Lorena Soto-Pinto¹, Yolanda Romero-Alvarado¹, Javier Caballero-Nieto², Gerardo Segura Warnholtz³

Shade-grown coffee is an agricultural system that contains some forest-like characteristics. However, structure and diversity are poorly known in shade coffee systems. In 61 coffee-growers’ plots of Chiapas, Mexico, structural variables of shade vegetation and coffee yields were measured, recording species and their use. Coffee stands had five vegetation strata. Seventy seven woody species mostly used as wood were found (mean density 371.4 trees per hectare). Ninety percent were native species (40% of the local flora), the remaining were introduced species, mainly fruit trees/shrubs. Diametric distribution resembles that of a secondary forest. Principal Coordinates Analysis grouped plots in four classes by the presence of Inga, however the majority of plots are diverse. There was no difference in equitability among groups or coffee yields. Coffee yield was 835 g clean coffee per shrub, or ca. 1668 kg ha^-1. There is a significant role of shade-grown coffee as diversity refuge for woody plants and presumably associated fauna, as well as an opportunity for shade-coffee growers to participate in the new biodiversity-friendly-coffee market.

Key words: Diversity, shade-grown coffee, Coffea arabica, vegetation structure, woody plants, agroecosystems.

Diversity loss concerns researchers and development agents who are studying the causes of diversity loss and trying to propose alternative solutions. In some countries researchers survey existing diversity, but many of these resources are accelerately being lost, it is estimated that around 150 species go extinct daily (Reid y Miller in Pimentel et al., 1992).

The loss of diversity has occurred mainly due to agricultural, industrial, and urban expansion that has penetrated the agricultural frontier, in addition to other factors such as use of pesticides, introduction of exotic species and forest fragmentation (Pimentel et al. 1992, Brown and Lugo 1994, Lugo 1995).

Some agricultural partially resemble to the natural environment; shaded coffee plantations, maintain soil, climatic and biological conditions similar to surrounding natural forests (Jiménez-Avila and Martínez 1979, Perfecto et al. 1996, Moguel and Toledo 1999, Zúñiga and Calvo unpublished). However, in many countries, coffee growers have used single genus combinations for shade. In other cases, they have cultivated only one species, and in the most extreme cases, they have used unshaded coffee. As a result, this simplification process has caused diversity loss and other problems associated with it, such as erosion, pest attacks, diseases and loss of resource availability in the coffee stand (especially for subsistence producers) (Jiménez-Avila and Martínez 1979, Moguel and Toledo 1999).

Recent studies have shown the significance of managed forests for bio-diversity conservation (Hansen et al. 1991), diverse shade-grown coffee plantations can be considered managed forests. It has been reported that shade-grown coffee is very important as habitat for birds (Aguilar-Ortiz 1982, Greenberg et al. 1997, 1997a), mammals (Estrada et al. 1993, Gallina et al. 1996), reptiles (Seib, cited by Perfecto et al.1996), insects (Torres 1984, Perfecto et al. 1997), arachnids (Ibarra-Núñez 1990), woody plants (Purata and Meave 1993) and orchids (Nir 1988), which find refuge within coffee stands. Additionally, shade-grown coffee plantations can be considered as corridors for fauna and flora, since they are part of the scarcely vegetated areas within fragmented zones (Moguel and Toledo 1999). However, there are few studies that describe structural characteristics and woody plant species diversity in coffee stands that make possible to define criteria for shade-grown coffee plantations. Such studies have acquired importance due to the recent developing bio-diversity friendly coffee markets in the United States and Europe. This market gives producers the opportunity to increase their income by selling "ecological friendly coffee"; additionally, it benefits consumers who prefer specialty coffee, and helps to maintain environmental health.

The present study describes and analyzes coffee stand structure and woody plant diversity in shade-grown coffee systems in Northern Chiapas, Mexico.

Materials and methods

Study area and selection of sampling sites: this study was carried out in two areas of Northern Chiapas. One in the municipality of Chilon and the other in the municipality of Jitotol. Both zones are located in the coffee belt of Northern Chiapas, Mexico, within the subtropical zone characterized by a warm and humid climate (A)C(m) (García 1988). The area presents a gradient between 800 to 1200m above sea level, having an annual rainfall of 1200 to 1500 mm in the higher altitudes; and 2000 mm at the lower altitudes. Average annual temperature is 22° C. Soils are recent, thin, and stony. Typical vegetation in the highest areas is the montane rain forest (bosque mesófilo de montaña), and in the middle and lowest zones semi-evergreen seasonal forest (bosque tropical subperennifolio (Rzedoswki 1978, Breedlove 1981).

