Silvopastoral systems with isolated timber trees within pastures in the Coffee region of Colombia

J C Camargo, A Feijoo, M C Zúñiga, H Cardona and J Gaviria

Facultad de Ciencias ambientales, Universidad Tecnológica de Pereira;
La Julita, A.A. 97, Pereira, Colombia
jupipe@utp.edu.co

Abstract

The abundance of isolated timber trees within pastures was evaluated in La Vieja river watershed, located in the coffee region of Colombia. Nine species were identified, being Nogal (Cordia alliodora) the most abundant. Principal Components and Discriminant Analyses showed that biophysical as well as socioeconomic variables influenced the presence of isolated trees within pastures. 

The most important variables showing effects on abundance of isolated timber trees were altitude, soil properties, weed control and controlled grazing. Three group sites defined by cluster analysis showed that the distribution of timber species changed according to ecological conditions and their abundance was limited by management practices within pastures. Farmers recognized the ecological and economic importance of isolated trees within pastures and they have defined uses for each species found. 

In this way, these species could be used to establish silvopastoral systems and contribute to convert cattle grazing to a more sustainable activity in the coffee region of Colombia

Key words: abundance, benefits, canonical variables, multivariate analysis, silvopastoral systems, use of timber trees

Introduction

In Latin America, more than 90 million ha of land are under pastures, most of them as a result of forest conversion to cattle ranching (FAO 1999). During the last years, timber production from cattle farming systems has increased due to an improvement of market possibilities (Howard 1995). In Central America, livestock farmers recognize the potential of valuable timber trees in their pastures to generate income to safeguard low animal product prices on the national and international markets and their contribution to recover degraded areas (Pomareda 2000). Thus the presence of timber species in pastures is not only an important economic alternative, but it is also a possibility to improve environmental conditions within livestock systems.

Agrosilvopastoral systems provide forage, shade for animals and other benefits. Valuable timber species such as Cordia alliodora, Cedrela odorata, Tabebuia rosea, Erythrina poeppigiana, Pithecellobium saman and Albizia sp. kept at low tree densities (4 to 15 trees ha -1), are common in the tropical lowland pastures (Kampen 1996; Barrios et al 1999; Camargo et al 2000, Souza et al 2000; Camargo et al 2004) and in the highland regions, where intensive dairying is practiced, there are good examples of planted and natural regeneration of Alnus acuminata in pastures (Russo 1990) and Cupressus lusitanica wind breakers (Harvey and Haber 1999). The presence of these trees has shown to be influenced by management of pastures especially with practices such as weed control (Camargo 1999). Also, it has been found that the presence and abundance of trees within pastures changes according to the cattle production system (dairy, meat or dual purpose) (Souza et al 2000).

In the coffee growing region of Colombia, problems concerning the drop of coffee bean prices in the international market lead farmers to change their land use mainly to pastures. In La Vieja river watershed most farmers have established intensive pasture systems, based on nitrogen fertilizer and use of herbicides which require large investments having potentially negative effects on the environment. However, it is possible to reduce the impacts, even increasing productivity by establishing or promoting trees within pastures.

The conversion of coffee plantations to pastures might mean a biodiversity loss, however if trees are retained and protected, it would be possible to consolidate silvopastoral systems with isolated timber trees using native species and this may also be a strategy for biodiversity conservation. Therefore, actions that promote the establishment of silvopastoral systems based on isolated trees within pastures should emphasize on strategies that guarantee the permanence and growth of these trees. Retaining and managing trees in pastures may improve farm productivity and sustainability by generating tree products and providing ecosystemic services (Ibrahim and Schlönvoigt 1999). Within fragmented forest landscapes, farm trees may also represent important habitats and biocorridors for plant and animal species that are important for maintaining local and regional biodiversity (Harvey and Haber 1999).

This paper shows the importance of isolated timber trees within pastures, determining biophysical and socioeconomic factors influencing their population. In addition, promising timber species that could be used to establish silvopastoral systems in the coffee region of Colombia are identified.

Materials and methods

Study area

The study area corresponds to the coffee region of Colombia and sites sampled are located within the municipality of Alcala, in an area of approximately 117.858 ha in La Vieja river basin. The altitude varies between 950 and 1600 m, the mean annual temperature is between 20°C and 27°C and the total average precipitation is between 950 and 2.500 mm per year. In the sample sites, most of the soils were classified as Andisols derived from volcanic ash, and since they are located near a river they show significant influences of alluvial sediments (Cardona and Gaviria 2003).

