For Patch and for Pond: Integrating Two Scale-dependent Ecohydrological Concepts of Water Redistribution to Support Livestock in Semiarid Flatlands

MAGLIANO, PN; BRESHEARS, DD

Nueva Orleans

Congreso; AGU FALL MEETING; 2021

Asociación Americana de Geo-Física

Livestock production in drylands, much of which has subtle topography (?flat?), requires consideration of ecohydrological redistribution of water. This has been accounted for primarily with two different scale-dependent concepts of water availability that have been developed in different parts of the world. Conceptual Model 1 was developed in large extensions of grasslands and woodlands of North America and Australia (300-700 mm/yr) and empathizes on forage production on the landscape while water supply for animal drinking is easily obtained from groundwater or conducted by aqueducts by a river. Here, redistribution of water from bare to grassy patches is emphasized as a means of forage production. In contrast, Conceptual Model 2 was developed in small extensions of flat deserts in Africa and Asia (100-300 mm/yr) and empathizes harvesting the small fraction of runoff that the landscape offers in intense but low-frequency rainfall events via ponding to produce grains and fruits. For flat drylands with intermediate rainfall (200-600 mm/yr), such as the extensive (almost one million km2) Dry Chaco rangelands of South America, we propose an integration of both ecohydrological concepts that also accounts for the geomorphic impacts of livestock. In particular, we postulate the hypothesis that: ?cattle transit and trampling alter the natural water circulation of the ecosystem, enhancing runoff of small areas (i.e., piosphere and long trails) and improving water harvesting in specific points of the landscape?. That is, livestock trampling and transit generate positive feedback providing freshwater but limited to a small fraction of the landscape so that it is not affecting forage production in the rest of it. This integrated conceptual model proposes that livestock is a geomorphological factor in flatlands (together with rainfall, soil and vegetation) that can be managed by ranchers to improve their production systems, for example, by enhancing water availability at different points of the landscape. We illustrate the integrated conceptual model with results from Dry Chaco. Our model is consistent with previous studies but extends existing scale-dependent ecohydrological concepts about water redistribution and maybe generally applicable in flat drylands where groundwater is not readily available.