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The importance of coffee agroforestry systems in Mesoamerica
Current agroforestry practices
The natural adaptation of coffee to shade has been a strong argument in favor of the development and maintenance of agroforestry practices in coffee production. However, little information is available on how these practices have evolved in Mesoamerica (Beer et al. 1997; DaMatta 2004; Leon 1998a; Leon 1998b; Muschler 2004). Originally, coffee was introduced during 1720-1724 to America via the French colonies (Guadalupe, Guyana, Haiti and Martinique). When the commercial coffee production was initially developed in Haiti and Jamaica, no special reference was reported regarding agroforestry practices. In Costa Rica, coffee began to be commercially cultivated in 1833 and in Colombia during the second half of the nineteenth century. Still, there is no mention, during this initial period, of the use of shade trees by the coffee industry in Latin-American countries. The adoption of shade was reported to begin in 1865 in Costa Rica and in 1872 in Colombia, mainly with the use of Erythrina species in lowlands and Inga species in highlands (Leon 1998b).
Nowadays, most shade trees used in association with coffee belong to the Fabaceae family due to their capacity to fix nitrogen. Even though farmers may not be aware of this property, they observe their beneficial results in terms of soil fertility. Genera such as Albizia, Inga, Leucaena of the Mimosoideae and Erythrina and Gliricidia of the Papilioniodeae are common in coffee systems, especially in Mesoamerica (Lambot and Bouharmont 2004; Leon 1998b; Muschler 2004; Muschler 1999).
In Costa Rica, the most common species in coffee agroforestry systems (AFS) is Erythrina poeppigiana (Muschler 1997; Muschler and Bonnemann 1997; Muschler 1999; Muschler 2001). Nonetheless, studies on the botanical composition of coffee systems showed more diverse shade vegetation that anticipated. For example, 62 tree species were reported in coffee AFS of the region of Turrialba, Costa Rica; 63 species in the region of Miraflor, Nicaragua; 124 species in the region of Tapalapa, Chiapas, Mexico; and 46 species in the region of Jitotol de Zaragoza, Chiapas (Escalante and Somarriba 2001; Linkimer et al. 2002; Llanderal and Somarriba 1999; Peeters et al. 2003; Yépez et al. 2002; Zuniga et al. 2004). Additionally, there is a recent tendency to incorporate timber trees in coffee AFS to improve profitability, especially during periods of low coffee prices. Timber trees associated with coffee are numerous such as Cordia alliodora, Eucalyptus deglupta, Eucalyptus grandis, Terminalia ivorensis, Terminalia amazonia, Cedrela odorata, Alnus acuminata. Among them, C. alliodora has been shown to develop at such rate in AFS that it compensates the reduction in coffee yield (Beer 1992; Beer et al. 1997; Hernandez et al. 1997).
Use of Inga as shade tree in coffee AFS
With the exception of Costa Rica where Erythrina poepigiana is the most abundant species in coffee AFS, the genus Inga has been used predominantly as a shade tree in coffee and cacao (Theobroma cacao) in Mesoamerica (Leon 1966; Leon 1998a; Pennington 1998). It is worth mentioning that Inga is used as a shade tree in agroforestry only in America, possibly because it is endemic of this continent. The history of the use of Inga (in the Neo-tropics) extends back to 2000 years when it was cultivated for its edible fruits (Inga feuillei called Pacae in Peru) by the tribes Chimu and Mochica in Peru (Leon 1966; Leon 1998a; Pennington 1998). However, the use of Inga fruits possibly began independently in different regions in the Neo-tropics and with different species. In Mesoamerica, the domestication of the genus began with I. juinicuil, I. densiflora and I. sapionoides as source of fruits (Leon 1998a; Leon 1998b).
