Impacts of gum-resin harvest and Lantana camara invasion on the population structure and dynamics of Boswellia serrata in the Western Ghats, India

Abstract

Assessing the effects of harvesting on the population dynamics of important non-timber forest products (NTFPs) species is important for informing species conservation options, guiding sustainable harvesting practices and offtake and supporting local livelihoods. However, harvesting is rarely the only pressure on NTFP populations, and it is vital that the effects of interactive pressures be considered. This applies to Boswellia serrata, an NTFP tree species which is widely harvested for gum-resin used in religious practices. However, in many settings populations are in decline, presumably due to heavy harvesting, but other factors may play a role, such as altered fire regimes and invasive species. Here we report on the effects of harvesting and invasion by Lantana camara on B. serrata populations in three protected areas in the Western Ghats biodiversity hotspot in southern India. We considered tree and juvenile density, size class distribution, and growth, mortality, and recruitment rates in harvested and unharvested populations over two years. Generally, tree density was higher in harvested populations. The negative effects of harvesting were most apparent at the site with the greatest harvesting pressure, with only limited effects at the other two sites, as reflected in the size class distribution and mortality and recruitment rates. Increasing cover of L. camara was associated with declining densities of B. serrata juveniles and, to a lesser extent, adult trees. The impact of L. camara cover was generally higher than that of gum-resin harvest. The results show that the viability of B. serrata populations is negatively affected by both harvesting and Lantana invasion, and that appropriate management intervention needs to be considered to address these.