Carolyn A. Copenheaver

Temporal variation in species recruitment and dendroecology of an old-growth white oak forest in the Virginia Piedmont, USA

The composition and temporal variation in species recruitment were examined in relation to annual dendrochronological data to determine the historical development and successional history of an old-growth mixed-oak (Quercus) forest in northern Virginia, USA. A ridge site in the upland Piedmont, along the Potomac River, was used to survey the old-growth forest, which is dominated by Quercus alba L., Q. rubra L., Liriodendron tulipifera L., Fagus grandifolia Ehrh., and Carya glabra (Mill.) Sweet. The present age structure indicates that the oldest Q. alba established between 1748 and 1790. All tree species other than Q. alba in the forest were <110 years of age, excluding a 166-year-old Nyssa sylvatica Marsh.. Quercus alba had fairly continuous recruitment between 1740 and 1925. Peak recruitment of Q. rubra and C. glabra occurred between 1900 and 1930. Since 1930, tree recruitment in the forest has been dominated by Fagus, Liriodendron, and Acer rubrum L.. Releases in radial growth, indicative of moderate- and small-scale disturbances occurred in most of the oldest trees during the last 200 years. The master tree-ring chronology exhibited a sharp decline from 1837 to 1844, associated with an extremely cold period in the region, followed by a general increase from 1850 to 1930; growth remained high from 1930 to 1998. The shift in dominance from white oak to red oak to mixed-mesophytic tree species after 1900 is consistent with successional variation in other oak forests in the mid-Atlantic region. # 1999 Elsevier Science B.V. All rights reserved.

The value of crossdating to retain high-frequency variability, climate signals, and extreme events in environmental proxies

High-resolution biogenic and geologic proxies in which one increment or layer is formed per year are crucial to describing natural ranges of environmental variability in Earths physical and biological systems. However, dating controls are necessary to ensure temporal precision and accuracy; simple counts cannot ensure that all layers are placed correctly in time. Originally developed for tree-ring data, crossdating is the only such procedure that ensures all increments have been assigned the correct calendar year of formation. Here, we use growth-increment data from two tree species, two marine bivalve species, and a marine fish species to illustrate sensitivity of environmental signals to modest dating error rates. When falsely added or missed increments are induced at one and five percent rates, errors propagate back through time and eliminate high-frequency variability, climate signals, and evidence of extreme events while incorrectly dating and distorting major disturbances or other low-frequency processes. Our consecutive Monte Carlo experiments show that inaccuracies begin to accumulate in as little as two decades and can remove all but decadal-scale processes after as little as two centuries. Real-world scenarios may have even greater consequence in the absence of crossdating. Given this sensitivity to signal loss, the fundamental tenets of crossdating must be applied to fully resolve environmental signals, a point we underscore as the frontiers of growth-increment analysis continue to expand into tropical, freshwater, and marine environments.

Dendroecology in young stands: case studies from jack pine in northern lower Michigan

Eight jack pine (Pinus banksiana) stands in northern lower Michigan were sampled to evaluate the potential of dendroecological methods for studying stand dynamics with young trees. At each stand, a minimum of 20 dominant and codominant trees were cored, and at two stands additional recruitment data were collected. The cores were all cross-dated and measured. The raw ring widths were used to identify growth suppressions and releases within the individual chronologies. Standardized master chronologies were developed, and the residual master chronology from each stand was correlated with temperature and precipitation to identify significant dendroclimatic relationships that may reduce the ecological signal in the tree-ring record. There were no important dendroclimatic relationships at any of the eight stands; therefore, the tree-ring record was largely a reflection of stand development. At all stands, suppression periods were more common than release events because all of the stands were composed of open-grown jack pine that had initial high rates of growth. The jack pine plantations had synchronous canopy closure (as evidenced by suppression), but the naturally regenerated stands had asynchronous canopy closure. Thus, the master chronologies were useful for identifying common stand-level growth patterns within plantations, but the individual tree chronologies were more useful within the naturally regenerated stands. One of the limitations of calculating suppression events in young trees was that the first and last 10 years of the chronology were excluded because of the equations used to calculate suppression events; therefore, any changes in growth pattern during these periods had to be visually identified. By combining quantitatively determined suppression events with recruitment data and visual interpretation of the chronologies, reconstruction of stand development events, canopy closure, thinning treatments and subsequent canopy re-closure, and changes in species composition associated with stand development were all identified within the tree-ring record. Thus, there is great potential for dendroecological studies in young trees to improve our understanding of the early stages of stand development.

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.

Dynamics of an Estuarine Forest and its Response to Rising Sea Level

Abstract To address the impact of rising sea level in a rapidly submerging Maryland estuarine forest, 15 loblolly pines (Pinus taeda) were cored for dendroecological analysis. The study area is a pure stand of loblolly pine that extends down an elevation gradient into surrounding marsh where dead stumps and snags indicate a retreating forest margin. Although relative sea level has risen considerably and there are dead trees at the forest-marsh interface, there is no associated decline in ring width, making sea level–induced mortality unlikely. Instead, ring width is correlated positively with annual precipitation and winter temperature and negatively with summer temperatures. Although recruitment of new pines was continuous between 1910 and 1930, there has been no more active recruitment except for a small age class established immediately after regional drought. Because recruitment is failing in the present forest despite abundant seedlings and an open canopy, recruitment ability appears to be limited by saturated soils associated with periods of high sea level. We predict that the forest margin will retreat stepwise, following storm-induced mortality, or continuously, following age-related adult mortality. The position of the forest margin is then a function of sea level position, but it represents the failure to recruit new individuals, not the ability of adults to survive a long term rise in sea level.

