Ken Prescott, Arbor Resource Committee
Second of two articles
As our climate changes, growing conditions for plants and trees will also change. The USDA Hardiness Zone Map now puts Bedfordin zone 6a (-10 to -5 F), but within 20 years we may be in zone 7b (5 to 10 F). These zones indicate the average minimum winter temperatures, which can help to determine which plants and trees are most likely to thrive at a given location.
We can expect climate change to bring more extreme weather. Warmer summers and winters, but also with some colder periods in winter that will stress trees. Drought coupled with occasional flooding events will challenge the health of our trees. Anticipated and unanticipated diseases and insects will attack and weaken trees.
As a result, the diversity of northern hardwood forests is expected to decline. Oak and hickory trees are expected to take over New England forests between 2070 and 2100.
Trees that cannot adapt well to extremes of temperature, droughts, floods, storms, pests, and diseases are expected to do poorly. These include some of our most common species such as red pine, black ash, eastern white pine, hemlock, balsam fir, quaking aspen, paper birch, red spruce, Norway maple, littleleaf linden and amur maackia.
Trees that are now in the middle of their range will probably be all right. These include sugar maple, Atlantic white cedar, beech(although beech bark disease causes the trees to die early), black cherry, holly, pitch pine and swamp chestnut oak.
Trees that are highly adaptiveshould also do well. Highly adaptive trees include Eastern red cedar, blackgum, mockernut hickory, Kentucky coffeetree and Kousa dogwood.
Other trees with low vulnerability to climate change include Eastern hophornbeam, serviceberry, yellowwood, ginkgo, Persian ironwood and cherries. Sourwood, pawpaw, Eastern redbud, sweetgum, baldcypress, tuliptree and persimmon may also find the changing climate to be beneficial, as their range moves north.
In the face of changing conditions, perhaps the most important consideration is to plant a wide variety of trees. We know that growing conditions will continue to change, but we can’t know exactly which trees will do well and which will not. Therefore, a wide variety of trees will give us the best chance of some success.
These recommendations come from the Metropolitan Area Planning Council, Green Cambridge and the Mass Woods website of UMass Amherst which give landowners tools to ensure the health of their trees and forests.These recommendations will be available on the Bedford Arbor Resource Committee site on the Town of Bedford website (bedfordma.gov). As conditions change BARC will update its recommendations.