Relative influence of local- and landscape-level habitat quality on aquatic plant diversity in shallow open-water wetlands in Alberta’s boreal zone: direct and indirect effects

Reclamation usually involves modification of the local environment to achieve some biotic target, but if the influence of Landscape Condition on that target is great, we may fail to meet it despite efforts at the local-level. We sought to determine the relative influence of local- and landscape-level habitat on aquatic plant diversity in shallow open-water wetlands. Furthermore, we asked whether the influence of Landscape Condition should be attributed to direct (dispersal-related) effects, or to the indirect effect of landscape variables that influence local habitat quality. Finally, we asked if spatial scale (300–2000 m) would affect conclusions about the relative influence of local- and landscape-level effects. Using structural equation modeling, we found that Local Condition is consistently more influential than Landscape Condition. As landscape size increases, the relative importance of Landscape Condition declines and there is a trade-off between its direct and indirect components. At ≤500 m direct landscape effects were of greater importance than indirect effects, whereas indirect effects of Landscape Condition became more important at ≥1500 m. This suggests that the dominant mechanism by which land use influences diversity depends on the spatial extent of the landscape. We recommend that reclamation designs include a high proportion of wetland habitat and incorporate seeding/planting if diverse plant communities are desired. Additionally, we note that the influence of the landscape is strongest within 300 m. Thus, the focus of reclamation efforts should remain at the in-lake level and the immediate surroundings: this is where efforts will achieve the greatest effect on aquatic plant diversity.