The Regeneration of oak (Quercus spp.) on highly productive sites of the east Gulf Coastal Plain, Tennessee : a post-harvest approach

Oak (Quercus spp.) regeneration success historically can be described as highly variable, especially within highly productive systems. Research has shown that establishing large advance oak reproduction, prior to overstory removal, is necessary to maintain oak populations in future stands. However, experience indicates that forest landowners are typically unwilling to wait the necessary time to develop natural advance oak regeneration, instead allowing short-term economics to dictate harvest times. The use of artificial oak reproduction is one alternative to maintain oak as an important component of future stands. However, to date the success of artificial oak regeneration has also been highly variable. In developing an improved understanding and enhanced methods of artificial oak regeneration we examined the growth of outplanted high-quality, genetically improved, 1-0 northern red oak (Quercus rubra L.) seedlings and the effects of competing herbaceous vegetation after four overstory treatments (no-cut, high-grade, commercial clear-cut, two-age) on the Ames Plantation in west Tennessee. Sixty seedlings from two known and proven genetic families were outplanted within each of twelve, two-acre treatment units, resulting in three replicates of the four treatments. Initial height, root-collar diameter (RCD) and number of first-order lateral roots (FOLR) were recorded for each seedling. Outplantings were monitored monthly during the growing season and after all seedlings entered dormancy. The greatest first-year height growth (8.80 cm) was recorded for the no-cut treatment. However, all new growth was etiolated and high levels (33 percent) of mortality were recorded. Height growth among the 3 overstory harvest treatments was similar, but less than the no-cut (control) treatment. However, mortality was much less (5 percent). No mortality was observed within the commercial clearcut treatment. White-tail deer (Odocoileus virginianus) herbivory occurred in the early growing season only and significantly influenced first-year seedling growth. Results from logistic regression analysis indicated that the initial height of the seedling at time of planting was related to herbivory of the terminal shoot. Linear regression results suggested that competition from an exotic-invasive grass, Microstegium vimineum, was also impeding seedling growth. This study indicates that light availability, seedling quality, herbaceous competition along with browse pressure are important factors contributing to first-year seedling development. While results from this study appear positive, only first year growth has been observed and reported. As seedling development continues, further examination and research will prove informative. Differences between treatments, genetic stock and seedling quality may become more apparent as development continues

Shifts in dominant tree mycorrhizal associations in response to anthropogenic impacts

Plant-fungal symbioses play critical roles in vegetation dynamics and nutrient cycling, modulating the impacts of global changes on ecosystem functioning. Here, we used forest inventory data consisting of more than 3 million trees to develop a spatially resolved “mycorrhizal tree map” of the contiguous United States. We show that abundances of the two dominant mycorrhizal tree groups—arbuscular mycorrhizal (AM) and ectomycorrhizal trees—are associated primarily with climate. Further, we show that anthropogenic influences, primarily nitrogen (N) deposition and fire suppression, in concert with climate change, have increased AM tree dominance during the past three decades in the eastern United States. Given that most AM-dominated forests in this region are underlain by soils with high N availability, our results suggest that the increasing abundance of AM trees has the potential to induce nutrient acceleration, with critical consequences for forest productivity, ecosystem carbon and nutrient retention, and feedbacks to climate change

Biological invasion hotspots: a trait-based perspective reveals new sub-continental patterns

