The following analysis uses data published in W. Wyatt Oswald et al., “Subregional Variability in the Response of New England Vegetation to Postglacial Climate Change,” Journal of Biogeography 45, no. 10 (2018): 2375–88, https://doi.org/10.1111/jbi.13407. The spreadsheet I used is available upon request.
- High-resolution data permits reconstruction of Holocene forest cover changes
- Initial forestation after deglaciation in 12 000 BCE led by birch and pine
- Dramatic decline in forest canopy between 1630 and 1708; almost complete recovery by 2001
Berry Pond is an unimaginatively named site north of Boston, Massachusetts (figure 1). Its low elevation (42 m), regular precipitation (1236 mm per year), and soil (mostly glacial till) make it a site typical of southern New England. The authors of this study present an impressively detailed pollen count stretching back to 16 000 years before present (BP), or 14 072 BCE. The sampling gives us data at a very high resolution. This data is freely available through the Neotoma Paleoecology Database. I downloaded this data and here present a brief analysis and interpretation with an eye to tracing the Holocene forest history of New England.
The graph tells a remarkably coherent story of the forest’s response to disturbance (figure 2). The canopy tree count includes species such as maple, chestnut, hickory, oak, and hemlock — characteristic trees of a well-established forest in southern New England. In this category, I also included pioneer trees, namely pine and birch. These trees like open canopy, so they are the first to “pioneer” an area that has no other trees in it. Thus we see that the initial response to deglaciation at 12 000 BCE is a steep climb in the percent of canopy trees, from 56% to 97% in less than 2 000 years. This dramatic increase in forest cover is led by birch and pine, which rise to their all-time high of 75% in 10 800 BCE. Over the next 11 500 years, the relative pollen counts stay pretty similar, with canopy trees at 95–100% and the percent of flowering grasses (indicators of open land) below 5%. In other words, the landscape that native people of New England encountered was mostly forest, without much open land (at least in the area of Berry Pond).Continue reading