How do β-deviation patterns change over the course of succession across a disturbance gradient?

Background/Question/Methods

Disturbance differentially changes local environment and resource conditions across a landscape. The Mount St. Helens (Washington) volcano erupted in 1980 creating primary successional habitat that differs in local topography, resource availability, and proximity to seed source. Null model β-deviation analyses provides insight into the role of environmental heterogeneity on community diversity over the course of succession. Thus, we examine changes in species turnover across space (between sites) and over time (between years) by calculating β-diversity and comparing to null model values. In addition, we correlate β-deviation across sites over time to local soil, topography, and climate conditions to determine how local resource heterogeneity could be driving succession across the disturbance gradient. 

Results/Conclusions

β-deviation patterns across primary successional habitats with varying proximity to seed source and local environmental conditions have shown that resource heterogeneity structures succession trajectories over time. Specifically, we found lower β-deviation in more isolated, disturbed areas and higher β-deviation in less isolated areas on Mount St. Helens. This suggests that a combination of lower dispersal rate and increased disturbance intensity drive more isolated, intensely disturbed areas to be more homogenous. Matching β-deviation to local soil, topography, and climate conditions indicate that soil microsite differences may be driving this pattern. Greater differences in soil roughness best explain the greater β-deviation found at certain primary successional sites. Overall, these findings provide evidence that resource heterogeneity drive spatial patterns of diversity over the course of succession.