First-order streams are small streams at the top of the watershed. This area is usually the steepest portion of the watershed and therefore can be more impacted by the loss of vegetation. Figures 3.40 through 3.42 show the difference between observed and expected values for vegetation loss, gain, and total change in first-order stream regions. The opposite seems to be the case for vegetation gain. This pattern suggests that some portion of vegetation gain is associated with human activities.
People tend to avoid developing land in the first-order region where slopes are steep.
Thus, we would expect that vegetation gain associated with human activity would be concentrated in the higher-order stream regions of the watershed. When vegetation is removed, the soil surface is exposed to erosion. The steeper the slope, the greater the potential erosion. Not surprisingly, there is little problem on the Coastal Plain, where land is generally flat, nor is there much in the Piedmont of south-central Virginia. Important areas of vegetation loss on steep slopes include eastern Pennsylvania, extending south to the Chesapeake Bay and west along the Maryland Panhandle into western Pennsylvania, central Virginia in the Ridge and Valley Physiographic Province, and southwestern Virginia in the southern Appalachian Mountains.