Change happens. Be ready for it.
Fire. Flooding and drought. Climate change. Pests and disease. Invasive species. The threats to your urban forest are many and diverse. But there are five key principles to help you manage risk.
- Know your urban forest resource. A forest inventory will determine the extent and condition of your urban forest. This becomes your baseline for planning and management.
- Understand your human capital. Organize a network of experts, practitioners and volunteer organizations who can help determine the changes occurring in your urban forest, how best to respond, and mobilize people to implement your plans.
- Manage your money. Scant budgets can impair day-to-day management of your urban forest. More importantly, it derails your ability to respond to risk. Budget realistically, and identify and [hopefully] secure funding from diverse sources to deal with current and emerging threats.
- Establish a diverse and healthy forest. The nature and extent of risk changes depending on species selection, diversity, age and distribution. The wrong mix [or no mix at all] maximizes the harm done by any single agent. Spending money on improving forest health now can help protect against future risks and promote resilience.
- Think locally. Broad principles are a starting point, but be sure to consider local risks [e.g. population change] and seek out the resources to address them.
A short list of risks to your urban forest.
Climate change works both ways. Trees can help mitigate its impact. But climate change creates risks for your urban forest; and that risk varies community by community, even site by site.
- To identify species at risk, check out USDA’s Plant Hardiness Zone Map, and the Climate Change Response Framework.
- The FORECAST project website can help identify species whose ranges may be shifting dramatically, and identify potential replacements.
- For guidance on long-term planning and best practices consult Urban Forests: A Climate Adaptation Guide and the Template for Assessing Climate Change Impacts and Management Options.
- EPA’s EnviroAtlas offers special guidance on the role healthy ecosystems can play in mitigating risk from natural disasters.
Sea Level Rise
Of the 25 most populous counties in the US, fully 23 are considered coastal.
NOAA predicts with “…very high confidence that global mean sea level will rise at least 0.2 meters and no more than 2.0 meters by 2100.”
And while it’s impossible to predict precise impacts, some facts are certain. Even the low estimate has the potential to flood significant portions of these communities’ urban forest.
- To assess your community’s vulnerability to rising waters, check out NOAA’s Sea Level Rise and Coast Flooding Viewer and The Nature Conservancy’s Coastal Resilience Project Best Practices.
- Low-lying coastal zones that already deal with the threat of sea level rise have begun to implement forest-based practices to mitigate flooding. Check out the Virginia Beach Urban Forest Management Plan to explore these strategies.
There are a number of tools to assess long-term and short-term fire risk on a variety of scales. Programs like FireWise Communities provide tools and examples of preventative planning for wildfire on scales from single homeowner to the municipality. In managing urban forests for wildfire risk, focus efforts on fire prevention because response following a wildfire will be focused on human and monetary impacts with the rehabilitation of the urban forest lagging far behind.
When planning for wildfire and urban forestry, be sure to look outside the city itself. Many resources on which your residents depend – in particular, water – can be degraded by fires that never touch the community itself.
Pests, Disease and Invasive Plants
Most urban forests are already stressed. And the dangers posed by pests, disease and invasive species continue to increase, with cities paying the bills. As always, planning for perils costs far less than waiting until the dust settles, or the trees fall. Don’t be surprised. Be prepared.
- The U.S. Forest Service hosts a portal for forest insect and disease reporting along with the ForWarn change detection system.
- Field methods designed for pest detection and tree health monitoring are also under development by the Healthy Trees, Healthy Cities initiative of The Nature Conservancy.
- At more local scales, it can be useful to engage community groups and engaged citizens to help identify new threats and monitor existing populations.
- Stock your toolkit from our resource library. Many communities have already developed ways to identify threats, prepare responses, and move into action at the right moment.
Natural Life Cycle Changes in your Forest
Age matters, especially in the urban forest. Like many of our elders in society, mature trees contribute a disproportionate share of the benefits of urban forestry. But maintaining old trees can be time-consuming and expensive – especially as age makes them more susceptible to pests and disease.
- Consider potential liability risks and take care to compare costs and benefits of maintaining old trees against planting new trees.
- Over the long haul, strive for a tapestry of trees of different ages and species. Uneven age distribution is important for sustainability because it spreads out the timing of all management activities – planting, maintenance, removal, and replacement – so they won’t all come due at once.
- Uneven-aged forest stands also help pace the delivery of ecosystem services, or tree benefits, so there will be a steady supply at all times. A newly-planted tree needs decades of growth before it can provide the same level of benefits as its elders.
Even more important, trees of similar ages are – surprise! – likely to die at about the same time. Organize your “big number” tree planting campaign wisely. [It can be done. ] Or your community may one day face a huge surge in expenses and a simultaneous deficit in ecosystem services.