Despite the large diversity of the genus, only few species have been used in AFS with coffee or cacao. For example, Peeters et al. (2003)cited that coffee AFS in Mexico are predominated by only four native Inga species: Inga latibracteata Harms, I. oerstediana Benth. I. punctata Willd, and I. pavoniana Donn (Peeters et al. 2003). In Costa Rica (and other Central American countries such as Nicaragua and Guatemala), few species of Inga (I. punctata, I. densiflora, I. oerstediana, I. edulis, I. spectabilis, I. juinicuil among others) are mentioned as shade tree species in coffee and cacao plantations (Zamora and Pennington 2001). However, possibly up to a total of 20 Inga species are in use in coffee AFS, which shows the importance of this neo-tropical genus as a shade tree in coffee AFS in this region (Lambot and Bouharmont 2004; Leon 1998b; Muschler 2004; Muschler 1999; Yépez et al. 2002). Interestingly, this genus can provide many ecological services in coffee and cocoa AFS such as soil protection and restoration, improved soil retention of water, nitrogen fixation and carbon sequestration, additionally to the production of high quality fuel-wood generated by pruning (Fernandez 1998; Hands 1998; Murphy and Yau 1998; Pennington 1998).
Description of the genus Inga
The genus Inga is very diverse, composed of around 300 species widely distributed from Mexico to Uruguay and found throughout the lowlands and mountainous regions of the humid tropical America (Leon 1966; Pennington 1998; Sousa-Pena 1993; Sousa-Pena 2001; Zamora and Pennington 2001). The speciation of the genus was concentrated in the past 10 million years, with many species arising as recently as 2 million years ago, which coincides with the most recent major uplifts of the Andes. Consequently, the largest center of diversity for Inga is in the Andean foothills of the Western Amazon (Bermingham and Dick 2001; Richardson et al. 2001). Thus, in Brazil for instance, 140 species have been reported, and only 80 species for the Mesoamerican region (Pennington 1998; Zamora and Pennington 2001). In Costa Rica, 53 Inga species are reported and 32 in Nicaragua (Sousa-Pena 2001), 33 species in Mexico (Peeters et al. 2003), representing the tree genus with the highest species diversity, and with 12 species reported as endemic (Zamora and Pennington 2001). Furthermore, the genus tends to be species-rich in different moist forest when local floras (florulas) are compared. For example, Gentry (1990) cited Piper, Ficus, Inga Ocotea, Psychotria, Philodendron, Anturium and Miconia, as the most speciose genera in moist forest of Costa Rica, Panama, Brazil and Ecuador (Gentry 1990).
Major effects of the use of shade in coffee plantations
Shade trees in coffee plantations present advantages and disadvantages for farmers, therefore the decision regarding their incorporation in coffee plantations depends on the farmers’ goal, the specific environmental conditions of the site and the availability of inputs (Beer et al. 1997; Fernandez and Muschler 1999; Muschler 2004; Muschler and Bonnemann 1997; Muschler 1999). The effects of associated trees in coffee production systems can be grouped into two categories:
(a) the effects of shade trees on the micro-environment; and (b) their effects on the crop itself and its management.
Effects of shade trees in coffee agroforestry systems
There are many arguments to use shade trees in coffee AFS with respect to their ecosystem services; the main ones are: biodiversity conservation, carbon sequestration and greenhouse gases reduction, soil fertility improvement and water resource preservation (due to erosion control and nutrient leaching reduction).
Biodiversity
Generally, shaded coffee plantations support many tree species that provide a multistrata canopy. Consequently, they are important refuges for biological richness for groups such as trees and epiphytes, mammals, birds, reptiles, amphibians, and arthropods (Moguel and Toledo 1999). Biotic diversity is vastly larger in AFS than in monoculture (MC). This is becoming more and more important as protected areas in the Mesoamerican region are decreasing in size and hence coffee AFS can play an increasingly important role as corridors between these conserved forest areas (Perfecto et al. 1996).
Many studies have recorded higher faunal diversity in AFS than in MC, sometimes with records in coffee AFS similar or higher than in forest areas. For example, more foraging ants, beetles, and non-formicid hymenopterans were recorded in coffee AFS when compared to MC (Perfecto and Snelling 1995). In a premontane moist forest at elevations of 1200 to 1800 in Panama, two species of Neotropical army ants (Eciton burchelli and Labidus praedator) were present only in forest and shade coffee, but not in MC (Roberts et al. 2000). In Nicaragua, a study of primates behavior showed that coffee AFS can be used as corridors between forest fragments for howler monkeys (Alouatta palliata) and possibly other forest mammals (Williams-Guillén et al. 2006). For birds, shaded coffee may play an important role in maintaining local biodiversity, and acts as buffer areas around forest patches, even if shaded coffee may be beneficial mostly for generalist species (including several migratory species), but of lower values for forest specialists (Tejeda-Cruz and Sutherland 2004). Coffee AFS with the presence of large shade trees (such as some Inga species) have a positive influence even on the diversity of epiphytic species, despite the less diverse and more homogeneous communities in coffee plantations than in forests (Hietz 2005).
