Climatic changes are multivariate in nature, and can be quantified using metrics that assess shifts in the magnitude, timing, availability, and location of climate parameters (e.g. near-surface air temperature, precipitation). Properly quantifying these changes is vital to our ability to make reliable forecasts about the future, to inform conservation, and to quantify the risks and impacts associated with climatic change. Specific mechanisms including climatic novelty, rates of climate displacement, and climate divergence have been hypothesized to cause the emergence of novelty in plant community assemblages. The detailed record of vegetation and climate during the last deglaciation enables us to test the effect of these proposed mechanisms on plant communities. Here, we use paleoclimatic simulations to quantify novelty, displacement, and divergence across Europe and eastern North America from the last glacial maximum to present. Then, using fossil pollen records we quantify community novelty and assess the effect of these mechanisms on novelty.
Results/Conclusions
Cross correlation of regional trends indicate an association between community and climate novelty, where community novelty leads climate novelty by 0 to 500 years in Europe and lags by 3500 to -1000 years in ENA. We find that mid-Holocene climates for both Europe and eastern North America are most dissimilar when compared to late glacial climates, and that the same pattern holds true when comparing the novelty of plant communities from those periods. Fitting a mixed-effects model supports the significance of climatic novelty in relation to community novelty for both regions, while also suggesting the importance of displacement rates in Europe. These results suggest that the 21st-century emergence of novel plant associations will be driven by both rapid rates of climate change and emergence of novel climate states.