Putting Climate Change in Context: What Is the Signal of Vegetation Change Over the Last 2000 Years?

Background/Question/Methods: PALEON (the PaleoEcological Observatory Network) is an interdisciplinary team of paleoecologists, ecological statisticians, and ecosystem modelers with the goals of reconstructing forest composition, fire regime and climate in forests across the northeastern US over the past 2000 years and applying these reconstructions to drive and validate terrestrial ecosystem models. PALEON members developed STEPPS, a Bayesian space time model, to quantify trends in a network of 23 high resolution fossil pollen time series from central and western Massachusetts spanning the last 2000 years. STEPPS estimates trends in forest composition with coherent uncertainty estimates, so that trends can be distinguished from the considerable noise in paleoecological data.

Results/Conclusions: American chestnut colonized our study area beginning in the northern Connecticut River Valley around 2000 years ago. Rather than spreading into forests dominated by oak-hickory assemblages, as might be expected from the bioclimatic envelope of this species, chestnut replaced beech in northern hardwood forests.  PALEON will use such detailed long-term empirical records of forest change to help assess the ability of terrestrial ecosystem models to accurately capture long-term forest dynamics.