How scattered trees matter for biodiversity conservation in active pastures

Abstract

Large areas of Tropical Forest have been cleared and deeply modified aiming at growing crops and producing livestock. Many of these areas are transformed in pastures with scattered trees. We investigated an area of 618.59 ha in Southeastern Brazil composed of active pastures of an African grass, Urochloa decumbens, with scattered trees and forest patches. We surveyed all the scattered trees in the active pastures and in 60 plots of 200 m2 within eight forest patches. To identify the ecosystem services and the history of scattered trees we applied a semi-structured survey to the landowners. We assessed regeneration, distance of propagules source, grass cover, microclimate, seed rain, and soil compaction under scattered tree crowns and in samples in the pasture without scattered trees. We found the scattered tree community highly diverse and associated this to apparent lack of preference for species showed by farmers during the clearing process for pasture, choosing the trees only by their shading capability (size). We also found that the scattered trees strongly affect seed rain and sapling regeneration in the pastures, improving microclimate and attracting dispersers, although this last effect is strongly dependent of the forest proximity. We found that the major difference between the scattered tree community and forest patches is associated with small trees lost during forest clearing and not to the largest trees left in the pastures. We see the scattered trees as key factors for promoting forest recovery, as well as an important biodiversity pool per si in highly fragmented landscapes.