Looking To The Future To Plant Trees With Staying Power

September 12, 2022  | Alex Hancock

As urban forestry experts, we must do our best to ensure the species we recommend for planting today can live long, healthy lives in the harsh conditions of the urban environment, even as the climate changes. Tree species are recommended for a variety of reasons, such as aesthetics, availability, size, and maintenance needs. Selecting trees with an overarching vision that encompasses citywide species diversity and climate resilience strengthens the urban forest, making it less susceptible to pests and disease, sea level rise, or extreme weather such as heat, drought, and flash flood events.

It requires careful planning to select trees that will thrive in the expected climate conditions 20, 30 and 60 years in the future. We were confronted with this task in a project in early 2022 to review and expand the planting palette for the City of Fremont, California. To crack the case we developed a new method called the Sister Climate City Analysis to model the future climate of Fremont with a real world example. This is a crucial challenge for any city so we decided to break down the information needed to identify tree species that have the best chance of benefiting cities for generations to come.

How Are Urban Trees Impacted by Climate Change?

Temperature, precipitation, and seasonal fluctuations are some of the factors that determine which species will suffer, survive, or thrive in a region. Trees around the world are experiencing climate change impacts in a variety of ways, including winter injuries caused by extreme temperature fluctuations, extreme heat, drought, wildfires, sea level rise, salt water intrusion, and increased frequency and severity of storms. These stressors all increase the vulnerability of trees to pests and disease.

Since climate change threatens trees from a multitude of angles, urban forests of the future need to be as intentionally resilient as possible. In turn, healthy urban forest will help our communities better withstand climate change impacts, including flood risk reduction, urban stormwater drainage relief, mitigation of urban heat island effects, and health benefits from cleaner air.

Oh, and let’s not gloss over that urban forests are a mitigating factor for climate change itself. The longer a tree lives the bigger its carbon appetite!

A Sister Climate City Analysis For The City of Fremont

After completing a public tree inventory and an urban tree canopy assessment, the City of Fremont was ready to develop an urban forest management plan. Their 2022 Urban Forest Management Plan (UFMP) extends beyond maintenance and operational guidance to include a variety of long-term goals to achieve optimal levels of sustainability and equity through urban forest management. Cities in the San Francisco Bay Area face dramatically intensifying weather and climate impacts including sea level rise, drought, long-term water shortages, flooding, and extreme heat. As such, Fremont’s UFMP aligns with the City’s 2022 Climate Action Plan 2.0 and other local and regional plans.

Fremont’s Master Tree List Update

Fremont’s UFMP called for an update to the City’s master tree list so species recommended and required for planting align with the overarching goals of the plan. Utilizing progressive methods to update master tree lists can help to encourage resilient urban forests more likely to adapt in the face of climate change. In order to build a climate-resilient master tree list, 4 main objectives were identified:

1. Apply climate adaptation strategies to urban forest management planning.
2. Use state-specific tools and data to identify cities with climate conditions similar to those projected for Fremont (aka sister climate cities).
3. Build a master tree list using sister climate cities, local knowledge, and best management practices.
4. Create an interactive public-facing tree selection tool.

Sister Climate Cities Discovered!

We used the Cal-Adapt online tool to get current and projected forecasts of Fremont’s temperature, precipitation, and wildfire conditions 60-70 years in the future. These projected forecasts were then matched to the current conditions of other California cities. This method identified the cities of Fresno, Los Angeles, Santa Monica, and San Diego as fair models of Fremont’s climate future.

We then gathered and reviewed the master tree lists, tree inventory data, urban forestry practices, and local ordinances and codes of these “sister climate cities”. Meetings with city foresters helped us determine which of the sister cities’ recommended species were performing well and would make good candidates for Fremont’s tree list.

Fremont’s master tree list was transformed into an interactive tree selection tool— a user-friendly, online workbook that helps community members decide what kind of trees to plant in their own yards. The tool presents a list of questions that filter the master tree list to display a list of viable options, with special attention given to climate-resilient species. The “Right Tree, Right Place” criteria included help to educate the public on tree maintenance while suggesting species that meet their expectations.

Fremont, California’s Master Tree List

These tools provide an example framework for urban forest management planning that ensures future generations can benefit from the trees we plant today. Please get in touch with our Urban Forestry Consultants if you would like to learn more about the Sister Climate City Analysis or want to have a specific conversation about planting for your city’s future.