Abstract
Post-fire succession is an ideal case for studying effects of disturbance on community assembly, and the key is to disentangle the contributions of assembly processes to the variation of community composition, namely beta diversity, and the contingent scales. The central Yunnan Plateau of Southwest China is characterized by monsoon related seasonal drought, and frequent forest fires. We sampled five fire sites burned in different years and a middle aged forest, measured species composition dissimilarity and its species turnover and nestedness components, within each fire site and across all sites. Results indicated species turnover as the primary component of beta diversity within all communities. There was no trend of change with year-since-fire (YSF) in beta diversity among early post-fire communities, but beta diversity in the middle aged community was significantly higher. Species turnover patterns across fire sites revealed a weak dispersal limit effect, which was stronger at lower than upper slope position for woody plants, and reverse for herbs. At the site scale, the species dissimilarity and turnover both enlarged with increasing slope position difference, especially in the middle-aged community, but the species nestedness had no consistent trend among sites, except a decreasing trend in the middle-aged forest. (Partial) Mantel tests indicated habitat filtering [primarily indicating total nitrogen (TN) and slope position] played a much stronger role than dispersal limit and YSF (indicating competition intensity) for the post-fire forest assembly at the landscape scale, for both woody and herbaceous layers. However, at the site scale, Mantel tests indicated a diminishing effect of soil nutrient filtering with increasing YSF, while effects of topography and spatial distance in the middle aged community was stronger. This divergence suggests the primary assembly mechanism gradually shift away from the soil constraint. While the seasonal drought and the mountain topography dominate the environmental legacy, our results imply that fires may reinforce a priority effect in the forests assembly in this region, by creating a habitat filtering (e.g., moisture and nitrogen limitation) effect on species composition in post-fire communities.
Highlights
The secondary vegetation dynamics after disturbances, including wildfires, have long been a central theme of ecological succession studies (Clements, 1916; Watt, 1947)
The effects of habitat filtering and the dispersal limitation on species pool were included as critical community assembly processes (Keddy, 1992)
We addressed the following questions: (1) What are differences between the spatial and temporal patterns of beta diversity and its nestedness and turnover components in the post-fire forest communities and a middle aged community? (2) What are differences of variation in beta diversity between the woody and herbaceous layers? (3) How much do the spatial distance, year-since-fire (YSF), and topography related environmental factors contribute to the community assembly of the post-fire forests in the central Yunnan Plateau?
Summary
The secondary vegetation dynamics after disturbances, including wildfires, have long been a central theme of ecological succession studies (Clements, 1916; Watt, 1947). Increasing efforts has emerged to integrate the theories of community assembly and succession, a clear perspective is yet to be inferred from divergent results (Bruelheide et al, 2011; Raevel et al, 2012; Ulrich et al, 2016) Natural disturbances such as wildfires, by breaking the biotic and abiotic legacies and resetting the start point for community assembly processes, provide a unique opportunity in exploring effects of succession on assembly rules (Myers et al, 2013, 2015; Liu et al, 2016; Harms et al, 2017)
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