Tara L. Keyser

Effects of Prescribed Fire on the Buried Seed Bank in Mixed-Hardwood Forests of the Southern Appalachian Mountains

Abstract This study characterizes the seed bank prior to and immediately following dormant-season prescribed fire in mature, mixed-Quercus spp. (oak) forests in the southern Appalachian Mountains. Thirty samples from the litter/duff (LD) and the top 5 cm of the mineral soil (MS) were collected from five 5-ha burn units (6 plots per experimental unit) before and immediately after low-intensity prescribed fires, where maximum fire temperatures varied from <79 to 316 °C. A split-plot ANOVA and multi-response permutation procedures (MRBP) were utilized to assess the effects of burn treatment (pre- or post-fire) and seed bank layer (LD and MS) on the diversity and density of the buried seed bank. An average of 471 emergents/m2 was observed in the buried seed bank comprising 133 identifiable taxa. No differences in total seed-bank density, Shannon-Weiners diversity index (H′) or overall species composition between pre- and post-fire sampling or between the LD and MS layers were observed. Species richness (S) of the seed bank, however, was slightly greater pre-fire than post-fire, regardless of layer. Similarity, as defined by Sørensons index, of species common to the seed bank and aboveground forest understory was low, with a slight increase in Sørensons index observed during post-fire sampling of the seed bank and aboveground vegetation. Although we observed only negligible effects of a once-applied, low-intensity prescribed fire on the buried seed bank, the effects of a low-intensity prescribed fire management regime—one that involves repeated low intensity burns—on the buried seed bank are unknown and should be a focus of future studies across mixed-oak forests in the eastern US.

Temporal Patterns of Oak Mortality in a Southern Appalachian Forest (1991-2006).

ABSTRACT: The sustainability of eastern oak-dominated forests is threatened by high oak mortality rates and widespread oak regeneration failure, and presents a challenge to natural area managers. We tracked the rate and cause of mortality of 287 mature oak trees of five species for 15 years to determine the temporal patterns and sources of mortality. We observed a 15.3% total mortality rate during the study period. Mortality was due to oak decline (7.3% of trees) and high-intensity wind events (6.6% of trees). Decline-related mortality was gradual, averaging 0.5% annually. Windthrow was episodic, occurring during hurricane-related weather events in 1995 and 2004. Within species, total mortality was disproportionately high for scarlet oak (Quercus coccinea Muenchh) (41.2%) compared to other species in the red oak group (13.8% for northern red oak (Q. rubra L.); 12.5% for black oak (Q. velutina Lam.)) or the white oak group (10.4% for white oak (Q. alba L.); 5.7% for chestnut oak (Q. prinus L.)). Decline-related mortality was highest for scarlet oak (15.7%) followed by black oak (8.3%), white oak (7.5%), northern red oak (6.9%), and chestnut oak (2.3%). Within the red oak group, the average age of decline-affected and surviving trees did not differ, but average dbh of decline-affected trees was smaller. Decline-affected trees in the white oak group were on average older, but average dbh did not differ from surviving trees. Wind-related mortality also was higher for scarlet oak (21.6%) than for northern red oak (5.2%), black oak (4.2%), white oak (3.0%) or chestnut oak (2.3%). Windthrown red oaks were smaller than survivors, but windthrown trees in the white oak group did not differ in size from survivors. Average age did not differ between windthrown and surviving trees for either group. Oak mortality rates observed in this study, coupled with oak regeneration failure, could result in a substantial reduction in the proportion of mature canopy oaks and change the relative abundance of oak species in southern Appalachian forests over the long-term.

Short-term response of breeding birds to oak regeneration treatments in upland hardwood forest.