Soil erosion and lixiviation control
Nowadays, soil erosion is an important concern in agriculture. In Mesoamerica, coffee is planted very often on medium to high slopes, as described for Miraflor in Nicaragua where the average slope was 29% and a range from 2% to 70% (Zuniga et al. 2004). An experiment conducted in the Andes (slope = 31%) demonstrated that erosion of the most biologically active fraction of the soil profile (<4mm) was larger in MC systems than in AFS coffee plantations with values of 1.57 and 0.73 t ha-1 y-1, respectively during the period of crop establishment (Ataroff and Monasterio 1997). Soil erosion is the result of high runoff, thus, on minimal slope (1%) the recorded runoff of 3% of annual rainfall in MC was comparable to 2% in AFS (Avila et al. 2004; Harmand et al. 2007). Nevertheless, these authors suggested that the higher litter layer in AFS of 8.5 t DM ha-1 compared to 2.5 t DM ha-1 in MC was a better protection of the soil surface against rain splash (Harmand et al. 2006). Similar results have been reported in other AFS such as alley cropping, in which the runoff was reduced substantially with the inclusion of trees (Lal 1989a; Lal 1989b). Furthermore, the inclusion of shade trees in coffee plantations may reduce nutrient leaching and water contamination with nitrate and other harmful substances. Harmand et al (2007) showed that in highly fertilized coffee plantations, the inclusion of E. deglupta as a shade tree: 1) increased N uptake during the dry season and N accumulation in litter and permanent biomass; 2) slightly reduced water drainage; and 3) reduced NO3- leaching especially when coffee berry production was low. Nevertheless, in years of high production of coffee in full sunlight, the negative effect of shade on coffee production could offset the advantage of N accumulation in trees as a mean of reducing N leaching. Hence, the inclusion of shade trees in coffee plantations intensively managed requires reducing N fertilization input in order to match plant needs and reduce NO3-leaching (Harmand et al. 2006).
Carbon sequestration and reduction of greenhouse gases
Tropical AFS can play an important role in the sequestration of carbon (C), hence acting as a sink and reducing CO2 concentration in the atmosphere. The potential C sequestration in AFS is estimated between 12 and 228 Mg ha−1 with a mean value of 95 Mg ha−1 (Albrecht and Kandji 2003). After 7 years, the aerial biomass accumulation of a coffee AFS accounted to 28.4 Mg ha−1 compared to 11.4 Mgha−1 in a MC, which showed the potential of tree inclusion to C sequestration in the coffee sector (De Miguel et al. 2004). In other coffee AFS, a C sequestration of 11 Mg ha−1 yr−1 over 10 years was reported in which 6 Mg ha−1 yr−1 corresponded to the shade tree aerial component (Albrecht and Kandji 2003). Reporting data from experiments and published literature, Harmand et al. 2006a showed that for approximately a ten year period, the conversion of coffee MC to AFS resulted in an additional mean annual increment in aerial phytomass (biomass + litter) varying from 1 t C ha-1 y-1 in the case of regulated shade by E. poeppigiana, to 1.7 – 3.1 C ha-1 y-1 in the case of shade timber trees. However, AFS may also generate greenhouse gases such as N2O. For example, an AFS with Inga densiflora increased slightly the emission of N2O in comparison to coffee MC, while N fertilizer was responsible for 70% of the emission (Hergoualc’h et al. 2007).
The effects of shade trees on coffee and its management
Additionally to their ecological impacts at the ecosystem level, shade trees influence directly the coffee plant and its management; trees influence the microclimate and hence, coffee productivity and quality as well as soil fertility through nutrient cycling, N-fixation and soil organic matter enhancement (Beer 1987; Beer et al. 1997; Vaast and Snoeck 1999; Willey 1975).