Identification of trees within pastures

Aerial photos that correspond to the study area were scanned and integrated to the geographic information system (GIS) through the software ArcView GIS 3.3. Then a systematic two stages sampling was conduced. In the first stage, primary units were defined by using a grid of 1Km*1 Km on aerial photographs. Within each primary unit, areas covered by pastures were defined and identified with GIS as pasture polygons. In the second stage, the central point of each pasture polygon was used as the reference to randomly select sixty potential sites for sampling. Afterwards, field work was carried out to identify the sites selected on aerial photographs and to become acquainted with the owners of farms where sites were located. Finally, thirty sites were selected for sampling. In these sites farmers accepted to participate and provided information about pasture management, pastures with cattle grazing and pastures that contained trees. The number of sites selected for sampling was based on available funds for this study.

Within each site a circular and temporary plot was marked in a nested sampling design and timber species were recorded in four categories according to different growth stages (Table 1). Thus, it was also possible to evaluate their natural regeneration. The importance value index (IVI), which is the sum of relative abundance, frequency and dominance (Lamprecht 1989), was calculated in order to determine the relevance of timber species.

Additional information collected from plots

In each plot, information about physical-chemical soils properties (0-20 cm), physiographic and vegetation composition was registered, including texture, apparent density (from soil core), compression or resistance to penetration (soil compaction) and effective soil depth. The soil chemical properties included pH, extractable acidity, P, Ca, Mg, K, acid saturation, base saturation, Ca/Mg, Mg/K, Ca/K, (Ca+Mg)/K, effective cationic exchange capacity (ECEC), cationic exchange capacity (CEC), organic carbon and total Nitrogen. The physiographic variables included altitude, slope, topographical position and climate conditions. Simultaneously, farmers were interviewed to evaluate socio-economic aspects such as land use dynamics and management practices such as weed control, fertilization, controlled grazing and use of nutritional supplements.

Factors that determined the presence of trees within pastures

Effect of site variables on abundance of isolated trees within pastures was evaluated first by correlation analyses trying to detect relationships of dependence between variables, selecting those with higher Pearson coefficient (>0.5). Then, to reduce the number of variables, most relevant variable were identified by Principal Components Analysis and these variables were used in a Cluster Analysis to identify sites with similar characteristics. For the separation of variables into clusters, a Discriminant Canonical Analysis was used. SPSS Release 8.0 for Windows was used to perform these analyses.

Results and discussion

General characteristics of the sites included in the sampling

Most the farms (70%) where sample sites were located presented areas with less than 50 ha (40 ha on average). More than 50% of the farms were totally covered by pastures and only in 12% of the total farms, pastures were of lesser proportion compared with other land-uses or covers. However, in the interview with farmers, cattle ranching represented the main economical activity. Intensive cattle management evaluated according to uses of nitrogen fertilizers and herbicides was reported by farmers in 40% of the sampled sites and in regards to nutritional supplements, 90% of farmers used some food source different to pastures. About 50% of them, used green fodder with species such as Gliricia sepium, Trichanthera gigantea and Leucaena leucocephala and 40% used concentrates. Regarding pasture management, a high number of sites have been fertilized (73%) and grazing was usually controlled in the evaluated sites (63%).

The mean, maximum and minimum values and standard deviations of the main biophysical variables evaluated within sites sampled are given in table 2.

Timber species found within pastures

Nine isolated timber tree species within pastures were identified, Nogal (Cordia alliodora) being the most abundant and dominant. Other species found were Laurel (Cinnamomum triplinerve), Písamo (Erythrina poeppigiana), Guacamayo (Croton draco), Doncel (Zanthoxylum rhoifolium), Dinde (Chlorophlora tinctoria), Samán (Samanea saman), Cedro (Cedrela odorata) and Mestizo (Guarea trychilioides). Values for number of individuals per ha according to the growth stage are given in table 3.

 According to IVI values (120), Cordia alliodora was the most important species compared to other species identified. The abundance of this species might in part be explained by the promotional use of this tree in reforestation programs given by government institutions and that Cordia alliodora has been usually intercropped within coffee plantations. During the coffee crisis, farmers replaced coffee plantations with pastures and some mature Cordia alliodora trees remained. Cinnamomum triplinerve and Erythrina poeppigiana also had important IVI values (72 and 65, respectively) and both are important species usually found in remaining or secondary forests of the coffee growing region, located mainly as riparian forest (Table 4).

Cordia alliodora results important due to its abundance and possibilities of adaptation to ecological conditions of pastures, even tolerating land use changes, appearing as a promising species in this context. It has been also shown by other studies conducted within farms in low lands of Costa Rica, where 25 timber species were found with natural regeneration in pastures, being Cordia alliodora the most common (Camargo 1999). Souza et al (1999) reported a density of 11 trees per ha of Cordia alliodora within pastures in Costa Rica, also being the most abundant tree species encountered.

 The evaluation of