AimUnderstanding degradation has become important with the proposed implementation of REDD+, particularly in heterogeneous forests where no baseline exists, to which an altered state of the forest can be compared. Further, whether changes in a forest constitute degradation also needs to be established, as degradation is increasingly defined as a shift in the equilibrium of a system to an alternative stable state.
MethodsField surveys (n=26) quantified tree species in 4 size classes (sapling, <4 cm DBH, <10 cm DBH, >10 cm DBH) at increasing intensities of use (quantified by GPS tracking cattle and human movement around 6 representative villages for 2 seasons in 2012). MANOVA tested whether class transition of tree species reduces with increasing frequency of use and GLM tested whether use intensities or plant traits were significant predictors of reduced class transition.
ResultsClass transition was significantly reduced in14 of 36 species at higher use when compared with control sites. Reduced class transition to trees (>4 cm DBH) was predicted by human density, growth form (moderate size, straight trunk) and generalized use for fuel and construction, and without specialized uses. Reduced class transition from sapling to trees (height <213 cm) was predicted by cattle density, and species impacted were those preferred by grazing ungulates.
ConservationEasily measured metrics such as class transition can be used to understand long-term impact on forest structure and community, as species with reduced class transition may become less frequent which may be termed as degradation. Grazing may be a more significant driver of degradation at the study site, as it prevents species from reaching reproductive age. Specifically harvested species may suffer less than other species, which must be incorporated in future studies.