Look at enough land in the lower 48 states and you will see that more than half of it is now covered by crops or something other than native vegetation. In the central grasslands, crops have replaced almost all the tall grass prairie and much of the short grass prairie. Croplands have also supplanted native short grasses in California's Central Valley, mixed woodland along the Atlantic coast, and much of the deciduous forest in the Great Lakes region. Aerodynamic roughness length is a measure of the roughness of a given vegetation type and thus its resistance to air movement. Albedo is a measure of the amount of solar radiation a particular plant type reflects.
Fractional coverage is a simple measure of the extent to which a vegetation type covers the land.
Copeland and his colleagues assigned numerical values for these four vegetative characteristics to all the indigenous vegetation and modified land cover types they used in their model. As indigenous vegetation in the model, they used data estimates of the vegetation types most likely to have occurred before European disturbance of the landscape. With this input, the researchers ran the model. W hen the modellers compared the input of the four vegetative characteristics with the output of the four atmospheric parameters, they found some close relationships. For instance, wind speed compared well with roughness length.