The northeastern United States is a predominately-forested region that, like most of the eastern U.S., has undergone a 400-year history of intense logging, land clearance for agriculture, and natural reforestation. This setting affords the opportunity to address a major ecological question: How similar are today's forests to those existing prior to European colonization? Working throughout a nine-state region spanning Maine to Pennsylvania, we assembled a comprehensive database of archival land-survey records describing the forests at the time of European colonization. We compared these records to modern forest inventory data and described: (1) the magnitude and attributes of forest compositional change, (2) the geography of change, and (3) the relationships between change and environmental factors and historical land use. We found that with few exceptions, notably the American chestnut, the same taxa that made up the pre-colonial forest still comprise the forest today, despite ample opportunities for species invasion and loss. Nonetheless, there have been dramatic shifts in the relative abundance of forest taxa. The magnitude of change is spatially clustered at local scales (<125 km) but exhibits little evidence of regional-scale gradients. Compositional change is most strongly associated with the historical extent of agricultural clearing. Throughout the region, there has been a broad ecological shift away from late successional taxa, such as beech and hemlock, in favor of early- and mid-successional taxa, such as red maple and poplar. Additionally, the modern forest composition is more homogeneous and less coupled to local climatic controls.

Aim This study uses the combination of presettlement tree surveys and spatial analysis to produce an empirical reconstruction of tree species abundance and vegetation units at different scales in the original landscape.Location The New England study area extends across eight physiographic sections, from the Appalachian Mountains to the Atlantic Coastal Plain. The data are drawn from 389 original towns in what are now seven states in the north-eastern United States. These towns have early land division records which document the witness trees growing in the town before European settlement (c. seventeenth to eighteenth century AD).Methods Records of witness trees from presettlement surveys were collated from towns throughout the study area (1.3 · 10 5 km 2 ). Tree abundance was averaged over townwide samples of multiple forest types, integrating proportions of taxa at a local scale (10 2 km 2 ). These data were summarized into genus groups over the sample towns, which were then mapped [geographical information system (GIS)], classified (Cluster Analysis) and ordinated [detrended correspondence analysis (DCA)]. Modern climatic and topographic variables were also derived from GIS analyses for each town and all town attributes were quantitatively compared. Distributions of both individual species and vegetation units were analysed and displayed for spatial analysis of vegetation structure. ResultsThe tally of 153,932 individual tree citations show a dominant latitudinal trend in the vegetation. Spatial patterns are concisely displayed as pie charts of genus composition arrayed on sampled towns. Detailed interpolated frequency surfaces show spatial patterns of range and abundance of the dominant taxa. Oak, spruce, hickory and chestnut reach distinctive range limits within the study area. Eight vegetation clusters are distinguished. The northern vegetation is a continuous geographical sequence typified by beech while the southern vegetation is an amorphous group typified by oak.Main conclusions The wealth of information recorded in the New England town presettlement surveys is an ideal data base to elucidate the natural patterns of vegetation over an extensive spatial area. The timing, town-wide scale, expansive coverage, quantitative enumeration and unbiased estimates are critical advantages of proprietor lotting surveys in determining original tree distributions. This historical-geographical approach produces a vivid reconstruction of the natural vegetation and species distributions as portrayed on maps. The spatial, vegetational and environmental patterns all demonstrate a distinct Ôtension zoneÕ separating Ônorthern hardwoodÕ and Ôcentral hardwoodÕ towns. The presettlement northern hardwood forests, absolutely dominated by beech, forms a continuum responding to a complex climatic gradient of altitude and latitude. The oak forests to the south are distinguished by non-zonal units, probably affected by fire. Although at the continental scale, the forests seem to be a broad transition, at a finer scale they respond to ...

A major ice storm in January 1998 provided an opportunity to study the effects of a rare, intense disturbance on the structure of the northern hardwood forest canopy. Canopy damage was assessed using visual damage classes within watersheds of different ages at the Hubbard Brook Experimental Forest (HBEF) and changes in leaf area index in two of these watersheds. Ice thickness was measured, and ice loads of trees were estimated using regression equations. In the 60- to 120-year-old forests (mean basal area 26 m2·ha–1), damage was greatest in trees >30 cm diameter at breast height and at elevations above 600 m. Of the dominant tree species, beech (Fagus grandifolia Ehrh.) was the most damaged, sugar maple (Acer saccharum Marsh.) was the most resistant, and yellow birch (Betula alleghaniensis Britt.) was intermediate. Trees with advanced beech bark disease experienced heavier ice damage. Little damage occurred in the 14-year-old forest, while the 24- to 28-year-old forest experienced intense damage. In the young stands of this forest, damage was greatest between 600 and 750 m, in trees on steep slopes and near streams, and among pin cherry (Prunus pensylvanica L.). Recovery of the canopy was tracked over three growing seasons, and root growth was monitored 1 year after the storm. Because of the high density of advance regeneration from beech bark disease and root sprouting potential in ice-damaged beech, HBEF will likely see an increase in beech abundance in older forests as a result of the storm. There will also be a more rapid change from pioneer species to mature northern hardwoods in the younger forests. These predictions illustrate the ability of rare disturbances to increase heterogeneity of forest structure and composition in this ecosystem, especially through interactions with other disturbances.

