Responses of ants to selective logging of a central Amazonian forest.
Abstract
Relatively little information exists on the effects of logging on rain forest organisms, particularly in the Neotropics where logging operations have increased dramatically in recent years. In this study the effects of selective logging on ground-living ants were investigated in a forest north of Manaus, in Amazonas, Brazil. The experimental design consisted of three 4-ha replicated plots representing control unlogged forest, and forests logged 10 and 4 yr before the start of the study (in 1987 and 1993). The logging operation removed 50% of the basal area of trees of commercial value, or about 8 trees/ha. This resulted in a significant decrease in canopy cover, and an increase in understorey vegetation density in logged plots relative to controls. Collection and identification of ants from a total of 360 one-m2 samples of leaf litter revealed 143 ant species, of which 97 were found in the control plots, 97 in the plots logged in 1987, and 106 in those logged in 1993. Species richness, evenness and mean abundance (ants/m2) per plot did not vary among treatments. Most of the species found in the control plots were also present in the logged plots. However, population density of many species changed as a result of logging, an effect that persisted for at least 10 yr after logging. Species commonly found in sites that were directly disturbed by logging (gaps and tracks) were rare in the undisturbed forest, as revealed by an additional collection of ants. These results suggest that the persistence of ant assemblages typical of undisturbed forest is likely to depend on the amount of structural damage incurred by logging. Thus management techniques that minimize logging impacts on forest structure are likely to help maintain the conservation value of logged forests for ground-dwelling ants. It is particularly important to minimize the extent of logging roads and tracks created by heavy machinery because these areas appear more prone to invasion by non-forest species.