Reforested landscapes in New England

Thoreau coined the term ``succession'' as used in ecology to describe the change in vegetation following natural disturbance. His first talk on the subject, ``The succession of forest trees,'' was presented to the Middlesex Agricultural Society, and it describes well the process of old-field succession.

• The process starts with the conversion of tilled field to pasture or its complete abandonment.

• White pine, pitch pine, and red cedar not only have small, easily dispersed seeds, they are able to tolerate drought under full sun, and are relatively unpalatable to grazing animals. Thus, pines and red cedar tend to be the first trees that become established in pastures. In recently tilled fields, however, red maple or birch often establish more quickly and become dominant.

• Oak generally begins to appear in the understory once a first-generation forest has been established.

Forest maps constructed by Charles Sprague Sargent and George Nichols at the turn of the century identified much of New England as part of the ``Northern Pine'' region (Figure 2), but

Extensive white pine forests were a transient phenomenon generated by cultural and natural history ... For many stands of pine and other pioneers, we can anticipate that with time and natural development the vegetation will become something very different ... The particular forest changes that have occurred in the New England landscape over the last century were actually a historical accident .... [6], p. 139.

And the effects of past land uses can linger for a long time. In spite of more than a century of regrowth, forest soils in New England still show a distinct plow horizon (Figure 3). Moreover, the effects of past land use on vegetation are detectable more than a century after it has been released from agricultural use (Figure 4)

Figure 2: One of Sargent's forest maps (from [9]).

Figure 3: Land use history and soil horizons in New England. The horizon on the left shows the effects of plowing more than a century after plowing stopped (from [4]).

Figure 4: Vegetation composition as a function of land use history at two sites in southern New England (from [4]).