Variations in Old-Growth Structure and Definitions: Forest Dynamics on Wachusett Mountain, Massachusetts

Abstract

One of the largest old-growth forests in southern New England was recently ‘‘discovered’’ on the exposed upper slopes of Wachusett Mountain, Massachusetts, a heavily used recreational area located ,80 km (,50 miles) from Boston. We analyzed historical records, dendroecological data, vegetation, and coarse woody debris to characterize the dynamics and development of four major old-growth stands on the mountain and explored the potential factors enabling these forests to survive and elude recognition as old-growth forests for .150 yr. Historical data suggest that most of the area’s forests were composed of a mixture of Quercus rubra and northern hardwood species. Species abundances and recruitment dynamics in the four stands exhibit highly variable spatial and temporal patterns across sites that differ in aspect and exposure. Three uneven-aged hardwood stands contain Quercus rubra in the largest size classes, various amounts of Fagus grandifolia, Acer, and Betula species in the middle size classes, and dense thickets of several shrub species in the small size classes. Several of a set of randomly aged individuals of Q. rubra, B. lenta, and B. alleghaniensis are at or very near the maximum longevity known for these species. A Tsuga canadensis stand contains unimodal size and age distributions, with trees ,60- cm dbh and 100–300 yr old. Quercus rubra recruitment occurred on all sites from the 1600s through the early 1800s, when it dropped precipitously on most sites and was replaced by either Tsuga or Acer and Betula species. These recruitment changes were apparently driven by changes in disturbance regime over the last two centuries, from fire in the early record to hurricanes (1815 and 1938), and more recently, frequent wind, ice, and snow damage but no fire. Asynchronous tree-ring releases and suppression and relatively low amounts of coarse woody debris corroborate this interpretation. Chronic canopy damage produced short-statured and unusually gnarled trees, which gave the forest unusual resistance to severe winds from hurricanes, discouraged logging, and prevented the recognition of the forest’s old-growth status despite its heavy recreational use.