Conservation and pasture value of remnant trees in a tropical agroecosystem
Deforestation is continuing at a rapid rate in Central America, contributing to a loss of forest habitat and threatening many endemic species, including arthropods. In Matiguás, Nicaragua, as little as 10% of the original forest reserves remain, with cattle pastures now dominating the once forested landscape. These open pastures are a relatively homogenous habitat, lacking in the complexity that may be appealing to arthropods. Trees dispersed within the cattle pastures may contribute to conservation of arthropod diversity and abundance at the landscape level by providing a more heterogeneous habitat. However, these trees are traditionally removed from pastures to prevent any negative impacts of the trees on pasture productivity (due primarily to the influence of shade). To determine any tradeoffs between reduced pasture productivity but increased arthropod biodiversity below trees, this study compared areas below three tree species—Albizia saman, Enterolobium cyclocarpum, and Guazuma ulmifolia—to areas without trees on working cattle pastures in Matiguás. Pasture growth was measured at three points in time during the dry season in all treatments, and arthropods were captured by pitfall trap to assess biodiversity and abundance during the water-limited dry season (January to May, 2008).
Results indicate that pasture grasses responded differently depending on the dominant local vegetation. By the end of the dry season, mean pasture growth below all trees was significantly higher than within the open pasture area (p<0.05), contrary to the original hypothesis that trees negatively affected pasture growth. Arthropods were more abundant (p<0.05) and diverse (p<0.05) at the morphospecies level below A. saman as compared to open pasture areas. Arthropod orders varied in their responses to trees and open pasture areas depending on the arthropod group, and on tree identity. The findings of this study provide insight for the direction of future research, and can assist conservation managers and producers in planning pasture systems with mutually agreeable landscape features.