Temporal and spatial heterogeneity of avian community dynamics within a forested landscape

Background/Question/Methods

Although extensive literature on the spatial distribution of avian species richness exists, few studies have focused on long-term abundance of individual species at large spatial scales, which includes habitat of both high and low suitability. Even fewer have tested the spatial and temporal dynamics of species richness and abundance simultaneously over a heterogeneous landscape. This information is necessary in order to understand both community- and population-level dynamics within a landscape as well as spatial stability of species richness and abundance through time. We used a long-term (16-yrs), large-scale (>3,000 ha) monitoring dataset within the Hubbard Brook Experimental Forest, NH (HBEF) to address the following questions:  1) what is the spatial patterning of avian species richness and abundance within a northern hardwood forest? and 2) Is species richness and abundance congruent over space and time? To address these questions we modeled species richness at 373 survey locations in each year using a hierarchical multi-species occupancy model that accounted for imperfect detection. In addition we modeled the abundance of each individual species using an open-population N-mixture model. We then interpolated estimates of species richness and abundance across the landscape in each year and performed spatial correlations on species richness,  abundance and richness and abundance.

Results/Conclusions

The spatial patterning of species richness within northern hardwood forest was heterogeneous throughout HBEF. However, areas of high or low species richness remained similar from 1999 to 2014. In contrast, the abundance of individual species varied dramatically throughout the landscape over the course of the study. However, overall avian abundance was positively correlated in space and time.  Interestingly, species richness and overall avian abundance were negatively correlated within the landscape. Together, these results suggest that within northern hardwood forest, the spatial patterns in species richness and abundance are not congruent and that they are each spatially stable over periods as long as this 16-yr study despite greater than two fold changes in total bird abundance across the landscape.