Plant metacommunity structure remains unchanged during biodiversity loss in English woodlands

The metacommunity concept provides important insights into large-scale patterns and dynamics of distributions of interacting species. However, temporal change of metacommunity structure is little studied and has not been previously analysed in the context of biodiversity change. As metacommunity structure is determined by multiple species distributions, it is expected to change as a result of biodiversity loss. To examine this process, we analysed structural change of a southern English woodland metacommunity at two points in time, seven decades apart. During this interval, the metacommunity lost beta-diversity through taxonomic homogenization. We performed an 'elements of metacommunity structure' (EMS) analysis to examine metacommunity structure, based upon three structural elements: coherence (i.e. gaps in species range along a structuring gradient), spatial turnover (replacements), and species range boundary clumping. We predicted that metacommunity structure would decrease in spatial turnover and thus become more nested over time. We tested for change in individual structural elements with z-scores and examined the role of spatial and environmental variables as potential structuring mechanisms through correlation with EMS ordination axes. Our results demonstrated that the metacommunity had a Clementsian structure that was maintained over time. Despite no change in broad structure, coherence and species range boundary clumping increased. Spatial turnover increased along the first structuring gradient but decreased on the second gradient. We hypothesise that this difference between gradients may reflect the presence of competing processes affecting spatial turnover. The mechanisms of biological structuring involved both environmental and spatial factors at the scale of the individual woodland. Therefore, our results suggest that broad metacommunity structure would not be a good landscape-scale indicator for conservation status. Conversely, knowledge that metacommunity structure does not change over time could assist in long-term conservation strategy because fundamental metacommunity structural processes are resistant to environmental change.