COS 13-2
Effects of climate change and land use on mid-Atlantic USA vegetation
Over the last 12000 years, North American vegetation has undergone changes due to climate as the glaciers began to retreat at the end of the last Ice Age. Over the last approximate 500 years, eastern North American vegetation has also changed as European colonists converted forests to agricultural land. We investigated whether changes in climate and land use affected the landscape differently since climate change tends to be episodic whereas changes in land use related to human activity are more chronic in nature. We analyzed the effects of these changes on the land by analyzing the pollen in dated sediment cores collected in tributaries and marshes of the Chesapeake Bay located on or draining areas of different geologic/soils substrates. Our previous studies showed a close relationship between extant forest associations and geology in Maryland, and we assumed that the response to change might differ along the geologic/soils template.
Results/Conclusions
The response of vegetation to climate change was synchronous at different locations but the species differed on different geology/soils substrates. At a site, where the substrate is clay/loam and the present vegetation is dominated by Liriodendron tulipifera, Betula nigra and Platanus occidentalis, 6000 years ago the vegetation was changing from Tsuga spp. to primarily Quercus spp. and members of the Ericaceae. At about the same time, the vegetation at a clay and sandy loam site dominated today by Quercus phellos and Pinus taeda, the shift was from members of the Cupressaceae to primarily Sphagnum spp. and Alnus spp. Between 4000 and 5000 years ago, the vegetation on sand and fragipan which today is dominated by Quercus prinus, Q. stellata and Q. marilandica, was shifting to Liquidambar styraciflua and Nyssa spp. Changes in land use which included cutting down the forests and draining a very wet land for agricultural crops was an immediate shift at all locations irrespective of substrate to a dry mainly herbaceous flora including Ambrosia spp., Rumex spp. and members of the Ericaceae and Gramineae from a wet herbaceous flora that included Typha spp., Sparganium spp., Sagittaria spp., Nymphea spp. and members of the Filicineae and Cyperaceae.