Patterns of savanna formation in former semiarid grasslands -- The interactive role of climate change, soil texture and neighbor identit

The encroachment of woody plants in former grasslands is one of the most widespread and consistent forms of land cover change in drought prone ecosystems worldwide. The ratio between woody plants and grasses is particularly sensitive to changes in the timing and magnitude of water availability. Changes in precipitation seasonality and grass composition across contrasting soil textures strongly alter water availability and are associated with changes in woody plant density, although the processes underlying this relationship are not well understood.;In this doctoral research I investigated how soil texture, plant interactions and precipitation seasonality interact to determine the establishment and encroachment of seedlings of mesquite (Prosopis velutina), a widespread woody legume. The goal of this dissertation is to understand how physiological processes and environmental constraints interact to shape observed patterns of savanna formation and woody plant encroachment in former semiarid grasslands.;I observed that recruitment of mesquite was dependent upon the existence of 'windows of opportunity' which originated when shallow soil moisture during the growing season was relatively high and there was no competition with grasses. Coarse texture soils are more favorable to mesquite encroachment than fine texture soils, because the lower soil water availability in the former diminishes the abundance of grasses on this substrate. I observed that carbon limitations are key for seedling survival, which lead me to the study of the mechanisms limiting carbon assimilation in woody plant seedlings. Finally, because of the apparent relationship between carbon limitations and plant survival, I tested whether carbon assimilation would be a reliable proxy for plant water stress.