CONTROLLING SITE TO EVALUATE HISTORY - VEGETATION PATTERNS OF A NEW-ENGLAND SAND PLAIN

The widespread and long-lasting impact of human activity on natural ec osystems indicates that land-use history must be treated as an integra l aspect of ecological study and a critical component of conservation planning. The New England landscape has undergone a complete transform ation as forests were converted to agriculture in the 18th and 19th ce nturies followed by succession to woodland as a result of widespread a gricultural abandonment. Despite the prevalence of human impacts, the effect and longevity of land-use practices on modern forest conditions are poorly understood. In the present study of pitch pine-scrub oak v egetation on a sand plain in the Connecticut Valley of Massachusetts, we address the following questions: (1) what is the relative importanc e of human and natural disturbance and environmental factors in contro lling vegetation composition, structure, and landscape patterns; (2) w hat are the mechanisms underlying human impacts on vegetation, and wha t is the duration of these impacts; and (3) what are the implications of land-use history for the interpretation and conservation of these c ommunities? Sand plain vegetation was selected for investigation becau se the homogeneity of site conditions facilitates the interpretation o f land-use and natural disturbance impacts, and because the uncommon v egetation and constituent species are priorities for conservation effo rts.Paleoecological data suggest that pre-European fires were common o n the study area, perhaps ignited by a large regional Indian populatio n. The area was noted historically as an extensive pine plain and was used for wood products from the 18th to the mid-19th century. Eighty-t wo percent of the area was subsequently plowed for agriculture before being abandoned in the early 20th century. Soil analyses confirm the h omogeneity of site conditions and suggest that land uses (plowing, woo dlot/pasture) were determined according to ownership pattern rather th an site factors. Previously cultivated parcels have distinct Ap (plow horizons) 15-33 cm deep, whereas uncultivated parcels have A horizons 3-10 cm in depth. Soil physical and chemical characteristics are simil ar among land uses and modern vegetation types. Aerial photographs doc ument a dramatic transformation in plant cover over the last 50 yr. In 1939, the vegetation was grassland or shrub-heath (49%), open-canopy forest (29%), and scrub-oak shrublands (15%). In 1985, 73% of the stud y area was forested with pitch pine (40%), hardwood (12%), or mixed st ands (21%), 9% was in open-canopy stands, and 3% was covered by grass or shrubs. Vegetation/land-use relations are striking. Pitch pine occu rs almost exclusively (97%) on former plowed sites, whereas scrub oak stands occur preferentially (89%) on sites that have not been plowed. Land use explains the greatest variation in modern vegetation as well as the distribution and abundance of many taxa. Fire has been common a cross the study area but has influenced vegetation largely within patt erns resulting from prior land use. Land-use patterns and factors cont rolling vegetation composition and structure are broadly paralleled at similar sites elsewhere in the Connecticut Valley. The study indicate s that conservation biologists interested in preserving species, commu nities, and landscape patterns on sand plains in the northeastern Unit ed States need to incorporate a dynamic perspective of biological syst ems that includes the overriding impact of prior land use. In order to appreciate, study, and display these land-use and vegetation patterns it is essential to conserve the mosaic of assemblages and historical uses within a landscape setting.