John M. Zobel

Microsites Supporting Endemic Populations of Mountain Stewartia (Stewartia ovata) in East Tennessee

ABSTRACTu2003 Mountain stewartia (Stewartia ovata) is the only member of the family Theaceae endemic to Tennessee. Apart from its physical description and rarity, little is known about this woody understory species. Accounts of stewartia populations and range descriptions are longstanding, but microsite descriptions are limited in detail. We quantified microsites supporting populations of stewartia across East Tennessee as a first step in determining whether stewartia is rare because of rare or altered habitat, limited sexual reproduction, poor dispersal, or a combination of these factors. Five populations of stewartia averaging 7.40 ± 1.08 stems per population were inventoried across four East Tennessee counties. Soils on all sites were strongly acidic, highly permeable, well-drained, cobbly loams associated with steep slopes and higher elevations and were low in phosphorus, potassium, calcium, and magnesium. A dense overstory comprised of sourwood (Oxydendrum arboreum), eastern hemlock (Tsuga canadensis), white oak (Quercus alba), eastern white pine (Pinus strobus), red maple (Acer rubrum), and mockernut hickory (Carya tomentosa) resulted in 7.05% ± 1.41% of full photosynthetically active radiation (PAR). The midstory and understory were dominated by eastern white pine, red maple, and eastern hemlock. Quantification of stand-level conditions in extant stewartia populations suggested similarities in soil pH, nutrient levels, drainage, overstory composition and structure, and PAR levels. Certain conditions in stewartia sites were unique in the region, suggesting that habitat may limit populations along with other factors. Further investigations of stewartia reproductive ecology, dispersal, and habitat requirements will be key to conserving this species.

A Diagnostic Assay to Detect Herbicide Resistance in Annual Bluegrass (Poa annua)

Turfgrass managers currently have few readily available means of evaluating herbicide resistance in annual bluegrass during the growing season. Research was conducted to determine if agar-based diagnostic tests developed for agronomic weeds could be used to reliably confirm herbicide resistance in annual bluegrass harvested from golf course turf. Annual bluegrass phenotypes with target-site resistance to acetolactate synthase (ALS; R3, R7), enolpyruvylshikimate-3-phosphate synthase (EPSPS; R5), and photosystem II (PSII; R3, R4) inhibiting herbicides were included in experiments along with an herbicidal susceptible phenotype (S). Single tiller plants were washed free of soil and transplanted into autoclavable polycarbonate plant culture boxes filled with plant tissue culture agar amended with a murashigee-skoog medium and trifloxysulfuron (6.25, 12.5, 25, 50, 75, 100, or 150 μM), glyphosate (0, 6, 12, 25, 50, 100, 200, or 400 μM), or simazine (0, 6, 12, 25, 50, 100, 200, or 400 μM). Mortality in agar was assessed 7 to 10 days after treatment (depending on herbicide) and compared to responses observed after treating individual plants of each phenotype with trifloxysulfuron (28 g ai ha-1), glyphosate (1120 g ae ha-1), or simazine (1120 g ai ha-1) in an enclosed spray chamber. Fishers exact test (α = 0.05) determined that mortality in agar with 12.5 μM trifloxysulfuron and 100 μM glyphosate was not significantly different than treating whole plants via traditional spray application. Mortality with all concentrations of simazine in agar was significantly different than that observed after treating resistant and susceptible phenotypes via traditional spray application. Our findings indicate that an agar-based diagnostic assay can be used to detect annual bluegrass resistance to ALS- or EPSPS-inhibiting herbicides in less than 10 days; however, additional research is needed to refine this assay for use with PSII-inhibiting herbicides. Nomenclature: Glyphosate; simazine; trifloxysulfuron; annual bluegrass, Poa annua L.

Impacts of Cattle, Deer, Small Mammals, and Drought on Bur Oak (Quercus macrocarpa Michx.) Seedling Survival in Remnant Savannas in Central Nebraska

ABSTRACT: n Oak savanna remnants contribute substantially to the biodiversity of graminoid-dominated landscapes in the Great Plains Region. Most of these ecologically important ecosystems have either been altered or lost altogether since the arrival of Europeans in the early to mid-1800s. Changes in land use have been accompanied by reduced oak regeneration, which may be attributable to grazing and other management practices. At present, numbers of surviving oak seedlings are insufficient for sustaining the recruitment of oaks into savanna overstory strata. Herbivore exclosures were used to distinguish sources of mortality in first-year bur oak (Quercus macrocarpa) seedlings to determine the impacts of large mammalian herbivores, small mammals, and drought on oak regeneration in savanna remnants in Custer County, Nebraska. Results suggested an uncertain future for extant oak savannas on private land in central Nebraska. Seedlings without exclosures exhibited 97% mortality over the first growing season, and 100% mortality was observed during the subsequent dormant season in seedlings without exclosures that had survived the growing season. Although drought and small mammals contributed to overall oak seedling mortality, cattle and deer impacts were the leading causes of mortality in seedlings without exclosures. Trampling, grazing, and browsing may compromise efforts to restore and sustain these ecologically valuable ecosystems. However, effects of these factors may be reduced through management involving exclosures and limiting grazing to seasons when young oaks are less susceptible to damage.