. Total N in plants (leaves and roots) was determined using the Dumas combustion
method. Samples were weighed in tin foil cups and encapsulated to contain the sample. The
encapsulated samples were then loaded into a LECO (St. Joseph, MI) FP-428 Nitrogen Determinator
sampler and purged of any atmospheric gases that may have entered when the sample was weighed.
The sample was then burned at 850°C in the presence of pure (99.999%) oxygen (O2) and the
resulting gases analyzed by a thermal conductivity cell to determine N2 content.

46
Soil
To assess soil fertility, three 150g aggregate soil samples were collected in each subplot at depths of
0-10cm, 10-20cm and 20-40cm. These samples were taken using a hand operated auger at a distance
of 2 m from each of the selected shade trees. These soils were air dried and sieved to pass 2mm
before being analyzed for nutrients and pH. The soil pH was measured in a 1:5 soil to water solution
using a pH meter (Mettler Toledo, Missisauga, Canada). The Dumas combustion method was
employed to determine soil N and soil C using a LECO (St. Joseph, MI) FP-428 Nitrogen
Determinator sampler. Soil available P was determined with the Olsen P method of extraction
followed by colorimetry. In areas where soils are very acidic, (pH<5.5), the Olsen P method can
often give inaccurate assessments, overestimating plant available P levels. Conversely, if soils are
too alkaline (pH>7.2), the Olsen P method can underestimate plant available P, which is especially
the case on recently limed soils. Tested soil levels in this study found both organic and
conventionally fertilized soils to have an average pH within the range of acceptable values for use
of the Olsen P test (pH=6.30±0.099 and 5.89±0.130, respectively; data not shown).
4.2.4 Measurement of shade tree characteristics
Tree species DBH was measured using DBH tape, and height measurements were calculated
using a clinometer (Suunto Inc, Vaanta, Finland). Biomass was then calculated using the equation
developed by Brown et al. (1989) for calculation of aboveground biomass in tropical moist forests
by life zone group. Due to the fact that this region had no distinguishable dry season, the equation
for moist lifezone species was used (Brown, et al., 1989). This provided the equation:
Y(g) = exp(-3.1141+0.9717ln((D
^2)H))
Whereby:

Campbell_Leslie_A_201203_MSc_thesis

Campbell_Leslie_A_201203_MSc_thesis

Recommended

Recommended

More Related Content

Viewers also liked

Viewers also liked (9)

Similar to Campbell_Leslie_A_201203_MSc_thesis

Similar to Campbell_Leslie_A_201203_MSc_thesis (20)

Campbell_Leslie_A_201203_MSc_thesis