University of Alabama Repository :: Browsing by Author "Schweitzer, Callie J."

Browsing by Author "Schweitzer, Callie J."

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Effects of an intermediate-scale wind event on forest composition, structure, and structural complexity
(University of Alabama Libraries, 2016) Cox, Lauren Elizabeth; Hart, Justin L.; University of Alabama Tuscaloosa
Forest disturbances alter environmental conditions, influence species composition and stand structure, and affect successional and developmental pathways. Natural disturbances differ in magnitude, severity, and return interval and range from frequent, gap-scale disturbances, to infrequent stand-replacing events. Disturbances at the gap and intermediate scale increase structural complexity and intra-stand heterogeneity. On 20 April 2011 in Lawrence County, AL, an EF1 tornado tracked 5 km, leaving a patchwork mosaic of disturbed areas. To analyze the intra-stand spatial patterns of tree morality and biological legacies after an intermediate-scale wind disturbance, I established a 100 × 200 m (2 ha) rectangular plot perpendicular to the path of the storm within an affected Quercus alba stand. Based on the basal area removed by the wind event, I divided the plot into disturbance classes (minimal, light, and moderate) to compare compositional and structural attributes across areas of increasing disturbance severity. I analyzed species- and size-specific mortality trends within each disturbance class. In addition, I quantified the structural complexity of each disturbance class and described the effect of the intermediate-scale disturbance on stand development. Composition was not substantially affected by the disturbance, but large stems were disproportionately removed by the storm. Structural complexity increased as a result of the wind event. However, the spatial distribution of stems was more uniform after the disturbance. The intermediate-scale wind event altered the stand size class from a mature stand to a mature–sapling mosaic stand. This size class characterizes a stand in the mixed stage of development. Results from this thesis contribute to the understanding of the compositional and structural attributes of upland Quercus stands after an intermediate-scale wind event. Quantitative descriptions of this stand may be used as references to inform silvicultural systems intended to enhance structural complexity and minimize the disparity between natural and managed stands.
The effects of intermediate-scale wind disturbance on forest composition, structure, and succession with implications for management
(University of Alabama Libraries, 2014) Cowden, Merrit; Hart, Justin L.; University of Alabama Tuscaloosa
Forest disturbances are discrete events in space and time that disrupt the biophysical environment and impart lasting legacies on forest composition, structure, and stand development. Intermediate-scale disturbances may promote stand heterogeneity, including uneven-aged structure, and their effects can range in size and distribution from small, patchy gaps to the removal of large portions of overstory vegetation. These events are often classified along gradients of intensity, which in this study were defined using post-tornado aerial photographs and visual assessments in the field. The specific objectives of this study, which took place two growing seasons after an EF1 tornado, were to quantify and compare canopy structure, understory light regimes, woody species composition, and species diversity along a gradient of canopy disturbance and to analyze the influence of intermediate-scale disturbance on the successional trajectory of an upland hardwood forest. We found no significant differences in tree layer Shannon diversity among the control (no storm damage), moderately, or severely disturbed plots. We found significant differences (P < 0.01) in percent of intercepted PAR between the control and severe classes and between moderate and severe classes. This disturbance acted primarily as a release mechanism for advanced regeneration and stems in the midstory. Our results can be used to refine silvicultural prescriptions that attempt to minimize the disparity between managed and unmanaged stands and to promote intra-stand heterogeneity.
Effects of thinning and burning on ground flora in mixed pinus-hardwood stands
(University of Alabama Libraries, 2018) Barefoot, Carson Reid; Hart, Justin L.; University of Alabama Tuscaloosa
Commercial thinning and prescribed fire are tools used to accomplish forest management objectives such as increased timber revenue, fuel reductions, and increased biodiversity. Silvicultural treatments can alter forest structure and nutrient flow to increase resiliency by promoting regeneration of native species, especially in the ground layer, where the majority of plant diversity is stored. Management regimes that optimize ground layer attributes in mixed Pinus-hardwood stands following timber monoculture are less understood. I examined the effects of thinning without fire and thinning with different fire frequencies to identify changes in community structure and species composition with a focus on taxonomic richness, evenness, diversity, and percent cover of ground flora in Pinus-hardwood stands on the Cumberland Plateau in northern Alabama. Overstory (live woody individuals ≥ 5 cm dbh; diameter at breast height, 1.37 m above the root collar) basal area and density decreased with increased management intensity. Sapling (live woody individuals < 5 cm dbh and > 1 m in height) density substantially increased with increased management intensity in the second growing season post-fire. Sapling density did not negatively affect light reaching the ground layer, as light availability increased with management intensity. Ground flora richness, diversity, evenness and cover were greatest in stands that were thinned, and then burned every three years, negatively correlated with litter depth and positively correlated with exposed mineral soil based on a non-metric multidimensional scaling (NMS) solution. Ground flora diversity was greater in thinned stands with fire compared to stands that were thinned and never burned, emphasizing the need of the combination of thinning and burning in these systems for native biodiversity conservation. Forest managers who wish to promote biodiversity may consider frequent burning to promote ground flora richness, diversity, and cover.
