Abstract
Identifying the ecological processes determining spatial variation in community composition and structure is a central issue in arid areas, especially in the face of climate change. This study aims to estimate how environmental and spatial processes jointly determine vegetation attributes across scales in the Min dry valley, one of the dry valleys in Hengduan Mountainous region suffering severe ecological degradation. A total of 48 plots along slope transects were investigated at three sites along the dry valley, with vegetation and environmental information gathered. Distance-based Moran’s eigenvector maps (dbMEM) was used to extract local spatial variables, while geographic coordinates were used as regional spatial variables. We used redundancy analysis (RDA) and variation partitioning to detect the relative importance of environmental and spatial processes in influencing community composition and vegetation structure (including biomass, coverage, height, density, α and β diversity), and to identify the most determinant environmental variables at different spatial scales. Results showed that both environmental and spatial processes accounted for significant and comparable variations in both vegetation composition and structure. Local spatial variables provided significant and comparable contribution as regional spatial variables to vegetation composition, while provided more contribution than regional spatial variables to vegetation structure. Topography had an overriding effect relative to soil on both vegetation composition and structure. Multi-scale analyses showed elevation was the most important variable (associated with soil moisture and nutrient) at the regional scale; while microtopography, especially slope aspect and shape, dominated at the local scale. We also demonstrated how vegetation composition and structure varied along environmental gradients. The study revealed the overriding role of topography in determining vegetation attributes in this mountainous dry valley, highlighting the advantage of multi-scale spatial analysis for better understanding spatial variation in vegetation pattern and with their important implications for biodiversity conservation and ecological management in the arid mountain areas.
Highlights
Spatial variation in community composition and structure and its underlying drivers are essential issues in community ecology, as they have significant practical implications for biodiversity conservation and ecological restoration in the face of climate change [1,2]
We addressed several questions: (1) What is the relative importance of environmental and spatial processes, of topography and soil property and of regional and local spatial processes, in explaining the variation in vegetation composition and structure? (2) Which environmental variables are most relevant in controlling the observed patterns of vegetation composition and structure at different scales? (3) How do the vegetation composition and structure vary along environmental gradients?
It is interesting that we found the same scale-specific environmental determinants of vegetation structure as that of community composition: elevation associated with soil moisture and nutrient at regional scale, and microtopography at local scale (Table 3)
Summary
Spatial variation in community composition and structure and its underlying drivers are essential issues in community ecology, as they have significant practical implications for biodiversity conservation and ecological restoration in the face of climate change [1,2]. Forests 2020, 11, 1140 suggests that species distribution and community composition are largely determined by niche-based processes, such as environmental filtering, biotic interactions, and interspecific trade-offs, while the neutral theory (i.e., spatial process) suggests that species are ecologically equivalent and community dynamics are governed by stochastic processes of dispersal, ecological drift, and speciation. Until recently a reconciliation has emerged that niche differentiation and neutral processes jointly determined community assembly [7,8,9,10,11]. Their relative importance varied depending on habitats, target species groups, and scale [7,12,13,14]. The spatial process contributed more to the spatial variation in composition for species with lower dispersal ability than those with higher dispersal ability [13,16]
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