State and Transition Models as Useful Tools for Understanding Vegetation Change in Mexican Deserts and Semideserts

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State and transition models are proposed to explain changes in vegetation in deserts and semideserts. These models provide a framework for organizing complex ideas about the multiple ecological processes and management practices that drive vegetation change. However, these models have not been used to study vegetation change in the Mexican deserts and semideserts, although these ecosystems occupy approximately 50% of the country's land area. The aim of this chapter was to describe the use of state and transition models for studying vegetation change in the Mexican deserts and semideserts. To achieve this goal, we first provide an overview of state and transition models. We then describe the use of state and transition models for different deserts and semideserts around the world. Finally, we use empirical evidence to illustrate the use of state and transition models to study vegetation change in the fluvial terraces of the Zapotitlán Salinas Valley, a semidesert located within the TehuacánCuicatlán Valley. The state and transition models for fluvial terraces had different states: abandoned crop fields with weeds, abandoned crop fields with mesquite, closed mesquite shrubland, open mesquite shrubland, and badlands. The transitions between these states were related to the decrease in canopy cover and visual obstruction caused mainly by rained agriculture and firewood extraction. We hope that this chapter encourages the use of state and transition models to elucidate vegetation changes in Mexican deserts and semideserts.