By Hadley Stein, September 6, 2016
Each year, millions of urban trees are destroyed by storms and other natural disasters. With urban populations on the rise and the increasing role of climate change in natural disasters, it is critical that communities prepare for extreme weather as it relates to trees and green infrastructure. Preparing involves not only implementing effective mitigation strategies, but also developing response and recovery plans.
Take 2012 Hurricane Sandy, the deadliest and most destructive hurricane of the 2012 Atlantic hurricane season, and the second costliest hurricane in U.S. history. The hurricane affected 24 states and the devastation was widespread. Trees were especially vulnerable in regions not accustomed to storms of this magnitude. Nearly 20,000 public trees in New York City were destroyed in the wake of the hurricane, which amounts to more trees lost in the city than in any other storm for which tree damage was documented. The NYC Parks and Recreation Department estimated tens of thousands more trees were flooded, left partially uprooted or otherwise compromised in ways not visible to the naked eye. For years following Sandy work was still being done to clean up downed trees and replanting efforts continue into present day.
Communities with more advanced urban forestry programs typically have complete tree inventories, tree canopy goals and management plans to help sustain the tree population. These core components provide a solid foundation for developing hazard mitigation and response plans in the event of a storm or other disaster. There are many different strategies for reducing both the damage and costs associated with natural disasters without taking down trees. In fact, during most storms with winds below 40 mph, trees in good condition are a net benefit and help moderate climate extremes. We’ve outlined some key considerations and proposed actions below.
Trees down on West 90th St. in New York during the brunt of Hurricane Sandy. (Photo by Robert Caplin)
We recommend implementing practices that reduce the potential for damage including annual inspections, structural pruning, selective removal and planting site-appropriate trees based on species, condition and location. These types of proactive management activities help communities more easily identify high-risk trees as part of day-to-day operations.
Tree inventories and canopy analyses are an important tool for communities to collect and manage data on the urban forest. Not only do inventories provide a baseline of tree and planting site-specific data, they can help communities identify mitigation strategies to improve resilience. The U.S. Forest Service (USFS) developed the iTree software to provide communities with a free tool for analysis and benefits assessment of the urban forest, which along with OpenTreeMap represent two of the inventory mapping solutions available today.
Additionally, many communities have development hazard mitigation guides. For example, New York City’s Emergency Management Department compiled a guide that outlines key features of the city’s risk vulnerability, assesses a range of hazards (i.e. flooding, earthquakes, water shortages, strong windstorms and the pandemic flu) and presents strategies for managing risks associated with those hazards.
While no disaster is the same, communities with post-disaster recovery plans and established contracts for required work can begin recovery efforts more quickly. Pre-planning ensures there is a process in place for debris estimation and management, hiring of contractors and restoration. By identifying and prioritizing the areas that present the highest risk – power lines, public rights-of-way, high traffic areas – cities can focus limited resources on work that will have the greatest impact.
Utility companies can also play a critical role by creating a Vegetation Risk Management Plan (VRMP), to ensure public safety, maintain optimum urban tree canopy, promote tree health and decrease emergency management costs.
Over 300 trees were lost after Hurricane Sandy in Central Park in New York City.
(Source: A Walk in the Park)
After Hurricane Sandy, New York City’s first priority was to clear trees from highways and streets to provide access to fire trucks and ambulances. Only after roads were clear did tree crews turn their attention to city trees that collapsed on houses and other buildings. Though some of the fallen wood was in good enough condition to be repurposed into building materials, much of it was shredded into mulch in an effort to expedite cleanup and avoid spreading invasive insects.
Less than a month following the Hurricane and ensuing northeaster, more than $12 million had already been spent on tree clean-up. Tree debris can be one of the most expensive aspects of storm response and if not addressed immediately can leave a community with even more expensive restoration costs. It’s important to note that costs can be exacerbated by unnecessary tree removal following a storm and by risks associated with damaged but not fallen trees.
A woman photographs a downed tree damaging several cars after Hurricane Sandy made its way through Brooklyn, New York. (Source: EPA)
The American Planning Association (APA) recommends developing a process for assessing debris with emergency management personnel to ensure the debris and wood residue is managed for its highest and best use. The APA also advises communities to require tree risk assessors during emergency response and recovery operation to have additional qualifications beyond those qualifications required for general pruning and removal contractors.
Crews from all over the country came to New York City to help remove fallen trees. Pictured here a crew from Gainesville, Florida clears a property in Queens. (Source: Marcus Yam, The New York Times)
Hurricane Sandy marks the first time forest systems in the northeast experienced saltwater flooding. The long-term effects of both flood and structural damage are not always immediately visible. In New York City, for example, the parks department inspected inspected nearly 48,000 trees in flood zones in the spring following the storm. More than 6,500 trees showed signs of stress and abnormal leafing and another 2,000 were presumed dead; these trees were completely healthy the previous year.
Disaster recovery does not happen overnight and longitudinal studies are important to determining a storm’s long-term impact on the tree population. As recently as this year, NYC Parks is exploring whether stress on trees from saltwater damage left them more vulnerable to other pests and disease, including a fungal growth recently found on many London Plane trees. Across the Hudson River in New Jersey, state officials are partnering with municipalities to distribute free seedlings to replace trees destroyed in the hurricane.
Trees are a form of green infrastructure, and like all other city infrastructure they provide value to residents in this case in the form of environmental, economic and social benefits. However, unlike other infrastructure, trees grow over the course of many years yet can be destroyed in a single event. Furthermore, healthy trees increase in value with age. That is to say, as trees grow the ecosystem benefits they provide including improved air quality, reduced stormwater runoff and carbon dioxide removal increase. The increase in value of a tree overtime makes regeneration a critical issue following a natural disaster.
In order for the urban forest to be adequately addressed in disaster management and recovery, it needs to be a local priority. Education and community engagement at the local level further support the mitigation of urban forestry related hazards. Communities must also advocate on for increased funding and attention for urban forestry-related issues at the state level, as states ultimately are the primary decision maker in matters related to hazard mitigation.
Has your community experienced a significant storm or other natural disaster? What were some of your biggest challenges? We would love to hear from you and give people the opportunity to learn from your story.