Influence of trees on soil fertility
Trees in AFS can improve the fertility of coffee soils (or many other associated crops) through the three following ways: a) an increase in nutrient supply (N-fixation) and a reduction of nutrient output (reduction of runoff and lixiviation); b) a more efficient nutrient cycling by means of a stable decomposition and a conversion of nutrients in more labile forms (for example P); and c) an improvement of the soil environment for a more favorable root growth through an improvement of the soil physical properties (Buresh and Tian 1997; Khanna 1997; Vaast and Snoeck 1999; Willson 1985).
In coffee AFS with legume trees, N-fixation and nutrients recycling are important ways of improving soil fertility and sustaining crop production (Harmand et al. 2006). For example, N input from shade tree litterfall alone could represent approximated 95 kg N ha-1 y-1 (Aranguren et al. 1982). In a coffee AFS with Erythrina poeppigiana, the biomass obtained from the pollarding added 330, 269, and 173 kg N ha-1 y-1 depending on whether the pruning frequency was one, two or three times a year, respectively (Russo and Budowski 1986). However, the nutrients added via pollarding in AFS, represent only a more efficient nutrient cycling and not an extra input of nutrients to the system; thus, only 14% to 50% of the total N in the pollarding originated from N-fixation (Palm 1995). On the other hand, some legume trees used as shade trees contain high content of polyphenols in their biomass, that release N slowly and over a longer period. This effect can increase the fraction of N-organic and the content of soil organic matter (SOM) in the long term (Palm and Sanchez 1990; Palm and Sanchez 1991). Finally, the biomass not only adds nutrients to the soil, but also increases the availability of nutrients to plants. Phosphorus is thought to be one of the most limiting nutrients in tropical soils, but its availability can be improved by the symbiosis with mycorrhizae or by the transformation of non-available inorganic forms to more available organic forms. This later process can be the result of the supply of energy to microorganism, stimulating the roots growth of associated plants or by the reduction of soil P absorption (Buresh and Tian 1997).
Influence of shade trees on microclimate
On top of their potentially advantageous impacts on soil fertility, shade trees modify the microclimate (light, relative humidity, temperature) for crop growing underneath and may compete with them for resources such as light, water and nutrients (Beer 1987; Beer et al. 1997; Willey 1975).
In a coffee AFS, it has been showed that trees reduced the maximal temperature by an average of 5.4ºC, and increased the minimal temperature by up to 1.5ºC (Barradas and Fanjul 1986). On the other hand, soil evaporation was reduced by 40% in comparison to plantation without trees, due to decrease in VPD and radiation. Vaast et al. (2005) observed a reduction in coffee transpiration under shade trees in the southern region of Costa Rica. On basis of the physiological responses of coffee to environmental factors, it is commonly accepted that the shade of trees is important mostly in regions of sub-optimal environmental conditions to coffee growth (Fernandez and Muschler 1999). Very often, these regions present environmental limitations such as temperatures higher than 30oC, high VPD, low water availability.
Influence of trees on yield and coffee quality
It has been suggested that the negative influence of shade trees on coffee yield is the product of lower whole-tree carbon assimilation, greater stimulus to vegetative rather than flower buds, and fewer nodes formed per branch and flower buds at existing nodes (Cannell 1974; Cannell 1975). From past and current research on coffee photosynthesis, seems unlikely that the shade of trees strongly reduces coffee photosynthesis due to coffee adaptation to shade. Indeed, it has been demonstrated that the most important negative impact of trees on coffee yield, is through lower flower induction and hence the lower number of productive nodes on a branch (Franck 2005). As a consequence of shade, coffee plants generally have lower fruit loads (Franck 2005), but shade also influences other variables of agronomic importance, as follows:
• larger individual leaf size, longer leaf longevity, reduction in leaf specific mass and hence a lower carbon investment for a similar LAI with coffee shade grown compared to sun grown plants (Franck 2005).
• An enhanced vegetative growth and carbon reserves in branches and roots of shade grown plants with lower fruit loads (Cannell 1971; Cannell 1974).
• A reduction of the branch mortality, phenomenon known as dieback (Clowes 1973).
• These last two effects allowing a better flower induction and a better yield during the next production cycle, hence reducing bi-annual production (Vaast et al. 2005a; Vaast et al. 2005b).
