David S. Buckley

Influence of litter removal and mineral soil disturbance on the spread of an invasive grass in a Central Hardwood forest

Soil and litter disturbances within Central Hardwood forests may facilitate exotic plant species invasion of interior forest areas. Microstegium vimineum is an annual exotic grass that has become common throughout the Southeastern United States. Three replicates of three different mineral soil and litter disturbance treatments, plus a control with no disturbance, were established on the leading edge of M. vimineum patches prior to seed fall. All patches were located in areas with similar forest canopy structure and slope in three Central Hardwood forest stands prior to seed fall. At the beginning of the following growing season, each individual M. vimineum seedling was mapped within the treatment plots. The mean number of M. vimineum individuals that established within each treatment did not differ significantly from the control. The distance at which 90% of the individuals had spread, and the overall mean distance spread were significantly farther for the litter removal treatment than the control. The farthest individual seedling from the boundary of existing patches in both the litter removal and the mineral soil disturbance and litter removal treatments were significantly farther than the control. The individuals that spread the farthest are of most concern due to the large number of viable seed that a single M. vimineum plant can produce. These results suggest that disturbance of the litter layer may increase the spread rate of M. vimineum and facilitate its invasion of new habitats, and that leaving litter layers intact may slow the spread of M. vimineum.

Competitive interaction between Microstegium vimineum and first-year seedlings of three central hardwoods1

Abstract We established an experiment designed to compare effects of Microstegium vimineum (Japanese stiltgrass) on seedlings of three native hardwood species to investigate the hypothesis that competitive effects of M. vimineum on juvenile trees will vary across different tree species. Growth and survival of Acer rubrum, Liriodendron tulipifera, and Quercus rubra first-year seedlings were compared in plots with and without M. vimineum in three planting beds under 50 percent shade. The tree species studied are abundant and of particular interest in the Central Hardwood Region. A. rubrum and L. tulipifera seedlings experienced reduced growth in several foliar characteristics in the presence of M. vimineum. Q. rubra did not exhibit any differences in foliar characteristics between plots with and without M. vimineum, however there was a reduction in Q. rubra stem weight as a result of the presence of M. vimineum. The differential responses of A. rubrum, L. tulipifera, and Q. rubra to the presence of M. vimineum observed in this study support the hypothesis that effects of this exotic species will vary across tree species. As a result of reductions in the growth of A. rubrum and L. tulipifera, the presence of M. vimineum in forest understories may reduce the rate at which seedlings of these species are recruited into larger size classes.

The effect of mercury on trees and their mycorrhizal fungi.

The Oak Ridge Reservation, established in 1942, was the designated site for the construction of the atomic bomb. During a 20-year period from 1944 to 1963 radioactive and toxic chemical pollutants, especially mercury compounds were released into the surrounding waterways. Tree diversity and mycorrhizal presence and abundance were analyzed in the mercury-contaminated floodplains of East Fork Poplar Creek Oak Ridge (EFPC) (Tennessee). A subsequent greenhouse study was conducted to assess the phytotoxic effects of different mercuric solutions on Platanus occidentalis (American Sycamore), inoculated with soils from EFPC. Total soil mercury in the field had no effect on tree diversity. Organic species of mercury proved to be more toxic than inorganic species of mercury and soil inoculants from EFPC had no protective effects against Hg toxicity in our greenhouse study. Comparison of the effects of mercury contamination in our field and greenhouse studies was difficult due to uncontrolled factors.

Recovery of Sasajiscymnus tsugae, released against hemlock woolly adelgid, Adelges tsugae, in the southern Appalachians

Abstract Eastern hemlock in the Great Smoky Mountains National Park is currently threatened by the hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae). As part of a management plan against this invasive insect pest, about 350,000 adults of the predatory beetle Sasajiscymnus tsugae (Sasaji and McClure) (Coleoptera: Coccinellidae) were released at ca. 150 sites in the Park from 2002 to 2007. Of these adult release sites, 33 were sampled in 2008 and 2009 using beat-sheet sampling for 4 man-hours. Sasajiscymnus tsugae adults (n=78) and/or larvae (n=145) were recovered from seven sites (21.2% of the release sites sampled). Recovery of S. tsugae was significantly associated with older release sites, with the most beetles recovered from 2002 release sites. These results indicate that S. tsugae may require more time (i.e., 5–7 years) than anticipated for population densities to reach readily detectable levels in some areas.

