Thursday, July 12, 2018

Four Centuries of New England's Trees

European 'copper' beech in July. Note top, in full sun, has
more red tint than the lower part of the tree.
See also The Hidden Life of Trees, 
June 27, 2018 post.

In 2013, Jonathan R. Thompson* and co-authors from the Smithsonian Institute and other research organizations published an article “Four centuries of change in northeastern United States Forests.” The title incorporates a bit of rounding up, as the Pilgrims landed at what is now Plymouth in 1620, followed by much larger numbers of Puritans arriving 1630-1640. Tree choppers all. These were the colonists who believed that every tree deserved an axe.

The colonists were flummoxed by the weather. Why, if New England was at the same latitude as southern France, was the land not temperate in climate, moderate in winter and summer? Instead, the land was wracked by horrific storms in all seasons, summers unbearably humid, winters long and so cold that “…water, cast up into the air, would commonly be turned into ice before it came to the ground.” (Minister Cotton Mather). Not knowing about the Europe-warming properties of the Gulf Stream, or how frigid Artic air comes swooping south from Canada, the colonists blamed the harsh weather on trees. In their minds, cutting trees and draining marshes would not only create farmland and pasture, it would shorten and temper winter.**

The deforestation of New England reached maximum around 1850. By that time more than half the forest cover had become field or pasture, the remainder mostly second or third growth, often what farmers referred to as their wood-lots, i.e., regrowth from stumps left behind, too small for lumber but large enough to cut for firewood. Reforestation was brought on by farmers abandoning the land, either to take up farming in the flatter and more fertile Midwest, or moving to cities to work in factories. Coal replaced wood as the preferred fuel for steam engines, and the invention of barbed wire obviated the need for rail fences for pastures.

Forest regrow is a process of succession. Fast-growing trees that prefer full sunlight are the pioneers, followed by mid-succession trees, and then the late successional beech, oak and evergreens. The latter, in time, displace the former and become the dominate forestscape. One might expect that the restoration would be near-complete 150-200 years later, but what with occasional forest fires, a smaller but still active lumber industry, and the massive impact of the 1938 hurricane, New England has not yet returned to a fully mature woodland tree mix.

What Thompson reported was a change in the percentages of tree species over almost 400 years. Chestnuts, elms and hemlocks lost to disease or insects. Beech trees declining from 22 percent of the forests to 6 percent. Oaks, 18 to 11 percent. Deer, which eat acorns, and gypsy moth caterpillars, which prefer oak leaves, contributed to this decline. Spruces, 8 to 4 percent. The biggest gain was for maples – from 11 to 31 percent. Ash, birch and wild cherry posted lesser increases. Regional differences lessened. Early colonial era forests were dominated by oak and hickory in southern New England versus spruce and fir in the north. Now, maple everywhere.       

And now for the big reveal – all this is why New England, moreso than other parts of the United States – is known for fall foliage colors. The centuries of deforestation and reforestation resulted in young forests populated by maple, birch, cherry, popular and ash trees. These species provide the reds, oranges and yellows sought by ‘leaf peeper’ tourists. Going forward, American beech, oak and spruce should displace the maples and birches. In time, fall will become a less colorful season.

Two leaves from the same maple tree - darker from the sunny
side, green from the shady side. Clink on photo to enlarge.
Summer leaf colors are also more varied now compared to 400 years ago because of the common landscaping use of European and Asian tree cultivars selected for color. Think red-leaf Japanese maples and European ‘copper’ beeches. Crabapple and plum trees also come in varieties with copper, red or purple leaves. More exotic are ninebark and redbud cultivars, same color palate. Chlorophyll – green in color – is still present in these leaves. It is the presence of anthocyanins – shades of red to blue – that give the leaves their darker hues. Many of these tree species are modest in size. The exception is European ‘copper’ beech, which can easily top out at more than 100 feet tall and almost as wide across. An example on Acton Street approaches 90 feet tall, with a trunk fifteen feet in circumference.

*Thompson JR, Carpenter DN, Cogbill CV, Foster DR. Four centuries of change in northeastern United States forests. PLoS One. 2013;8(9):e.72540. PMID:24023749.

**Buck S. The first American settlers cut down millions of trees to deliberately engineer climate change.  

Much of what Buck writes appears to be based on a 1998 book by James Roger Fleming "Historical Perspectives on Climate Change", which can be read on line at:

No comments:

Post a Comment