Novel communities emerge as a result of individualistic shifts in species' ranges and abundances in response to changing climates, biotic interactions, disturbance regimes, or anthropogenic activity. Such assemblages pose a challenge to researchers and managers, in part because it is unclear to what extent novel associations will maintain ecosystem function relative to a baseline of interest. The very nature of such communities makes predictions difficult when relying on contemporary observations alone, but the well-documented no-analog plant associations from North American paleorecords provide a promising model system. These late-glacial novel communities were 1) geographically widespread, 2) persisted for several millennia, and 3) were composed of associations of boreal and temperate taxa found in eastern North American forests today which are likely to coexist in the future.
Results/Conclusions
We reconstructed vegetation dissimilarity, climate dissimilarity, and community trait dissimilarity from present throughout the last 21,000 years, to test whether late-glacial no-analog plant associations exhibited altered function compared to modern systems due to differing community trait profiles. Vegetation dissimilarity from present was calculated as the squared chord distance between pollen assemblages in the Neotoma Database and the Modern Surface Sample Dataset. Climate dissimilarity from present was calculated from the downscaled CCSM3 climate reconstructions. Trait dissimilarity was calculated for community-weighted values for seed weight, maximum height, and specific leaf area, using modern measurements applied to pollen-based vegetation reconstructions. Results show the overall pattern of ecosystem function across space and time as a function of changes in vegetation and climate, and allow us to ask: were novel communities also novel ecosystems? The spatiotemporal pattern of plant trait means and dissimilarity from present also shed light on the mechanisms of vegetation response to climate change, megafaunal extinction, and human activity since deglaciation.