Motivation
The concept of the forest transition describes the tendency for forest cover to decrease in response to colonization and population growth, and then subsequently rebound as societies undergo economic development, industrialization and urbanization. The forest transition can occur when scarcity of forest products prompts governments and landowners to plant trees and shift to silvicultural land management. An alternate narrative suggests that forest cover can also resurge where higher wages or decreasing commodity prices induce the abandonment of marginal farmlands to natural forest regeneration. Although these secondary forests are often comprised of novel species assemblages, they nonetheless function as refugia for native species, as well as eventually develop species richness and structural characteristics similar to native stands (Lugo and Helmer 2004).
Spatially explicit regression models measure the impact on land cover of geographic characteristics while accounting for location relative to settlements, markets, and transportation networks. Spatially explicit models often have been used to explain patterns of forest clearing (e.g., Blackman et al. in press). However, forest resurgence has been less frequently studied using these techniques, and the factors that encourage reforestation are less well understood. The studies that currently exist come largely from the landscape ecology, geography, and social science literature (e.g., Rudel et al. 2000, Helmer 2000, Rudel et al. 2002, Perz and Skole 2003, Hecht and Saatchi 2007). None of these previous analyses provide a formal rationale connecting variable selection to agent objectives in land use change. Moreover, several use administrative units as the unit of study, rather than spatially disaggregated data. Thus,their methodology cannot incorporate a wide variety of locally variable land-use determinants, such as land and soil characteristics.
El Salvador provides a suitable case study of forest resurgence. Extensive habitat alteration, from agricultural and urban development, left only two percent of the country’s primary forest vegetation remaining. A civil war lasting from 1980 to 1992 had a notable impact on forest cover: lack of security in rural areas resulted in widespread abandonment of pasture and cultivated land. Consequently, secondary growth and advanced pasture successions comprise the largest forest types in the country. Other factors possibly influencing the growth of secondary forests have been decreasing international prices for agricultural commodities, combined with trade liberalization and elimination of most agricultural subsidies.
Project Objectives
The project described here is part of a dissertation study attempting to overcome the shortcomings in the previous literature by using spatially explicit land cover, geophysical, and socioeconomic data to econometrically determine which geophysical and socioeconomic characteristics encourage reforestation in El Salvador. Specifically, I need to generate comprehensive vegetation cover and land use maps for 1990, 2000, and 2010 in order to obtain data on land use and land cover change.