The effects of ecosystem engineers on plant diversity and dynamics at multiple spatial scales

The activities of ecosystem engineers can strongly affect community structure and impact patch dynamics.  Their effects on dynamics at one scale (local patch) often create another set of dynamics operating at a different scale (larger network of disturbance-created patches).  We evaluated how an ecosystem engineer, the beaver (Castor candenesis), influences patch dynamics and species richness of wetland plant communities at local and landscape scales.  Our research was conducted in the riparian wetlands in the sandhills of North Carolina, where the successional dynamics were rapid and permitted observation of transition dynamics between patches affected and not affected by beaver. We surveyed the vegetation communities in different habitat types with previous beaver activity and compared results to areas with no history of beaver modification.  Species richness at the local plot scale was the highest in habitats with no beaver activity and increased slightly with successional stage.  This relationship did not remain consistent at patch or landscape scales; species diversity was highest in open water habitats with recent beaver activity and areas without any history of beaver engineering, while species diversity was lowest in early- and late-successional stages.  When we pooled sites with and without beaver activity, we observed a turnover of 57 plant species (31% of total observed species).  Our findings demonstrate that ecosystem engineers can have strong effects on succession by mediating changes in patch transitions.  This research also illustrates the importance of the role of ecosystem engineers in influencing plant community dynamics and diversity at multiple spatial scales.