Katherine J. Elliott

Long-term changes in forest composition and diversity following early logging (1919–1923) and the decline of American chestnut (Castanea dentata)

Chestnut blight fungus (Endothia parasitica [Murr.] P.J. And. & H.W. And.)) is a classic example of an invasive species, which severely damaged populations of its host, Castanea dentata, and had widespread and long-term impacts on eastern North American forests. Concurrently, forests were further disturbed by lumbering, which was common across the region from the mid 1800s to the early 1900s. In 1926, local infestations of chestnut blight were reported in the Coweeta Basin, Southern Appalachian Mountains of North Carolina. We used permanent plot inventories of the Basin (first sampled in 1934 and twice afterward in 1969–72 and 1988–93) to describe the distribution of species along a complex environmental gradient. Specifically, we asked: How does vegetation change over approximately 60xa0years following logging and the demise of C. dentata? Does the association between vegetation and environment determine the pattern of species distributions through time? Which species replaced C. dentata across this complex environmental gradient? We used nonmetric multidimensional scaling ordination and multiresponse permutation procedure for the analyses of the inventory periods. In 1934, C. dentata was the most important species in the Coweeta Basin. It was present in 98% of the plots and contributed 22% of the total density and 36% of the total basal area. Diversity increased significantly over time and was attributed to an increase in evenness of species distribution. The canopy dominant, C. dentata, was replaced by more than one species across the environmental gradient. Importance values of Quercus prinus, Acer rubrum, Cornus florida, Tsuga canadensis, and Oxydendrum arboreum increased by 2–5% across the basin following the decline of C. dentata. Tsuga canadensis increased in abundance and distribution, especially near streams across elevations. Liriodendron tulipifera replaced C. dentata in moist coves, which have low terrain shape and high organic matter content. In contrast, Q. prinus and A. rubrum were ubiquitous, much like C. dentata before the chestnut blight becoming dominant or co-dominant species across all environmental conditions.

Effects of understory prescribed burning on shortleaf pine ( Pinus echinata Mill.)/mixed-hardwood forests

Abstract Elliott, K. J. and J. M. Vose (Coweeta Hydrologic Laboratory, Southern Research Station, USDA Forest Service, Otto, NC 28763). Effects of prescribed burning on shortleaf pine (Pinus echinata Mill.)/mixed-hardwood forests. J. Torrey Bot. Soc. 132: 236–251. 2005.—We examined the effects of a single dormant season fire on overstory and understory species diversity and composition and tree seedling regeneration patterns the first and second years following a prescribed burn in the Conasauga River Watershed of southeastern Tennessee and northern Georgia. We asked: Can a single dormant season fire initiate a trajectory of overstory and understory species change consistent with restoring Pinus echinata/mixed-oak/bluestem (Andropogon gyrans and Schizachyrium scoparium)-grass community types? Six sub-watersheds (similar in vegetation, soil type, stream size, and disturbance history) were located within the Conasauga River Watershed; four of the sites were burned in March 2001, and two sites were designated as controls. Within each site, vegetation was measured in layers: the overstory layer (trees ≥ 5.0-cm DBH), the midstory layer (woody stems < 5.0-cm DBH and ≥ 0.5 m height), and the ground flora layer (woody stems < 0.5-m height and all herbaceous species). All plots were sampled before the prescribed burn (Sept. 2000) and after the burn in July of 2001 and 2002. Consistent with the goals of the land managers, all the prescribed fires resulted in low-to-moderate intensity and low severity fires. However, we found no significant change in overstory, midstory, or ground flora species diversity after burning. We found no regeneration of P. echinata seedlings after the prescribed fire. Although fire reduced basal area of woody species in the midstory, prolific sprouting from hardwoods resulted in higher density of fire-sensitive hardwoods such as Acer rubrum, Oxydendrum arboretum, and Nyssa sylvatica. Density of Pinus strobus, an undesirable species, was reduced by 20% and its basal area was reduced by 50% after the burn. Overstory mortality occurred in small size class hardwoods as a result of the fire, but most of the mortality occurred in P. echinata and P. virginiana Miller due to infestation with pine bark beetles. The prescribed fires were not of sufficient intensity to: reduce overstory basal area, prepare a seedbed for successful pine germination, affect diversity of any of the vegetation layers, or promote A. gyrans and S. scoparium recruitment. Thus, additional fire treatments or a combination of fire and thinning treatments will be necessary to restore these ecosystems to P. echinata/mixed-oak/bluestem grass community types.

