Multiple climatic mechanisms have been hypothesized to cause community reshuffling and the emergence of novel communities. These include novelty, velocity, displacement, and divergence. The paleoecological record enables tests of these hypotheses by combining analyses of past environmental conditions with analyses of community turnover and novelty. Prior work has focused on linking climate novelty to community novelty or to test for disequilibrium, but there has been no recent integrative analysis that assesses multiple mechanisms leading to novelty. This work is also the first to jointly assess patterns and drivers of novelty across both Eastern North America and Europe. Using paleoclimatic simulations, we quantify climatic novelty, displacement, and divergence across North America and Europe from the last glacial maximum to present. Then, using existing records of fossil pollen recovered from lake sediments, we quantify community novelty. We then combine the two to test hypotheses about which mechanisms are most closely associated with highly novel and no-analogue plant assemblages.
Results/Conclusions
This work is the first to assess the relationship between multiple metrics of climatic change and their potential effects on past plant communities. Our results support prior linkages between climatic novelty and community novelty, while suggesting that in some time periods and regions displacement and divergence are important predictive factors. The rates of displacement and the variance across these rates and directions are important factors contributing to community novelty. The spatial correlation of these climatic metrics and novel communities varies over time, with analyses conducted at 500-year intervals dating back to the last glacial maximum. Comparative analyses between Europe and Eastern North America help establish common underlying drivers of long-term patterns of vegetation dynamics in both regions, which have been the subject of study for over a century.