Long-term Vegetation Dynamics on the Massachusetts Coast from 2000 BP to Present

We use a retrospective approach to reconstruct the past distribution of fire in New England and to investigate the important drivers of this pattern across the period of European arrival to North America. Our study sites are in New England, and range from pitch pine and oak forests of coastal Massachusetts, pine and hardwood forests of central Massachusetts, and northern hardwood and spruce fir forests of northern Massachusetts and Vermont. We collected sediment profiles from 18 lakes across the study area to assess fossil charcoal and pollen abundance over the past 1000 years and including the time period of European arrival and settlement. Based on presettlement pollen composition, our study sites are divided into three vegetation types: 1) pitch pine and oak, 2) oak, pine, and hardwood, and 3) northern hardwoods. The abundance of presettlement charcoal in these lakes is closely related to climate and the composition of surrounding vegetation. Charcoal is most abundant in pitch pine forests and least common in northern hardwood and spruce forests. Following the arrival of Europeans, charcoal abundance increases, at most sites substantially, and vegetation composition changed in a direction of either greater dominance by pitch pine or white pine, depending on whether the forests were located in the southern or northern part of New England. The major factor influencing the distribution of fire across New England is climate, which has a direct effect on the physical conditions conducive to fire ignition and spread and an indirect effect on fire through its control on the distribution of vegetation at this spatial scale. We find evidence that other factors exert some control over local fire regimes as well including landforms and their impact on vegetation composition, firebreaks, and prevailing winds. Native Americans likely influenced the local occurrence of fire, but their impact on regional fire regimes in New England is not apparent from this or other studies. However, additional paleoecological, archaeological and historical work needs to be done to better address this question. In contrast, Europeans had a dramatic effect on fire throughout the New England landscape, increasing its occurrence almost everywhere.

本研究采用回溯式研究方法，重建新英格兰（New England）地区的历史火灾分布格局，并探究欧洲人抵达北美时段内该格局的关键驱动因子。本研究的采样点均位于新英格兰地区，涵盖马萨诸塞州（Massachusetts）沿海的脂松（pitch pine）与栎林、马萨诸塞州中部的松林与硬叶林，以及马萨诸塞州北部与佛蒙特州（Vermont）的北部硬叶林和云杉冷杉林（spruce fir forests）。本研究在研究区域内的18处湖泊采集沉积柱样，以重建过去1000年（含欧洲人抵达与定居时段）的化石炭屑与孢粉丰度变化。基于欧洲人定居前的孢粉组成，本研究将采样点划分为三类植被类型：1）脂松栎林；2）栎、松与硬叶混交林；3）北部硬叶林。这些湖泊中定居前的炭屑丰度与区域气候及周边植被组成密切相关。脂松林中的炭屑丰度最高，而北部硬叶林与云杉冷杉林中的炭屑丰度最低。欧洲人抵达后，多数采样点的炭屑丰度出现显著上升，植被组成也发生定向改变：根据林分位于新英格兰南部还是北部，分别向脂松占优或白松（white pine）占优的方向演替。影响新英格兰地区火灾分布的核心驱动因子为气候：气候一方面直接调控利于火灾引燃与蔓延的物理环境，另一方面通过调控该空间尺度下的植被分布间接影响火灾活动。本研究发现，其他因素同样对局地火灾制度存在一定调控作用，包括地形及其对植被组成的影响、防火隔离带与盛行风。北美原住民或许对局地火灾的发生存在影响，但本研究与其他相关研究均未发现其对新英格兰地区区域火灾制度的显著作用信号。不过，未来需开展更多古生态学、考古学与历史学相关研究，方能更深入地解答这一问题。与之形成鲜明对比的是，欧洲人对新英格兰全境的火灾活动产生了极为显著的影响，几乎所有区域的火灾发生频次均出现上升。