Initiating Autogenic Restoration on Shallow Semiarid Sites

Our objectives were to evaluate the use of microcatchments in the establishment of Leucaena retusa (little‐leaf leadtree) and Atriplex canescens (four‐wing saltbush) and their role in the initiation of autogenic landscape restoration processes on a shallow semiarid site. Three six‐month‐old seedlings of either Leucaena retusa or Atriplex canescens were planted in 1.5‐m² microcatchments. An equal number of seedlings was planted in control plots (unmodified soil surface). The water collection effects on shrub survival, standing biomass, and the natural immigration of herbaceous vegetation were determined over 42 months. Planting in microcatchment basins doubled Leucaena seedling survival and resulted in a five‐fold increase in standing biomass, compared to the control, during the first growing season. There was a significant increase in soil organic matter in the microcatchment basins within 32 months. At the same time, microcatchments planted with Atriplex canescens seedlings had a ten‐fold increase in seedling standing biomass compared to the control. Forty‐two months after transplanting, the herbaceous standing crop was significantly greater near Atriplex canescens or in microcatchment basins than in plots with unmodified surface soil. Basins containing Atriplex produced significantly more herbaceous vegetation than basins containing Leucaena, and empty basins produced the least herbaceous vegetation of three basin treatments. These data suggest that landscape‐scale procedures that concentrate scarce resources (water, organic matter, nutrients, and propagules), establish keystone species, and ameliorate microenvironmental conditions can initiate autogenic restoration of degraded semiarid ecosystems.