CANCELLED - Biotic velocity of North American trees over the last 21,000 years and climate: past responses and future tracking potential

Background/Question/Methods

A longstanding challenge in ecology is how to infer biotic velocities: the rate at which species’ biogeographic ranges shift across landscapes. Understanding biotic velocity has practical importance for identifying which taxa can track modern climate change. Current understanding is primarily based on modern data (e.g. forest inventory, genetic, or occurrence) limited in temporal extent, and with limited climate variability compared to the near-future large and rapid climate changes. Past periods of rapid climate change can serve as analogues, offering insight into the magnitude and direction of species’ range shifts. Using a network of fossil pollen records, we infer biotic velocity for North American tree taxa from the Last Glacial Maximum (LGM) to present. First we develop a Bayesian spatio-temporal model to jointly estimate relative abundance of tree taxa. Then we quantify biotic velocity and its uncertainty through time. We do this using several measures of biotic velocity (e.g. centroid, northern and southern edge). We calculate climate velocities, which define the rate of past climate change from Global Circulation Model output, from the LGM to present, and into the future. We compare climate and biotic velocities, and infer the potential of taxa to track future climate change.

Results/Conclusions

Biotic velocity varied through time and among taxa. Biotic velocity estimates were ~10-1000 m/yr. Temporal patterns in biotic velocity differed among taxa. However, several general trends emerge. First, uncertainty in biotic velocity was largest during ~21-15 Kybp; this is a result of limited pollen count data from this period. Second, biotic velocity values were more dynamic directly after the LGM, and showed greater stability during the Holocene. Third, taxa exhibited more movement during periods corresponding with shifts in climate, particularly the Bølling-Allerød (~15-13 Kybp) and the Younger Dryas (~12.9-11.7 Kybp) periods. We found that biotic velocity was related to climate velocity, although the strength of this relationship varied among taxa. We infer that the ability of taxa to track climate change is variable among taxa; some can likely keep up while others may not. This work extends previous efforts to quantify and compare biotic and climate velocities by inferring relative abundance of tree taxa from pollen without auxiliary information such as climate, and by characterizing uncertainty in velocity estimates. Results from this work will be used to make predictions about the potential of trees to keep up with expected rates of climate change.