NOAA/WDS Paleoclimatology - Great Dismal Swamp (Virginia and North Carolina) Pollen Assemblage Data

The Great Dismal Swamp wetland, spanning >400 km2 along the Virginia and North Carolina border, was shaped by a complex combination of geomorphic, climatic, and anthropogenic forcings during the last 14,000 years. Pollen, macrofossils, charcoal, and physical properties from sediment cores at seven sites provide a detailed record of the spatial heterogeneity of the wetland and the roles played by natural hydrologic variability, wildfire, and human modification of drainage in shaping vegetation and habitats. Cold-temperate forests occupied regional uplands from at least 13.5-10.3 ka. Marshes dominated by grasses and other herbaceous taxa began developing along low-elevation streams as early as 10.3 ka, resulting in accumulation of organic silts. Long-hydroperiod, peat accumulating marshes, with abundant floating aquatic plants, developed as early as 9.6 ka, as rapid rates of sea-level rise elevated the water table and facilitated wetland development and peat accumulation along stream courses. By the mid-Holocene (c. 7-6.5 ka), when local sea-level rise began slowing and reached about 12-15 meters below present, shorter hydroperiod, peat-accumulating marshes dominated the landscape, with increased wildfire activity. Great Dismal Swamp vegetation shifted from marshes to peat-accumulating forested wetlands by c. 3.7 ka, which were dominated by varying combinations of Nyssa (tupelo), Taxodium (cypress), and Chamaecyparis thyoides (Atlantic white cedar). Wildfires were infrequent during this time, and the forested wetlands persisted, with minor compositional changes related to climate-driven fluctuations in stream flow, until colonial ditching and logging began in the swamp during the late 18th century. These activities decreased cypress and cedar populations, and, by the mid-20th century, expanded ditching resulted in even drier conditions and expansion of maple-gum (dominated by Acer and Liquidambar), and pine-pocosin (dominated by Pinus) forests. The distribution of these forests differs from that of the late Holocene and represents a fundamental shift in hydrology, peat structure, vegetation, and fire regime due to landscape alterations of the last few centuries.

沿弗吉尼亚州与北卡罗来纳州边境分布、面积超400平方千米的大迪斯默尔沼泽湿地（Great Dismal Swamp wetland），在过去14000年间受地貌、气候与人为驱动力的复杂共同作用塑造而成。7个采样点的沉积物岩芯所获取的花粉、大化石（macrofossils）、炭屑与物理性质数据，详细记录了该湿地的空间异质性，以及自然水文变异性、野火与人类改造排水系统在塑造植被与生境过程中发挥的作用。
至少在13.5~10.3千年前，区域高地就已被寒温带森林覆盖。早在10.3千年前，以禾本科与其他草本类群为主的沼泽就开始沿低海拔溪流发育，进而促成有机粉砂的堆积。早在9.6千年前，伴随大量浮水水生植物的长水文周期泥炭积累型沼泽就已形成——当时海平面快速上升抬高了地下水位，促进了河道沿线湿地的发育与泥炭堆积。
到全新世中期（约7~6.5千年前），当地海平面上升速率开始减缓并降至现今海平面以下约12~15米，短水文周期泥炭积累型沼泽占据了景观主体，野火活动也随之增强。约3.7千年前，大迪斯默尔沼泽的植被从沼泽转变为泥炭积累型森林湿地，其优势类群为紫树属（Nyssa，tupelo）、落羽杉属（Taxodium，cypress）与大西洋白崖柏（Chamaecyparis thyoides）的不同组合。在此期间野火发生频率较低，森林湿地持续存在，其组成仅因气候驱动的溪流流量波动发生小幅变化，直到18世纪晚期该沼泽开始出现殖民式沟渠改造与伐木活动。
这些活动导致落羽杉与崖柏种群数量下降；到20世纪中期，持续扩大的沟渠改造使得沼泽环境愈发干旱，进而促使以槭属（Acer）、枫香属（Liquidambar）为主的枫胶林，以及以松属（Pinus）为主的松-波科辛林扩张。此类森林的分布格局与全新世晚期存在显著差异，反映了近几个世纪景观改造所引发的水文、泥炭结构、植被与火动态格局的根本性转变。