Effects of competition from young northern hardwoods on red pine seedling growth, nutrient use efficiency, and leaf morphology

Abstract The effects of competition from three northern hardwood tree species on red pine ( Pinus resinosa Ait.) seedlings were examined on two clear-cut sites in western Maine. We examined how planted red pine seedlings altered their nutrient use efficiency and shoot morphology under changing environmental conditions and how these changes related to their ability to tolerate competition. A three-factor experimental design was used to determined the effects of species of competitors and their abundance as well as fertilization on red pine seedling growth, nutrient use efficiency, and leaf morphology. The competitors were striped maple ( Acer pensylvanicum L.), red maple ( Acer rubrum L.), and pin cherry ( Prunus pensylvanica L.) established at two densities (high and zero) with two levels of fertilization (0 and 224 g m −2 of 10-10-10 NPK commercial fertilizer). Nitrogen and phosphorus use efficiencies were calculated as total aboveground biomass divided by total nutrient content. Specific leaf area (cm 2 g −1 ), leaf area ratio (cm 2 g −1 ), and total leaf area (cm 2 ) were measured for all red pine seedlings. Plots were harvested at two time periods, when pine seedlings were 2 years old (1989) and 3 years old (1990). Total biomass, annual production, and leaf area index (m 2 leaf area m −2 ground surface area) were calculated for competitors on each plot. Red pine seedlings had higher specific leaf area, leaf area ratio, and nitrogen use efficiency on competitor plots than on plots free of competition, suggesting a phenotypic response to resource depletion of light and nutrients by competitors. Fertilization decreased growth of red pine seedlings and decreased nitrogen use efficiency. Red pine total leaf area and biomass were lower on the competitor plots. Higher competitor biomass, leaf area index, and nutrient uptake explained the lower growth of red pine seedlings on competition plots. Pin cherry was the most significant competitor eith striped maple being intermediate; red maple had the least effect on pine seedling growth. The results of this study indicate that the growth of red pine seedlings was governed by the availability of resources as influenced by the competitor species, the efficiency of nutrient use, and the ability of red pine to adjust its growth pattern in response to resource availability.

Effects of prescribed fire in mixed oak forests of the southern Appalachians: forest floor, soil, and soil solution nitrogen responses

Abstract We examined nutrient cycling responses to prescribed fire on three sub-mesic, mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each study site was located within a sub-watershed that drained a first order stream. Our objective was to quantify the effects of prescribed burning on forest floor mass, nitrogen and carbon pools; and soil and soil water available nitrogen. Each site included a burned and unburned control area; both burned and control areas were sampled before and after burning. Within each plot, we sampled forest floor mass, carbon and nitrogen, soil and soil solution nitrate (NO3-N) and ammonium (NH4-N) concentrations before and after the prescribed burns. All prescribed fires were conducted in the dormant season and were low to moderate intensity. All sites lost a significant amount of forest floor mass due to burning; 82 to 91% of the Oi layer and 26 to 46% of the Oe + Oa layer. Soil NH4-N concentrations increased in surface soils (0–5 cm) only, immediately after burning, but return to pre-burn levels by mid-summer. Burning had no measurable effect on soil solution inorganic nitrogen concentrations. Low levels of solution NO3-N and NH4-N after burning and no change in stream NO3-N concentrations indicated that no inorganic nitrogen was lost from these sites.

Functional Role of the Herbaceous Layer in Eastern Deciduous Forest Ecosystems

The importance of the herbaceous layer in regulating ecosystem processes in deciduous forests is generally unknown. We use a manipulative study in a rich, mesophytic cove forest in the southern Appalachians to test the following hypotheses: (i) the herbaceous functional group (HFG) in mesophytic coves accelerates carbon and nutrient cycling, (ii) high litter quality input and rapid nutrient turnover associated with HFG will have a positive effect on overstory tree growth, and (iii) the HFG regulates tree regeneration with negative effects on seedling establishment due to competition for resources. We established treatment plots in a mesic, cove-hardwoods forest and removed the herbaceous flora (HR, removed twice per year) or added herbaceous organic material (OMA, once per year) for comparison to a no removal (NR) reference for a total of 14xa0years. The OMA treatment stimulated soil N-mineralization and increased litterfall mass and N content. OMA N-mineralization rates were more than two times greater than both the NR and HR treatments; however, we did not detect significant differences in soil CO2 efflux among treatments. Higher overstory litterfall mass and N in the OMA treatment plots indicated that overstory trees were benefiting from the enhanced soil N-mineralization. Higher overstory leaf mass and N suggests an important linkage between HR and aboveground net primary production even though this did not translate into greater tree basal area increment. We found an increase in regeneration of all tree species with HFG removal, and the response was particularly evident for Acer rubrum seedlings.

Equations for Estimating Biomass of Herbaceous and Woody Vegetation in Early-Successional Southern Appalachian Pine-Hardwood Forests

Allometric equations were developed to predict aboveground dry weight of herbaceous and woody species on prescribe-burned sites in the Southern Appalachians. Best-fit least-square regression models were developed using diameter, height, or both, as the independent variables and dry weight as the dependent variable. Coefficients of determination for the selected total biomass models ranged from 0.620 to 0.992 for herbaceous species and from 0.698 to 0.999 for the wood species. Equations for foliage biomass generally had lower coefficients of determination than did equations for either stem or total biomass of woody species.

