Emerging Issues in Rangeland Ecohydrology: Vegetation Change and the Water Cycle

Abstract

Rangelands have undergone-and continue to undergo-rapid change in response to changing land use and climate. A research priority in the emerging science of ecohydrology is an improved understanding of the implications of vegetation change for the water cycle. This paper describes some of the interactions between vegetation and water on rangelands and poses 3 questions that represent high-priority, emerging issues: 1) How do changes in woody plants affect water yield? 2) What are the ecohydrological consequences of invasion by exotic plants? 3) What ecohydrological feedbacks play a role in rangeland degradation processes? To effectively address these questions, we must expand our knowledge of hydrological connectivity and how it changes with scale, accurately identify ''hydrologically sensitive'' areas on the landscape, carry out detailed studies to learn where plants are accessing water, and investigate feedback loops between vegetation and the water cycle.

Does rangeland degradation have implications for global streamflow?

“…As an example, at a study site on the Edwards Plateau in central Texas we have documented an increase in streamflow at the catchment scale following the removal of an encroaching shrub, Ashe juniper (Huang et al, 2006). We estimated this increase to amount to some 50 mm/year, a magnitude consistent with those found by other small-scale field studies (summarized in Wilcox et al (2006b) as well as by regional modelling estimates (Afinowicz et al, 2005). By extrapolation, we would expect to see a decline of about the same magnitude in regional streamflows during the last century because of the general increase in juniper cover.…”

Evapotranspiration partitioning, stomatal conductance, and components of the water balance: A special case of a desert ecosystem in China

“…Loss of water through ET represents either the largest (where significant groundwater uptake occurs) or the second largest component (where groundwater uptake does not occur and rainfall is therefore the largest single component) of the water balance in water-limited ecosystems. ET can account for more than 92.7% (or more than 100% if groundwater uptake occurs) of rainfall (Zhang et al, 2001;Wilcox and Thurow, 2006;Wang et al, 2010;Kool et al, 2014). In our study, ET a accounted for more than 98.3% of water consumption.…”

“…Evapotranspiration (ET) is the largest process of ecosystem water loss and is a major determinant in the ecosystem water budget and energy balance (Law et al, 2002;Scott et al, 2006;Hu et al, 2009). In arid zones, ET can account for up to 95% of all water inputs (Wilcox and Thurow, 2006). Generally, ET is the aggregate of water loss measured using micrometeorological techniques and soil parameters and does not distinguish the pathway and components of water loss.…”

Redistribution of Runoff Among Vegetation Patch Types: On Ecohydrological Optimality of Herbaceous Capture of Run-On

“…A central tenant of ecohydrology is that the water budget and vegetation patterns and dynamics are tightly interrelated in rangelands and other water-limited ecosystems (Noy-Meir 1973;Rodríguez-Iturbe 2000;Eagleson 2002;Ludwig et al 2005). Understanding these ecohydrological interrelationships is becoming increasingly important for effective rangeland management by scientific, management, and policy communities (Newman et al 2006;Wilcox and Thurow 2006), particularly as rangeland degradation continues to progress in a significant portion of the world's semiarid regions (Middleton and Thomas 1997). Degradation of rangeland is often preceded by a reduction in vegetation cover (Dregne 2002).…”