William A. Patterson

Microscopic charcoal as a fossil indicator of fire

Abstract Charcoal preserved in lake sediments, peat, and soils provides a record of past fire occurrence. An understanding of fire history is important in evaluating interactions between vegetation, climate and human disturbances through at least the last several millennia. In this paper we review information concerning the production, dispersal, sedimentation and preservation of charcoal. We present examples of studies that have used charcoal analysis in palaeoecological reconstructions, with special emphasis on analytical techniques and problems of interpretation. Unlike pollen, which is produced continuously in fairly constant amounts, charcoal is produced in large quantities but at irregular intervals. These are a function of fire regimes that are often unique to specific vegetation types and/or climatic regions. Charcoal particles vary in size from sub-microscopic to macroscopic, with small particles presumably being transported further by wind and water than large particles. Charcoal preserves well, but it may be subject to breakage, especially when transported by water. We present theoretical models of dispersal and discuss potential problems associated with post-depositional mixing. A variety of charcoal analysis techniques have been employed during the past four decades. Most involve microscopic identification and quantification of numbers or size of individual fragments occurring in samples prepared for pollen analysis. The most commonly used method — estimating charcoal area by categorizing particles in several size classes — is both tedious and time consuming, and recently introduced techniques attempt to estimate past fire occurrence based upon point count estimation, elemental carbon analysis, magnetic measurement of sediments, electron microscope, and spectrographic analyses. A lack of standardization both within and among analysis techniques has hampered interpretation of charcoal profiles. Taphonomic processes affecting charcoal are less well understood than for pollen, and as a result interpretations of historic interactions between vegetation and fire based upon pollen and charcoal analyses are difficult. We review several studies through which advances have been made and suggest questions for future study.

Indian Fires in the Prehistory of New England

Humans have inhabited the northeastern United States for approximately 12,000 years (Figure 1). During that period the vegetation of the region changed first from tundra to boreal spruce and fir forests. For the past 8,000 years or so, mixtures of pines, spruces, fir, hemlock, and a variety of hardwoods including beech, several oaks, maples, hickories, and birches have occupied the landscape. Changing climate and the differential migration of plant species were responsible for the vegetation changes that occurred over time periods spanning several hundred to a few thousand years (Davis 1983). Today we see a vegetation pattern that can be related to regional variations in climate, topography, soils, and human settlement. Alpine tundra is found at high elevations in the White Mountains, spruce and fir forests cover much of northern Maine, Vermont, and New Hampshire, and pitch pine and oaks occupy the xeric, sandy soils of southern coastal areas. Mesic forest species occur over a broad area of central New England (Westveld et al. 1956).

EFFECTS OF ROAD SALT AND PHRAGMITES AUSTRALIS INVASION ON THE VEGETATION OF A WESTERN MASSACHUSETTS CALCAREOUS LAKE-BASIN FEN

Kampoosa Bog in Stockbridge, Massachusetts, USA is a 70-ha wetland comprised of calcareous basin fen and red maple swamp bordered, in part, by roads including the Massachusetts Turnpike. High salt concentrations in the ground water (due to the application of deicing salts on the Turnpike) and Phragmites australis colonies appear to be impacting the native vegetation at this site. Sodium and chloride concentrations at Kampoosa Bog are generally below previously published threshold levels for impacting vegetation, although such levels vary by species and in relation to other environmental stress conditions. Giant reed (Phragmites), a salt-tolerant invasive species, invaded the northern portion of the wetland adjacent to the Turnpike and a gas pipeline sometime after they were built in the 1950s. By 1998, Phragmites had formed dense colonies that continued to spread across the wetland, which supports several state-listed rare plant and animal species. High salt concentrations (Na+ > 112 mg/L, Cl >54 mg/L) are present up to 300 meters from the Turnpike. Phragmites colonies occur in areas with high and low salt concentrations, and the species abundance is not well-correlated with elevated salt levels. Although high salt concentrations and Phragmites abundance do not seem to produce an interaction effect on the vegetation of the wetland, the graminoid fen community is impacted by both factors separately. We attribute decreases in the abundance of species between invaded and non-invaded areas to the presence of Phragmites. In the graminoid fen, we attribute decreases in both community measures (richness, evenness, and overall cover) and individual species abundances to high salt concentrations.

Acorn size and geographical range in the North American oaks (Quercus L.)