Invader traits (including plant growth form) may play an important, and perhaps overlooked, role in determining macroscale patterns of biological invasions and therefore warrant greater consideration in future investigations aimed at understanding these patterns. To assess this need, we used empirical data from a national-level survey of forest in the contiguous 48 states of the USA to identify geographic hotspots of forest plant invasion for three distinct invasion characteristics: invasive species richness, trait richness (defined as the number of the five following plant growth forms represented by the invasive plants present at a given location: forbs, grasses, shrubs, trees, and vines), and species richness within each growth form. Three key findings emerged. 1) Th e hotspots identified encompassed from 9 to 23% of the total area of our study region, thereby revealing many forests to be not only invaded, but highly invaded. 2) Substantial spatial disagreement among hotspots of invasive species richness, invasive trait richness, and species richness of invasive plants within each growth form revealed many locations to be hotspots for invader traits, or for particular growth forms of invasive plants, rather than for invasive plants in general. 3) Despite eastern forests exhibiting higher levels of plant invasion than western forests, species richness for invasive forbs and grasses in the west were respectively greater than and equivalent to levels found in the east. Contrasting patterns between eastern and western forests in the number of invasive species detected for each growth form combined with the spatial disagreement found among hotspot types suggests trait-based variability in invasion drivers. Our findings reveal invader traits to be an important contributor to macroscale invasion patterns

Interactions between white-tailed deer density and the composition of forest understories in the northern United States

Forest understories across the northern United States (US) are a complex of tree seedlings, endemic forbs, herbs, shrubs, and introduced plant species within a forest structure defined by tree and forest floor attributes. The substantial increase in white-tailed deer (Odocoileus virginianus Zimmerman) populations over the past decades has resulted in heavy browse pressure in many of these forests. To gain an objective assessment of the role of deer in forested ecosystems, a region-wide forest inventory across the northern US was examined in concert with white-tailed deer density information compiled at broad scales. Results indicate that deer density may be an additional driver of tree seedling abundance when analyzed along with stand attributes such as above ground biomass, relative density, and stand age. Tree seedling abundance generally decreased as deer density increased above 5.8 deer km2 for all forest type groups with the exception of oak-dominated forests. Findings indicate that introduced plant species, of which 393 were recorded in this study, increased in areas with higher deer density. The abundance of white-tailed deer is just as important as forest stand and site attributes in the development of forest understories. Given the complexity of forest and land use dynamics across the northern US, this study provides directions for future research as more data linking forest-dependent wildlife and forest dynamics at regional and national scales become available

Documentation of Significant Losses in Cornus florida L. Populations throughout the Appalachian Ecoregion

Over the last three decades the fungus Discula destructiva Redlin has severely impacted Cornus florida L. (flowering dogwood—hereafter “dogwood”) populations throughout its range. This study estimates historical and current dogwood populations (number of trees) across the Appalachian ecoregion. Objectives were to (1) quantify current dogwood populations in the Appalachian ecoregion, (2) quantify change over time in dogwood populations, and (3) identify trends in dogwood population shifts. Data from the USDA Forest Service Forest Inventory and Analysis (FIA) database were compiled from 41 FIA units in 13 states for county-level estimates of the total number of all live dogwood trees on timberland within the Appalachian ecoregion. Analysis of covariance, comparing historical and current county-level dogwood population estimates with average change in forest density as the covariate, was used to identify significant changes within FIA units. Losses ranging from 25 to 100 percent of the sample population (<.05) were observed in 33 of the 41 (80 percent) sampled FIA units. These results indicate that an important component of the eastern deciduous forest has experienced serious losses throughout the Appalachians and support localized empirical results and landscape-scale anecdotal evidence

Forest Ecology and Management Winter litter disturbance facilitates the spread of the nonnative

We investigated the impacts of winter litter disturbance on the spread of the nonnative invasive plant Microstegium vimineum (Trin.) A. Camus through experimental removals. We hypothesized that light penetration through the litter layer facilitates the spread of M. vimineum in forested systems. Our objective, therefore, was to quantify M. vimineum spread following litter removal. Linear spread and cover expansion from established M. vimineum patches was documented for one growing season under intact, undisturbed hardwood canopies within plots receiving one of two treatments. Treatments included litter removal (hereafter &quot;removal&quot;) and no litter removal (hereafter &quot;undisturbed). After one growing season, plots receiving the removal treatment experienced a spread of M. vimineum 4.5 times greater than plots receiving the undisturbed treatment (P &lt; 0.0001; 1.66, and 0.37 m expansion, respectively). Cover expansion (measured as percent cover in 0.5 m2 blocks at 0.5, 1, 1.5, and 2 m from established M. vimineum) averaged 16, 4, 0, and 0%, respectively, for the undisturbed treatment and 87, 64, 31, and 9%, respectively, for the removal treatment. Differences existed in cover expansion between treatments at the 0.5, 1, and 1.5 m distances (P &lt; 0.0001, P &lt; 0.001, and P = 0.01, respectively). Our results suggest that winter litter removal as a result of harvest activities, floodwater scour, or animal activities can drastically increase M. vimineum spread and may enhance potential ecological impacts of invasions by increasing M. vimineum percent cover. Previous studies have shown that M. vimineum responds to canopy removal with dramatic increases in biomass. This study suggests one mechanism facilitating rapid expansion of M. vimineum following site disturbance, and indicates that M. vimineum can experience rapid growth in response t

