Assessing forest degradation in tropical deciduous forests in Central India

Background/Question/Methods

Understanding degradation has become important with the proposed implementation of REDD+. However, while degradation has been successfully understood in relatively homogenous forests, this needs to be extended to heterogeneous, mixed forests, where there is no baseline to which an altered state of the forest can be compared. Human culpability also needs to be established for it to qualify as degradation. 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.

This study modifies the matrix approach and uses class transition of forests species in heterogeneous, tropical deciduous, mixed forests in Central India, to understand impact of increasing human use on long-term forest composition and structure. For this, field surveys (n=26) were conducted at increasing intensities of human and livestock use, that were quantified by GPS tracking cattle and human movement in forests around six representative villages for three seasons in one year. Field surveys quantified tree species in 4 size classes (sapling, <4 cm DBH, <10 cm DBH, >10 cm DBH). Multivariate analysis of variance (MANOVA) tested whether class transition of tree species is reduced with increasing frequency of use. Generalized linear models (GLM) tested whether cattle density, human populations, distance to market, frequency of use or plant traits were significant predictors of reduced class transition.

Results/Conclusions

Class 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 environmental variables such as human population and frequency of use, and plant traits such as growth form (moderate size, straight trunk) and generalized use for fuel and construction, and without specialized uses or commercial value. Reduced class transition from sapling to trees (height <213 cm) was predicted by cattle density, and species impacted were those preferred by grazing ungulates.

This study demonstrates that easily 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 can be expected to become less frequent, which may be termed as degradation. Grazing may be a more significant driver of degradation in the study region, as it prevents species from reaching reproductive age. Further, specifically harvested species may suffer less than other forest species, thus impacting forest community, and must be incorporated in future studies.