ABSTRACT
Plant establishment and productivity in arid lands are primarily limited by water availability, nutrients and soil instability, which are in turn regulated by belowground interactions of roots, microorganisms and soils. In arid ecosystems, succession appears to initiate in patches as "islands of fertility", rather than in large, homogeneous units. Understanding the factors that regulate development of these islands may be critical to revegetating disturbed arid lands. Major changes occur in soil and microbial spatial patterning following disturbances. Nutrients become low and diffuse, soil vertical structure is destroyed, and soil aggregation is diminished. Root systems change architectures due both to genetic capacity and the altered soil structure. Following plant establishment, microorganisms and the processes they regulate reestablish around the roots and where litter accumulates. The reformation of a desirable ecosystem depends not only upon the establishment of plants, but on the concentrating of initially diffuse nutrients to plant foci both horizontally (by surface roots, mycorrhizae and wind deposition) and vertically (by deep rooted species and their microbial associations). Thus, I hypothesize that efficient land reconstruction may depend not only on planting highly productive species, or genetically-engineering "better" organisms, but also on replacing the structural characteristics of mature ecosystems.
