Rangelands are of enormous importance, making up close to half the terrestrial global landscape. Defined as areas capable of producing forage but unable to support rain-fed agriculture, rangelands are amazingly diverse but are generally water-limited for at least part of the year. Another unifying feature of many rangelands-unfortunately-is that they have undergone (and continue to undergo) rapid transformation as a result of factors such as overgrazing, deforestation, woody-plant encroachment, and invasion by nonnative plant species. Each of these factors has altered rangeland water cycles and related biogeochemical processes in ways that appear to be significant but are not well understood. In addition, the demand for scarce water in rangeland environments has increased as human populations and their associated water needs-agricultural, residential, and municipal-have grown, increasing the conflict between human and ecosystem maintenance needs.
Given the challenges posed by these transformations, the theme of this set of papers-Emerging Issues in Rangeland Ecohydrology-is especially appropriate. Ecohydrology focuses on the hydrology-ecology interface, i.e. the interrelated dynamics of hydrology and ecology. Research in this area is developing rapidly, addressing temporal and spatial issues across the spectrum of conceptual hierarchies (e.g. organism, population, community, ecosystem, watershed). Research in ecohydrology is strengthening the fundamental scientific insights that are necessary to effectively address environmental concerns (e.g. ecological processes that influence water yield and water quality; hydrological processes that influence succession or desertification). This kind of work is critical if we are to develop innovative restoration strategies for rangelands and provide policy-makers with relevant information about the ecological and hydrological tradeoffs associated with land management decisions.
The catalyst for this Special Issue was a Society for Range Management Symposium, convened to summarize the status of research being conducted across the spectrum of ecohydrological issues that pertain to rangelands. A unifying feature of the 13 invited papers was analysis of the influence of biotic components on the water cycle of a rangeland ecosystem, and how those biotic components are affected by land-use practices. Each of the papers addresses some important aspect of a key issue related to the ecohydrology of rangelands. These include the temporal and spatial components of evapotranspiration (ET); interrelationships between carbon and water fluxes; the influence of vegetation cover and land management on runoff and erosion processes; the implications of woody-plant encroachment for streamflow and recharge; the influence of topographic characteristics on hydrological, ecological, and soil processes; groundwater and surface water interactions as modulated by vegetation; and the societal drivers and ecohydrological implications of desertification. Our hope is that collectively, this set of papers will not only provide a synthetic overview of the state of our knowledge concerning the ecohydrology of rangelands, but will point the way for future research.