Discovering the Chesapeake: The History of an Ecosystem

THREE: Forests before and after the Colonial Encounter

chapter three Forests before and after the Colonial Encounter grace s. brush Sediment cores from the Chesapeake estuary,tributaries,and marshes contain pollen grains,seeds,charcoal,and other materials that are used as evidence for changes in forest composition and the environment. Changes in climate are reflected by increased charcoal in sediments which indicate warm, dry conditions. Widespread disturbance of the land, such as deforestation and cultivation for agriculture, gives rise to increased ragweed pollen and sediment accumulation from soil erosion. The present landscape surrounding the Chesapeake Bay is a patchy mosaic of forests, cultivated and abandoned agricultural fields, wetlands, residential lawns, gardens, urban asphalt, and other kinds of land cover. The entire drainage area, except for tidal wetlands, serpentine barrens, and scattered Native American dwellings, was forested prior to European settlement. Precolonial forests were all removed at one time or another within the last 200 to 300 years for lumbering, mining, agriculture, and road and railroad building. At present, the region surrounding the Chesapeake is about 40% forested. Most existing forests represent new growth on abandoned fields or lumbered areas; few are older than a century and most range in age from 30 to 70 years. The history of the forests in the Chesapeake drainage area includes response to climate change over several millennia before European settlement as well as sudden and massive deforestation after colonization. Both sets of changes had profound effects on the landscape. Because land and water are intimately linked, land use also transformed parts of the estuary from a system of mostly bottom dwellers to one dominated by floating and swimming organisms. The effect of climate change is well documented on the land, but less so in the estuary. The history of land use and deforestation has resulted in ecologically different landscapes through time. For example, early tobacco farming, in which small fields were planted for a few years and then abandoned to become fallow fields, resulted in fragmentation into a fine mosaic of forest patches interspersed with patches of young trees, herbs, and shrubs. In contrast, large-scale agriculture, particularly as it became more highly mechanized, stripped extensive areas of the landscape of all vegetation, leaving only a few trees in locations unsuitable for cultivation and in hedgerows used to separate property and as windbreaks. Deep plow furrows altered soil structure and likely destroyed many native perennial species that reproduce by root and rhizome growth, such as woodland orchids and violets. This in turn would have affected the microorganism populations in the soil, many of which grow symbiotically on the roots of perennials and make nitrogen available for plant consumption. Intensive fertilization of agricultural fields also changed soil nutrients and microstructure . The most extensive land clearance in the region of the Chesapeake occurred in the late 1800s and early 1900s, when 80% of the land was cleared of forests. Later, wetlands were drained for arable land. The net result of these alterations to the land was a more homogeneous landscape.There has been some afforestation since the 1930s,as increased numbers of abandoned farms were vegetated primarily by seedlings of natural plants. Over time these abandoned fields have become forest stands. Species composition has changed since European colonization as a result of disease.The chestnut blight, introduced in the late 1920s, brought about the demise of the American chestnut, which in many areas in Maryland constituted about 30% of forests. More recently, American elm, common throughout the region, has been greatly reduced by the Dutch elm disease, and Eastern hemlock by the woolly adelgid. Distributions of existing forests in Maryland were compiled into a map based on field data collected from 1973 to 1976 (Brush, Lenk, and Smith, 1980). The different species associations are related to geologic substrate and soils (Fig. 3.1). The region surrounding the Chesapeake includes parts of the Coastal Plain and Piedmont Provinces. Extensive floodplains and numerous tidal marshes characterize the topographically flat Coastal Plain, where crystalline metamorphic and sedimentary bedrock is overlain by partially unconsolidated sedimentary deposits. Soils Forests before and after the Colonial Encounter 41 Fig. 3.1. A map of the major rock and soil types in the Coastal Plain, Piedmont, and Appalachian Provinces throughout Maryland (from Pomerening, 1967). include fine silt and clay, with some gravel adjacent to the streams, where flooding is frequent; mesic silt-loam, with a high water-holding capacity and sufficient drainage...