Steyaert, L.T., and R.G. Knox, 2008: Reconstructed historical land cover and biophysical parameters for studies of land-atmosphere interactions within the eastern United States, J. Geophys. Res., 113, D02101, doi:10.1029/2006JD008277.
The abstract reads
“Over the past 350 years, the eastern half of the United States experienced extensive land cover changes. These began with land clearing in the 1600s, continued with widespread deforestation, wetland drainage, and intensive land use by 1920, and then evolved to the present-day landscape of forest regrowth, intensive agriculture, urban expansion, and landscape fragmentation. Such changes alter biophysical properties that are key determinants of land-atmosphere interactions (water, energy, and carbon exchanges). To understand the potential implications of these land use transformations, we developed and analyzed 20-km land cover and biophysical parameter data sets for the eastern United States at 1650, 1850, 1920, and 1992 time slices. Our approach combined potential vegetation, county-level census data, soils data, resource statistics, a Landsat-derived land cover classification, and published historical information on land cover and land use. We reconstructed land use intensity maps for each time slice and characterized the land cover condition. We combined these land use data with a mutually consistent set of biophysical parameter classes, to characterize the historical diversity and distribution of land surface properties. Time series maps of land surface albedo, leaf area index, a deciduousness index, canopy height, surface roughness, and potential saturated soils in 1650, 1850, 1920, and 1992 illustrate the profound effects of land use change on biophysical properties of the land surface. Although much of the eastern forest has returned, the average biophysical parameters for recent landscapes remain markedly different from those of earlier periods. Understanding the consequences of these historical changes will require land-atmosphere interactions modeling experiments. “
The conclusion has the text
“The eastern half of the United States has experienced extensive land cover transformations over the past 350 years. Land use change has fundamentally altered the land cover of entire vegetation regions (e.g., wetland forests in the lower Great Lakes region and lower Mississippi River floodplain, tallgrass prairie, and southeastern pine savannas and open woodlands). Forest management practices, pests, and disease have modified forest composition and structure. Wetlands have been converted by intensive agriculture, plantation forestry, flood control, navigable waterway development, and urban development. Few areas of the eastern United States have escaped considerable alteration by human land management. (Even these have been exposed to increases in the average partial pressure of atmospheric CO2, enhanced nitrogen deposition, and changing distributions of anthropogenic aerosols, as well as numerous human-introduced pests, pathogens, and invasive exotic competitors.) Although seminatural vegetation reestablished on many former cutover or agricultural lands during the 20th century, it typically persists in landscapes fragmented by transportation corridors, residential-urban development, agriculture, industrial forestry, and other intensive land uses. Recent land cover provides an insufficient basis for understanding the functional responses and feedbacks of historical land cover. Modeling experiments and sensitivity tests incorporating coupled land-atmosphere interactions are needed to understand and quantify the feedbacks, interregional connections, and integrated consequences of these land cover and land use changes.”
Two figures from their paper dramatically illustrate the substantial amount that land surface climate forcings have changed. To illustrate the magnitude of this effect, if the value of solar radiation received at the ground were 600 Watts per meter squared, a change in albedo of 12% to 16%, translates to a 24 Watt per meter squared increase in solar energy absorbed at the surface.
This paper, therefore, represents a landmark study for the use of the climate modeling community in order to quantify the role of human land management effects on the climate system, relative to other human climate forcings.