Historical and computational analysis of the long-term environmental change: Forests in the Shenandoah Valley of Virginia.

摘要

The increase and decrease of forests is a major factor of land cover change. This study of forest change in the Shenandoah Valley builds upon the rich historiography of the region through the analysis of generalized and spatially explicit primary and secondary sources covering the period of 1700 to 2000. Combining geo-historical and geo-computational approaches produced a more robust picture of land cover change than would be possible using only one method. Comparing modern and historical reports on the timing of forest clearance and re-growth revealed that a discrepancy existed between the spatially explicit sources and existing historical interpretations regarding the timing and location of forest clearance and re-growth. Understanding this discrepancy is important for the interpretation of forest change and its implications in the Shenandoah Valley and beyond.; Two main aspects of the study are the thorough interrogation and comparison of different data sources, and the subsequent analysis and interpretation of the data. Historic maps (1864, 1906, and c. 1945) and digital data sets derived from remotely sensed images (c. 1974 and c. 1992) were analyzed in a geographic information system (GIS) and compared to agricultural census data and published reports of land use and land cover change. Three major findings came out of this study. First, the spatially explicit sources produced values for the amount of cleared area that were within 0.5 to 2.7% of the same information derived from the agricultural census. Second, the maximum amount of forest clearance occurred 25--50 years later than existing published reports indicated. Third, the commonly held explanations of federal land acquisition and the abandonment of farms on steep slopes did not account for the observed patterns of forest re-growth. The documented variations in spatial and temporal patterns and reasons for the variations have impacts on our understanding of cultural and physical processes that took place in the region.