As invasive species are so prominent, the influence of wildfire intensity on fuel loading, invasives, species richness, diversity, and evenness were studied at Shenandoah National Park. Most National Parks identify invasive species as the biggest threat to their goal of maintaining native ecosystems. Eight study sites were stratified into three burn classes (high intensity, low intensity, and control), and three transects were randomly located so that nested plots and fuel transects were measured at a distance of 50 ft (15 m), 150 ft (45 m), and 250 ft (75 m) from a road or trail. Field sampling was conducted between May 15, 2004 and June 30, 2004. A subsample of these plots were used to determine specific gravity and quadratic mean diameter for each size class of fuel and to determine the bulk density of the duff and litter layers. High intensity wildfires initially reduced species diversity and evenness in the tree and herbaceous strata, but after 14 years tree species diversity and evenness returned to levels found in unburned areas, while herbaceous strata diversity was not associated with time since burn. Low intensity wildfires resulted in the greatest impacts in the shrub stratum. Presence of invasive species was associated with more even and diverse vegetation in all strata, perhaps because invasive species were relatively sparse. Fuel loadings were reduced initially by high intensity wildfires, but quickly returned to the same level as unburned areas. Although these initial findings indicate that invasive species will not persist after wildfire disturbance, continual monitoring by National Parks would be prudent. / Master of Science

Deadwood, characterized as both downed woody material (DWM) and standing and dead stems, i.e., snags, is a significant component of terrestrial forest ecosystems. Deadwood amount and structure may influence potential wildfire hazard by altering combustible DWM mass and creating fuel structures that increase fire intensity and spread. Deadwood is also critical to carbon storage and nutrient cycling and may vary based upon the size classes of individual deadwood pieces. Lastly, deadwood structural variability has been found to positively affect species richness in bees, salamanders, birds, and small mammals, such as shrews and woodland mice. However, in the Mid-Atlantic Piedmont, there are no accessible tools to rapidly estimate deadwood of long unmanaged second growth forests to help inform future management decisions. Management agencies within this region, such as the National Park Service, may benefit from a greater understanding of the potential factors that influence deadwood accumulation, retention, and decomposition. Therefore, a project was funded by the National Park Service to investigate deadwood dynamics at Prince William Forest Park (PRWI). From May to August 2023, a deadwood inventory was conducted using planar intercepts nested within fixed radius plots along the gradient of forest cover types, aspect, elevation, and soil orders found within PRWI. Forest cover type was significant in the generalized linear model for percent dead basal area, total DWM, fine woody material, litter, and duff mass. The Virginia pine (Pinus virginiana) forest cover type had the highest percent dead basal area and total DWM mass per hectare. Elevation, aspect, and soil order were not significantly related to percent dead basal area, total DWM, 1,000 hr, fine woody material, litter, and duff mass. Data from this study may serve as a baseline for similar second growth forests of the mid-Atlantic Piedmont. / Master of Science / Visitors to Prince William Forest Park (PRWI) in eastern Virginia have voiced concern about forest health within PRWI. The perception of a high number of standing and dead stems, or snags, and a high number of decaying logs, branches, and twigs on the ground has been a focal point for visitors. Some perceive the dead material on the ground as a potential source of fuel for wildfires. Others perceive the potential hazard to humans along trails and vistas if snags were to fall. However, snags and downed woody material, known as deadwood, are critical components of forests because they store carbon and nutrients long-term and may provide habitat and resources for many wildlife species. Many other heavily used recreation locations in the eastern US face similar deadwood and forest health challenges. To respond to this, we assessed deadwood in PRWI to determine how it may be distributed differently across the variety of landscape features that are present within the park. We found the amount of total downed and dead material on the forest floor increased as the percentage of trees that were standing and dead increased. The amount of dead material on the ground was greatest for the Virginia pine (Pinus virginiana) forest community type, whereby PRWI's stands have reached their life expectancy. Prince William Forest Park's managers and those elsewhere at similar locations throughout the eastern US may benefit from this information as they seek to evaluate the status of their resources, manage those resources, and provide thoughtful messaging to the public regarding the significance and maintenance of deadwood as an ecosystem resource.

Doctor of Philosophy / Department of Horticulture, Forestry, and Recreation Resources / Charles J. Barden / Recurrent, landscape-level fires played an integral part in the development and persistence of eastern oak (Quercus spp.) forests of the United States. These periodic surface fires helped secure a competitive position for oaks in the regeneration pool by maintaining a desirable species composition and forest structure. This historical fire regime was altered with the European settlement of North America, and fire suppression within forestlands became a standard practice since 1930s. With decades of fire suppression, mature oak-dominated woodlands have widely converted to shade-tolerant tree species. Prescribed fire has successfully been used to enhance oak regeneration in eastern forests. However, oak woodland restoration within the forest-prairie ecotone of the Central plains has not been systematically studied. Fuel beds under shade-tolerant species are often less conducive to fire. Therefore, monitoring fuel loading (FL) and its changes are essential to inform management decisions in an oak regeneration project. Rapid expansion of eastern redcedar (Juniperus virginiana/ERC) is another ecological issue faced by land managers throughout North America’s midcontinent forest-prairie ecotone. Hence, it is worthy to monitor ERC expansion and effects on deciduous forests, to inform oak ecosystem restoration interventions within this region. Therefore, the main objectives of this dissertation were three-fold: (1) understand the effects of prescribed burning and mechanical thinning to encourage oak regeneration; (2) investigate the initial effects of an oak regeneration effort with prescribed fire and mechanical thinning on FL; and (3) monitor the spatio-temporal dynamics of ERC expansion in the forest-prairie ecotone of Kansas, and understand its effects on deciduous forests. The first two studies were conducted on a 90-acre oak dominated woodland, north of Manhattan, Kansas. The experimental design was a 2 (burn) x 2 (thin) factorial in a repeated measures design. The design structure allowed four treatment combinations: burn only (B), thin only (T), burn and thin combined (BT), and a control (C). Burning and thinning treatments were administered in spring 2015. Changes in the FL estimates after the burn treatment revealed that the BT treatment combination consumed more fuel and burned more intensely compared to the B treatment. This observation was reflected in vegetation responses. The thinning reduced the canopy cover significantly, but under enhanced light environments, both oaks and competitive species thrived when no burn was incorporated. In contrast, burn treatments controlled the competitive vegetation. Hence, the most promising results were obtained when both fire and thinning were utilized. The remote sensing study documented the expansion of ERC in three areas of eastern Kansas over 30 years. The use of multi-seasonal layer-stacks with a Support Vector Machines (SVM) supervised classification was found to be the most effective approach to map ERC distribution. Total ERC cover increased by more than 6000 acres in all three study areas investigated in this study between 1986 and 2017. Much of the ERC expansion was into deciduous woodlands. Therefore, ERC control measures should be incorporated into oak woodland restoration efforts within the forest-prairie ecotone of Kansas.

