1) Chronology revision

Goal: update the fossil sites so their chronologies are as accurate as possible, with quantifiable uncertainty.

• Developed a set of criteria to identify fossil-pollen sites with highly accurate and precise radiocarbon-based chronologies (i.e. "benchmark" sites).


• Used the benchmark sites to revise the chronologies of all late Quaternary pollen cores in eastern North America contained in the Neotoma database and quantified the amount of error built into each fossil-pollen core. See Blois et al. 2011


• Re-dating key mammal fossil deposits to increase the temporal resolution of the late Quaternary mammal dataset in eastern North America.

Figure 1. Benchmark (red) and other (gray) sites, for the period 10.5 to 14.5 thousand years ago. Over 400 pollen cores span the crucial Bølling-Allerød and Younger Dryas periods, yet less than 30 sites meet our criteria for benchmark sites.

2) Generalized Dissimilarity Models (GDMs) of community change

Main questions: Are no-analog mammal and vegetation communities synchronous in space and time? What aspects of climate drive their formation?

• We are using GDM (Ferrier et al. 2007) to understand how climate drives community turnover through space and time.


• We are first developing GDMs for eastern North America vegetation community change over the past 21 thousand years, then we will look at the joint responses of vegetation and mammal communities.


• Additional collaborators include Matt Fizpatrick and Simon Ferrier

Figure 2. Spatial community dissimilarity (top row) predicted by GDM and summer temperature (middle row) at 14, 11, and 7 thousand years ago. The corresponding GDM functions of community dissimilarity along the summer temperature gradient is at the bottom, with three locations along the gradient indicated. From Blois et al, in review.