Vegetation Patterns in Northeastern North America 1500-2000

Over the last few centuries, human activities have changed the landscape of northeastern North America from mostly forested to a patchwork of forest, farmland and logged areas, back in many areas to mostly forested. Meanwhile, there have been many rapid changes in the composition of the remaining forests, for example, the amounts of hemlock (Tsuga canadensis) and beech (Fagus grandifolia) have decreased while the amount of birch (Betula spp.) has increased. How stable have been the basic vegetational patterns under the onslaught of these landscape and compositional changes? In preliminary analyses, the assemblages of major tree taxa have been zoned for every other century, using optimal splitting by information content and other techniques, to study changes in vegetation groupings over the last 500 years. Several patterns seem to be emerging on a centennial scale: First, vegetation patterns were changing in the centuries before European colonization of the area. Second, the number of zones (vegetation types, based on pollen), was greater in 1700 and 1900 than in 1500 or now. Third, the zone boundaries have moved north from 1500 to the present. Further analyses, including several more data sets will be used to refine these conclusions and to suggest explanations for the changes.