Spruce-fir forests extend along the Appalachian Mountains of eastern North America from 35 ° to 49 ° N.This montane vegetation differs from boreal spruce-In" forest in that it is dominated by Picea rubens, has a higher vascular species richness, has wind, rather than fire, dominated dynamics, and has a mean annual temperature above 2 ° C. Using field reconnaissance, remote sensing, and literature review we described and modeled the latitude-elevation relationship for Appalachian spruce-fir. The elevation of the sprucefir/deciduous forest ecotone decreases from 1,680 m at 35 ° N to 150 m at 49 ° N, while the elevation of treeline (spruce-fir/tundra ecotone) decreases from 1,480 m at 44 ° N to 550 m at 55 ° N. Linear regressions gave latitude-elevation relationships of -100 m/1 ° Latitude for the spruce-fir/deciduous forest ecotone and -8 3 m/1 ° Latitude for treeline. These values compare to literature reports of -5 4 to -230 m/1 ° Latitude and are most similar to values reported from eastern Asia. The latitude-elevation relationship for mean July temperature ( -94 to -121 m/1 ° Latitude) was more similar to the slopes of these ecotones than is the slope for mean annual temperature ( -170 to -220 m/1 ° Latitude). The spruce-fir/deciduous forest ecotone was correlated with a mean July temperature of approximately 17 ° C. Treeline was correlated with a mean July temperature of approximately 13 °C.

Analysis of recent precipitation samples from the northeastern United States has shown a consistent pH of less than 4.4, when the expected pH based upon equilibrium with CO2 would be 5.6. A stoichiometric formation process being assumed, some 65% of the acidity is due to H2SO4, 30% to HNO3, and less than 5% to HCl. The pH values may be predicted from chemical content and generally agree to within 0.1 pH unit with the observed pH. The distribution of acid precipitation encompasses most of the northeastern United States. This pattern apparently has existed since about 1950–1955, but the intensity of acid deposition, especially that due to HNO3, has increased since then. Analysis of prevailing winds indicates that much of the acidity originates as a general source over industrial areas in the Midwest.

BackgroundEuroAmerican land-use and its legacies have transformed forest structure and composition across the United States (US). More accurate reconstructions of historical states are critical to understanding the processes governing past, current, and future forest dynamics. Here we present new gridded (8x8km) reconstructions of pre-settlement (1800s) forest composition and structure from the upper Midwestern US (Minnesota, Wisconsin, and most of Michigan), using 19th Century Public Land Survey System (PLSS), with estimates of relative composition, above-ground biomass, stem density, and basal area for 28 tree types. This mapping is more robust than past efforts, using spatially varying correction factors to accommodate sampling design, azimuthal censoring, and biases in tree selection.Changes in Forest StructureWe compare pre-settlement to modern forests using US Forest Service Forest Inventory and Analysis (FIA) data to show the prevalence of lost forests (pre-settlement forests with no current analog), and novel forests (modern forests with no past analogs). Differences between pre-settlement and modern forests are spatially structured owing to differences in land-use impacts and accompanying ecological responses. Modern forests are more homogeneous, and ecotonal gradients are more diffuse today than in the past. Novel forest assemblages represent 28% of all FIA cells, and 28% of pre-settlement forests no longer exist in a modern context. Lost forests include tamarack forests in northeastern Minnesota, hemlock and cedar dominated forests in north-central Wisconsin and along the Upper Peninsula of Michigan, and elm, oak, basswood and ironwood forests along the forest-prairie boundary in south central Minnesota and eastern Wisconsin. Novel FIA forest assemblages are distributed evenly across the region, but novelty shows a strong relationship to spatial distance from remnant forests in the upper Midwest, with novelty predicted at between 20 to 60km from remnants, depending on historical forest type. The spatial relationships between remnant and novel forests, shifts in ecotone structure and the loss of historic forest types point to significant challenges for land managers if landscape restoration is a priority. The spatial signals of novelty and ecological change also point to potential challenges in using modern spatial distributions of species and communities and their relationship to underlying geophysical and climatic attributes in understanding potential responses to changing climate. The signal of human settlement on modern forests is broad, spatially varying and acts to homogenize modern forests relative to their historic counterparts, with significant implications for future management.

Analyses of species composition and tree increment cores from 145 stands in central Québec were used to determine the forest history and stand dynamics. Windspread fires, possibly synchronous, burned across central Québec in at least three periods of record (1661–1663, 1779–1791, 1869–1871). The average fire rotation (time interval between natural fires burning the equivalent of a large area) for spruce – feather moss forests was approximately 130 years, and 70 years in either deciduous or jack pine forests. The traditional succession concept of continual recruitment leading to an all-aged forest was not evident in these forests. About 70% of the overstory trees were established in the first 30 years after fire disturbance, with little recruitment after this time. These initial trees dominate the canopy for up to 250 years with mortality becoming prominent after 130 years. The short average time between disturbances precludes the probable degeneration into old shrub-filled stands typical of old age.

Cover PhotoMontane ecosystems, as seen from Mount Jefferson on the White Mountain National Forest. These ecosystems are particularly vulnerable to climate change. Photo by Toni Lyn Morelli, U.S. Geological Survey.