Christine J. Small

Changes in a hemlock-dominated forest following woolly adelgid infestation in southern New England1

Abstract Small, M. J., C. J. Small (Department of Botany, Connecticut College, New London, Connecticut 06320), and G. D. Dreyer (Goodwin-Niering Center for Conservation Biology and Environmental Studies, Connecticut College, New London, Connecticut 06320). Changes in a hemlock-dominated forest following woolly adelgid infestation in southern New England. J. Torrey Bot. 132: 458–470. 2005.—The hemlock wooly adelgid (HWA; Adelges tsugae), a small aphid-like insect introduced from Japan, has caused widespread hemlock (Tsuga canadensis) mortality throughout the mid-Atlantic and southern New England region over the last twenty years. We examined long-term (1952–2002) changes in hemlock-dominated stands before and after the appearance of the HWA in 1987 in the Connecticut College Arboretum, southeastern Connecticut. With HWA infestation, basal area of T. canadensis declined dramatically, dropping 70% from 1982 to 2002. Forest communities responded to the elimination of the dominant species by quickly filling various sized gaps. Black oaks (Quercus velutina, Q. coccinea, Q. rubra) increased from 28% of canopy basal area in 1982 to 41% in 2002. Sapling density increased markedly following HWA infestation, from 80 stems/ha in 1982 to nearly 5600 in 2002, with greatest increase in Sassafras albidum (0 to 1900 stems/ha) and Acer rubrum (4 to 1100 stems/ha). Ledge and ravine communities, formerly dominated by T. canadensis, became more compositionally distinct, with greater importance of black oaks on more xeric ledge sites and mixed canopy dominance in mesic ravine sites. Major trends associated with the decline of T. canadensis included a shift in canopy dominance to oak and mixed hardwoods, considerable understory development, including greater herb richness and abundance and increased density of clonal saplings, and expansion of several invasive shrubs and woody vines.

Spatial and temporal variation in the response of understory vegetation to disturbance in a central Appalachian oak forest

SMALL, C.J. AND B.C. MCCARTHY (Department of Environmental and Plant Biology, Ohio University, Athens, Ohio 45701). Spatial and Temporal Variation in the Response of Understory Vegetation to Disturbance in a Central Appalachian Oak Forest. J. Torrey Bot. 129: 136-153. 2002.-Understory vegetation in stand-initiating (7 year clearcuts) and understory-reinitiating (> 125 year mature second-growth) oak-dominated forest stands in southeastern Ohio was examined relative to topographic aspect, micro-environmental conditions, and sampling season to explore patterns of understory dynamics and stand development following management disturbance. Plots were established on upper and lower slopes across a range of aspect positions and sampled in spring and summer to capture topographic and seasonal changes in herb layer dynamics. Micro-site light, temperature, and physical soil properties differed significantly with stand age whereas fertility and moisture varied with aspect. Species richness was greater in clearcut than mature forest stands, associated with greater resource availability and spatial heterogeneity. Herb richness and abundance were greater on NWand SE-facing slopes and lower slope positions, corresponding to greater soil moisture and fertility. Greater frequencies of non-native species were also found in resource rich, clearcut plots. Canonical correspondence analysis showed stand age, aspect, and fertility to strongly influence herb layer composition. Non-metric multidimensional scaling showed compositional divergence of spring vs. summer and clearcut vs. mature forest herb samples. Composition of clearcuts and mature forests differed markedly in June, suggesting that management influences may be more pronounced in summer herb communities. Most studies of understory dynamics in eastern forests fail to account for spatial and temporal variations in site and vegetation characteristics, however, understory disturbance response appears strongly linked to these ecosystem properties. A better understanding of these factors is needed to fully understand the effects of forest management on herb layer communities in our eastern forests.

Recovery of Black Cohosh (Actaea racemosa L.) Following Experimental Harvests

Abstract Since European colonization and subsequent commercialization of Appalachian medicinal and edible plants, millions of kilograms of plant material have been extracted from our forests, with little effort to manage these species as natural resources. Roots and rhizomes of black cohosh, a native Appalachian forest herb, are extensively harvested for treatment of menopausal symptoms. As nearly all cohosh sold commercially is collected from natural populations, the potential for harvest impacts is considerable. To better understand wild-harvest impacts and the likelihood of post-harvest recovery, we studied the effects of 2 to 4 y of experimental harvest on natural black cohosh populations in the George Washington-Jefferson National Forest in southwest Virginia. After 2 to 3 y of intense harvest (66% plant removal), we found significant reductions in foliage area, stem production, and mean and maximum plant height. The effects of moderately intense harvest (33%) were less clear, producing growth measures between, yet not significantly different from, control (non-harvest) and intensively harvested plots. After three successive years of experimental harvest, harvest treatments were terminated to assess population regrowth. Populations experiencing intensive harvest showed no evidence of recovery after 1 y. Results suggest that black cohosh is highly responsive to harvest intensity and that low to moderate harvest intensities and/or longer recovery periods will be necessary for prolonged and sustainable harvests at our study site. While this study has increased our understanding of harvest impacts on black cohosh, continued assessment is needed to determine the sustainability of low to moderate harvest levels and minimum recovery periods necessary for population reestablishment.

