Shade vs. Sun Coffee: A review

Coffee is traditionally grown as an understory plant, consistent with its shade tolerant nature. During the mid-twentieth century, farmers were encouraged to grow coffee in full sun to improve yields and reduce fungal infection, however, widespread acceptance of this practice did not take place until the 1970’s (Perfecto et al. 1996). At about the same time, a fierce controversy emerged regarding the environmental threat posed by growing coffee in full sun.

Shade coffee offers substantial advantages over coffee cultured in full sun, but not without costs. Overstory trees protect the relatively sensitive coffee bush from harsh wind, excessive light and soil erosion, and they buffer temperature and humidity. Predation poses little threat to covered coffee, and nutrient deficiency is seldom a problem. Furthermore, shaded plantations support biodiversity comparable to that in some rain forests, and provide alternative crops when demand for coffee falls. Slower maturation and lower yields constitute the major disadvantages.

Sun plantations, also known as modern or “technified” plantations, require more maintenance, hence are not economically viable when output and/or price falls below a fairly high threshold. Also, sun plantations typically experience greater run-off and nutrient leaching and remain productive for only one-third to one-half as long as comparable shaded plantations (Perfecto et al. 1996). Other characteristics include low biodiversity and high inputs of agrochemicals.

The socioeconomic aspects of sun vs. shade coffee culture are often overlooked. Though shade coffee culture damages the environment less, poor farmers have little incentive to be eco-conscious. Some commercial buyers have begun to educate farmers and consumers about the benefits of shade coffee and some offer them incentives to compensate for low yields.

This article evaluates the literature on the environmental impacts of sun versus shade grown coffee; socioeconomic factors are not discussed.

Erosion

Soil erosion is a major concern in agriculture; thin or infertile soils reduce yields and shorten the lives of perennial crops. An experiment conducted in the Andes (slope = 31°) demonstrated that erosion of the most biologically active fraction of the soil profile (<4mm) was greater in exposed than shaded coffee plantations (1.57 and .73 t ha-1 yr-1, respectively; Ataroff and Monasterio, 1997). However, this disparity was temporary following establishment of the technified plantation and by the 9th and 10th years had all but disappeared. Second to the establishment of a plantation, the most important cause of erosion is human disturbance, which occurs more routinely in sun plantations. Moreover, sun plants age more rapidly than shade grown stock and must be replaced more often, specifically at about 6 versus 30 year intervals, respectively (Ataroff and Monasterio, 1997). It is important to note the extremity of these values, particularly when examples of century old, healthy trees exist (Skip Bittenbender, personal communication).

Nitrogen Cycling

Nitrogen supply, more than that of any other nutrient, limits coffee production (Carvajal, 1984). Coffee fields planted at densities below 5000 bushes ha-1 require less than 100 kg N ha-1 annually (Bornemisza, 1982). Bornemisza estimates that legume-shaded plantations acquire substantial N through symbiotic fixation by the overstory and mineralization of organic matter. Measurements by Aranguren, Escalante and Herrera (1982) agree. They showed that N input from shade tree litterfall alone approximated 95 kg N ha-1 yr-1. Fallen leaves from Erythrina poeppigiana and the debris provided by pollarding added 330.5, 269.3, and 173 kg N ha-1 yr-1 depending on whether trees were trimmed one, two or three times a year, respectively (Russo and Budowski, 1986).

Babbar and Zak (1995) found that N lost by leaching in modern systems exceeded that in traditional systems almost three-fold. However, results from laboratory experiments showed 60% greater denitrification rates in shaded systems.

Stress and Competition

Advocates for shade coffee recognize the potential for competition for water and nutrients in those systems. However, Cassidy and Kumar (1984) found that most of the roots of shade coffee plants occupy the upper 50 cm of soils with well defined surface plates (Purseglove, 1968, p 464; Cuenca et al., 1983), suggesting relatively little opportunity to interact with typically deeper rooted overstory trees. Canopy trees may improve the water relations of crops by hydraulic lift, although, this possibility has not yet attracted the attention of investigators. Kanechi et al. (1996) showed that water stress inhibits photosynthesis more in sun plants under laboratory conditions.

Like many tropical flora, Coffea cultivars are sensitive to frost. Caramori et al. (1996) studied frost protection provided by Mimosa scabrella Benth. Leaf and air temperatures remained 2-4 and 1-2°C warmer at night, respectively, in traditional plots, and plants experienced less damage and produced higher yields. Air temperature was 5.4°C higher and the minimum 1.5°C lower in sun compared to shade plantations in Mexico (Barradas and Fanjul, 1986; Baggio et al., 1997). Piché evaporation, soil temperature and vapor pressure deficits also were lower under shade trees. Overstory trees also reduced wind speed below their canopies (Schroeder, 1951; Caramori et al., 1986).