FIRE IN EASTERN NORTH AMERICAN OAK ECOSYSTEMS: FILLING THE GAPS
(Springer, 2016) Varner, J. Morgan; Arthur, Mary A.; Clark, Stacy L.; Dey, Daniel C.; Hart, Justin L.; Schweitzer, Callie J.; Virginia Polytechnic Institute & State University; University of Kentucky; United States Department of Agriculture (USDA); United States Forest Service; University of Alabama Tuscaloosa
This special issue of Fire Ecology is focused on the fire ecology of eastern USA oak (Quercus L.) forests, woodlands, and savannas. The papers were presented as part of the Fifth Fire in Eastern Oak Forests Conference in Tuscaloosa, Alabama, USA, in 2015. The topic of fire in Eastern oak ecosystems is one that has received insufficient interest from the broader fire ecology community. Specific papers in this issue address the historical role of fire in the region, the response and adaptations of plant and animal species to fire and fuels treatments, and the future of these important ecosystems under a future of global change. We hope that this issue provokes future research on the past, present, and future of fire in eastern North American oak ecosystems.
Gap dynamics in mature, mesic quercus stands on the Cumberland Plateau, Alabama
(University of Alabama Libraries, 2011) Richards, Jacob Douglas; Hart, Justin L.; University of Alabama Tuscaloosa
Gap scale disturbances are important processes in forest stand development in the southern Appalachian Highlands. Canopy gaps within secondary forest throughout the southern Appalachian Highlands have been documented as critical mechanisms in canopy tree replacement and stand regeneration. I quantified gap characteristics, gap formation and closure mechanisms, and intra-gap tree and sapling distribution patterns for 60 canopy gaps in secondary mesic, Quercus stands on the Cumberland Plateau in north Alabama. Snag-formed gaps were the most common. We documented the influence gap formation mechanisms had on gap size, which ultimately contributed to gap closure. The projected closure mechanism was significantly related to the area of the gap whereby smaller gaps usually closed via lateral crown expansion and larger gaps typically closed by subcanopy recruitment. Based on the results, I hypothesized that gaps exceeding 200 m2 had higher probabilities of closing via subcanopy recruitment rather than lateral crown expansion. Several gaps projected to close by subcanopy recruitment were doing so through Quercus capture. However, Quercus capture of gaps was restricted to upper slope position with low understory competition from shade tolerant species and adequate light levels based on the ratio of gap diameter to peripheral canopy height. Liriodendron tulipifera was projected to capture seven gaps, all of which were smaller than the hypothesized minimum gap area for capture by the species. The majority of gaps were projected to close via lateral crown expansion. Based on the composition of saplings and trees in gap environments, I project the forest to transition from a Quercus dominated system to one with much stronger Fagus grandifolia and Acer saccharum components. My study fills a void in the literature on the role of canopy gaps in secondary, mesic Quercus stands that established just prior to 1900 for the southern Appalachian Highlands region.