Vegetation classification and invasive species distribution in natural areas of southern New England1

Abstract Invasive plant species pose serious threats to ecosystem function and community diversity, dominating many natural systems through suppression of, competition with, and replacement of native species. This study examines the distribution of invasive alien plant species relative to vegetation, site characteristics, and disturbance indicators in a relatively unfragmented matrix forest block (∼8,000 ha) in southern New England and provides the first quantitative description of the forested vegetation of this region. Within 139 - 10 × 10 m sample plots, percent ground coverage was estimated for each vascular plant species and basal area determined for all woody species reaching breast height (1.4 m). Site conditions, including topography, soil moisture and fertility, and evidence of current and historical site disturbance, were assessed to identify factors influencing invasive plant abundance. Fifteen relatively distinct vegetation types were identified using NMS ordination and cluster analysis, including wetland forest, terrestrial open woodland, and terrestrial closed canopy vegetation types. Of the 209 species occurring in sample plots, only 10 (4.8%) were invasive. Most abundant were Berberis thunbergii, Celastrus orbiculatus, and Rosa multiflora, each occurring in 5% or fewer plots. Moist sites were invaded most frequently, especially those with high species richness, lower canopy cover, and those dominated by Acer rubrum or Pinus strobus. Site disturbance, particularly roads, trails, and former land use, also was correlated with invasive abundance. The low frequency of invasive plant species in our study area offers an exceptional opportunity to identify ecosystem characteristics inhibitory to invasive plant species and the opportunity to preserve a series of relatively unfragmented and uninvaded natural habitats in this region.

Allelopathic influences of the invasive Ailanthus altissima on a native and a non-native herb 1,2

Abstract As a highly aggressive non-native invasive and an allelopathic species, Ailanthus altissima (tree of heaven) has the capacity to negatively affect native plant communities by suppressing resident species and altering competitive interactions. We examined effects of A. altissima on the establishment and growth of two herbaceous species common in invaded natural areas. Soil samples were collected from six replicate A. altissima-dominated stands and six control stands (no A. altissima present) in the Appalachian Ridge and Valley province of southwestern Virginia. Two target species, Verbesina occidentalis, native to the southeastern US, and Dipsacus fullonum, non-native and invasive throughout North America, were selected for their high germination success and contrasting native vs. invasive status. Germination and growth of target species were monitored in greenhouse flats for six weeks. We found severe reductions in all measured aspects of V. occidentalis when grown in Ailanthus versus control soils, including seed germination (P  =  0.002), seedling height (P  =  0.001), leaf production (P < 0.001), and root∶shoot ratio (P  =  0.008). In contrast, Dipsacus fullonum appeared resistant to allelopathic effects, with no significant differences in germination or growth relative to soil type (P > 0.25 for all measures). Our results support the role of allelopathy in the invasive success of A. altissima and further suggest that A. altissima may differentially affect resident native versus non-native species, potentially facilitating the spread of other non-natives in the invaded community.

Integrating Quantitative Skills in Introductory Ecology: Investigations of Wild Bird Feeding Preferences

ABSTRACT Undergraduate biology education is undergoing dramatic changes, emphasizing student training in the “tools and practices” of science, particularly quantitative and problem-solving skills. We redesigned a freshman ecology lab to emphasize the importance of scientific inquiry and quantitative reasoning in biology. This multi-week investigation uses observations of avian form and function and an extensive student-generated data set to introduce hypothesis testing, experimental design, and biological statistics. Research groups compare feeding preferences (location and seed selection) between selected species of wild birds, evaluating their findings quantitatively through descriptive statistics, graphing, and data analysis, and ecologically through comparisons of species biology and natural history.

Experimental harvest and regrowth in Appalachian black cohosh ( Actaea racemosa , Ranunculaceae) populations: Implications for sustainable management of a medicinal forest herb

Abstract A broad range of understory forest herbs are harvested for medicinal properties, particularly from species-rich forests of the central and southern Appalachian Mountains. Many species have been collected and used for centuries with little understanding of harvest impacts, some with resulting population declines. Species valued for belowground components, such as Actaea racemosa L. (black cohosh), appear particularly vulnerable to harvest impacts. Between 2005 and 2011, we conducted experimental harvests on natural A. racemosa populations in central Appalachian oak (Quercus L.) forests. Responses were examined during 3 yr of moderate (33% plant removal) and intensive (66% removal) harvest treatments and up to 3 yr of regrowth, to simulate local harvesting practices and assess recovery potential. After 2 yr of moderate harvests, aboveground growth remained similar to controls. However, after 3 yr of moderate harvests or 2 yr of intensive harvests, significant declines were evident. After our third harvest year, leaf area and stem density were 65–80% lower in moderate harvest plots and 80–90% lower in intensive harvest plots, compared with controls. These differences persisted for at least 2 yr after harvests treatments ended. Curve-fitting models suggested recovery of leaf area and mean plant height to preharvest levels after 4–7 yr without further plant removal. In contrast, stem density showed little to no increase during our study period, and model projections suggested declines, rather than recovery. Thus, although individual growth metrics suggested that limited harvesting may be sustainable, results for stem density indicated little new recruitment into the population and concern for long-term population persistence. Forest herbs harvested for belowground components create particular challenges for sustainable management. Our concerns for A. racemosa are applicable to other economically important forest perennials in our region and worldwide and emphasize the need for continued study and monitoring to maintain viable populations and associated natural systems.