the diversity and productivity of arid lands depend on the interaction between environmental limitations and the complex of adaptive features that allow organisms to maintain their water and energy balance. the central monte is located in the aridsemiarid zone from western argentina, with mean annual rainfall that varies between 30 and 350 mm, concentrated in summer, mean temperature between 13 and 18 oc and with water deficit during most of the year. here we analyze plant adaptations to water stress and the water use strategies of the dominant life forms in central monte: trees, shrubs and perennial grasses. trees and shrubs from the monte include species with different levels of xerophytism. their adaptations range from exploitation of deep water reservoirs with extensive root systems to a wide variety of physiological, morphological and architectural strategies to tolerate drought and salinity. prosopis flexuosa, a phreatophytic tree, plays central ecological roles in plant communities, affects the hydrological cycle, and is an important economical resource locally and regionally. grasses, with shallow root systems, have growth pulses associated to rainfall dynamics. diversity in water use by the dominant plant growth forms determines negative and positive interactions among species that modulate the ecosystem productivity and, consequently, its productive potential. the hydrological cycle is strongly linked to vegetation (and viceversa) in the monte ecosystems, both locally and regionally (in several areas with groundwater accessible to plant roots, recharged by andean precipitations). therefore, the knowledge of the mechanism driving this connections helps to understand ecosystem functioning and to predict future scenarios in relation to global climate change and land use.