In this work we show that among North American oak species, acorn size and geographical range are correlated. Two geographically isolated sets of oak species are evaluated. The ecological significance of a positive relationship between acorn size and geographical range is explored

Leaf phenology and herbivory along a temperature gradient: a spatial test of the phenological window hypothesis

In this study, we documented patterns of variation in leaf phenology and leaf herbivory in scrub oak (Quercus ilicifolia Wang) along the slope of a closed topographical depression, 15 m deep and 400 m wide, in the pine barrens of eastern Massachusetts. Minimum temperatures over the grow- ing season averaged 6.5 ?C lower at the bottom of the depres- sion than at the top. Bud break at the bottom of the depression was 2-3 weeks delayed compared with the top. In both years of this study, 1988 and 1989, leaf damage by thrips increased down slope producing differences of about 10 % in the pro- portion of leaf area damaged between the top and the bottom of the depression. Because thrips fed exclusively on the young- est leaves, this pattern could be attributed to a closer synchrony between the timing of leaf flushing and the period of insect feeding activity towards the bottom of the depression. Aver- age differences in leaf damage between years could also be accounted for by variation in leaf phenology. These patterns support the hypothesis that the degree of temporal overlap between availability of high quality foliage and the period of insect feeding activity may greatly determine spatial and tem- poral variation in leaf damage by insect herbivores.

Vegetation development in a southern Maine pitch pine-scrub oak barren.

oak, mixed deciduous woodland, scrub oak, and open-canopy pitch pine. We investigated five factors that potentially influence vegetation distribution in the 856-ha preserve: soil texture, moisture, and fertility; topography; and disturbance history. Although analysis of variance revealed significant differences in soils and topography among plots in the five communities studied, multivariate analyses indicated a weak relationship between these environmental variables and species composition and structure. In contrast, disturbance history clearly influenced community and species distribution within the preserve. Effects of historic logging, charcoaling, and cultivation for blueberries persist despite a stand-replacing wildfire that swept through most of barrens in October, 1947. Pollen and charcoal analysis of sediments from a pond near the preserve suggests fire has influenced the barrens for at least the last several centuries, but that prior to European settlement of the area in the 18th century the character of the vegetation differed somewhat from that of today. Our results demonstrate that both fire and edaphic factors have influenced the vegetation of the area, but that historic land use has also played a strong role in determining the present character of the plant communities studied.

The relationship between site factors and white ash (Fraxinus americana L.) decline in Massachusetts

Abstract Forest inventory records incorporating individual tree data are an important source of information about the extent and severity of past rates of forest decline, thus providing a temporal perspective for contemporary observations. We demonstrate the potential of this approach by using continuous forest inventory (CFI) data to reconstruct the extent, severity, pattern of development and site-factor associations for white ash decline in Massachusetts. White ash (Fraxinus americana L.) increased in basal area on Massachusetts CFI plots at about 1.5% per year from 1962 to 1979. Ash decline is, however, locally severe. Plot decline status was estimated, based on vigor rating, and growth and mortality rates of white ash. Plots with a mean change in basal area per year of ⩽ −0.5% and/or with a mean vigor rating of ⩽2.0 (on a scale of 0–4) were classified as ‘decline’. Using these criteria, 20% of the 82 CFI plots with ⩽10% total basal area of white ash in 1962 were classified as ‘decline’ in both 1979 and 1991. These results suggest that statewide there has been no net loss of ash basal area since 1962. The total forest area affected by ash decline has not increased in the past decade. Analyses of the CFI data indicate that decline was most prevalent on mesic sites, high on the landscape and/or on steep slopes. Such sites are potentially subject to large fluctuations in soil moisture availability during drought periods. Relationships identified between the prevalence of ash decline and site factors were further evaluated within a 2 ha intensived study site in the center of a 13 ha white ash stand affected by ash decline in 1990. Decline was heterogeneously distributed within the stand, with declining trees most frequent on the ‘decline-prone’ site-type identified through CFI plot analyses.

Paleoecology of Calf Island in Boston's Outer Harbor

Abstract We used microfossils preserved in salt-marsh peat to understand the landscape processes (both natural and anthropogenic) that have influenced the environment. Variations in the abundance of fossil pollen of native species suggest that the vegetation of this small, exposed island has been dominated by low, shrubby vegetation since before the arrival of Europeans in the early 1600s. Increases in non-native species since that time may reflect disturbance of the soil associated with grazing and other activities. Sorrel (Rumex) pollen, which indicates local grazing, declines by the late 19th century, whereas Chenopodiaceae/Amaranthaceae pollen, an indicator of disturbed soil, is most abundant since 1900. Charcoal abundance shows that fires, probably ignited by humans both before and after 1600 A.D., have burned on the island throughout the last 1000 years. In addition, increases in soot and opaque spherules in sediments reflect increased air pollution during the last 100 years. Our analyses provide benchmarks for modern management by documenting pre-European conditions as well as the extent to which the modern environment differs from that prior to the settlement of Massachusetts Bay by Europeans.