The Effect of Selective Logging and Climate Change on Understory Bird Communities

Abstract

Climate change and anthropogenic land-use change are both processes that threaten natural ecosystems. These global change drivers do not act in isolation, but interact with each other to affect biotic communities in complex ways. This thesis aims to understand how communities respond to the synergistic effects of these global change drivers. Using a trait-based approach, this thesis looks at the responses of climate change and selective logging (extraction of a subset of economically beneficial timber) over a fifteen-year period in an avian community at a mid-elevation site in the Eastern Himalaya. I compared functional diversity and trait distributions (of traits related to thermoregulation, foraging and diet) between primary and logged forest. In addition, I examined how functional diversity and trait values changed over a fifteen-year period, to understand the differential effects of climate change in primary and logged forest. There was no evidence for a significant difference in average functional dispersion between intact and modified habitat although mean functional dispersion was marginally higher in primary forest. In addition, and contrary to expectation, functional dispersion and community-weighted body mass increased over time in logged forest. Increases in functional dispersion in logged forest over time might be because of (a) a decline in functionally similar species because of increased competition (b) upslope range shifts of species from lower elevations to mid-elevations that increase functional diversity at mid-elevations (because low elevation communities tend to be more functionally diverse that higher elevation communities). An increase in community-weighted body mass could be because of an increase in abundance of a few species driving the increase in body mass at the community level. Similar changes were not observed in primary forest in either functional dispersion or body mass. This indicates that the effects of climate change on the average values and distributions of functional traits are likely not equal across a disturbance gradient; more studies should investigate the effects of climate change and land-use change and how they interact with each other rather than treating these two global change drivers in isolation.