Browsing by Author "Hiers, J. Kevin"
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- Estimating heat tolerance of buds in southeastern US trees in fire-prone forestsMcClure, Adam B.; Coates, T. Adam; Hiers, J. Kevin; Seiler, John R.; O’Brien, Joseph J.; Hoffman, Chad M. (2022-12-19)Background Traits of mature trees, such as bark thickness and texture, have been documented to promote resistance or resilience to heating in fire-prone forests. These traits often assist managers as they plan and promote prescribed fire management to accomplish specific land management objectives. Species are often grouped together as pyrophobes or pyrophytes as a result of these features. Nonetheless, little is known about species-specific traits of other structures, such as bud diameter, length, mass, moisture content, and surface area, that might be related to heat tolerance. Many prescribed fires are utilized in the eastern United States to control regeneration of less desired species, which could apply a more mechanistic understanding of energy doses that result in topkilling mid-story stems. In this study, we investigated potential relationships between terminal bud mortality from lateral branches of midstory stems and species-specific bud features of six eastern US deciduous trees. Characterized at maturity as either pyrophytes or pyrophobes, each was exposed to different heat dosages in a laboratory setting. Results Bud diameter, length, mass, moisture content, and surface area differed by species. Bud percent mortality at the first heat flux density (0.255–0.891MJm−2) was highest for two pyrophobes, chestnut oak (Quercus montana Willd.) and scarlet oak (Quercus coccinea Münchh). For the second heat flux density (1.275–1.485MJm−2), bud percent mortality was highest for these species and red maple (Acer rubrum L.). Principal component analysis suggested that bud surface area and length differentiated species. Red maple, chestnut oak, and scarlet oak produced clusters of buds, which may explain their more pronounced bud mortality. Yellow-poplar (Liriodendron tulipifera L.) was also present in that cluster, suggesting that its unique bud architecture of pre-emergent leaves may have elicited responses most similar to those of the clustered buds. Conclusions Contrary to expectations, lateral buds of species regarded as pyrophytes at maturity displayed some of the highest values of bud percent mortality when heated at two heat flux densities generated in a laboratory. Their responses may be related to clustering of their lateral buds. Testing of additional species using these methods in a laboratory setting, and perhaps additional methodologies in the field, is warranted.
- Estimating Heat Tolerance of Tree Buds in the Southeastern United StatesMcClure, Adam Blake (Virginia Tech, 2021-01-11)Tree diameter, bark thickness and texture, litter bulk density and chemistry, and sprouting ability are a few, species-specific adaptations and properties that may be related to an individual tree stem's potential fire resistance. Based upon these features and others, trees exhibiting similar characteristics have been broadly classified as pyrophytic or pyrophobic. To our knowledge, few if any, research studies have been conducted to determine if tree buds may exhibit speciesspecific fire or heat tolerance. Understanding potential relationships between bud characteristics and fire tolerance may assist prescribed fire managers as they target control of specific undesired tree species while promoting desired tree species. Buds of six common hardwood species in the southeastern U.S. were harvested and exposed to different heat dosages using a propane gas tube burner: red maple (Acer rubrum L.), yellow-poplar (Liriodendron tulipifera L.), American beech (Fagus grandifolia Ehrh.), mockernut hickory (Carya tomentosa Lam.), scarlet oak (Quercus coccinea Münchh.), and chestnut oak (Quercus montana Willd.). These species are commonly categorized as pyrophobic (American beech, red maple, yellow-poplar) and pyrophytic (chestnut oak, mockernut hickory, scarlet oak). Using electrolyte leakage of heated and unheated buds, the mean difference in bud percent mortality between heated and unheated buds was compared by species, functional group, and differing heat dosages. The mean difference in bud percent mortality differed between the heated and unheated buds by species (p < 0.0001). Heated buds of yellow-poplar, mockernut hickory, and chestnut oak displayed similar percent mortality; however, the presumed pyrophytic species had greater heated bud percent mortality (34.0 %) than the pyrophobic species (26.8 %) (p = 0.0003). Heated bud percent mortality differed based upon differing heat dosage levels (height above the propane burner and heat exposure time) and their species-specific interactions. Fire tolerance, as assigned and assessed by features such as bark texture and thickness, may not be directly related to mid-story tree bud physical properties (i.e. length, mass, and diameter) or fire tolerance. Research including additional species, heat dosages, and different sampling times (i.e. late fall vs. late winter) would be valuable for investigating these dynamics further. Deploying a similar, field-scale experiment before and after prescribed burns would be useful to determine how tree buds may respond to different heat dosages that could be exacted during prescribed burns.
- Suites of Fire-Adapted Traits of Oaks in the Southeastern USA: Multiple Strategies for PersistenceVarner, J. Morgan; Kane, Jeffrey M.; Hiers, J. Kevin; Kreye, Jesse K.; Veldman, Joseph W. (2016-08-01)Fire is integral to the functioning of terrestrial ecosystems of the southeastern USA and is a strong selective force on plant species. Among woody plants, oak species (Quercus spp. L) have diverse life history traits that appear to reflect their evolution in this fire-prone region. Oaks also occur across wide gradients of fire frequency and intensity, from annually burned savannas to fire-protected forests. As such, oak functional traits are presumed to reflect adaptations to acquire limited resources (i.e., "physiological traits") or survive environmental stress (i.e., "protective traits"). Oak functional traits may also influence fire regimes (i.e., via "flammability traits") by altering fire behavior through effects on fuels and their combustion. We synthesized evidence from ecophysiological measurements, laboratory burning and drying experiments, and field experiments to determine the suites of functional traits that reflect fire adaptive strategies in eight Southeastern oaks for which abundant data were available. We found strong correlations among Principal Components Analysis axes for flammability (litter burning and drying), protective (bark and wound responses), and physiological (growth) traits. The eight oaks clustered into three strategies: 1) pyrophytic species that produce highly flammable leaf litter, accrue thick bark rapidly, close wounds rapidly, and grow slowly; 2) mesophytic species that produce low flammability litter, have thin bark, and are fast growing; and 3) fire-avoider species with a mixture of traits from the two extremes. This synthesis clarifies the relative pyrophily of Southeastern oaks and suggests how suites of fire-related traits influence fire regimes and species habitat preferences.