ABSTRACT: Population declines of several successional-scrub bird species are partly associated with decreased habitat availability as abandoned farmlands return to forest and recently harvested forests regrow. Restoration of mixed-oak (Quercus spp.) forest is also a concern because of widespread oak regeneration failure, especially on moist, productive sites where competition from faster-growing tree species is fierce following stand-replacing disturbances. Several silvicultural methods are proposed to promote oak regeneration but many are not experimentally tested, especially on productive sites. We surveyed birds in 19 stands to assess response to initial application of three proposed oak regeneration treatments on productive sites: prescribed burning (B); oak shelterwood by midstory herbicide (OSW); shelterwood harvests (SW); and controls (C), for one breeding season before, and two breeding seasons after, implementation. Relative density of successional-scrub species Indigo Buntings (Passerina cyanea), Eastern Towhees (Pipilo erythrophthalmus), and Chestnut-sided Warblers (Setophaga pensylvanica) increased, while Ovenbirds (Seiurus aurocapilla) decreased within 11 to 18 months after SW harvests; understory disturbance treatments B or OSW had no effect. Our results indicated that partial harvests created habitat for breeding birds associated with both young and mature forests, whereas understory treatments had little effect. Additionally, we show that even small patches of young forest habitat are used by more individuals and more species of breeding birds than surrounding closed-canopy forest, and may benefit successional-scrub species by enabling their occurrence in an otherwise forested landscape. Absence of several lower-elevation successional-scrub bird species in our mid-elevation SW harvests suggests that comprehensive conservation in the southern Appalachians necessitates creating and maintaining young forest habitats across elevation gradients.

Structure and Species Composition of Upland Hardwood Communities After Regeneration Treatments Across Environmental Gradients

Early successional habitats can be created with a broad array of silvicultural techniques that remove all or most canopy trees in one to several cuttings and small to large patch sizes. Composition and early structural development of the resulting vegetation can be variable. Arborescent species composition is a function of regeneration sources already present and those that arrive during or after the cutting. The suite of species available for regeneration of a site, large or small, is a cumulative effect of disturbances and varies across multiple environmental gradients that include moisture, elevation (temperature), and soil chemistry.

Drought response of upland oak (Quercus L.) species in Appalachian hardwood forests of the southeastern USA

Key messageIn Appalachian hardwood forests, density, stem size, and productivity affected growth during drought for red oak, but not white oak species. Minor effects of density suggest that a single low thinning does little to promote drought resilience for oaks in the region.ContextManagement is increasingly focused on promoting resilience to disturbance. Because stand density can modulate climate-growth relationships, thinning may be an adaptation strategy that promotes resistance/resilience to drought.AimsWe examined how density, manipulated via thinning, stem size, and site productivity, influences the drought response of northern red, black, chestnut, and white oak.MethodsWe modeled the role of density, stem size, and site productivity on resistance, recovery, and resilience during two drought events.ResultsChestnut and white oak displayed greater resistance, recovery, and/or resilience than did northern red and black oak. For black oak, density and stem size negatively affected resistance during the first and second drought, respectively. Density, stem size, and site productivity had no effect on chestnut and white oak.ConclusionThe lack of sensitivity of chestnut and white oak to the ranges of density, stem size, and site productivity observed in this study and generally better resistance, recovery, and resilience suggests that management focused on the maintenance of these species, as opposed to a single silvicultural low thinning, may be a possible strategy for sustaining the growth and productivity of oak species in Appalachian hardwood stands. Drought response as affected by alternative thinning interventions should be evaluated.

Carbon Dynamics Following the Creation of Early Successional Habitats in Forests of the Central Hardwood Region

Across a forested landscape, stand-level management actions or natural disturbances that create early successional habitats result in a short-term loss of carbon in any given stand, but are often offset by carbon gains in other, undisturbed stands. Standing carbon stocks and rates of sequestration vary with species, site productivity, stand age, and stand structure. The age distribution of forest stands has a particularly large effect on landscape-level carbon storage. Consequently, forest management activities, including creation of early successional habitats, have short-term implications for stand-level carbon storage, but their impact on forest- or landscape-level carbon storage ultimately depends upon the temporal distribution and spatial scale of young forest stands on the landscape.