Eight decades of compositional change in a managed northern hardwood landscape

Abstract

We analyzed over 8 decades of change in forest composition (represented by species proportion of basal area) and size class from more than 400 permanent plots located on the Bartlett Experimental Forest in the White Mountains of New Hampshire. These data represent one of the longest-term landscape-scale records of forest change based on permanent plots in North America. We analyzed the plots based on elevation class, land type indicating assumed successional direction (grouped into coniferous and deciduous), and inventory period within managed and unmanaged portions of the forest. An ongoing shift from small- to large-diameter stems is clear across all species, in response to the overall aging of the forest following exploitative harvesting in the 19th century. Major compositional changes include a continuing decline in shade-intolerant species (paper birch and aspen), along with the mid-tolerant yellow birch. An increase in red maple abundance through the early 1990s has leveled off or reversed. Among shade-tolerant species, increases in beech and red spruce were largely consistent with assumed land type on unmanaged plots, but heavy marking against diseased beech on managed plots restricted increase of that species. Sugar maple declined in abundance except where silvicultural intervention helped maintain it. By contrast, eastern hemlock showed a continuing expansion at all elevations below 600 m. The data continue to show little or no evidence of upward migration of species, despite evidence of recent regional change in climate. However, the BEF is poised for substantial changes when emerald ash borer and hemlock woolly adelgid, both of which are known to infest nearby areas, do arrive.