Many authors report fewer weeds in shaded plantations (Haarer, 1962, pp 86-96; Vishveshwara and Jacob, 1983; Nestel and Altieri, 1992; Muschler, 1997). Additionally, overstory trees reduce the invasiveness of weedy Graminaceae (Huxley, 1975; Goldberg and Kigel, 1986).

Biodiversity

Concern has recently emerged about the inability of technified plantations to sustain native flora and fauna. Without the food and shelter that overstory trees can provide, many organisms avoid coffee plantations. Traditional plantations typically support many species that provide a multistratal canopy (Moguel and Toledo, 1999). Also, various wild type herbs and shrubs densely populate the forest floor. Although no data are available, many epiphytes inhabit the canopy (David Benzing- personal communication).

Biotic diversity is vastly greater in shade than sun plantations. Nestel et al. (1993) identified almost twice as many macro-Coleoptera; Perfecto and Snelling (1995) noticed more foraging ants, and Perfecto et al. (1997) recorded more beetles, ants and non-formicid hymenopterans in shaded systems. Wunderle and Latta (1998) witnessed fewer birds foraging in modern than shade plantations. Greenberg et al. (1997) observed more avians in shaded sites and that those birds resided in the overstory. Work by Gallina, et al (1996) suggests that reducing plantation complexity could decrease mammalian diversity by 43%. Reviews by Perfecto et al. (1996) and Moguel and Toledo (1999) contain additional information about biodiversity in coffee plantations.

Yield

Higher yields, more than any other factor, justify the choice to grow sun coffee. Shade trees reduce production because they intercept significant amounts of photosynthetically active radiation. Older cultivars of Coffea tolerated direct sunlight poorly; the consequences included overbearing, dieback, soil exhaustion and shortened life spans. Intensive breeding programs prompted by this behavior resulted in sun tolerant varieties that also require more fertilizer.

Several authors reported that shade tree removal increased yields in Puerto Rico (Abruña et al., 1965; Vicente-Chandler et al., 1968; García and Lugo, 1972). Njoroge and Kimemia (1995) generally found that intercropping with 12 annual food crops lowered coffee yields. In contrast, Baggio et al. (1997) reported greater yields with shade coffee, possibly because shade trees moderate microclimate. Beer et al. (1998) cite many sources that report higher and lower yields in shade.

These variable performances suggest that yield is strongly influenced by growing conditions. When environments are ideal (e.g. temperature, humidity, altitude, water availability…), sun coffee produces more berries (H.C. Bittenbender- personal communication; Amoah et al., 1996; Beer et al., 1998). However, coffee grown in mixed culture tolerates suboptimal conditions better (Muschler, 1998).

Diseases and Pests

No general statement about the effect of shade on diseases and pests can be made. Organisms respond differently under different light regimes. Whether these behaviors arise from light levels or microclimate is uncertain.

Nataraj and Subramanian (1975), Muschler (1998) and Fawole (1999) demonstrated an inverse relationship between percent shade and the incidence of brown-eye-spot disease (Cercospora coffeicola B. and CKE). The fungi coffee leaf rust (Hemileia vastatrix) and Mycena citricolor were unaffected by any shade regime (Muschler, 1998). Compared to sun treatments, the occurrence of the green scale (Coccus viridis) was not only lower in shade treatments, but the percent mortality after treatment with the entomopathogenic fungus Cephalosporium lecanii Zimm was greater. Research in an organic, shaded plantation showed less brown-eye-spot disease, more Mycena citricolor and no difference in leaf rust than a conventional, unshaded plantation (Samayoa-Juarez and Sanchez-Garita, 2000). In India, the coffee berry borer (Hypothenemus hampei) was found to be more prominent under shade (Vijayan et al., 1999).

Uses of Shade Trees

Many countries rely on coffee as the cornerstone of their economies, therefore, low demand or prices can devastate those economies and the farmers’ (Pendergrast, 1999). Averting such a disaster requires a diversified farm economy. Fortunately, coffee plantations need not be eliminated; shade trees can be added that offer additional crops. Specifically, shade trees can be used for timber (e.g. fuel, construction materials…), fruits (e.g. citrus, banana, oilpalm…) and medicines (Herzog, 1994). Also, annual food crops can be successfully grown with coffee (Njoroge and Kimemia, 1995).

Coffee Quality

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The quality of the coffee product is arguably the most important aspect of any production system and must be included in any discussion of shade. Coffee quality is generally defined in three parts: bean size, the number of defects and organoleptic properties. Presently, the link between bean chemistry and coffee quality is not well defined.

To date, research on the effects of shade on coffee quality are scarce. Many reports are vague and contain copious amounts of supposition. These reports typically argue that shade improves the quality of coffee by slowing down cherry maturation rate and allowing the bean to accumulate greater amounts of sucrose.

