Long-term selection of lakes by beaver: Have we underestimated the value of aquatic plants to beaver persistence and density?

Background/Question/Methods

In spite of growing knowledge about the importance of aquatic plants (macrophytes) in beaver year-round diets, most work to assess beaver habitat suitability has not considered macrophyte communities. Research on beaver occupancy and abundance has also emphasized stream habitats over short time periods, while less is known regarding lake habitats over multi-decadal timeframes.  In the present study, we assess whether macrophytes, woody species, and/or basin morphology traits affect the duration and density of beaver occupancy in 23 lakes over a 50 year period.  We incorporate field-based study of aquatic vegetation that includes all species of aquatic plants, to extend previous work that has focused primarily on water lily species (Nymphaea spp., Nuphar spp.).

Results/Conclusions

Lake perimeter and total macrophyte cover independently explained ~70% (R²_adj) of the variation in duration of beaver occupancy. Percent cover floating leaf macrophytes was a strong predictor of beaver colony density in lakes, independently explaining 72% (R²_adj) of the variation in density. Variables related to water lily species and trees were not strong predictors of beaver colony density or duration, but percent tree cover had a weak inverse relationship with the duration of beaver occupancy. Overall, results suggest that aquatic plants and basin morphology have important effects on the duration and density of beaver occupancy in lakes. An exclusive focus on water lily species in beaver habitat suitability assessments may not sufficiently account for the value of other species in the macrophyte community.