Pinyon-juniper woodland encroachment threatens ecosystem function and diversity on sagebrush steppe. Decreased fire frequency likely favors proliferation of pinyon-juniper woodlands and subsequent decline in desirable understory species. Increased tree cover produces hazardous canopy fuel loads that contribute to severe crown fires and threaten life and property at the wildland-urban-interface. Mechanical mastication converts large canopy fuels into small woody debris, altering wildfire dynamics from a potential crown fire to a more controllable surface fire. We measured fuel loading and cover on untreated, masticated, and masticated + burned treatments on 30-m transects within 30 X 33-m subplots, representing 45 different sites throughout Utah. All variables were analyzed using mixed-model analysis of covariance with untreated or pretreatment tree cover as the covariate. Shredding trees reduced large-diameter fuels to primarily 10-hour fuels (6.4-25.4 mm diameter). Reduced fuel sizes, fuel redistribution, and fuelbed compactness resulting from mastication treatments can aid wildfire suppression. Masticated + burned treatments effectively reduced woody surface fuel loading to that of pretreatment conditions. Prescribed burning could be used outside the growing season in cool-weather, high-moisture conditions to remove surface fuels, mitigating lethal soil heating and plant mortality. Shrub loading was not adversely affected by mastication treatments, but was significantly reduced with masticated + burned treatments. Masticated and masticated + burned treatments significantly increased herbaceous fuel loading. Treating at lower tree cover values reduced fuel buildup, and provided more opportunity for a positive herbaceous response. Fuel loading estimates measured in this study were provided to populate fire behavior models for mastication treatments on our study sites when such models become available.

Rosebay rhododendron (Rhododendron maximum L.) is an evergreen ericaceous shrub that plays a dynamic role in the southern Appalachian forests. Commonly located on mesic sites, this understory shrub forms dense thickets that greatly reduce the amount of light available to herbaceous and woody plants found on the forest floor. Past research has shown that silvicultural methods can be used to eradicate R. maximum, however it is unclear which of these methods is most efficient and what effects other than stem mortality may occur. In this study, treatments involving prescribed fire, mechanical cutting, and herbicide applications were applied to R. maximum dominated forests in southwestern Virginia to determine what effect seven different silvicultural treatments had on 1) controlling of R. maximum as a forest weed 2) fuel loading inside of a R. maximum thicket, and 3) canopy tree seedling regeneration. Mechanical cutting treatments were successful in reducing R. maximum basal area per acre; however stump sprouting and increased fuel loading occurred. Herbicide applications were successful in controlling only the smallest diameter class of R. maximum stems. Prescribed fire reduced litter layers and caused delayed mortality on R. maximum stems three years following treatment. Hemispherical photographs taken within each plot showed that silvicultural treatments that successfully increased the amount of light entering each plot were influential in seedling establishment three years following treatments. Results from this study can be used to further perfect silvicultural applications that alleviate R. maximum cover on the forest landscape. / Master of Science

Rosebay rhododendron (Rhododendron maximum L.) is an ericaceous shrub commonly found in riparian areas of the Appalachian Mountains. After more than a century of fire exclusion in the U.S., the distribution of R. maximum and its dominance of forest understories have increased. Rhododendron expansion has caused a decline in overstory regeneration and the potential for dangerous fuel conditions around suburban structures near the wildland-urban interface. The purpose of this study was to determine the effects of seven silvicultural treatments on both the fuel loading within an R. maximum thicket and the control of R. maximum as a forest weed. The final objective of the project was to determine the cost effectiveness of each implemented treatment. Due primarily to moisture conditions, a single prescribed burn was relatively ineffective in reducing fuel loading and causing R. maximum mortality. Mechanical cutting caused a drastic shift in the size-class distribution of R. maximum but resulted in heavy sprouting and increased fuel loading. Herbicide application did not reduce or increase fuel loading and was important in R. maximum control only when combined with other treatments. The prescribed burning treatment was the least expensive individual treatment while mechanical cutting was the most expensive. Combination treatments showed increased effectiveness in controlling R. maximum but were more expensive than the individual treatments. The results of the treatments from this study will be used over the long term to demonstrate to land managers the effects of vegetation control on rhododendron. / Master of Science