Theodore H. Shear

VEGETATION ALONG HYDROLOGIC AND EDAPHIC GRADIENTS IN A NORTH CAROLINA COASTAL PLAIN CREEK BOTTOM AND IMPLICATIONS FOR RESTORATION

We described the vegetation of two alluvial swamp forest stands along Durham Creek in Beaufort County, North Carolina, USA in relation to elevation, hydrologic, and edaphic gradients. Over 3,000 surveyed elevations of individual plant microsites were used in conjunction with 26 years of stream gage data to examine individual species responses to annual and growing season flooding frequencies. Direct gradient analyses combined with plot ordinations derived from detrended correspondence analysis and canonical correspondence analysis suggested that differences in vegetation between the stands were primarily the result of variations in elevation, growing season flooding frequency, percent base saturation, exchangeable acidity, and soil physical properties. Although the stands were less than 4.5 km apart and without significant intermediate tributaries, growing season flooding frequency and duration were magnified in the lowest elevations of the downstream stand. An elevation difference of as little as 10 cm resulted in a 20% difference in the frequency of surface flooding during the growing season. Species distributions were significantly correlated with depth to mottling (r2=0.75), flooding frequency (r2=−0.57), elevation (r2=0.70), and several soil chemical properties. The two stands had very similar annual surface flooding regimes, but subtle differences in growing season flooding frequency, soil characteristics, and disturbance history have apparently resulted in dissimilar plant community composition and structure. These results suggest that the lack of quantitative data on vegetation-environment interactions occurring at the microtopographic scale (10−1 m) in alluvial swamp forests makes precise prediction, planning, or design of created or restored wetland composition and function a formidable challenge.

Effects of vegetation removal on native understory recovery in an exotic-rich urban forest1

Abstract Urban forests represent patches of biodiversity within otherwise degraded landscapes, yet these forests are threatened by invasion by exotic plant species. We investigated the response of a forest understory to removal of four common exotic species: Elaeagnus umbellata Thunb., Lonicera japonica Thunb., Ligustrum sinense, Laur., and Microstegium vimineum (Trin.) A. Camus in a forest within the city of Raleigh, NC, USA. In the summer of 2001, we initiated a removal experiment with three treatments. In the “repeated removal” treatment, all understory vegetation was initially removed by clipping and new exotic seedlings were repeatedly removed every 2 weeks throughout the study period. The “initial removal” treatment involved a one-time understory vegetation removal with no further weeding. Control plots had no intervention throughout the study period. We conducted vegetation surveys of the plots prior to treatment initiation and in April and August of 2002 and 2003. With a non-metric multidimensional scaling (NMS) ordination, we were able to discern differences in species composition between the repeated removal treatment and the other two treatments. However, using repeated measures ANOVA, we found no significant differences in native species richness, cover, and abundance among treatments during most sampling periods. We also used a seedbank study to determine that while some early successional species were present, no native shrubs and few native trees emerged from the seedbank. These results suggest that (1) repeated removal is required to decrease the importance of exotic species, especially if the site is in close proximity to a source of exotic propagules; and (2) subsequent to exotic removal, native species may not recover sufficiently without supplemental plantings. Therefore, restoration plans for urban forests should incorporate both long-term monitoring and native plant re-introduction to achieve a diverse native community.

Testing the Paradigms of Exotic Species Invasion in Urban Riparian Forests

Abstract Exotic species research has generated several paradigms about the effects of invasion on native ecosystems and the site characteristics that promote invasibility. We are interested in translating these theoretical paradigms into management recommendations. Using vegetation surveys of urban riparian forests in central North Carolina, we tested the competition and resource availability paradigms. We assessed the association between exotic and native species and identified potential resources that promote invasion. Exotic and native species richness was negatively correlated (r = −0.66, p = 0.0009), conforming to the predictions of the competition paradigm. In particular, native woody species were negatively associated with several exotic growth forms. Two of the most common exotic species, Hedera helix (English ivy) and Microstegium vimineum (Japanese stilt grass), did not co-occur with several native woody plants, suggesting that they may preclude the establishment and regeneration of native woody plant communities. Our results have less direct implications for the resource availability paradigm. There were no correlations between light availability (indexed by canopy cover) and either cover or richness of exotic species. However, exotic species richness was generally positively correlated to soil fertility. These results suggest that the competition and resource availability paradigms are useful for understanding the dynamics of urban riparian forests that are invaded by a suite of exotic species. Removal efforts should focus on two of the most common invasive plants, H. helix and M. vimineum, and native woody plants should be re-established. While soil fertility is difficult to manage at a site level, we urge managers to lobby for strict regulations on nutrient inputs from upstream and adjacent development.

