Feasibility of Igniting Prescribed Fires in Bottomland Hardwood Forests

There is emerging interest in using prescribed fire to manage bottomlands for wildlife habitat, invasive species control, and overall forest function. We evaluated the feasibility of conducting prescribed fires in bottomland hardwood forests in west-central Alabama as part of a broader strategy to control the invasive shrub Chinese privet (Ligustrum sinense). We used 22 small-scale plots (0.04 hectares) in areas with residual slash from privet cutting operations and initiated prescribed fires on each to assess the overall feasibility and the relation of in-stand weather (i.e., microclimate), stand composition, and litter measurements to fire behavior. Overall, prescribed fire ignition was difficult, and only half the trials successfully burned >10 percent of the plot. We found that stand composition was most correlated with percent plot burned, and plots with higher proportions of tree species with flammable leaf traits (e.g., Quercus spp.) tended to burn best. Although further investigation is warranted, managers interested in using prescribed fire for bottomland hardwoods likely face short time windows and limited forest conditions in which fires can be reliably set. Study Implications There is increasing interest in using prescribed fires in bottomland hardwood forests. This exploratory study evaluated whether prescribed fires could be reliably set in bottomlands. Prescribed fires were difficult to establish and tended to be very patchy with fire spread related to tree canopy composition (because of differences in leaf litter flammability) and litter loads. Results suggest that it would be difficult to apply fire on a large scale in bottomland hardwood forests and that small-scale fires could only be set under certain conditions.

Diversity or Redundancy in Leaf Physiological and Anatomical Parameters in a Species Diverse, Bottomland Hardwood Forest?

Research Highlights: Bottomland hardwood forests exhibit seasonal flooding, are species diverse, and provide numerous ecosystem services including floodwater storage, wildlife habitat and nutrient mitigation. However, data are needed to adequately predict the potential of individual species to achieve these services. Background and Objectives: In bottomland hardwood forests, increasing tree species richness may increase functional diversity unless species exhibit an overlap in physiological functioning. Therefore, the objectives of this study were to (1) compare physiological and anatomical leaf parameters across species, (2) determine if leaf anatomical and nutrient properties were correlated with physiological functioning, (3) determine intra-species variability in leaf stomatal properties and determine how whole crown metrics compare with leaves measured for gas exchange and (4) measure soil nitrogen for evidence of denitrification during inundation periods. Materials and Methods: We measured gas exchange, leaf nutrients and anatomical properties in eight bottomland hardwood species including Carya ovata, Fraxinus pennsylvanica, Quercus michauxii, Quercus nigra, Quercus pagoda, Quercus phellos, Ulmus alata and Ulmus americana. Additionally, we quantified soil ammonium and nitrate content during winter inundated conditions to compare with non-inundation periods. Results: We found that leaf-level water use parameters displayed greater variability and diversity across species than photosynthesis and leaf nitrogen parameters, but green ash and shagbark hickory exhibited generally high leaf N concentrations and similar physiological functioning. Elms and oaks displayed larger variability in leaf physiological functioning. Stomatal density was significantly correlated with photosynthetic capacity and tree-level water use and exhibited high intra-species variability. Conclusions: This bottomland hardwood forest contains more diversity in terms of water use strategies compared with nitrogen uptake, suggesting that differences in species composition will affect the hydrology of the system. Green ash and shagbark hickory exhibit higher leaf nitrogen concentrations and potential for nutrient mitigation. Finally, leaf anatomical parameters show some promise in terms of correlating with leaf physiological parameters across species.