Human modifications of coastal zones worldwide have increasingly become a focus of both ecological and social concern. However, little is known about the complex interactions between environmental, socio-economic and policy factors that drive changes in coastal land-use patterns. In this study we are investigating the processes of human-induced transformations of coastal lands in southern Sonora, Mexico between 1973 and the present. We combine remote sensing data with government census and environmental records, and institutional and household surveys, to develop a multivariate model of patterns of land-use change. Our analysis focuses on understanding the proximate causes of the spatial patterns of shrimp aquaculture development to provide insight into the relative influence of recent national policy reforms on changing land-use patterns.

Using a combination of supervised and unsupervised maximum likelihood classification, we produced thematic land use and land cover maps of subscenes from two mosaicked Landsat images from 1973 (MSS), 1992 (MSS), and 2001 (ETM), for change detection and modeling. Preliminary results show that the most prevalent form of land-use change in the region over the study period has been the transformation of Pithaya forest and coastal wetlands to shrimp aquaculture. Shrimp farms that did not exist in the region in the early 1980s now represent over 8% of the study area. Our analysis suggests that this boom in shrimp farming was influenced by a series of policy reforms instituted by the Mexican Government over the last decade intended to open the rural economy to global markets. These reforms include modifications to the Fisheries, Foreign Investment and Land Tenure Laws, changes in the rural credit system, and liberalization international trade policies (NAFTA). The data indicate overall increased rates of land conversion from natural covers (Pitahaya forest, Mesquite forest, choyal, salt flats) to human dominated ecosystems (aquaculture, agriculture, salt ponds, urban) in the post-reform period (1992 - 2001) compared to the pre-reform period (1973 - 1992). This analysis highlights the importance of monitoring local impacts in evaluating national policies.

As part of our study we have conducted an analysis of the responses of the coastal ejido sector to the national policy reforms and the recent growth of shrimp farming along the Sonoran coast. Drawing on data collected at the ejido and shrimp farm level, we begin to link the reform of Article 27 to land-use decisions along the coast. We argue that the reform has been a pivotal part of a package of neo-liberal policies promulgated in the 1990s that have shaped the pattern of growth of the shrimp farming industry and restructured the land tenure of the region. We find that there has been a rapid shift in land tenure from the ejido to the private sector over the last six years. In this region, the most critical aspect of the 1992 reform has been the titling process that provided land tenure security and allowed for the first time the legal sale and rental of ejido lands. However, the land titles have proven to be of little collateral value in the severely credit limited coastal ejido sector.

Furthermore, we illustrate that the changes brought about by the reforms of the 1990s and their implications for the coastal ejido sector are not uniform throughout the region, but rather depend on local land distribution history, access to credit, the ethnic composition of the communities, and the dependence on the coastal resources. Finally, we argue that while the opening up of a land market may be increasing economic efficiency, the trade off appears to be long term environmental and equity concerns that may pose problems to the region in the future.