Free-ranging livestock cause forest understory degradation in giant panda (Ailuropoda melanoleuca) habitat

Abstract

Free-ranging livestock are common in reserves established for giant pandas (Ailuropoda melanoleuca), which rely almost exclusively on bamboo in the montane forests of southwestern China. Previous studies have showed that overgrazing by livestock had led to a reduction in bamboo abundance. However, there is limited knowledge of how livestock impact the structure of the understory vegetation. Conducted in the Wanglang National Nature Reserve with a livestock exclosure experiment, our study aimed to fill this gap by examining the impact of livestock grazing on two important elements of forest understory bamboo and moss in giant panda habitat, and quantifying their recovery after excluding livestock. Measurements of bamboo and moss showed that both elements were severely degraded. With a closer examination, we found moss growth was worse in areas with dense bamboo or no bamboo at all, but better when there were many dead stems in bamboo clump, suggesting bamboo exerted both negative competition and positive shelter effects from livestock trampling on moss. Livestock exclusion with fence indeed exempted bamboo and moss from continuous damage which were exemplified by more bamboo shoots inside the fence and significantly decreased moss height outside the fence. However, we observed no recovery of damaged bamboo and moss inside fenced quadrats in two years. Neither the sprouted bamboo shoots matured into stems after the growing season, nor the height of moss increased. Collectively, our results suggested that long-term livestock grazing drastically altered understory layer of bamboo and moss and interactions in between, and there was hardly recovery of the understory bamboo and moss in a short term. Therefore, we recommend artificial intervention with bamboo and moss planting in severely degraded areas and long-term monitoring of understory vegetation to restore the habitat of giant panda.