Influence of gap-scale disturbance on development and succession in a Cumberland plateau quercus-pinus forest
(University of Alabama Libraries, 2014) Weber, Tom; Hart, Justin L.; University of Alabama Tuscaloosa
Quercus-Pinus forests of the eastern US span > 13 million ha. It is important for managers to understand the methods used to sustain Pinus spp. in these mixtures or progress toward a more natural mixture of hardwoods. Understanding developmental and successional patterns in this forest type can help assess the need to actively manage natural processes, or to inform silvicultural prescriptions to achieve management goals. Little research has been conducted on localized disturbance processes in Quercus-Pinus forests. I examined 60 canopy gaps in a Quercus-Pinus forest on the Cumberland Plateau in Alabama to analyze their influence on development and succession. Most canopy gaps (53%) were single treefall events caused by snapped stems. The majority of gap maker trees (56%) were Pinus individuals while 44% were hardwoods. Most gaps (58%) closed by height growth of subcanopy trees. The majority of these gap filler taxa were hardwoods: Quercus (39%), Carya (14%), Pinus (14%), Nyssa Sylvatica (12%), and other (15%). Significant positive relationships existed between gap size and sapling diversity (r² = 0.15, P = 0.002), tree diversity (r² = 0.21, P = 0.0002), and total stem diversity (r² = 0.29, P < 0.0001). The number of Pinus gap makers and the number of gaps projected to fill by subcanopy recruitment of hardwoods indicated the forest was in the latter stages of a composition shift from Pinus to a much stronger Quercus component. To maintain a Pinus component, managers would likely need to create canopy gaps larger than those documented here and remove hardwood competition from the regeneration layer.
Influence of intermediate-scale wind disturbance on development and succession in quercus stands on the Cumberland Plateau
(University of Alabama Libraries, 2014) White, Stephen Daniel; Hart, Justin L.; University of Alabama Tuscaloosa
Natural disturbances play important roles in shaping the structure and composition of all forest ecosystems and can be used to guide silvicultural practices. Disturbance intensity is measured along a gradient ranging from highly localized, gap-scale events to stand-replacing events. High wind storms such as downbursts, derechos, and low intensity tornadoes typically fall in the center of this gradient and result in intermediate-scale disturbances, removing 30-60% of basal area. Despite their frequency and widespread occurrence, little is known about how intermediate-scale disturbances drive stand development. On 20 April 2011, the Sipsey Wilderness Area in Alabama was affected by an EF1 tornado with accompanying straight-line winds. Stands were sampled in a stratified subjective sampling design to evaluate the effects of intermediate-scale wind disturbance on the development of Quercus stands in regard to structure and recruitment. My specific objectives were to: 1) quantify damage severity in basal area reduction and percent canopy loss of this particular disturbance along a gradient of wind disturbance, 2) detect structural acceleration or retrogression of stand development caused by an intermediate-scale wind disturbance, and 3) elucidate compositional acceleration or retrogression for an intermediate-scale wind disturbance. I established 109 0.04 ha plots across a gradient of disturbance, classified as control (undamaged), light, and moderate to inventory the effect of wind damage on development and succession. Basal area was reduced from 25.5 m2 ha-1 to 24.0 m2 ha-1 and 15.5 m2 ha-1 (p < 0.001) for light and moderate damage, respectively. The percent of live and damaged trees for control, light, and moderate was 0.3%, 3.0%, and 10.7%, respectively. PAR was significantly increased within the moderately damaged areas (p < 0.001). Logistical regression showed an increasing probability of mortality during wind disturbance with increasing diameter. Based on my findings, this intermediate-scale disturbance increased intra-stand heterogeneity and accelerated succession, favoring shade-tolerant taxa established in the understory.
Patterns of competition and insolation along a canopy disturbance severity gradient: implications for the Quercus bottleneck
(University of Alabama Libraries, 2015) Keasberry, Amanda Marie; Hart, Justin L.; University of Alabama Tuscaloosa
Regeneration failure of Quercus has been widely reported throughout the Central Hardwood Forest of the eastern United States across all but the most xeric site types. Quercus seedlings are often abundant in upland hardwood stands, but typically fail to recruit to larger size classes (i.e. the Quercus bottleneck). The goal of my study was to investigate the competition with small-sized Quercus stems to elucidate what variables may cause resistance or facilitation of Quercus recruitment. I established a 2 ha plot in the Sipsey Wilderness, AL that was subdivided into 5 x 5 m quadrats to encompass the entire extent of damage caused by an EF1 tornado in 2011. The study area encompassed a range of damage (light, moderate, severe), starting from the center of the tornado tract and ending in an undamaged area (control). The canopy disturbance provided a range of light conditions in the understory (0.5–91.0% full sunlight). In each quadrat, the height of all small-sized Quercus stems (≥ 0.5 m in height to >5 cm DBH) were measured and recorded. The nearest neighbor was identified by species and measured for height and distance from the focal Quercus stem. Photosynthetically active radiation was quantified at 1.4 m above the forest floor. Quercus’ competition was largely interspecific and the majority of competitors were shade-tolerant species such as Acer saccharum and Ostrya virginiana. Competitive indices of Quercus’ primary competitors were significantly different (p < 0.01) revealing the relative competitive ability amongst species within the plot. Disturbance neighborhoods had no significant (p > 0.01) effect on the competitive ability of species. Spatial patterns of Quercus stems, their nearest neighbor, and percent full sunlight were analyzed at 5 x 5 m, 10 x 10 m, and 20 x 20 m. Analysis at a fine-scale resolution revealed spatial patterns which would otherwise not be apparent at coarser scales. Creative and flexible silvicultural techniques may need to be implemented at finer scales to optimize the recruitment of Quercus spp.
