Alternative system to slash-and-burn for agriculture in the eastern Amazon region: Impacts on ant species richness

Slash-and-burn is the most widespread approach to preparing land for agriculture and livestock in Brazil’s Amazon region. Leaf-litter biomass may be totally burned in affected areas, destroying a vital habitat for thousands of invertebrate, such as ant communities. An alternative to slash-and-burn has been developed, using tractor-driven equipment to mulch vegetation, leaving organic material on the soil surface. This study focuses on evaluating ant species richness in plantations of cassava under slash-and-burn and mulch systems. We measured and used a set of pertinent environmental variables in order to understand and control for factors determining ant community diversity. The study was conducted in northeastern of Pará State, Brazil. We used pitfall-traps spaced 25 meters apart, with three replicates and 20 traps per replicate. We used multiple regressions with a quasi-Poisson error distribution. In our analysis, we found greater ant species diversity in mulching as compared to slash-and-burn systems (p<0.005). Higher magnitudes in the variables plant height (p<0.005), leaf litter biomass (p=0.016) and litter phosphorus content (p=0.020) were significantly related to increased ant species richness in both systems. Higher litter nitrogen content was significantly related to increased ant species richness in mulching systems (p=0.030). In a model analyzing slash-and-burn sites, soil hardness (p<0.005), phosphorous (p<0.0005) and aluminum content (p=0.015) were found to be significantly related to increased ant species richness. In a model analyzing mulch systems, leaf litter biomass (p<0.0005) and distance from the nearest forest fragment (p=0.012) were the environmental variables correlating to greater richness. Our results showed that land-use systems using different crop preparation approaches have different impacts on biodiversity, specifically that systems using fire reduced ant species richness as compared to the fire-free mulch systems. The fire-free systems appeared to maintain the environmental variables within the agricultural matrix that are vital for resource and habitat conditions for ant species.