David Lefcourt, Cambridge City Arborist, gave a presentation on the Urban Forestry Department’s program to tend and monitor the status of the city’s urban forest, to share this information with residents, and to engage residents in helping to care for our public trees.
Status of the Urban Forest
Cambridge has 19,000 public trees and over 130 species of trees. This number reflects climate change as the area becomes warm enough for trees native to more southern planting zones to establish themselves. This organic infrastructure, which is considerably larger than some of its inorganic siblings—parking meters (3070) and street lights (6600)—increases in value over time.
To keep this urban forest healthy, the Urban Forestry program handles both reactive services—pruning, emergencies, stump removal—and programmatic services, planting between 300 to 500 trees each year. A map of tree inventory is available here:
https://gis.cambridgema.gov/dpw/trees/trees_walk.html
The Committee on Public Planting meets monthly on the second Wednesday. Lefcourt noted that a representative from Porter Square would be welcome. For more information about joining this committee, contact dlefcourt@cambridgema.gov.
Urban Forestry Master Plan
The alarming rate at which the city has been losing its tree canopy, including both public and private trees, has been widely reported. The Urban Forest Master Plan (UFMP) Task Force began work in June to develop an effective plan to sustain and grow this canopy. Its first report, released in October, is available here:
Among its many informative charts and maps is a map of the city’s “heat islands,” which are the areas that have few to no trees. Porter Square and the stretch of Mass Avenue north to Arlington is one of them. To mitigate this heat, a small, but growing, group of Cambridge residents are working to restore the tree canopy that is seen in many historical photographs along Mass Ave.
More information about the task force's work is available at www.cambridgema.gov/UFMP.
Programs of the Urban Forestry program
- Pruning
City contracts to prune public trees are on a 6-year cycle. The regular pruning allows Cambridge to clean up faster after storms that down trees or limbs.
EverSource is on a 4-year pruning cycle. At the beginning of this cycle, the City walks the circuit with EverSource to establish what is needed for each tree, ensuring that pruning is limited to a 3-foot window around wires. Without supervision, EverSource prunes to achieve a 15-ft clearance on top and 10 feet on each side of wires that run through trees.
- Planting
To ensure that the trees planted each year survive, the City has implemented a warranty in contracts to require contractors who plant the trees to keep them alive for the first 3 years. Because payments are linked to the watering schedule, the frequency of watering has improved significantly.
The tree stickers in sidewalks and other areas that provide public notice of plantings to come is a relatively new program.
The Participatory Budget allocated money to plant 50 additional trees in North Cambridge (and 50 in East Cambridge). About 10 of these trees were planted in North Cambridge this fall; the others will be planted in the spring.
The city never plants more than 10% of a genus as hedge against impact of pests and diseases that attack specific trees.
Lefcourt noted that tree roots usually grow in the top 2-3 feet of soil. To protect and nourish these roots, the city has been experimenting with using a structural soil that can both support sidewalks and nourish trees. The city is beginning to replace grates in tree wells with Flexipave, which looks a bit like asphalt, but handles water better.
To improve planting practices on private property, Lefcourt recommends using certified contractor that is insured.
- Construction coordination
Protecting well-established trees around construction areas is a common concern. Protecting he oak trees along Beech Street near the St. James Church is the local one. The arborist is working with Acorn Developers and Nauset Construction to insure these oaks aren’t damaged or killed in the construction process.
- Pest control
The mass clearing around Worcester of trees attacked by the Asian long-horned beetle 10 years ago prompted the city to establish a program to monitor a new pest, the emerald ash borer. This critter attacks ash trees only. This program is the first of its kind in the state.
- Water-by-Bike program
All trees need to be tended and watered regularly throughout the summer and early fall. For the summer, the Water-by-Bike program hires interns to supplement contractors’ watering efforts and to encourage neighbors to become stewards of the trees. These “tree ambassadors” tend as many as 60 trees each day.
- Adopt a tree program
The city encourages to residents to sponsor newly planted and more established trees. Cambridge residents who adopt public trees agree to water them at least once a week between May and October. Each watering requires 15-20 gallons.
The Adopt-A-Tree program will be very useful in the efforts to restore the tree canopy along Mass Ave. Although contractors are obligated to water newly planted trees, supplemental watering, especially during heat waves and droughts, greatly enhances the odds that the trees will survive.
One challenge of caring for trees along Mass Ave is finding water when there is no spigot available nearby. One suggestion was to provide incentives for business owners to water trees in front of their windows. The city welcomes all suggestions for how to meet this challenge.
To adopt a tree, check the city’s interactive map to find a tree near you: https://www.cambridgema.gov/iwantto/adoptatree
Q&A
Responses to questions raised yielded this information:
- Winter! Salt on sidewalks is bad for trees; so is sand because it blocks pipes, leading to more floods in summer. The 2015 winter killed the trees planted in 2016 because the salt didn’t leach out.
- Resilience and invasive trees. The city does not have a policy to remove invasive species. Few species do well in our urban forest. Which trees do best? Honey locust, shingle oak, tulip tree, sweet gum–and, to the chagrin of many, Norway maples. Although these maples are an invasive species, their ability to survive in a climate that is changing may become a reason to love them.