Using Repeat Landscape Photography to Assess Vegetation Changes in Rural Communities of the Southern Appalachian Mountains in Virginia, USA

Abstract Repeat photography is a useful tool for evaluating historical landscape change. The objective of this study was to use ground-based repeat photography to quantify landscape vegetation changes during the period of 1880–2008 and to evaluate methods employed in repeat photography. The historical photographs included 237 landscape photographs taken in 1880 in the southern Appalachian Mountains. Fifty-five photographs were successfully relocated, and the photograph pairs were analyzed for changes in cover classes and changes by topographical position. From 1880 to 2008, forest land was the most stable cover type (98% of forested land in 1880 remained forested in 2008). Some of the main patterns of land conversion during this time period were (1) agricultural land converted to forest (19%), (2) residential and commercial land converted to forest (18%), and (3) transportation systems converted to forest or agricultural land (57%). When combined with other historical land use methods, repeat photography can yield a detailed reconstruction of the historical profile of an area; however, if the original locations of the photographs are unknown, repeat photography is a very time-intensive technique.

Lack of gender bias in citation rates of publications by dendrochronologists: what is unique about this discipline?

Abstract Most academic disciplines have a gender bias that exists in the recognition of research publications: womens publications are cited at lower rates than mens publications. In this paper, we examined whether a similar gender bias existed for publications by dendrochronologists. Tree-ring research is a fairly small field where males outnumber females, and therefore the sample size was limited to 20 female dendrochronologists and 20 male dendrochronologists. It was determined that native language (English or non-native English speaker), current employment (government or academic), and gender of the first-author do not significantly influence a papers probability of being cited. However, years since dissertation completion was a good predictor of a papers citation rate. We suggest that the high productivity of female dendrochronologists and a pattern of co-authoring with male colleagues bring the work of females to the attention of their male colleagues and thus eliminate the gender bias in citation of womens work common to other disciplines.

Tree Encroachment in Forest Openings: a Case Study From Buffalo Mountain, Virginia

Abstract In eastern forests, openings dominated by grasses, forbs, or shrubs are areas of conservation concern because they typically contain endemic, threatened, and rare plants. Understanding the ecology and mechanisms of tree encroachment would be valuable for conservation managers and would add to a substantial body of literature on forest openings. In this study, we worked in grass-dominated forest openings on Buffalo Mountain, Virginia using a method that combined dendrochronology and belt transects to assess tree encroachment. We discovered both stable ecotones and areas where trees were invading the formerly grass-dominated openings. Both gradual and episodic patterns of tree encroachment were identified; however, successful tree establishment always initiated from the edge of the forest-grass ecotone and progressed towards the center of the opening rather than occurring across the entire forest opening. This spatial pattern of recruitment implies that successional facilitation is necessary for tree encroachment in forested openings at Buffalo Mountain.

Forest Stand Development Patterns in the Southern Appalachians

Abstract Composition of southern Appalachian forests are influenced by disturbance and topography. This study examined six stands in southwestern Virginia. Within each stand, a 0.3-ha plot was established, and all trees and saplings were measured and aged. Burned stands had lower densities of saplings and small trees, but appeared to have greater Quercus regeneration. Ice damage from the 1994 ice storm was most evident in Pinus strobus saplings. A stand on old coal-mine slag appeared to be experiencing a slower rate of succession than other sites. A variety of stand development patterns were observed, but one common pattern was that oak-hickory overstories had different species in their understory, which may indicate future changes in species composition.

Boundary-line growth patterns to determine disturbance history of remnant longleaf pine (Pinus palustris P. Mill.) in mixed forests of southeastern Virginia1

Abstract Removal of canopy dominant trees in temperate closed-canopy forests due to natural or anthropogenic disturbance may allow for the release of co-dominant and sub-canopy trees into the canopy. Historical growth releases of these trees can be reconstructed from the analysis of their annual rings and compared with historical disturbance events to better understand forest dynamics. We applied boundary-line growth patterns, a method for the reconstruction of historical release from disturbance, to annual-ring series of co-dominant longleaf pine in two closed-canopy successional forest sites (Everwoods and Seacock Swamp) the Mid-Atlantic Coastal Plain of southeastern Virginia. The somewhat degraded stands were co-dominated by mixed hardwoods and loblolly pine (Pinus taeda L.) after a long fire-free history. Our study documented recruitment patterns through age-class distribution and reconstructed disturbance events (growth releases) using a modified version of the boundary-line growth method. Ages for all cored individuals at Everwoods (n  =  37) ranged from 32–184 years (x¯  =  53 years), and at Seacock Swamp (n  =  32), from 56–175 years (x¯  =  94 years). Longleaf pine has failed to recruit over the past two decades at Everwoods, and over the past half-century at Seacock Swamp, probably due to increased competition and habitat decline in the absence of fire. Boundary-line growth patterns revealed moderate and major release events for longleaf pines at both sites that we linked to anthropogenic disturbances, such as silvicultural operations (1900s to the 1930s) at both sites and logging by the landowner (early 1950s) at Seacock Swamp. We interpreted extremely low growth rates and dramatic growth-change pulses after disturbance as evidence of heavy suppression atypical for this species, which has been conceptualized as shade-intolerant. Our findings fit with other studies that have suggested that longleaf pine may be less shade-tolerant than formerly thought, at least in some areas or sites. Applications of the boundary-line growth patterns method to old-growth and second-growth longleaf pine forests throughout the southeastern U.S. could help to document possible spatial variability in disturbance histories, responses to releases, and suppression patterns.