Land use systems in the Amazon: Impacts on ant biodiversity

Abstract

Tropical forests cover less than two percent of the surface of the Earth but they host an estimated 50 percent of terrestrial species on the planet. The Amazon region, in particular, is the largest reservoir of biodiversity in the world, home to more than 40,000 described vascular plant species, more than half of the described animal species in the world and major river basins that contain an extraordinarily high diversity of fresh water organisms. The great diversity of the Amazon is highly threatened by deforestation. Agriculture and cattle ranching are the primary causes of deforestation in the region, with cattle ranching accounting for 65 to 70% of forest clearings, small-scale agriculture for 20- 25% and large-scale agriculture for another 5-10%. There are many different land use systems in the Amazon region and most of them do not have any sustainable management planning. As these different systems -- agriculture, forestry and livestock -- get establish and fragment the forest and other natural ecosystems like the cerrado, it is important to understand the structure and dynamics of the biodiversity that colonize these land-use systems. That knowledge will allow us to measure the impacts on biodiversity of the various production systems as well as the tradeoffs and potential synergies regarding production and conservation objectives. Studies of biodiversity have often used a variety of taxonomic groups as indicators. Ants are often used as bioindicators of impacts on biodiversity in the tropics ecosystems because they are sensitive to anthropogenic habitat disturbances, they have complex ecological interactions with many other biotic organisms in terrestrial ecosystems and they are relatively easy to sample and identify. In this study we compare ant diversity in a variety of land use systems in the Amazon region of Brazil with the aim at identifying systems that should be promoted and those that should be avoided based on their impact on ant biodiversity. We also want to understand what are the environmental variables that support high ant biodiversity among and within each land use system. To address these questions we used seven land use systems that are found in the State of Pará in the Brazilian Amazon and that have not received much attention from the scientific community, and we sample a set of environmental variables within each system. Overall this study found that leaf litter biomass and floristic diversity of the herbaceous layer were different among all land use systems and were highly correlated with ant species richness, suggesting that they play an important role for the conservation of biodiversity of ants within the agricultural matrices found in the Amazon region. This study also found that agroforestry systems, orange orchard under organic and conventional management and native forest tree plantations (paricá) were the best land use systems (of those examined) for the conservation of ant biodiversity in region. While soybean plantations, cattle pastures, and exotic forest tree plantations (teak), were found to be the worst for ant biodiversity. From this study it is also evident that those systems that support the higher ant diversity are those that include trees (agroforestry systems, orange orchards and paricá plantations), although not all tree-base systems were beneficial for biodiversity, as demonstrated by the extremely low ant diversity found in teak plantations. Nonetheless, the presence of trees seems to contribute to biodiversity. Therefore, when making decisions regarding land use systems in the Amazon, it is important to consider systems that incorporate trees, such as diverse agroforestry systems. Furthermore, more research should be conducted on diversifying these systems to provide habitat for biodiversity, promote migration between forest fragments, ensure other ecosystem services, such as carbon sequestration and pollination services, and at the same time contribute to improve the livelihood of the people of the Amazon region.