Tracy S. Hawkins

Growth and intraspecific competitive abilities of the dioecious Lindera melissifolia (Lauraceae) in varied flooding regimes.

Abstract The contribution of sexual dimorphism to male-biased colony ratios observed in field populations of the federally endangered Lindera melissifolia was investigated. Growth characteristics and intraspecific relative competitive abilities were determined for first-year male and female L. melissifolia plants grown at varied densities and receiving three flooding treatments. In the no-flooding and 30-day-flooding treatments, stem height, stem diameter, and total leaf area for male plants were significantly greater than that of higher density male plantings and of female plants without respect to density. In both male and female plants, stem growth ceased and leaves were abscised in response to flooding. Although density effects in combination with hydrologic regime influenced intersexual competition, male-bias from competitive exclusion was not indicated. Growth characteristics for male plants grown alone suggest potential for greater interspecific competitive abilities than that of female plants. Therefore, male plants may be better adapted for colonizing suitable habitat, thus contributing to male-biased colony ratios observed in naturally occurring populations.

Bottomland Forests in the Lower Mississippi Alluvial Valley Associated with the Endangered Lindera melissifolia

Abstract Forest canopy and subcanopy data were collected from and compared among five disjunct bottomland hardwood forests in the Lower Mississippi Alluvial Valley, each with known occurrence of a population of the federally endangered shrub Lindera melissifolia. All study sites are cut-over forests, underlain by hydric soils, and have a seasonal high water table. Canopy and subcanopy species are similar among sites, but species differ in relative importance, and flood tolerant tree species exceed that of flood intolerant species. Distribution of L. melissifolia colonies within each study site was not associated with mean tree density or d.b.h. Forest composition and structure at each study site reflect hydrologic regime, topography, historical disturbance, and an absence of recent disturbance. Results of this study provide a quantitative description of bottomland forests that currently sustain L. melissifolia populations. This information may be utilized for development of forest management plans aimed at ensuring continued sustainability of existing L. melissifolia populations and assessing other bottomland hardwood forests for potential reintroduction of this endangered species.

Seed ecology of Lindera melissifolia (Lauraceae) as it relates to rarity of the species

Abstract The seed ecology of the federally endangered shrub, Lindera melissifolia was investigated to determine if this aspect of the species life history contributes to the rarity of the species. Lindera melissifolia has the capacity to form a short-lived (two growing seasons) persistent soil seed bank if fruit pulp remains on seeds following dispersal and subsequent winter flooding occurs. Seeds, both with or without pulp (i.e., mesocarp and exocarp), exhibited tolerance to submergence, but were not hydrochorous. Following 6–12 weeks cold stratification (5° or 5/1° C) or submersion in cold water (5/1° C) for 12 weeks, ≥ 63% of seeds germinated when incubated in light and at temperatures of 35/20° and 30/20° C. When incubated in darkness, 100% of seeds germinated following 6 weeks of cold stratification. Giberrelic acid was moderately effective in breaking dormancy. Collectively, our results indicate that seeds of L. melissifolia have nondeep physiological dormancy. Aspects of the seed ecology of L. melissifolia that may contribute to continued rarity of the species include absence of a long-term persistent soil seed bank, no obvious mechanism of long-distance dispersal, and late season germination that prevents seedling growth to a sufficient size for survival prior to cold temperatures and flooding.

Interannual consistency of gross energy in red oak acorns

Abstract Red oak Quercus spp., Subgenus Erythrobalanus acorns are forage for mallards Anas platyrhyncos, wood ducks Aix sponsa, and other wildlife that use bottomland hardwood forests in the southe...