Signs to detect regeneration and degradation of agroecosystems in the coffee growing region of Colombia
A Feijoo, M C Zuñiga, J C Camargo
Universidad Tecnológica de Pereira. Facultad de Ciencias Ambientales.
AA 97. La Julita. Pereira, Colombia
afeijoo@ambiental.edu.co
Abstract
In order to estimate signs of degradation or recovery in agroecosystems after anthropogenic use, research was carried out in La Vieja river basin to evaluate perturbation impacts on soil macroinvertebrate populations of 22 land use systems.
A Main Component Analysis (PCA) showed that that 659% of the variability of macroinvertebrate abundance is given by three factors. Considering results from a diversity index, the evaluated land use systems were grouped according to their forms of intervention. Information on how macroinvertebrates respond to different levels of intervention on a landscape under tropical conditions is given and on how these organisms can be use as potential indicators under diverse soil practices.
Key words: Andean hillside, diversity, macroinvertebrates, perturbation.
Introduction
The Andean region of Colombia represents 27% of the country's area and it is gradually being settled. This has caused environmental degradation, soil erosion and deterioration of natural resources in areas that are important for river basin management and biodiversity conservation. In the coffee region of Colombia, problems concerning the fall of coffee bean prices in the international market led farmers to change their land use mainly to pastures. In La Vieja river basin most of the farmers have established intensive cattle grazing systems, which require large investments and they have potentially negative effects on the environment, as well as affecting the livelihoods of people. These developments have created a need to generate prediction tools to evaluate the damage caused by perturbation in ecosystems (use of insecticides, farming, chemical fertilization, mono-cropping) and to determine soil sustainability. These bio-indicators can be used to predict biodiversity and biological activity from small plots to landscape levels.
Disturbances can be characterized by frequency, duration, size (or spatial extent), intensity or severity, usually having temporal and spatial characteristics (Bengtsson 2002); which favor the arrival or elimination of some species of macro-invertebrates. There are recent and controversial studies that discuss the importance of macro-invertebrates as indicators of change in agro-ecosystems (Feijoo et al 1999). It has been demonstrated that different land use practices have diverse effects on soil structure causing changes on earthworm diversity, abundance and biomass making them potentially important as indicators of soil recovery or degradation. Few studies have been done in the Andes; therefore we need to investigate earthworms as an additional tool for the creation of technological programs that incorporate soil fauna diversity in agricultural production processes.
This article seeks to show the interactions that macro-invertebrates have with diverse levels of landscape perturbation according to agro-ecosystems and their usage.
Materials and methods
The study was carried out between January and February of 2002 at 22 sites in La Vieja river basin of Valle Department, Colombia (4° 4' and 4° 49' latitude north and 75° 24' and 75° 57' longitude west), located 260 km away from Bogotá. The altitude ranges from 950 to 1600 masl. The mean annual temperature varies between 20 and 27°C and the precipitation is between 950 and 2,500 mm year -1. The precipitation is bimodal, with two wet seasons (March-May, September-November) and two dry seasons (December - February, June - August). The area is characterized as subtropical rain forest. The soils of the study area correspond to Andosols (USDA 1994), which are characterized by their depth and high water retention. Fertility varies from low to moderate, with high fixation of phosphorus and potassium. The soils of this region are susceptible to acidity due to their sandy texture, straightforward lixiviation and Aluminum salts contained in the parental material.
Eleven land use patterns were sampled with two repetitions,
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Forest >40 years old (1, 2);
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Forest > 20 years old (3, 4);
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Harvested Guadua angustifolia (1, 3),
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Guadua angustifolia without harvest (2, 4);
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Traditional coffee plantation (1, 2);
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Coffee plantation intercropped with Plantain (1, 2);
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Organic coffee plantation (3, 4);
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Coffee plantation (1, 2);
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Coffee plantation with the use of chemicals (3, 4);
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Pastures with Cynodon nlemfuensis, Paspalum notatum and P. conjugatum (1, 2, 3, 4).
Samples were taken, following the TSBF methodology (Anderson and Ingram 1993). Invertebrates were grouped into: earthworms, ants, Coleoptera, Diplopoda, Diptera, Chilopoda, Dermaptera and others. Taxonomic units of organisms (TU, order, family, genera and species) were determined, as well as abundance (ind / m-2 x 0.3 m) and biomass (gpf / m-2 x 0.3 m). Earthworms were kept in 5% formaldehyde and the other invertebrates in 70% alcohol. To reduce the volume and variability of the information, a principal component analysis (PCA) (SAS version 609) was used involving 17 taxonomic units from the 22 sites. To distinguish the impacts caused by different land use patterns, a diversity index was calculated (DI=1-Σ(ni/nT)2, where ni=number of individuals in each species, nT = total number of individuals in all species combined.. The values obtained for the diversity index range between 1 and 0, being 1 the "perfect diversity" and 0 being no diversity. The means and standard error of the means were calculated for abundance values.