Guyot et al. (1996), studied the effects of shade on C. var Catuai. Bean size increased slightly with shade as did several chemical constituents: chlorogenic acids by 10%, total acidity by 16%, caffeine by 4% and sucrose by 3%. Trigonelline content decreased by 10%. A panel of 8 cuppers determined that the only organoleptic property affected by shade was bitterness, which decreased by 18%.

Working in a sub-optimal coffee-zone, Muschler (1998) observed the effects of various shade regimes on 2 varieties: Caturra and Catimor. Both varieties exhibited a substantial bean size increase as well as improvement in visual appearance. The total amount of defects was less under shade for both varieties. Organoleptic properties were evaluated by a single individual. Acidity and body improved with shade but aroma was slightly negatively affected in Catimor.

These studies suggest that shade positively affects coffee quality. However, the interaction of shade with the environment and genetic composition are poorly understood. Further research is necessary.

The longstanding controversy about the benefits and liabilities of growing sun vs. shade coffee is far from over. The literature indicates that shade grown coffee typically degrades environments less and benefits farmers more than sun grown coffee when resources are limited or environmental conditions are sub-optimal. Modernized plantations remain popular because their higher yields increase the incomes of farmers and national economies.

Although much is already known about shade and sun coffee, more answers are needed, particularly about competition for water and nutrients between shade trees and coffee, yield, the incidence of pests and diseases, pollution from agrochemicals, the capacity of traditional plantations to sustain biodiversity and endangered species and shade’s effect on quality. Additional evaluation of wild coffee in Africa could reveal undiscovered genotypes that outproduce modern varieties. Finally, new genetic techniques may permit the development of shade-tolerant stock capable of higher production than possible with existing cultivars. While scientists and conservationists continue research on the advantages of shade coffee, existing sun plantations continue to threaten the environment. Consumers can help by demanding shade coffee and wholesalers can charge more for sun than shade coffee. However, the most effective solutions lie with the farmer. Perfecto et al. (1996) suggest that growers be responsible for certain associated costs such as those obliged by pollution cleanup, the development of water supplies, diminished yields caused by excessive chemical input and erosion, the health care needs of employees working with pesticides and fish kills in habitats degraded by excessive sediments. Additionally, governments could impose taxes on sun plantations or the products required to support sun plantations i.e. fertilizers.

Coffee is one of the most valuable commodities and millions of people are involved in its production, preparation and consumption. A ubiquitous product like coffee establishes a paradigm for all agroforestry systems. Furthermore, the cultivation of shade coffee can help preserve our endangered ecosystems, particularly tropical rain forests.

References

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Amoah F, Osei-Bonsu K and Oppong F. 1997. Response of Improved Robusta Coffee to Location and Management Practices in Ghana. Experimental Agriculture. 33: 103-111.

Aranguren J, Escalante G and Herrera R. 1982. Nitrogen Cycle of Tropical Perennial Crops Under Shade Trees: Coffee. Plant and Soil. 67: 247-258.

Ataroff M, Monasterio M. 1997. Soil erosion under different managemnet of coffee plantations in the Venezuelan Andes. Soil Technology. 11: 95-108.

Babbar L and Zak D. 1995. Nitrogen Loss from Coffee Agroecosystems in Costa Rica: Leaching and Denitrification in the Presence and Absence of Shade Trees. Journal of Environmental Quality. 24: 227-233.

Baggio A, Caramori P, Androcioli Filho A and Montoya L. 1997. Productivity of Southern Brazilian Coffee Plantations Shaded by Different Stocking of Grevillea robusta. Agroforestry Systems. 37: 111-120. Barradas V and Fanjul L. 1986. Microclimatic Characterization of Shaded and Open-Grown Coffee (Coffea arabica L.) Plantations in Mexico. Agricultural and Forest Meteorology. 38: 101-112.

Beer J, Muschler R, Kass D and Somarriba E. 1998. Shade Management in Coffee and Cacao Plantations. Agroforestry Systems. 38: 139-164.

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Cassidy D and Kumar D. 1984. Root Distribution of Coffea arabica L. in Zimbabwe. Zimbabwe Journal of Agriculture. 22: 119-132.

Cuenca G, Aranguren J and Herrera R. 1983. Root Growth and Litter Decomposition in a Coffee Plantation Under Shade Trees. Plant and Soil. 71: 477-486.

Easwararamoorthy, S and Jayaraj, S. 1977. The Effect of Shade on the Coffee Green bug, Coccus viridis (Green) and its entomopathogenic fungus, Cephalosporium lecanii Zimm. Journal of Coffee Research 7(14): 111-113

Fawole, E. 1999. Influence of Shade and Exposure on the Incidence of Brown Spot Disease of Coffee. Nigerian Journal Of Tree Crop Research. 3(2): 64-70.

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