LAND-USE HISTORY AS LONG-TERM BROAD-SCALE DISTURBANCE - REGIONAL FOREST DYNAMICS IN CENTRAL NEW-ENGLAND

Human land-use activities differ from natural disturbance processes an d may elicit novel biotic responses and disrupt existing biotic-enviro nmental relationships. The widespread prevalence of land use requires that human activity be addressed as a fundamental ecological process a nd that lessons from investigations of land-use history be applied to landscape conservation and management. Changes in the intensity of lan d use and extent of forest cover in New England over the past 3 centur ies provide the opportunity to evaluate the nature of forest response and reorganization to such broad-scale disturbance. Using a range of a rchival data and modern studies, we assessed historical changes in for est vegetation and land use from the Colonial period (early 17th centu ry) to the present across a 5000 km(2) area in central Massachusetts i n order to evaluate the effects of this novel disturbance regime on th e structure, composition, and pattern of vegetation and its relationsh ip to regional climatic gradients. At the time of European settlement, the distribution of tree taxa and forest assemblages showed pronounce d regional variation and corresponded strongly to climate gradients, e specially variation in growing degree days. The dominance of hemlock a nd northern hardwoods (maple, beech, and birch) in the cooler Central Uplands and oak and hickory at lower elevations in the Connecticut Val ley and Eastern Lowlands is consistent with the regional distribution of these taxa and suggests a strong climatic control over broad-scale vegetation patterns. We infer from historical and paleoecological data that intensive natural or aboriginal disturbance was minimal in the U plands, whereas infrequent surface fires in the Lowlands may have help ed to maintain the abundance of central hardwoods and to restrict the abundance of hemlock, beech, and sugar maple in these areas. The moder n vegetation is compositionally distinct from Colonial vegetation, exh ibits less regional variation in the distribution of tree taxa or fore st assemblages defined by tree taxa, and shows little relationship to broad climatic gradients. The homogenization of the vegetation disrupt ion of vegetation-environment relationships, and formation of new asse mblages appear to be the result of (a) a massive, novel disturbance re gime; (b) ongoing low-intensity human and natural disturbance througho ut the reforestation period to the present; (c) permanent changes in s ome aspects of the biotic and abiotic environment; and (d) a relativel y short period for forest recovery (100-150 years). These factors have maintained the regional abundance of shade intolerant and moderately tolerant taxa (for example, birch, red maple, oak, and pine) and restr icted the spread and increase of shade-tolerant, long-lived taxa such as hemlock and beech. These results raise the possibility that histori cal land use has similarly altered vegetation-environment relationship s across broader geographic regions and should be considered in all co ntemporary studies of global change.