Variations in old-growth structure and definitions: Forest dynamics on Wachusett Mountain, Massachusetts

One of the largest old-growth forests in southern New England was recently "discovered" on the exposed upper slopes of Wachusett Mountain, Massachuset ts, a heavily used recreational area located <80 km (<50 miles) from Boston . We analyzed historical records, dendroecological data, vegetation, and co arse woody debris to characterize the dynamics and development of four majo r old-growth stands on the mountain and explored the potential factors enab ling these forests to survive and elude recognition as old-growth forests f or >150 yr. Historical data suggest that most of the area's forests were co mposed of a mixture of Quercus rubra and northern hardwood species. Species abundances and recruitment dynamics in the four stands exhibit highly vari able spatial and temporal patterns across sites that differ in aspect and e xposure. Three uneven-aged hardwood stands contain Quercus rubra in the lar gest size classes, various amounts of Fagus grandifolia, Acer, and Betula s pecies in the middle size classes, and dense thickets of several shrub spec ies in the small size classes. Several of a set of randomly aged individual s of Q. rubra, B. lenta, and B. alleghaniensis are at or very near the maxi mum longevity known for these species. A Tsuga canadensis stand contains un imodal 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 th e 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 hv changes in disturbance regime over the last two centu ries, from fire in the early to hurricanes (1815 and 1938), and more recent ly, 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-stat ured and unusually gnarled trees, which gave the forest unusual resistance to severe winds from hurricanes, discouraged logging, and prevented the rec ognition of the forest's old-growth status despite its heavy recreational u se.