Lake Sediment Pollen and Charcoal from Fresh Pond in Falmouth MA from 11982 BP to Present

Aim
We analyzed a dataset composed of multiple palaeoclimate and lake-sediment pollen and charcoal records from New England to explore how postglacial changes in forest composition and spatial patterns of vegetation and fire were controlled by regional-scale climate change, a subregional environmental gradient, and landscape-scale variations in soil characteristics.

Location
The 120,000-km2 study area includes parts of Vermont and New Hampshire in the north, where sites are 150-200 km from the Atlantic Ocean, and spans the coastline from southeastern New York to Cape Cod and the adjacent islands, including Block Island, the Elizabeth Islands, Nantucket, and Martha’s Vineyard.

Results
Boreal forest featuring Picea and Pinus banksiana was present across the region when conditions were cool and dry 14,000-12,000 calibrated 14C yrs before present (ybp). Pinus strobus became regionally dominant as temperatures increased between 12,000 and 10,000 ybp. The composition of forests in inland and coastal areas diverged in response to further warming after 10,000 ybp, when Quercus and Pinus rigida expanded across southern New England, while conditions remained cool enough in inland areas to maintain Pinus strobus. Fire severity was high during 10,000-8000 ybp. Increasing precipitation allowed Tsuga canadensis, Fagus grandifolia, and Betula to replace Pinus strobus in inland areas during 9000-8000 ybp, and also led to the expansion of Carya across the coastal part of the region beginning at 7000-6000 ybp. Abrupt cooling at 5500-5000 ybp caused sharp declines in Tsuga in inland areas and Quercus at some coastal sites, and the populations of those taxa remained low until they recovered around 3000 ybp in response to rising precipitation. Throughout most of the Holocene, sites underlain by sandy glacial deposits were occupied by Pinus rigida and Quercus.

Main conclusions
Postglacial changes in the composition and spatial pattern of New England forests were controlled by long-term trends and abrupt shifts in temperature and precipitation, as well as by the environmental gradient between coastal and inland parts of the region. Substrate and soil moisture shaped landscape-scale variations in forest composition. Climate and fuels largely controlled fire severity in New England during the postglacial interval.

研究目的：本研究分析了一套包含多序列古气候（palaeoclimate）、湖泊沉积物（lake-sediment）花粉与炭屑（charcoal）记录的新英格兰地区数据集，旨在探究冰期后（postglacial）森林群落组成、植被与火的空间格局变化，如何受区域尺度气候变化、次区域环境梯度以及景观尺度土壤特征变异的调控。

研究区域：本研究区域面积达12万平方千米，北部涵盖美国佛蒙特州与新罕布什尔州部分区域，该区域内的采样点距大西洋150~200千米；研究区域同时覆盖从纽约州东南部至科德角及其周边岛屿的海岸线，周边岛屿包括布洛克岛、伊丽莎白群岛、楠塔基特岛与马撒葡萄园岛。

研究结果：在距今14000~12000年的校准放射性碳年代（calibrated ¹⁴C ybp）冷干气候阶段，区域内广泛分布以云杉属（Picea）和班克松（Pinus banksiana）为特征种的北方针叶林。12000~10000 ybp期间，随着气温升高，北美乔松（Pinus strobus）成为区域优势群落。10000 ybp之后气候进一步变暖，内陆与沿海地区的森林组成出现分化：栎属（Quercus）与刚松（Pinus rigida）在新英格兰南部扩张，而内陆地区仍维持适宜低温以保留北美乔松种群。10000~8000 ybp期间，区域火灾烈度较高。9000~8000 ybp期间，降水量增加使得加拿大铁杉（Tsuga canadensis）、大果山毛榉（Fagus grandifolia）与桦木属（Betula）得以在内陆地区取代北美乔松；而自7000~6000 ybp起，降水增加同样推动山核桃属（Carya）在区域沿海区域扩张。5500~5000 ybp发生的突发性降温，导致内陆地区的加拿大铁杉以及部分沿海站点的栎属种群急剧减少；两类类群的种群数量始终维持低位，直至约3000年前后随降水增加才得以恢复。全新世（Holocene）大部分时期内，以砂质冰碛沉积物为基底的采样点区域始终以刚松与栎属为优势群落。

主要结论：新英格兰地区冰期后森林群落组成与空间格局的变化，受气温与降水的长期演变趋势及突变事件、区域沿海与内陆间的环境梯度共同调控。基质与土壤水分状况主导了森林组成在景观尺度上的空间变异。冰期后时段内，新英格兰地区的火灾烈度主要受气候条件与可燃物载荷共同调控。