Nursery and field establishment techniques to improve seedling growth of three Costa Rican hardwoods

Seedlings of three economically important and ecologicallydifferent native hardwoods, Cordia alliodora (Boraginaceae),Hyeronima alchorneoides (Euphorbiaceae), and Calophyllumbrasiliense (Clusiaceae), were grown in Rootrainers® (abook-type container), paper pots, and plastic bags filled witheither soil, soil with fertilizer, or compost substrates. Aftertransplanting in the field, treatments with and withoutfertilizer and herbicide were applied to all nursery stock types.In the nursery, species responded primarily to substrate type.Cordia grew better in bags of soil with NPK fertilizer andcompost than in unamended soil, probably responding to highernitrogen availability. Despite large treatment differences atplanting, there were no significant differences in plant sizeafter one year in the field between book containers and bags. Theexception were stump plants that were shorter and had highermortality. Hyeronima grew better in compost than in soil with orwithout fertilizer, probably responding to higher phosphorusavailability and lower bulk density of the compost. Plantsproduced in compost were also bigger after one years fieldgrowth. Plants produced with soil or in paper pots had highermortality. Calophyllum grew less in compost compared to soil andgrew better when micronutrients were added to the compost andsoil. In the field, seedling produced in soil or withmicronutrients had higher survival or growth, respectively. Ingeneral, species grew better with herbicide and fertilizerapplication after transplanting. However, there were nointeractions with nursery treatments. Responses to fieldtreatments were independent and thus additive to the nurserytreatments. Differences in species response can be related tobiomass allocation patterns and ecology of the species.

Japanese Stiltgrass (Microstegium vimineum) Management for Restoration of Native Plant Communities

Abstract Japanese stiltgrass is a nonnative invasive grass occupying a range of habitats in the eastern United States. Conventional management recommendations include hand-removal, mowing, or a nonselective herbicide application in autumn prior to flowering. However, no study has directly compared the ecological impacts of long-term management strategies on Japanese stiltgrass populations or recruitment and establishment of native flora. An experiment was initiated in 2002 and continued for three growing seasons in mixed pine-hardwood forests in central North Carolina. Conventional treatments included hand-removal, mowing, or an application of glyphosate (1.1 kg ai/ha) once in autumn, and selective removal by hand or fenoxaprop-P (0.19 kg ai/ha) season-long as needed. All treatments were compared to nontreated plots. Percent vegetation cover by species was recorded twice annually. Data were aggregated into five classes; Japanese stiltgrass, other exotic plants, native forbs, native monocots, and native woody plants. The soil seed bank of all species was estimated annually by extracting soil cores and documenting seedling emergence. All Japanese stiltgrass management treatments significantly reduced Japanese stiltgrass cover and seed bank over time compared to no management. However, recruitment and reestablishment of native plants and overall species richness were greater with selective Japanese stiltgrass management treatments including both hand-removal and fenoxaprop-P. Relative cover of other exotic plants decreased 2% to 49% after 3 yr with all Japanese stiltgrass management treatments except season-long hand-removal, which increased relative cover of other exotic plants 51%. Nomenclature: Japanese stiltgrass, Microstegium vimineum (Trin.) A. Camus MCGVM.

An approach to optimal wetland mitigation using mathematical programming and geographic information system based wetland function estimation

We developed and tested a quantitative geographic information system (GIS)-based approach for selecting wetland restoration sites. Our approach uses a combination of an existing wetland function evaluation program, a GIS and integer programming methodology with an objective to minimize cost of restoration subject to meet environmental requirements. Investigations were conducted on the formulation to examine the effects of problem size, site ordering for input, and restoration targets. The formulation could be solved for the largest problem size tested of 996 integer variables. The larger the problem, the more time it took to solve. Larger restoration targets usually took more sites and more time to solve. Sorting sites by size was found to lead to inefficient and often unfeasible solutions. Random sorting of sites was found to be the more efficient method of inputting restoration sites into analysis.

