Using landscape hierarchies to guide restoration of disturbed ecosystems

Reestablishing native plant communities is an important focus of ecosystem restoration. In complex landscapes containing a diversity of ecosystem type s, restoration requires a set of reference vegetation conditions for the ec osystems of concern, and a predictive model to relate plant community compo sition to physical variables. Restoration also requires an approach for pri oritizing efforts, to facilitate allocation of limited institutional resour ces. Hierarchy theory provides a conceptual approach for predicting plant c ommunities of disturbed ecosystems and, ultimately, for prioritizing restor ation efforts. We demonstrate this approach using a landscape in southwestern Georgia, USA . Specifically, we used an existing hierarchical ecosystem classification, based on geomorphology, soil, and vegetation, to identify reference plant c ommunities for each type of ecosystem in the landscape. We demonstrate that ecosystem identity is highly predictable using only geomorphic and soil va riables, because these upper hierarchical levels control the development of vegetation, a lower hierarchical level. We mapped the potential distributi on of reference ecosystems in the landscape and used GIS (geographic inform ation systems) to determine relative abundance of each ecosystem, as a meas ure of its historical rarity. We joined the reference ecosystem map with a current cover map to determine current abundance of each reference ecosyste m, and percentage conversion to different disturbance classes. We show that over half of the landscape supports something other than reference plant c ommunities, but degree of rarity varies widely among ecosystems. Finally, w e present an index that integrates information on historical and current ra rity of ecosystems, and disturbance levels of individual polygons, to prior itize restoration efforts. The premise of the index is that highest priorit y be given to restoring (1) currently rare ecosystems that were also histor ically rare and (2) the least disturbed examples of these ecosystems, as th ese will require the least effort to restore. We found that 80% of high-pri ority sites occur within just three (of 21) ecosystems, Moreover, the high- priority ecosystems all occur within stream valleys. Our approach provides managers with a straightforward methodology for determining potential distr ibution of reference ecosystems and for allocating efforts and resources fo r restoration in complex landscapes. Development of a priority index for a specific landscape requires an understanding of the hierarchical relationsh ips among geomorphology, soil characteristics, and plant communities, in ad dition to well-defined restoration objectives.