species density and diversity

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POPULATION DYNAMICS OF SUGAR MAPLE (ACER SACCHARUM MARSH.) AT THE SOUTHERN PORTION OF ITS RANGE: IMPLICATIONS FOR RANGE MIGRATION AND SUCCESSION by CRAIG TURBERVILLE

ABSTRACT Evidence for climate change driven range migration exists for a variety of tree species in eastern North America. Northward range migration for tree species in the region requires a decrease in population density near the southern range boundary coupled with an increase in population density at the northern range boundary. Sugar maple (Acer saccharum Marsh.) is one such species that has been projected by some biogeographic models to shift north in accord with climate. However, a widespread pattern of increased sugar maple density has been reported in the forest science literature from a variety of sites throughout the species&apos; range. This pattern is linked to a complex of interacting factors and has been hypothesized to represent a positive feedback that facilitates sugar maple regeneration. The primary goal of my study was to test which of these hypotheses (range migration or succession) was correct for the southern portion of the sugar maple range. I used Forest Inventory and Analysis program data to compare regionwide population dynamics for this species on a plot-by-plot basis. Changes in frequency, density, and dominance of sugar maple trees and seedlings were compared over multiple years for the states of Alabama, Kentucky, North Carolina, Tennessee, Virginia, and West Virginia. Plot data for all states were combined to determine changes in frequency, density, and dominance for the contiguous and non-contiguous regions of sugar maple&apos;s southern range portion. Results indicated increases in frequency, density, and dominance of sugar maple within its contiguous range coupled with decreases outside of the contiguous range. It is postulated based on these data that sugar maple&apos;s southern range boundary will remain stabilized while the northern boundary will continue to migrate with increasing global temperatures. iii ACKNOWLEDGEMENT

Biological invasion hotspots: a trait-based perspective reveals new sub-continental patterns

Invader traits (including plant growth form) may play an important, and perhaps overlooked, role in determining macroscale patterns of biological invasions and therefore warrant greater consideration in future investigations aimed at understanding these patterns. To assess this need, we used empirical data from a national-level survey of forest in the contiguous 48 states of the USA to identify geographic hotspots of forest plant invasion for three distinct invasion characteristics: invasive species richness, trait richness (defined as the number of the five following plant growth forms represented by the invasive plants present at a given location: forbs, grasses, shrubs, trees, and vines), and species richness within each growth form. Three key findings emerged. 1) Th e hotspots identified encompassed from 9 to 23% of the total area of our study region, thereby revealing many forests to be not only invaded, but highly invaded. 2) Substantial spatial disagreement among hotspots of invasive species richness, invasive trait richness, and species richness of invasive plants within each growth form revealed many locations to be hotspots for invader traits, or for particular growth forms of invasive plants, rather than for invasive plants in general. 3) Despite eastern forests exhibiting higher levels of plant invasion than western forests, species richness for invasive forbs and grasses in the west were respectively greater than and equivalent to levels found in the east. Contrasting patterns between eastern and western forests in the number of invasive species detected for each growth form combined with the spatial disagreement found among hotspot types suggests trait-based variability in invasion drivers. Our findings reveal invader traits to be an important contributor to macroscale invasion patterns