However, in compensation to yield reduction, shade improves quality in coffee. Shaded plants produce coffee beans of larger size and higher quality, and hence improve farmers’ income (Vaast et al. 2005a; Vaast et al. 2005b; Vaast et al. 2002). In Guatemala, shade and altitude improved quality with shade grown coffee plants producing a higher portion of beans with larger size and increased chlorogenic acid and sucrose concentration (Guyot et al. 1996). In Costa Rica, shade improved quality in a sub-optimal zone for coffee cultivation, with mean bean weight and size increasing with increasing shade from full sun to 80% of shade (Muschler 2004; Muschler 1999; Muschler 2001).
New arguments in favor of agroforestry
Quality and niche markets
The certification of coffee for sustainable and environmentally friendly production practices potentially adds value to the coffee product and can increase profitability for farmers that follow the recommended practices of certification schemes. This niche market is divided into five main certifications: Organic, Fair Trade, Rainforest, Starbucks and Bird Friendly certified; although, new ones are underway such as Nespresso AAA and 4C. The market for these certifications seems to increase between 10 to 20% per year, especially in Europe (50%), United States (39%), Japan (9%) and Canada and Taiwan (2%). From this point of view, agroforestry practices can increase the profitability of coffee farming since all these certification programs require or recommend the use of shading trees, in addition to other ecological and social requirements; therefore, there is a direct link between environmental conservation and the market for coffee. For example, Bird Friendly Coffee is marketed by conservation groups and birders’ associations (Castro et al. 2004).
Table of contents :
1 GENERAL INTRODUCTION
1.1 COFFEE
1.1.1 The coffee plant, related species and origin
1.1.2 Distribution and economical importance, markets
1.1.3 Importance of the coffee as a crop in Mesoamerica
1.2 ECO-PHYSIOLOGY OF COFFEE
1.2.1 Edaphic and climatic boundaries for acceptable yield of C. arabica
1.2.2 Photosynthesis and stomatal conductance
1.3 THE IMPORTANCE OF COFFEE AGROFORESTRY SYSTEMS IN MESOAMERICA
1.3.1 Current agroforestry practices
1.3.2 Use of Inga as shade tree in coffee AFS
1.3.3 Description of the genus Inga
1.3.4 Major effects of the use of shade in coffee plantations
1.3.5 New arguments in favor of agroforestry
1.3.6 Biological interactions in AFS, with a special focus on water competition
1.3.7 What remains to be documented on coffee water relations?
1.4 MY RESEARCH HYPOTHESES
1.5 MY RESEARCH QUESTIONS
2 MATERIAL AND METHODS
2.1 SITE DESCRIPTION AND EXPERIMENT
2.2 METEOROLOGY AND MICROCLIMATE
2.2.1 Radiation transmission and interception
2.2.2 Leaf temperature
2.2.3 Soil water content
2.3 INGA DENSIFLORA GROWTH
2.4 COFFEE GROWTH
2.4.1 LAI dynamics
2.4.2 Yield monitoring
2.4.3 Coffee biomass monitoring
2.5 WATER BALANCE
2.5.1 Rain Interception
2.5.2 Transpiration
2.5.3 Runoff
3 RESULTS AND DISCUSSION
3.1 INFLUENCE OF TREES ON MICROCLIMATE
3.2 INFLUENCE OF SHADE TREES ON COFFEE GROWTH AND YIELD
3.2.1 Yield
3.2.2 Coffee LAI and biomass
3.3 TREES GROWTH AND TOTAL SHOOT BIOMASS
3.4 INFLUENCE OF TREES ON WATER BALANCE COMPONENTS
3.4.1 Rainfall interception loss
3.4.2 Transpiration
3.4.3 Runoff
3.4.3 Soil volumetric water
3.5 WATER BALANCE AT PLOT SCALE
3.6 COMPETITION FOR WATER
4 CONCLUSIONS AND PERSPECTIVES
4.1 INFLUENCE OF TREES ON THE MICROCLIMATE EXPERIENCED BY COFFEE PLANTS
4.2 INFLUENCE OF TREES ON COFFEE YIELD AND BIOMASS
4.3 INFLUENCE OF TREES ON WATER BALANCE
4.3.1 Canopy Rainfall Interception
4.3.2 Transpiration
4.3.3 Runoff
4.4 WATER USE AND TREE-CROPS INTERACTIONS
4.5 PERSPECTIVES
5 REFERENCES
