Restoration of Spatial Heterogeneity and Ecohydrological Processes in Deserts: Development of Artificial Islands of Hydrologically-Enhanced Productivity

Temporal and spatial heterogeneity in biological productivity, from the scale of plants to landscapes, is characteristic of arid and semi-arid ecosystems. The processes which control the formation of resource islands and determine the size, shape, longevity and distribution of resource islands across the landscape are influenced by climate, topography, soils and biota. The installation of water retention dikes (7.5-30 cm tall, 50- 150 m long) at the Jornada Experimental Range (3-6 dikes/site at 4 sites) in the Chihuahuan Desert from 1975- 1981 enabled us to test whether increased surface water retention was sufficient to initiate the formation of islands of enhanced resource availability and biological productivity. Compared to nearby reference areas, soil moisture was 20-45% higher behind dikes. Clay and silt soil fractions tended to be greater behind the dikes, though the detailed pattern depended upon the local site conditions. Soil aggregate stability was higher and saturated infiltration rates were up to 80% lower behind the dikes. Vegetation cover behind the dikes was more than twice that in nearby reference areas. Plant species richness was up to 4 times greater behind the dikes. Mesquite (Prosopis spp.) and unpalatable shrubs were less dominant behind the dikes, while cover of small shrubs, grasses and forbs was greater than in reference areas. Rehabilitation of degraded arid ecosystems often entails the restoration of spatial heterogeneity and the creation of islands of concentrated resources. Artificial water retention structures can mimic natural processes that reduce surface water flow rates, allowing more time for infiltration, and can initiate formation of islands of increased resource availability and increased biological productivity. The effects of these water retention dikes persisted for up to 30 years without maintenance.