A “possibility-based” approach to ecological restoration of urban forests: incorporating biophysical and social constraints

Background/Question/Methods

Highly altered conditions may preclude attainment of reference conditions that are often used to judge the success of ecological restoration. Urban areas cover an increasingly large portion of the Earth’s surface and are now home to more than half of humanity. Ecological restoration can provide critical environmental benefits, and restoration of urban forests is becoming a common method for addressing a suite of urban environmental problems. To evaluate the urban applicability of models for restoration used in less degraded sites, we examined long-term effects of ecological restoration in urban forest remnants in five New York City parks 15-20 years after invasive woody species (Celastrus orbiculatus, Ampelopsis brevipedunculata, and Rosa multiflora) were removed and a diversity of native trees were planted. We compared plant community composition and structure in forests that were restored with forests that were similarly invaded but not restored over the same time period.

Results/Conclusions

Restored forests differed significantly in their composition and structure from forests that were not restored. Structural complexity and native tree regeneration were greater in restored sites. Degree of management effort was important to these differences, and biophysical factors, especially soil conditions, were key to community composition. Successional trajectories of these restored forests were redirected, but their location in urban environment guarantees a future of human-caused disturbance. Our findings suggest that in the urban environment, long-term management and legacies of past disturbance are both key to predicting restoration outcomes. Site history (particularly soil legacies) and the resources available for long-term management must be considered when setting pragmatic goals for urban restoration.