Age and distribution of an evergreen clonal shrub in the Coweeta Basin: Rhododendron maximum L.1

Abstract Rhododendron maximum L. is an evergreen, clonal shrub that forms a dominant sub-canopy layer and is a key species in southern Appalachian forests. We investigated the age and distribution of R. maximum across the Coweeta Basin, a 1626 ha watershed in western North Carolina. We selected 16 perennial, second-order streams and used a Global Positioning System to establish site boundaries and map the coverage of R. maximum across the hillslopes from stream to ridge. In each site, three transects from stream edge to the ridge were used to measure diameters of overstory trees (≥ 2.5 cm dbh), tree saplings (< 2.5 cm dbh) and shrubs including R. maximum stems. Along each transect, we cut cross-sections of R. maximum ramets and extracted increment cores from nearest neighbor trees to determine ages. The 16 sites ranged in size from 0.3 to 1.9 ha depending on the distance from stream to ridge. Rhododendron maximum cover ranged from 25 to 100% and ages ranged from 6 to 120 years. Rhododendron maximum establishment year showed a skewed unimodal distribution with the peak establishment occurring between 1928 and 1940. Although the R. maximum age and distance-from-stream relationship was statistically significant, the relationship was not meaningful as distance-from-stream only explained 2.6% of the variation in R. maximum age (r2 u200a=u200a 0.026, P u200a=u200a 0.0003, n u200a=u200a 487). Distance from stream only explained 4.2% of the variation in overstory tree age (r2 u200a=u200a 0.042, P u200a=u200a 0.0015, nu200a=u200a237). It appears that R. maximum has not expanded upslope over the last 100 years; rather the ranges in sizes and ages suggest that ramets are recruiting under established R. maximum canopies particularly in the wetter, near stream locations.

Short-term effects of prescribed fire on mixed oak forests in the southern Appalachians: vegetation response

Abstract We examined vegetation responses to prescribed fire on three mixed-oak sites located in the Blue Ridge Physiographic province of the southern Appalachian Mountains: Alarka Laurel Branch (AL), Robin Branch (RB), and Roach Mill Branch (RM). Each of the study sites was within a sub-watershed that drained a first order stream. Our objectives were to: 1) evaluate overstory mortality following prescribed fire treatments; and 2) assess changes in composition, abundance, and diversity of overstory (stems ≥ 5.0 cm dbh), understory (stems < 5.0 cm dbh, ≥ 0.5 m height), and herbaceous layer (woody stems < 0.5 m height and all herbaceous plants) vegetation in mixed-oak ecosystems. Each site included a burned and unburned area (control). Before the prescribed fire treatments were applied, we established permanent plots (10 × 20 m) in the prescribed burn areas (12 plots in AL, 12 plots in RB, and 10 plots in RM) and adjacent unburned areas (5 plots in AL, 6 plots in RB, and 4 plots in RM), for a total of 49 plots. Within the plots, we sampled vegetation before and after the prescribed burns. All of the prescribed fires were low to moderate intensity; i.e., they had moderate flame temperatures and low flame heights. After the prescribed fires, overstory mortality was low for all sites, and there were no significant differences between mortality in burned areas and that in unburned areas. Understory density was lower on the burned than the unburned plots the first (t u200a=u200a −5.26, P < 0.0001) and second (t u200a=u200a −3.85, P u200a=u200a 0.0020) growing seasons after burning. There was either an increase (AL, RB) or no change (RM) in herbaceous layer cover depending on the site and no significant change in species diversity after burning for any site. Thus, we found no negative effects of prescribed fire on herbaceous flora.

Disturbance history and stand dynamics in secondary and old-growth forests of the Southern Appalachian Mountains, USA

Abstract Understanding the patterns of past disturbance allows further insight into the complex composition, structure, and function of current and future forests, which is increasingly important in a world where disturbance characteristics are changing. Our objectives were to define disturbance causes, rates (percent disturbance per decade), magnitudes and frequency (time since last disturbance) for both secondary and old-growth mixed-oak stands, and to determine if all mixed oak stands experience similar disturbance history. The study was located in two southern Appalachian forests in western North Carolina, USA: Coweeta Hydrologic Laboratory, a 2,185 ha experimental forest with some history of harvesting, and the Joyce Kilmer Wilderness, a 6,805 ha old-growth forest with no known harvesting. We used dendroecological techniques to evaluate the disturbance histories and create chronologies of these mixed-oak forests. Average decadal disturbance rates ranged from 4.3% to 13.8%, similar to rates common in eastern temperate forests (5% to 20%). The decades of peak recruitment common to several stands were the 1840s, which coincides with the historical accounts of a hurricane; the 1900s through the 1940s, which coincide with logging and elimination of Castanea dentata (Marshall) Borkh. by chestnut blight; and the 1960s, which coincides with drought and an elm spanworm infestation. The large peaks of disturbance were often synchronous and widespread, affecting stands across both Coweeta and Joyce Kilmer. However, there were also scattered pulses of disturbance unique to single stands, suggesting that localized events also played a role in the disturbance dynamics. Periods of constant low rates of disturbance present in all stands also indicate the importance of small canopy gaps in these forests. We found that stands similar in disturbance regimes were also similar in species composition. Results from our study provide information on how past disturbances, both regional and local events, have shaped the current forest. This understanding could help inform models to better predict how forests might respond to future climate (e.g., rising temperatures and increasing precipitation variability) and disturbance patterns (e.g., more frequent and severe events).