A characterization of main environmental and technical conditions in which coffee is grown was carried out. A questionnaire was given to 102 producers from Chilon and Jitotol to identify the main variants in regional coffee systems. Sixty-one sampling sites were chosen, controlling for coffee plant age, variety, and type of shade and management (organic vs. chemical). In each of the 61 plots a permanent sampling area of 10m x 10m was selected, where measurements of the studied variables were conducted. The square size was defined in order to relate community structure and canopy cover (Anderson 1966) based on the assumption that resulting image from hemispherical photographs gives an almost 180 degree view in all directions, with the zenith at the center and the horizon at the edges of the photograph (Roxburgh and Kelly 1995).

Measurements of coffee stand structure and diversity: Coffee density, slope and plot aspect were measured. In each plot a forest inventory with the following variables was carried out: number of individuals of each shade species, separated into nine diametric classes (1-10cm, 10.1-20cm, 20.1-30cm, 30.1-40cm, 40.1-50cm, 50.1-60cm, 60.1-70cm, 70.1-80 cm, and > 80 cm in breast height diameter (breast height being 1.3m); life forms (tree, shrub, palm and tall herbs). The number of strata in coffee stand as well as height, use of the species and qualitative presence of woody plant seedlings were recorded. With the above-mentioned information the following variables were estimated: density, frequency, abundance, species richness, diversity index and importance value (Mueller-Dumbois 1974, Whittaker 1975). All trees and shrubs in the plots were mapped in order to define number of strata. Light density class, crown form, and number of dead trees were also recorded (Hutchinson 1988). Illumination classes considered by the position of tree crown with respect to the canopy were the following: 1) emergent, 2) full overhead light, 3) some overhead light, 4) mainly oblique light, and 5) indirect light. Crown form classes included: 1) complete circle, 2) irregular circle, 3) half circle, 4) less than half circle, 5) few branches, 6) mainly sprouts, 7) alive without crown. Voucher specimens were collected for identification and deposited in the ECOSUR’s herbarium (El Colegio de la Frontera Sur) and at the National Herbarium of Universidad Nacional Autónoma de México (MEXU).

Hemispherical photos were taken in each plot (for methodology see Soto-Pinto, 2000). Hemiphot (a computer program) was used to calculate canopy cover and photon flux density below the canopy (Steege 1996).

A Principal Coordinates Analysis (Everitt and Dunn 1991) based on the Jaccard’s Similarity Index (Sneath and Sokal 1973) was carried out in order to identify groups of plots by floristic composition though the computational program NTSYS. Unidentified species were not included in the analysis. For each group, plot equitability was estimated through the following formula:

Where:

E= plot equitability

BA= average basal area

R= species richness in 100m²

Coffee producers are indigenous people, which possess in general less than 5 hectares in total; about one fifth of this land is devoted to coffee production. Shade-grown coffee is managed as a low-input system. In Jitotol there are organically-grown coffee, chemical-grown-coffee and natural-grown coffee (no inputs), while in Chilon the natural-coffee prevails. Producers do not control any pest or disease besides the berry borer, what is controlled by cultural methods. Weeds are handling removed twice a year. Cultural practices, except for harvesting are based upon family labor.

Coffee stands present a mixture of varieties Bourbon, Caturra, Mundonovo and Typica in an average density of 1500 shrubs per hectare. Shade trees are densely non-uniformly distributed in the plots, since producers tolerate seedlings growing naturally in the coffee plantation.

Shade vegetation structure in coffee stands showed a complex vertical profile. There were five strata of shade vegetation: one herbaceous stratum, two shrubby strata and two tree strata. The average profile showed 26.4% of emergent trees in the canopy; 21.5% of individuals with full overhead light, 18.9% of individuals with some overhead or oblique light; and 34.2% with trees or shrubs with indirect light (not including coffee shrubs). Different species were represented in each stratum. The species: Inga pavoniana, I. punctata, Belotia mexicana, Heliocarpus appendiculatus and I. sapindioides were mainly emergent trees with full overhead light, while Heliocarpus appendiculatus, Citrus sinensis, Musa sapientum and Croton draco mainly had some overhead or oblique light. Additionally, the species Oecopetalum mexicanum, Piper auritum, Astrocharium mexicanum, Chamaedorea cataractarum, Musa sapientum and Neurolaena lobata represented the stratum receiving indirect light. Frequency of species by illumination classes is presented in Table 1. Canopy cover ranged between 23 and 80%.

Table 1.

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Fig. 2. Species frequency presented in shade-grown coffee plantations in northern Chiapas, Mexico.

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Fig. 3. Plot space projection of the first and second principal coordinates
resulting from the Principal Coordinate Analyses based on a Jaccard index
similarity matrix.