Long-term Dynamics of Vegetation and Environment in Central Massachusetts 1000-2000

Historical and ecological data from north-central Massachusetts suggest that widespread and intensive human disturbance after European settlement led to a shift in forest composition and obscured regional patterns of species abundance. A paleoecological approach was required to place recent forest dynamics in a long-term context. Pollen and charcoal data from 11 small lakes in north-central Massachusetts were used to reconstruct local vegetation dynamics and fire histories across the region over the past 1000 years. The sites are located across an environmental gradient. Paleoecological data indicate that prior to European settlement, there was regional variation in forest composition corresponding to differences in climate, substrate, and fire regime. Oak, chestnut and hickory were abundant at low elevations, whereas hemlock, beech, sugar maple, and yellow birch were common at high elevations. Fire appears to have been more frequent and/or intense at lower elevations, maintaining high abundances of oak, and archaeological data suggest Native American populations were greater in these areas. A change in forest composition at higher elevations, around 550 years before present, may be related to the Little Ice Age (a period of variable climate), fire, and/or activity by Native Americans, and led to regional convergence in forest composition. After European settlement, forest composition changed markedly in response to human disturbance and there was a sharp increase in rates of vegetation change. Regional patterns were obscured further, leading to homogenization of broad-scale forest composition. There is no indication from the pollen data that forests are returning to pre-European settlement forest composition, and rates of vegetation change remain high, reflecting continuing disturbance to the landscape, despite regional reforestation.

美国马萨诸塞州中北部的历史与生态学数据表明，欧洲殖民后广泛且高强度的人类活动干扰，引发了森林组成的转变，并掩盖了区域物种丰度的分布格局。为将近期森林动态置于长期演化背景之中，需采用古生态学（paleoecology）方法。本研究利用马萨诸塞州中北部11处小型湖泊的花粉（pollen）与炭屑数据，重建了该区域过去1000年的局地植被动态与火历史。所有采样点沿环境梯度分布。古生态学数据显示，欧洲殖民前，森林组成存在区域分异，这与气候、土壤基质及火状况的差异密切相关：低海拔区域以栎树、栗树和山核桃树为主，而高海拔区域则常见铁杉、山毛榉、糖枫与黄桦。低海拔区域的火发生频率更高、强度更强，这维持了栎树的高丰度；同时考古数据显示，这些区域的原住民人口规模更大。约距今550年时，高海拔区域的森林组成发生变化，这可能与小冰期（Little Ice Age，一段气候波动期）、火活动及原住民活动相关，并最终导致森林组成的区域趋同。欧洲殖民之后，受人类活动干扰影响，森林组成发生显著改变，植被变化速率大幅提升；区域分布格局进一步被掩盖，最终引发大范围森林组成的同质化。尽管该区域已开展区域性造林，但花粉数据并未显示森林正恢复至欧洲殖民前的组成结构，且植被变化速率仍处于高位，反映出区域景观仍持续受到人类干扰。