Vegetation and Avian Response to Oak Savanna Restoration in the Mid-South USA

Abstract Oak (Quercus spp.) savannas are among the most imperiled ecosystems in the United States. Consequently, associated vegetation and avian communities are also in decline. Furthermore, restoration of savanna communities may be an important strategy for conserving avian species that require early successional habitat, a type underrepresented on regional landscapes. Therefore, we evaluated savanna restoration on twelve sites in the Mid-South USA. Specifically, we examined grass, forb, legume, and woody understory cover, regeneration and sapling density, and breeding bird use of the sites following mechanical overstory thinning and dormant-season fire using a hierarchical linear model. Total grass cover was negatively related to canopy cover (P < 0.01) and total forb cover was negatively related to total basal area (P  =  0.04). Oak regeneration density was positively related to canopy cover (P < 0.01), while oak competitor regeneration density was positively related to percent slope (P  =  0.01) and s...

Influence of Microstegium vimineum Presence on Insect Abundance in Hardwood Forests

Abstract Microstegium vimineum (Japanese Stiltgrass) is an exotic, annual grass that has invaded hardwood forests throughout the Southeastern United States. Four forests, in four Tennessee counties, were selected, and insects and plant communities were sampled along transects with and without M. vimineum. Insects were sampled using a terrestrial vacuum sampler. Percent plant cover was measured using a point-intercept technique, and plant species richness and diversity were calculated. Of the 60 families collected, significantly more individuals in the families Acrididae, Cicadellidae, and Gryllidae, were collected in areas with M. vimineum, whereas areas without M. vimineum resulted in significantly more individuals in the families Blattellidae and Chrysomelidae. Herbaceous plant richness and diversity did not significantly differ between areas with and without M. vimineum. Areas without M. vimineum had significantly lower percent vegetation cover (30.41%) than areas with M. vimineum (91.48%). The overall herbaceous plant community diversity and structure may be more influential factors in the abundances of insect families in central hardwood forests than the invasion of M. vimineum.

Factors Affecting Establishment and Recovery of Sasajiscymnus tsugae (Coleoptera: Coccinellidae), an Introduced Predator of Hemlock Woolly Adelgid (Hemiptera: Adelgidae) on Eastern Hemlock (Pinales: Pinaceae)

ABSTRACT To reduce populations of hemlock woolly adelgid, Adelges tsugae Annand (Hemiptera: Adelgidae), >500,000 Sasajiscymnus tsugae (Sasaji and McClure) (Coleoptera: Coccinellidae) have been released in the Great Smoky Mountains National Park since 2002. To determine factors affecting establishment and recovery of these predatory beetles, 65 single release sites were sampled using beat sheets from 2008 to 2012. Several abiotic and biotic factors were evaluated for their association with establishment and recovery of S. tsugae. Information on predatory beetle releases (location, year of release, number released, and season of release), topographic features (elevation, slope, Beers transformed aspect, and topographic relative moisture index), and temperature data (minimum and maximum temperatures 1 d after release and average minimum and maximum temperatures 7 d after release) were obtained from Great Smoky Mountains National Park personnel. These factors were evaluated using stepwise logistic regression and Pearson correlation. S. tsugae was recovered from 13 sites 2 to 10 yr after release, and the greatest number was recovered from 2002 release sites. Regression indicated establishment and recovery was negatively associated with year of release and positively associated with the average maximum temperature 7 d after release and elevation (generally, recovery increased as temperatures increased). Several significant correlations were found between presence and number of S. tsugae and year of release, season of release, and temperature variables. These results indicate that releases of S. tsugae should be made in warmer (≈10–25°C) temperatures and monitored for at least 5 yr after releases to enhance establishment and recovery efforts.