Environmental Controls of Reproduction and Early Growth of Lindera melissifolia (Lauraceae)

ABSTRACT Lindera melissifolia is a federally endangered endemic shrub of the southeastern United States. Numerous populations are gender-biased. The goal of this study was to determine environmental conditions most appropriate for establishment and growth of seedlings and adult females. Seedlings were grown under varied moisture and light to compare growth rates and morphological ratios. Seedlings were clipped to simulate two levels of disturbance, and their shoot sprouting ability was assessed. Densities of adult flowering stems, co-occurring species, and solar transmittance were analyzed within two North Carolina populations. The lowest levels of light resulted in decreased growth, but light and moisture did not interact to affect seedling growth rate significantly. Morphological ratios and growth responses followed patterns expected for plants exhibiting plasticity in response to varied light levels, but not to moisture. Clipping immature plants below root collars decreased survivorship to 31%. Growth rates of new shoots when clipped below and above the root collar were 40% and 58% percent lower, respectively (p < 0.001). Percent cover of Lindera melissifolia explained 52% of the variation in the number of male flowering stems per plot and 14% of the variation in female stems per plot. No relation of stem density to percent transmittance was found. Indicator species analysis revealed association of males with facultative wetland species and a weak association of females with wetland obligates, but overall difference in vegetation composition between plots with or without females present was slight (MRPP: A = 0.02, p = 0.016). We concluded hydrology should be a primary concern for future studies.

An Assessment of Rainforest Distribution and Threats in the West Usambara Mountains, Tanzania

Abstract Biodiversity hotspots across the globe have gained increasing attention in recent years. To accurately assess natural resource values and threats, timely information which characterizes the distribution and extent of natural land cover is needed. Many hotspots are in developing countries that have neither the resources nor the capability to carry out these tasks. This study seeks to address these issues in the West Usambara Mountains, within the Eastern Arc Mountain chain, of Tanzania. These mountains are one of the top biodiversity hotspots in the world. By incorporating remote sensing and Geographic Information System technology, this study develops spatial databases used to map current resource conditions and threats to existing biodiversity. Accuracy for landcover mapped with satellite imagery is 94%. Less than 10% of forest remains in large patches which are highly fragmented. The majority of this forest cover is found at high elevations, which correspond to relatively low potential biodiversity. Only 6% of forests are found at high biodiversity, lower elevation zones. More than half of the forest patch edges at these elevations are adjacent to conflicting landcover, such as small‐scale agriculture. This information can assist land managers and conservation professionals in the prioritization of protection efforts, conservation management, watershed stabilization, and forest restoration planning.

Sensitivity analysis of transportation corridor location in wetland areas: A multiobjective programming and GIS approach

A multiobjective programming approach for locating transportation corridors through areas containing wetlands is presented. The approach uses a geographic information system in combination with multiple objectives for environment and construction costs, and the North Carolina Coastal Region Evaluation of Wetland Significance (NC-CREWS) program. The multiobjective function is a weighted combination of wetland values and construction cost. The objective minimizes total cost of construction and wetland impacts resulting from a specific transportation corridor. The transportation designer specifies starting and ending points of the desired corridor. The model then finds the best path given the weights placed on each individual objective (i.e. habitat quality, water quality, hydrology, and construction expense). By varying the weight set, several different paths can be found. The approach is tested on a watershed in Carteret County North Carolina using a benchmarking procedure. One benchmark minimizes a combined wetland significance loss (cost). This path avoids crossing wetlands. The other benchmark minimizes construction expense. Varying the weight placed on each of the objective function components generates additional paths. The approach is useful in locating alternative road corridor paths in attempts to satisfy conflicting societal interests.

Interspecific Genetic Variation of Loblolly Pine Tolerance to Soil Waterlogging

Loblolly pine (Pinus taeda) is the most important commercial tree in the southern United States. It attains maximum size and growth rate on moderate to wet sites adjacent to wetlands (i.e. swamps and river bottoms). Individual trees grow in headwater swamps and other shallowly inundated wetlands. Hence, there is evidence of interspecific variation in tolerance to waterlogging.