Experimental landscape connectivity decreases temporal variability in communities over 24 years of assembly

Landscape connectivity is a key regulator of dispersal, which is an important process in community assembly. Theory predicts that connectivity may influence spatial and temporal patterns of community assembly; however, empirically evaluating the role of connectivity is nearly impossible due to the need to isolate its influence over long time frames and large spatial extents. We overcome these challenges through a large-scale, long-term connectivity experiment to test how connectivity affects plant community turnover and directionality of change over 24 years of assembly. Plant communities within connected patches had lower temporal variability in composition compared to plant communities within unconnected patches. Differences in composition between patches and the directionality of compositional changes were driven more by the amount of edge habitat in a patch and the time since the start of assembly. All community responses to connectivity were stronger for species with wind or unassisted dispersal compared to those with seeds dispersed by animals. Connectivitys role in regulating local community dynamics is critical for understanding community assembly and increasingly relevant in an era of anthropogenic land-use change. Significance StatementConnectivity between habitat patches facilitates dispersal to localities, yet the impact of connectivity on local species assemblages is exceptionally challenging to isolate from other spatial changes over time. In a 24-year experiment, we found that connectivity stabilized local community composition as a higher number of species persisted across years within patches connected by corridors. Independent of connectivity, edge effects were more important for driving compositional differences between patches. Importantly, these patterns would not have been captured with short-term data or without controlling for confounding spatial changes. Our findings have broad conservation relevance. Anthropogenic landscape changes that result in a loss of connectivity or increased edge effects may disrupt local community assembly over time.