Sacred forests are keystone structures for forest bird conservation in southwest China’s Himalayan Mountains
Introduction
As humans consume an ever-increasing proportion of the Earth’s resources, biodiversity declines at an accelerating rate (Chapin et al., 2000, Foley et al., 2005), making the protection of “keystone structures”, i.e., discrete spatial features that maintain biodiversity at multiple spatial scales, ever more important (Belsky and Canham, 1994, Manning et al., 2006, Stagoll et al., 2012, Tews et al., 2004). For example, forest gaps, large trees, and temporary wetlands are keystone structures whose presence adds heterogeneity to the resources available in landscapes, facilitating greater species richness. The question is how to identify such keystone structures, and how to protect them.
Sacred forests, i.e., natural areas protected by local people for cultural or religious reasons (Dudley et al., 2009), may be keystone structures for biodiversity in traditional landscapes around the world. Sacred forests are numerous, dispersed across a broad range of topographic and micro-climatic conditions, and range in size from a single hectare to thousands of square kilometers (Ormsby, 2011). As such, they likely serve multiple ecological functions, including as corridors, refugia, and source habitats (Bhagwat and Rutte, 2006, Dudley et al., 2010). Sacred forests may be critical components of protected area networks (Verschuren et al., 2010), but we have little understanding of their potential role for biodiversity conservation, especially in the less-studied biodiversity hotspots.
The traditional land management systems that sustain sacred forests may create optimum conditions for species diversity at multiple spatial scales. For example, sacred forests are typically managed by communities (Dudley et al., 2009) and often experience a gradient of human disturbance (UNESCO-MAB, 2003), where a variety of organisms can utilize variable resource conditions (Belsky and Canham, 1994). In addition, sacred forests are typically embedded in landscapes with matrix habitats that are hospitable to at least some species, and thus conventional assumptions of patch size and fragmentation effects (MacArthur and Wilson, 1967) may not apply (Prugh et al., 2008). Furthermore, the edges between sacred forests and their matrix are often not abrupt barriers, but a gradient of disturbance to levels characteristic of the surrounding matrix. These edges may serve as “ecotones”, facilitating ecological interactions between the patch and the matrix, and offering supplementary resources not available in the core habitats (Ries et al., 2004). Despite their potential importance for species dispersal and persistence, we have little understanding of how sacred forests are influenced by patch size, edge effects, and interactions between patch and matrix habitats.
One region where sacred forests are relatively common are the Himalayan mountains (Barbhuiya et al., 2010, Luo et al., 2003, Mallarach, 2008, Salick et al., 2007, UNESCO-MAB, 2003, Xu et al., 2005). Several ethnic minority groups recognize sacred areas as part of their religion, including sacred beyuls (which protect entire valleys), sacred mountains (10s to 100s of km2), and village-level sacred forests (1–1000 ha). The Himalayan mountains also contain three biodiversity hotspots (Myers et al., 2000) and forest birds are of special conservation concern (Renner, 2011). The region exhibits high levels of bird diversity and endemism and ranks highest in global assessments of threatened bird species richness (Grenyer et al., 2006). Many forest bird species in the Greater Himalayas follow a Sino-Himalayan distribution (Renner, 2011, Renner and Rappole, 2011), which includes the Himalayan range, the mountains of southwest China, and the Qinghai Tibetan plateau (Fig. 1a). Forest degradation has accelerated throughout this region in recent decades (Brandt et al., 2012, Renner et al., 2007, Spehn et al., 2010), destroying bird habitats (Dumbacher et al., 2011). Sacred areas may be critical for bird conservation throughout this rapidly changing region, but their importance for Himalayan forest bird communities across multiple spatial extents is not well understood.
Our overarching objective was to understand the role of sacred forests for the conservation of Himalayan forest birds. We studied bird communities within and outside of Tibetan sacred forests in northwest Yunnan, China, with the following specific objectives:
- 1.
Determine whether bird community composition and diversity is different within sacred forests compared to the surrounding matrix.
- 2.
Identify the critical habitat characteristics structuring bird diversity, abundance, and community composition.
- 3.
Investigate how patch size and edge habitats influence bird community composition, diversity and abundance patterns.
Section snippets
Study area
Our study area is in Shangrila, northwest Yunnan Province, China (Fig. 1a). Northwest Yunnan is a biodiversity hotspot in the Hengduan Mountains of the southeastern sub-Himalayan mountains, bordering Myanmar, Tibet and Sichuan Province. Three major rivers (the Yangtze, Mekong, and Salween) create steep gorges, with elevations ranging from 1800 to 6740 m, creating a large array of ecological niches in a relatively small area.
Northwest Yunnan has great importance for local, regional, and global
Habitat
The 62 plots captured a wide range of variability in vegetation disturbance, structure and species composition (see Appendix S1 in Supporting Information). PCA identified two prominent habitat gradients in our study area (Fig. 2a). The first axis (eigenvalue = 3.59, explaining 44.8% of the variance) corresponded to differences between sacred and matrix habitats, which had significantly different vegetation composition and structure in the canopy, sub-canopy and ground layers (see Appendix S2).
Sacred forests as keystone structures
Our results indicated that Tibetan sacred forests conserved some characteristics of old-growth forests, and thus protected unique forest bird communities in the Chinese Himalayan mountains. In addition, sacred forests had the highest bird diversity of all habitats at multiple spatial scales and in both years. Since detection probabilities were considerably lower in the sacred forests compared to their matrix, it is likely that our estimates of differences are conservative, and that sacred
Acknowledgements
This work was supported by NSF IGERT Grant No. DGE-0549369, a NASA Earth and Space Science Fellowship and an NSF Doctoral Dissertation Enhancement Program Grant. We gratefully thank W.Y. Song and M. Haynes for assistance in the field, and J. Posner and T. Allendorf for logistical support. We thank R. Hart and the Kunming Institute of Botany for providing precipitation data from the Shangrila weather station. We thank two anonymous reviewers for their insightful comments which greatly improved
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