Land use change and gully erosion in the Piedmont region of South Carolina

摘要

Land use change played an important role in the formation of gullies present today in the Piedmont of the Southeastern United States. Forested areas that were once cleared to cultivate cotton and consequently gullied are now, once again, covered with forest vegetation. Despite this forest cover, gullies are still considered to be important contributors of sediment to streams, and restoration efforts are still ongoing. However, the data available to assess the extent of gully contributions of sediment are limited.This study assessed the present day stability of these gullies relative to the land use conditions from 1939 to 1999. Based on 1939, 1954, 1970, and 1999 aerial photographs, land areas were classified into those found to be open or cultivated in 1939 that had converted to forest by 1999 (cultivated-to-forested) versus areas that were forested throughout this period (continually forested). An analysis was then conducted that quantified the number and morphological characteristics of gullies in these areas. Characteristics assessed during the field surveys that quantified the presence of recent erosion, such as percent bare soil or forest floor displacement, revealed that the majority of the gullies in both areas are stable. Surprisingly, more frequent (4 vs. 2 per transect), deeper (54 vs. 46 cm), and longer (36 vs. 30 m) gullies were found in the continually forested areas. This equated to a higher estimated average total volume eroded in the continually forested areas (299 m~3) compared to the cultivated-to-forested areas (107 m~3). It is believed that the continually forested areas, which had steeper average slopes, were cultivated but abandoned prior to 1939 due to severe gully formation.