Temporal dynamics affecting ground flora recovery after fire in thinned pinus-quercus stands
(University of Alabama Libraries, 2018) Willson, Kevin; Hart, Justin L.; University of Alabama Tuscaloosa
The ground flora stratum affects stand structure, resource acquisition, nutrient cycling, and taxonomic richness in forest ecosystems. Disturbances, such as thinning and prescribed fire, alter understory growing conditions that generally increase ground flora cover and richness in stands across the U.S. However, few studies have quantified annual changes in ground flora after a prescribed fire in thinned stands to provide finer temporal resolution of ground flora recovery. I performed a space-for-time study that quantified changes in ground flora assemblages over three growing seasons post-fire in thinned and frequently burned Pinus-Quercus stands. My results corroborated trends from other forest types and regions that indicated greater ground flora richness and cover after thinning and burning compared to thin-only treatments. I also found that the stratum experienced relatively rapid succession between growing seasons. Forbs had annual reductions in cover and richness with increasingly difficult growing conditions after the first growing season, while woody plants and shrubs increased in richness over time. The transition from herbaceous to woody dominance in three years was indicative of changing competition dynamics that favored quick growth in the first growing season and long-term investment in vertical growth in the third growing season. Although beneficial for increased ground flora cover, forb taxonomic richness, and reduced fuel levels, the three-year fire return interval did not produce comparable Pinus and Quercus regeneration to overstory composition. Management of eastern U.S. Pinus-Quercus stands may need to account for potential mesophytic dominance in seedling and sapling size classes that occur in thinned and burned stands over time. If mesophytic dominance becomes an issue, managers could include growing season fires and a secondary thin to foster desired regeneration to recruit into the overstory, although general weather conditions during the growing season could make fires hard to routinely implement.
Vegetation-environment relationships and species assemblages in three vertical strata after an intermediate-scale wind disturbance in a quercus forest
(University of Alabama Libraries, 2015) Jackson, Charles A. T.; Hart, Justin L.; University of Alabama Tuscaloosa
Natural disturbance is a fundamental process that exerts a strong influence in shaping forest structure, composition, and function. Canopy disturbances are often classified based on spatial extent and severity along a gradient ranging from highly localized, gap-scale events to stand-replacing or catastrophic events. The overwhelming majority of research on wind disturbance and forest response has focused on events near the two endpoints (catastrophic and gap-scale) of the disturbance classification gradient. As such, a paucity of data is available on intermediate-scale disturbances. Furthering our understanding of these events provides information on natural processes that can be used to make informed management decisions. On 20 April 2011, an EF1 tornado coupled with straight line winds affected portions of the Sipsey Wilderness in Bankhead National Forest. I subjectively established 109, 0.04 ha plots in Quercus dominated stands adjacent to the track of the tornado three growing seasons post-disturbance to quantify damage and possible effects on species assemblages in three vertical strata. Non-metric multidimensional scaling (NMS), indicator species analysis (ISA), and multi-response permutation procedures (MRPP) were used to examine vegetation-environmental relationships in each vertical stratum by species using PC-ORD v. 5.31. Species appeared to be aligned most strongly along elevation and diversity gradients and the effects of the disturbance on seedling and sapling establishment was limited because of the well-developed mid-story layer. The overstory remained dominated by Quercus and Carya spp. However, the disturbance released the shade-tolerant stems present in the understory and mid-story, thereby accelerating succession

Browsing by Author "Schweitzer, Callie J."

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