Lake Sediment Pollen and Charcoal from Umpawaug Pond in Redding CT from 9377 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：本研究分析了一组来自新英格兰（New England）的多套古气候（Palaeoclimate）与湖泊沉积物孢粉、炭屑记录数据集，旨在探究冰期后森林组成、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：本次研究区域面积达12万平方千米，北部涵盖佛蒙特州与新罕布什尔州的部分区域，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（Cape Cod）及其邻近岛屿的海岸线，包括布洛克岛、伊丽莎白群岛、楠塔基特岛与玛莎葡萄园岛。

研究结果：在距今14000~12000校正放射性碳年（calibrated ¹⁴C yr BP）的冷干气候条件下，区域内广泛分布以云杉属（Picea）和班克松（Pinus banksiana）为优势类群的寒温带针叶林。在12000~10000校正放射性碳年期间，随着温度升高，北美乔松（Pinus strobus）成为区域优势树种。10000校正放射性碳年之后，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，而内陆地区仍维持足够凉爽的气候，得以保留北美乔松种群。10000~8000校正放射性碳年期间，火烈度较高。9000~8000校正放射性碳年期间，降水增加使得加拿大铁杉（Tsuga canadensis）、美洲山毛榉（Fagus grandifolia）和桦木属（Betula）在内陆地区取代了北美乔松；同时，自7000~6000校正放射性碳年起，山核桃属（Carya）在区域沿海区域扩张。5500~5000校正放射性碳年期间的气候骤冷，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下降，这些类群的种群数量始终处于低位，直至3000校正放射性碳年前后，伴随降水增加才得以恢复。在全新世（Holocene）的大部分时期，覆盖冰川砂质沉积物的采样点区域均以刚松和栎属为优势类群。

主要结论：新英格兰森林组成与空间格局的冰期后变化，受到温度与降水的长期变化趋势和突变事件，以及区域沿海与内陆间的环境梯度共同调控。基质类型与土壤水分决定了森林组成的景观尺度变异。在冰期后时段，新英格兰地区的火烈度主要受气候与可燃物状况调控。