Results and Discussion
Macro-invertebrates were separated into 132 taxonomic units such as ants (20 sp), earthworms (20 sp), Coleoptera (27), Diplopoda (22), Chilopoda (10) and others (33). The unit classified as "Others" included those groups with less than 1% of the abundance and biomass, such as Isopoda, Mollusca, Crustacea, Blattida, Hirudinea, Pseudoescorpionida and Mermithidae. From PCA analysis, three factors explained 64.9 % of the total macro-fauna variability. Factor one (35.7%) differentiated a high presence of Diplopoda, Chilopoda, Arachnida, Homoptera, Isopoda and Blattida, and low abundance and biomass of earthworms, which could be associated with the type of vegetation and superficial ground coverage. Factor two (17.3%) was characterized by high diversity and prevalence of earthworms and ants. Factor three (11.9%) was interpreted as erosion, it presented low diversity and high abundance and biomass, with some groups of Chilopoda; this factor differentiated places with animal traction pathways or with over grazing by cattle, and the presence of gullies which are indications of physical, chemical and biological degradation.
The earthworms dominated in abundance and biomass in most of the land uses. In Forests 1, 2, 3, 4, the abundance of macro-invertebrates was inconsistent (3600, 2368, 6272 and 6736 ind / m-2 x 0.3 m) while the biomass was greater in Forest 2 and 3 (209, 239, 231 and 193 gpf. / m-2 x 0.3 m). The highest values were found in the Coffee plantation intercropped with Plantain 2 (7760 ind / m-2 x 0.3 m, 772 gpf / m-2 x 0.3 m), while the lowest were found in Guadua angustifolia 2 (1456 and 211). In Pastures 1 and 2 the abundance of macro-invertebrates was low (1312 and 2160 ind / m-2 x 0.3 m,) as well as the biomass (137 and 181 gpf / m-2 x 0.3 m), but in Pastures 3 and 4 the values for abundance and biomass were high (4240 and 3760 ind / m-2 x 0.3 m) (440 and 325 gpf. / m-2 x 0.3 m) (Figures 1 and 2).
Figure 1: Abundance of macroinvertebrates in 22 land uses
In this study the diversity abundance of earthworm species found under pasture was low (2 to 4), but high under forest (9 to 11). The number of species given in grasslands or in other agro-ecosystems ranges from 1 to 15, but in most communities is around 3 to 6 species (Bardgett and Cook 1998; Fragoso et al 1999; Feijoo 2001). The change of land use has affected the structure and composition of the communities in the systems evaluated in the Andean mountain range; for example, the dedication of the soil to activities of livestock rearing (2-4 species) or to mono-cropping systems (1-1 sp) has reduced the diversity of the macro-invertebrates drastically compared with the forests (between 6 and 11 sp). Changes in soil mulch, food sources and the process of decay have caused a reduction in species richness, density and biomass. The study was able to differentiate the stress intensity for soil communities in agricultural systems; in coffee plantations and coffee with agrochemicals for example, there was a greater decrease in species richness compared to systems with coffee plantation intercropped with plantain or with organic coffee. The conversion of natural systems into intensive production systems reduces biodiversity and favors the disappearance of functional key groups such as decomposers (harsh environment with great temperature fluctuations and soil humidity) and producers (narrowing of the spectrum of the quality of the resources; lixiviation and erosion) (Feijoo 2001).
Figure 2: Biomass of macroinvertebrates in 22 land uses
The diversity index showed three types of answers to how macro-invertebrate communities react to disturbances (introduction of mono-cropping or pastures and toxic impact of agrochemicals). Type I, with Diversity Index values above 0.57 contained those agro-ecosystems rich in ground mulch (superficial covering) and those with shade (Forest 1, 3 and 4, Guadua 3 and 4 and Organic Coffee 3 and 4). Type II with values between 0.41 and 0.56, contained agro-ecosystems with signs of degradation due to human activities (Forest 2, Guadua 1, Guadua 2, Traditional Coffee 1 and 2, Coffee plantation intercropped with Plantain, Monocropping Coffee 1, Chemical Coffee 3). Type III with values below 0.4 pointed out those systems with high soil degradation (Chemical Coffee 4, Pasture 1, 2, 3 and 4) (Figure 3).
Figure 3. Diversity index for 22 land uses (number of samples = 7)
