Overland flow directs soil moisture and ecosystem processes at patch scale in Mediterranean restored hillslopes

Semiarid and arid environments are frequently structured in vegetation patches that heterogeneously distribute water resources (water runoff and soil moisture). This redistribution is interrelated with episodes of rainfall triggering pulses of plant growth according to the Trigger–Transfer–Reserve–Pulse (TTRP) model. Spatial heterogeneity in the hydrological behaviour of surface patches has been described in Mediterranean mining restored hillslopes. Nevertheless studies describing the interactions of this hydrological heterogeneity with ecological processes on restored environments are lacking. This study investigates the relationships between overland flow running at hillslope scale and ecosystem processes at patch scale in restored hillslopes. We selected three approximately 20 year old restored hillslopes along a gradient of overland flow (hillslope runoff coefficients are 15.9%, 2.2% and 0.3% for the three experimental hillslopes). We studied environmental conditions describing the ecohydrological interactions under the TTRP approach for arid and semiarid environments. Our results indicate that in restored hillslopes: 1) soil moisture content was associated to the type of vegetation patches; 2) higher soil water content enhanced vegetation diversity and soil properties, improving vegetation performance and colonization opportunities; and 3) there was an inverse relationship between the volume of overland flow and soil moisture at the hillslope scale, influencing, in turn, ecohydrological processes at the patch scale. Overall our results highlight the importance of overland flow modifying soil moisture distribution at patch scale and hence, influencing vegetation dynamics and ecological succession in these novel ecosystems.