Climate change is threatening many communities of Greater Boston and will only worsen over the course of the rest of the century if we don’t quickly accelerate our mitigation efforts. According to Climate Ready Boston, average temperatures, extreme precipitation events, and sea level rise will continue to increase over time. Climate change models make it clear that the ecosystems and weather patterns of Boston will change, and city and town officials need to adapt to those changes.
Several factors will directly influence the work of those in charge of trees and urban forests in the Greater Boston area, according to Paul Kirshen, professor and academic director of the Sustainable Solutions Lab at the University of Massachusetts Boston. Rainfall will increase: 10-year storms, or storms with rain levels that occur once every 10 years, will deposit 6.5 inches of water instead of today’s five. Increased flooding and storm surges will push up groundwater. Increased warmth will mean increased evaporation and increased amounts of rainfall in the winter, but more heat and a higher chance of drought in the summer. Winter may start later and end sooner, lengthening the growing season, but blistering hot days in the summer could damage plants used to cool conditions.
These changes and more were the basis of a workshop held by MAPC in late January, in partnership with the Northern Institute of Applied Climate Science, USDA Forest Service, USDA Northeast Climate Hub, USDA Northern Forests Climate Hub, The Trust for Public Land, City of Cambridge, MIT, and Massachusetts Department of Conservation and Recreation. “Preparing Urban Forests in the Boston Region for Climate Change” was aimed at urban forestry professionals and planners and focused on ways to plan around the changing climate.
Speakers presented on ways that climate change will directly influence trees, case studies of local initiatives, and tips on what to consider going forward.
Leslie Brandt, a climate change specialist with the Northern Institute of Applied Climate Science and the USDA Forest Service, gave examples of species of trees whose habitats will change within the next 100 years. Northern conifer species and other northern species such as balsam fir, quaking aspen, paper birch, red spruce, and red pine – trees that are at the southern extent of their range in Massachusetts – will most likely lose habitat here. Trees that are in the middle of their ranges here, such as sugar maple, Atlantic white cedar, beech, black cherry, holly, pitch pine, and swamp chestnut oak, should still be able to comfortably grow, while species from central hardwood forest ecosystems like many oak and hickory species could gain suitable habitat in Massachusetts.
“We also expect that by the end of the century we might have conditions in which species that aren’t currently here can survive,” Brandt said.
These include sourwood, pawpaw, eastern redbud, sweetgum, and persimmon.
It should be noted that because trees’ habitats will change does not mean that they will rapidly migrate northward naturally. Instead, it means that gardeners, foresters, and tree wardens will be able to plant these species and they will have a viable habitat to survive. To figure out what might survive in the Massachusetts climate in the coming years, one option is to look at what people are planting in New York or Philadelphia – many of these trees can now survive in Massachusetts or will be able to soon.
With storms expected to become more frequent and harsh, summers expected to be hotter and possibly drier, and winters expected to be wetter with more storms, it’s also important to plant trees with high adaptive capacities – species that aren’t susceptible to pests, floods, droughts, or storms and can survive a wide range of temperatures. Species such as eastern red cedar, blackgum, mockernut hickory, and kousa dogwood have high adaptive capacities, while red pine, black ash, eastern white pine, and hemlock all have low adaptive capacities.
Planting trees in general can help mitigate some climate change risks – for example, one tree planted near a home can cool the area, lowering electricity costs from air conditioning. Areas in cities without many trees or plants often experience the urban heat island effect, in which an area doesn’t cool down overnight and gets hotter during the summer. These areas are often parts of the city with low-income populations. Many programs – locally and nationally – are working to increase tree planting in these communities to help low-income residents lower their electricity bills and to alleviate their risks of experiencing dangerous health impacts from extreme heat.
One tree can help 10 to 20 households living in multifamily housing on an acre, according to Bob O’Connor, the director of the Division of Conservation Service at the Massachusetts Executive Office of Energy and Environmental Affairs. The state is continuing a tree planting program this year, planning to add 2,400 trees in select neighborhoods in 13 cities this year. Eighty percent of these trees will be planted on private property at no cost to residents, while 20 percent will be planted on streets.
David Bloniarz, a research scientist with the USDA Forest Service Northern Research Station, described a similar project in Springfield, Massachusetts. After a tornado in 2011 destroyed street trees and ecosystems, Green Streets Springfield planted 1,500 trees on private property in three weeks, helping homeowners save energy and greening the town.
To support local planting and forestry efforts, the USDA Forest Service has a free tool called “Forest adaptation resources: Climate change tools and approaches for managers.” This book – which can be accessed in PDF format online – includes a menu of adaptation strategies and a workbook process to incorporate climate change considerations into forest management planning.
Other speakers at “Preparing Urban Forests in the Boston Region for Climate Change” included Paul Kirshen Patrick Roche, Julie Conroy, Shaun O’Rourke, Katie Theoharides, Jarlath O’Neil-Dunne, Erin Lane, and David Lefcourt.