Wednesday November 7, 2012

John Burk

Many enjoy New England’s fall foliage for its aesthetics alone, and with good reason: it’s a spectacle that draws visitors from around the world. However, the unique progression of each foliage season also provides careful observers with insight related to forest health and short and long-term climate.

As the last flickers of color fade from northern New England, we can now evaluate 2012’s"big show" and how it relates to other years, and also use that famous 20/20 hindsight to evaluate the "preseason" predictions that everyone seemed to have as those first red hues emerged in early September.

Let’s start the 2012 recap by going all the way back to 2011, when, as you might remember, a combination of several unusual events -- including a cool, wet spring and an abnormally mild autumn with late frost -- resulted in largely dull and/or late foliage in most areas. Wet spring conditions in 2011 led to a proliferation of anthracnose and other fungal diseases that caused leaves on many hardwood trees, especially sugar maples, to brown and fall prematurely. Many sugar maples had also been stressed by a high seed year that year.

In contrast, the spring of 2012 saw record warmth that caused many trees to break buds early. There was then a late frost, followed by an abnormally dry summer. The good news was that the hot, dry weather mitigated some of the fungal issues. The bad news was that the late frost damaged some leaves, and the lack of summer precipitation led to premature leaf drop in some areas. Aerial surveys by Vermont’s Department of Forests, Parks and Recreation indicated roughly 50,000 acres were affected by "hardwood browning," a blanket term that covers leaf spots, insects, blight, frost, and drought damage.

Though it might seem logical to expect early bud break to result in an early fall foliage season, long-term observations compiled by Dr. John O’Keefe at the Harvard Forest in central Massachusetts indicate no apparent correlation. For example, an even earlier bud break in 2010 was followed by average to late leaf drop in autumn, while very early leaf drop in 2006 occurred after late budding that spring.

Clear and seasonably cool late summer and early autumn weather prompted a relatively early start to the foliage season this year, and vibrant colors -- especially on red maples -- erupted throughout Vermont’s Northeast Kingdom and New Hampshire’s Great North Woods and northern White Mountain regions in September. Based on early observations and the weather pattern, meteorologists, foresters, and other prognosticators anticipated a similarly colorful October throughout the south-central regions.

After a promising start, however, the weather and foliage changed markedly during late September through mid-October, demonstrating their relationship on short-term intervals. A series of weather fronts tracked slowly across the Northeast, ushering in a prolonged period of overcast, rainy days with little temperature variability. The Mount Washington Weather Observatory recorded 12 rainy days over one 16-day period. Most of the bright early color was blown down and color changes for trees that hadn’t turned were delayed, resulting in a prolonged interval of largely dull color similar to that of 2011.

By the close of Columbus Day weekend, the northern hardwood forests of the western White Mountains were already past peak with high leaf drop, while the lower-elevation woodlands of the nearby Lakes region remained largely green. Similar mosaics of bare trees and green leaves, with few areas of peak color, were the norm throughout much of interior New England during this time.

By the third week in October, the return of sunny days and cool nights, including one widespread frost, prompted late-turning species -- oaks, beeches, and some straggler sugar maples that were green before the rains -- to finally change color. In spite of the delay, the foliage was still noticeably ahead of where it was in 2010 and 2011, when colors were present well into November in southern areas such as New Hampshire’s Monadnock region. Leaf drop was fairly rapid after the color change in many areas, even before the arrival of Hurricane Sandy at the end of October.

In summation, the 2012 fall foliage season marked a change in the pattern of later autumns that has been evident in recent years. And like 2011, it offered ample evidence of the relationship between weather and foliage on short- and long-term intervals.

John Burk is a writer, photographer, and historian from central Massachusetts who has published several guides and books related to the New England outdoors, including New England’s Natural Wonders: An Explorer’s Guide. The Outside Story is assigned and edited by Northern Woodlands magazine and sponsored by the Wellborn Ecology Fund of New Hampshire Charitable Foundation: wellborn@nhcf.org.