Assessing the tree health impacts of salt water flooding in coastal cities: A case study in New York City

Hurricane Sandy was the second costliest hurricane in United States (U.S.) history. The category 2 storm hit New York City (NYC) on the evening of October 29, 2012, causing major flooding, wind damage, and loss of life. The New York City Department of Parks & Recreation (NYC Parks) documented over 20,000 fallen street trees due to the physical impact of wind and debris. However, salt water flooding may have caused additional stress to approximately 48,000 street trees located in the storm's inundation zone. Early in the first growing season following Hurricane Sandy (June 2013), NYC Parks staff examined these street trees and found that 6,864 of the flooded trees had a significant proportion of their crown fail to leaf out. Thirty percent of those trees did not leaf out at all. The most commonly affected trees were London plane (Platanus x acerifolia) and maple species (Acer spp.). Here we show that red maple (Acer rubrum) is negatively impacted by salt water flooding but can recover over time. London plane trees, on the other hand, experience high mortality and show no signs of recovery 3 years post Sandy. We demonstrate that by 2080 a similar storm could impact almost 100,000 of NYC's street trees. These findings have global implications for coastal urban forests as we face sea level rise and an increasing frequency and magnitude of coastal storms.