Functional ecohydrological differences among native and exotic grassland covers in sub-urban landscapes of Chihuahua city, Mexico

Vegetation characteristics of sub-urban areas might play underestimated regional roles in the provision of ecohydrological services such as the recharge of wells and superficial water reservoirs (dams), dust control and climate buffering. We hypothesized that potential hydrological processes at the soil-grass interface in a sub-urban area in Chihuahua are affected differently by native and exotic plant species, in that vegetation patches of native grasses favor infiltration and percolation over bare soil (interspaces) and over vegetation patches of exotic species. We examined these hypotheses by monitoring infiltration and permeability of adjacent soils in sub-urbanized semiarid grasslands dominated by native or exotic grass species. Our study revealed that both, soil textural characteristics and plant species composition are important controls of percolation and infiltration in semiarid grassland ecosystems. The test of homogeneity of slopes showed significantly higher infiltration rates in patches compared to vegetation-free interspaces in sites with Eragrostis superba (F > 199, P < 0.001), Digitaria californica (F > 632, P < 0.001), Eragrostis lehmanniana (F > 533, P < 0.001) and Bouteloua gracilis (F > 102, P < 0.001). High similarity in potential percolation rates in vegetation patches of E. superba and D. californica suggests an overall beneficial effect of both native and exotic species on ecohydrological ecosystem services. However, the exotic species E. lehmanniana showed higher shallow infiltration than B. gracilis. Our study demonstrates that rather than promoting preferentially native grass species, species-specific functional traits should be considered for restoring soil-water related regulatory ecosystem services in degraded grasslands.