Long-term outcomes of urban forest restoration: Assessing trajectories in plant community ecology to improve environmental health

Background/Question/Methods

Natural areas in urban environments are important reservoirs of biodiversity that provide valuable ecological functions. However, urban environments present a unique set of stressors to natural communities, resulting in altered and degraded ecological conditions. Ecological restoration of urban forests is becoming a common environmental remedy. 

This study investigates the long-term fate of efforts to restore ecological integrity to forests in New York City parks. In 1992 the New York City Department of Parks and Recreation’s Natural Resources Group initiated restoration of woodlands heavily invaded by woody vines such as porcelainberry (Ampelopsis brevipedunculata) and oriental bittersweet (Celastrus orbiculatus). Restoration practices were typical of those being used to restore woodlands across the United States: removal of invasive, non-native species by herbicide and mechanical means, followed by planting of desired native tree species. Pre-treatment and initial site conditions following restoration were recorded, and survivorship and growth of planted tree species were monitored during the two years following initial restoration.

In 2009, after 17 years, research plots at thirty sites were revisited to determine whether the goal of a more diverse forest structure had been achieved. In 2010, an additional thirty plots that were reported to be similarly degraded in 1992, but which were not restored, were sampled. Data collection protocols for forest health monitoring include ecological data on successional trajectories (as indicated by community composition), effects of restoration practices, the role of invasive species in restoration outcomes, and the relationship of these to site history and adjacent conditions. 

Results/Conclusions

Planted woody species persisted in restored areas. Target invasive species were dominant in all invaded/untreated plots. Restored plots were rarely (but not never) dominated by these species. There were significantly fewer trees in invaded/untreated plots. The herbaceous layer was less diverse, and saplings of native trees were fewer in non-restored plots. Many goals of this management treatment were reached. Together, these data may improve the effectiveness of urban restoration work.