Abstract:

Aims: The Gaoligong hoolock gibbon (Hoolock tianxing) is a typical arboreal primate species whose habitat has been highly fragmented due to long-term human disturbance. This study evaluated the impacts of human disturbance and altitude on tree community diversity and availability of food resources in the habitat of H. tianxing.

Methods: From July to August 2023, we surveyed 26 tree plots (20 m × 20 m) established in the core activity areas of six H. tianxing groups in Sudian Lisu Ethic Township, Yingjiang County, Yunnan Province, China. A new quantitative index of human disturbance intensity, the habitat disturbance index (HDI), was developed using land-use data. Linear mixed models were used to assess the effects of HDI and altitude on α and β diversity of tree communities, and generalized linear mixed models were used to evaluate their effects on the richness of food tree species. Dominant tree species were identified using species importance value (IV) and the cumulative IV proportion, with species contributing to the first 50% of cumulative IV being defined as dominant. We further assessed the retention status of food tree species.

Results: We recorded 146 tree species belonging to 58 genera, 34 families, and 21 orders. The α diversity of tree communities was not significantly affected by HDI or altitude. In contrast, both HDI and altitude significantly and negatively affected the gradient of β diversity. Among the 26 dominant tree species, 10 (38.46%) were food tree species for H. tianxing. The total IV of all food tree species accounted for 24.84% of the total IV across all species, suggesting that food resources were currently well retained and remained relatively abundant. Additionally, altitude had a significant positive effect on the richness of food tree species, whereas HDI did not, indicating that higher-altitude areas may play an important role in sustaining food resources and that food tree species may show ecological resilience to moderate disturbance.

Conclusion: Disturbed forest patches can still provide meaningful support for H. tianxing by retaining food resources at appreciable levels, while human disturbance and altitude jointly affect the variation in tree community composition in its habitat. Disturbed areas should not be automatically treated as low-value habitat in conservation assessments; instead, forest quality and disturbance levels should be evaluated integratively, and areas retaining important food resources should be incorporated into conservation planning.

Key words: Hoolock tianxing, human disturbance, habitat disturbance index, food resources, tree diversity