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Changes in land use and land tenure can influence both physical fragmentation and ownership fragmentation of landscapes, with implications for biodiversity. In this study, we evaluated changes in land use and land tenure in the Tijuana River Watershed, a region of high biodiversity and endemism, following the implementation of a new Agrarian Law which allowed for privatization and sales of communal land (ejidos) beginning in 1992. In order to understand changes in land use and cover, we constructed maps from aerial photographs and Aster images and measured changes between 1994 and 2005. In order to understand changes in land tenure, we collected data from Mexican government sources on ejido land size, ownership, and sales, and we conducted 55 structured interviews with ejidatarios in the watershed. Our results demonstrate that land-use/cover change between 1994 and 2005 was dominated by an increase in urban area and grasslands, and a decrease in coastal sage scrub, chaparral, and, to a lesser degree, agriculture. In particular, the conversion of coastal sage scrub has left a far more fragmented landscape than existed in 1994. In addition, most of the ejidos in the watershed, as well as individuals interviewed, had participated in some stage of the land certification and titling process allowed by the new Agrarian Law, resulting in substantial changes in land tenure. However, land tenure security appeared to play a larger role than a desire to sell land and, contrary to studies from other regions, full title to the land was obtained in a range of urban and rural settings, rather than primarily on land closest to urban zones. Our results suggest that past predictions regarding future urban growth and fragmentation of native vegetation in the region have proven accurate and highlights regions of change that merit further study.
