Composition and structure of forest ecosystems are associated with physical factors (e.g., moisture, nutrients, and light) and biological factors (e.g., competition between plants and consumption by animals). Disturbances affect plants by altering physical and biological factors, but we often fail to appreciate how long these disturbances continue to influence the ecosystem. Sometimes our only clue to past disturbances may come from characteristics of the forest itself, long after visible signs of the disturbance have faded.
The land-use history of the Holt Research Forest is a case in point. It is bisected by a former property line that separated the "North Farm" from the "South Farm". The farms differed in many respects, including the amount of land cleared for agriculture and cut for forest products, and the date of farm abandonment (Moore and Witham 1996). This is reflected by composition and structure of the forest vegetation on either side of the line. For example, spinulose woodfern is far more abundant in the understory of the north, whereas trailing arbutus primarily occurs in the south.
The historical development of two forest stands on either side of the line differed (Clark 1996). In the northern stand, most of the white pine reached breast height (130 cm) from 1910 to 1930. Their big-limbed structure and wide early growth rings indicate that they established under open conditions. The red oak in this stand did not reach breast height until the 1940s. In contrast, the pines and oaks in the southern stand established more or less together between 1910 and 1930. In both stands, periods of light cutting are indicated by abrupt increases in radial growth, primarily of the pine.