New York City Urban Field Station

Urban Tree Health

[photo:] Research team records sapling growth and seedling recruitment in a newly planted urban forest.  Phtoto by Rich Hallett, US Forest Service, Northern Research StationEvery tree in an urban forest is expected to provide a multitude of benefits to the city. Because of this, municipalities invest tremendous resources in their urban trees, making the trees’ growth and success even more important. The ability to quantify how healthy a tree is will provide added value to urban forest managers, allowing them to make proactive management decisions and plan for stress mitigation instead of focusing on reactive tree replacement. In addition, fine scale health metrics that can be used to assess large areas of a city may also help with early detection of new invasive pests such as Asian longhorned beetle (ALB) and emerald ash borer (EAB).

NYC Urban Field Station researchers are developing, deploying and validating a rigorous methodology designed to quantify urban tree health at a relatively fine scale, and throughout all phases of tree decline. Tree health metrics include: chlorophyll fluorescence, canopy transparency, fine twig dieback, leaf discoloration and live crown ratio. Working with the NYC Department of Parks & Recreation and other partners, researchers are testing the efficacy and feasibility of this approach for a broad-scale assessment of urban forest health, invasive detection, and long-term monitoring efforts.

Hurricane Sandy Flooding Impacts

Flooding from Hurricane Sandy has inspired a close look at the response of NYC’s trees to the disturbance. One of the costliest hurricanes in U.S. history, Sandy came ashore in New York City on October 29, 2012. Almost 20,000 public trees in NYC were destroyed as a result of the storm. The full impact of the storm on the city’s remaining trees, however, has yet to be determined. According to NYC Parks Department estimates, Sandy flooded 47,900 street trees in the city throughout the inundation areas. During June 2013 (eight months after the hurricane), NYC Parks employees surveyed the inundation zones and found almost 10,000 trees that had not fully leafed out and estimated whether the tree had 0, 25, 50, or 75% of its leaves. The four most impacted tree types were London Planetree, Maple species, Cherry species, and Oak species. Questions remain regarding whether these trees will continue to decline or recover over time. In a more focused study, NYC Urban Field Station staff assessed the health of red maple street trees in Queens that were flooded by the storm surge, comparing them to red maples that were not impacted by salt water. Preliminary analysis shows that flooded trees are significantly more stressed than those that were not flooded. These data will provide the basis for future work as we strive to understand the longer-term impacts of hurricanes and other disturbances on urban forests in coastal areas.