THE INFLUENCE OF DIFFERENT GROUND COVER TREATMENTS ON THE GROWTH AND SURVIVAL OF TREE SEEDLINGS ON REMINED SITES IN EASTERN TENNESSEE 1

There is growing interest in the reforestation of surface mined lands for various land uses including forest products and wildlife habitat. These objectives can be met by planting native tree species and seeding a ground cover to control erosion. However, many ground covers compete aggressively with tree seedlings in this region, preventing establishment. A research project was designed with two main objectives; to investigate the competitive effects of different ground cover species on the growth and survival of tree seedlings, and to identify the relationship between the growth and function of tree seedlings and microsite variables. Five tree species, native to the eastern hardwood forest surrounding the mine site, were planted in 2005: yellow poplar (Liriodendron tulipifera L.), sugar maple (Acer saccharum Marsh.), northern red oak (Quercus rubra L.), eastern redbud (Cercis canadensis L.), and Virginia pine (Pinus virginiana Mill.). Five different ground cover treatments were applied to the planted area. Two mixes consisted of native warm season grasses (NWSG), two standard reclamation mixes, and one control. Growth and survival, seedling transpiration, soil respiration, and groundcover biomass were analyzed. At each seedling, light measurements and percent herbaceous cover based on the Braun-Blanquet scale were collected. Seedling survival was related to size at planting, and to the density of ground cover. Survival was highest in moderate amounts of cover, although root collar diameter growth decreased with increasing cover in redbud and pine. Tree seedling growth and survival tended to be greatest in the native warm season grass treatments.

EFFECTS OF SEEDLING SIZE AND GROUND COVER ON THE FIRST-YEAR SURVIVAL OF PLANTED PINE AND HARDWOODS OVER AN EXTREME DROUGHT

Poor growth and survival has been noted in tree seedlings planted into an existing ground cover. Such observations are ascribed to competition between root systems of ground cover and trees for water and nutrients. During drought, competition for water becomes intense and could result in mortality. Seedlings of shortleaf pine, green ash, northern red oak, and shagbark hickory were planted on twelve plots on a loosely graded ridge-top in eastern Tennessee that had been reclaimed and planted with native warm season grasses in 2006. Plots were planted in spring of 2007 with pine alone, hardwoods (ash, oak and hickory) alone, or alternating pine and hardwood seedlings. Planting was followed by an extreme and extended drought. In December of 2007, survival of shortleaf pine averaged 35%, while northern red oak averaged 95%, green ash 87%, and hickory 88%. Seedling size at time of planting was related to the probability of survival, with larger seedlings showing low mortality rates. Survival was greater on the northwestern facing slope, while seedlings on the southeastern slope had the greatest growth. Cover of native grasses at the time of planting ranged from 8 to 44%, but there was no clear relationship between ground cover density and seedling survival. Additional

EARLY TREE AND GROUND COVER ESTABLISHMENT AS AFFECTED BY SEEDING AND FERTILIZATION RATES IN TENNESSEE

Planted ground covers can compete strongly with planted tree seedlings, hindering reforestation efforts. Fertilization increases the growth of ground cover, but its effects on hardwood tree seedlings and competitive interactions between trees and ground cover species are unclear. A 3x3 factorial experiment with 3 levels of fertilizer application and 3 seeding rates was established in 2006 to test for differences in tree seedling growth and survival, and for differences in ground cover establishment and composition. The ground cover was applied by hydroseeding a mixture of native warm-season grasses, annual rye and Korean lespedeza, along with lime, mulch and tackifier. Bareroot, 1-0 tree seedlings of scarlet oak, white oak, black walnut and mockernut hickory, along with mockernut hickory seed, were planted on an 2.4 x 2.4m spacing. Tree growth and survival, and ground cover establishment have been monitored. Generally, seeding rate had little effect, while increased fertilization rate was associated with increased percent cover for legumes and non-leguminous forbs. However, there was high variability between blocks, with substantially greater ground cover on the block immediately below intact forest. At the highest seeding rate, fertilization significantly increased cover of clovers. First year survival of white and scarlet oak was greater than 90%. Survival of direct seeded and planted 1-0 mockernut hickory seedlings was similar after one year. Continued monitoring of longer term survival and growth of trees is planned. Additional