Expansion of pine into mid-elevation Himalayan oak forests: Patterns and drivers in a multiple-use landscape

Abstract

Oak species worldwide are experiencing declines, with negative consequences for hardwood forests and their associated biodiversity, but the causes of these declines vary across species and habitats. We examine changes in extent of banj oak-dominated (Quercus leucotrichophora) moist temperate hardwood forests in a Western Himalayan landscape between 1991 and 2017. Using classified satellite imagery from 1991, 2001 and 2017, we found that dense banj oak forests have undergone substantial degradation and loss of area, while chir pine (Pinus roxburghii) forests have expanded, largely by replacing degraded banj oak stands. This transition was most likely to occur at sites that had lower levels of winter precipitation and Topographic Wetness Index (TWI) values and more pine forest in the surrounding landscape. Our findings are consistent with known requirements of shade and moisture for the recruitment of banj oak. Loss of banj oak forests is likely to reduce biodiversity and a number of ecosystem services linked to the well-being of local communities.