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Autumn Foliage Color: Past, Present, and Future
Autumn colors were different a century ago in southern New England, and they will likely continue to change during this century. These changes are largely due to human activity, including land-use changes, introduced pests and diseases, forest management, and climate change from fossil fuel emissions. At present, the timing of color production is quite consistent from year to year, although very unusual weather conditions can retard or advance the timing.
At the start of the twentieth century, much of this landscape was covered by white pine forests that had naturally established on fields and pastures when they were abandoned in the late nineteenth century. As these white pines were harvested, they have typically been replaced (succeeded) by a mixture of broadleaf species (including maples, oaks, birches, ash and others), significantly increasing the autumn color in the landscape.
The American Chestnut, which produces a nice yellow color during autumn, was a very common broadleaf tree in these forests a century ago. All large mature trees were destroyed by the Chestnut Blight, an introduced fungal disease, and only small sprouts linger on in our forests. Our forests would have produced more yellows and fewer reds with these trees in the mix.
This beautiful native conifer, particularly common in valleys, on steep slopes, and along streams, is being removed from our forests by an introduced insect pest, the hemlock woolly adelgid. The insect is presently infesting trees at the Harvard Forest, and trees may begin to die in several years. It is not clear how far north this insect pest will move. As these hemlocks die, they will likely be replaced by black birch, which will replace the dark green with yellow foliage during the autumn.
This is one of our most spectacularly colorful trees during the autumn. It is near the southern end of its natural range in Massachusetts, although it can be grown as a landscape tree further south. Its abundance in eastern Massachusetts and coastal southern New England is a result of extensive planting along roadsides during the eighteenth and nineteenth centuries to provide a source of sap for maple sugar. It is likely that its natural distribution will move towards the north over the next century, with the anticipated increase in temperatures due to the accumulation of greenhouse gases. Over time, the autumn colors of our forests may diminish as conditions become less favorable for this tree.
Temperature increases brought on by accumulation of greenhouse gases may affect other trees. Diseases, such as those of ash, dogwood and other species, may reduce the abundances of these colorful trees, and these diseases may be promoted by climate change. Climate change is yet another stress that may increase susceptibility to existing diseases, rather than killing trees outright. USDA has a climate change tree atlas for the Eastern USA.