Abstract. In contrast to stable inland systems, coastal landscape positions are dynamic, changing as shorelines migrate and storms alter topography. We define landscape position by distance to ocean shoreline and elevation above sea level, two metrics that integrate a suite of environmental and biotic factors. As shoreline and elevation change, suitability of a geo-referenced position for a given plant species may also change. The objectives of our study were to use two methods for measuring landscape position (GPS and hyperspectral/light detection and ranging or LIDAR) to develop habitat polygons, compare habitat polygons for five species representing several adaptive strategies, and illustrate change in landscape position due to migrating shoreline for a Virginia, USA barrier island. Habitat polygons for each species were distinct, represented several growth forms or functional groups, and were indicative of tolerances to biotic and abiotic stresses. The habitat polygon for Cakile edentula (annual forb) was relatively small, indicating narrow habitat requirements for the strand environment. Cirsium horridulum (biennial forb), with succulent shoots and roots, occurred on dunes where water is most limiting. For the dunebuilding grass, Ammophila breviligulata, as distance from shoreline increased, minimum elevation also increased. Two woody species occurred across the entire island; however, Morella cerifera (N-fixing shrub), was limited to mesic swales whereas Juniperus virginiana (evergreen tree), with the largest habitat polygon, occurred on both dunes and swales. For a geo-referenced point on the north end of Hog Island, distance to shoreline increased from the shoreline to 1100 m inland over 139 years. In contrast, the geo-referenced point on the eroding portion of the island decreased from 1700 m to 120 m from the ocean shoreline over the same time period. Where sea level rise and storms are expected to alter shorelines and island topography, generation of habitat polygons from hyperspectral and LIDAR imagery provide rapid assessment of potential effects on species distribution patterns at local and regional scales. Habitat polygons have broad applicability beyond coastal systems and may contribute to a rapid assessment or identification of vulnerability for species as climate patterns shift through time.

No abstract

Abstract. Woody expansion has been documented for years in many different systems, often the result of anthropogenic changes to the environment. Causes and consequences of woody expansion have been well documented, but comparatively few studies have focused on functional traits that mechanistically allow for dramatic expansion in range. Our objectives were to investigate functional traits and plant resource strategies that contribute to rapid expansion of an invasive, nitrogen-fixing shrub, Elaeagnus umbellata Thunb. (Elaeagnaceae) compared with two sympatric native shrubs, Clethra alnifolia L. (Clethraceae) and Vaccinium corymbosum L. (Ericaceae). We quantified morphological, physiological and biochemical functional traits linked explicitly to three main resources that directly influence plant growth: light, water and nutrients. We attribute high photosynthetic efficiency found in E. umbellata to traits associated with light capture and use (e.g., specific leaf area, pigment concentrations, leaf display). Compared to coexisting species, leaf-level water demand was supported through high hydraulic capacity, yet E. umbellata also maintained high water use efficiency evident in d13 C values. Fixed nitrogen allowed for higher foliar %N observed in E. umbellata. This supports both high rates of electron transport and hydraulic capacity as seen in the relationships between foliar %N and electron transport rate (ETR) and percent loss of conductivity (PLC midday ). Overall, functional traits of E. umbellata allowed for high resource acquisition that when combined contribute to success in a wide variety of habitats. Conversely, native sympatric shrubs exhibited functional traits representative of slower-growing species (e.g., lower light capture, water use and nutrient acquisition). Our results support the hypothesis that traits associated with photosynthesis, water use efficiency, specific leaf area and leaf N are under selective pressure and highlight the importance of relationships among photosynthetic efficiency, hydraulic capacity and leaf N content that allow for the success of an expanding woody species.

No abstract

Myrica cerifera L. (Myricaceae), the dominant woody species on many barrier islands along the southeastern coast of the United States, is expanding into grass-dominated, mesic, interdunal depressions where it forms dense thickets. Expansion may be attributed to a symbiotic nitrogen fixation with the bacterium Frankia, an evergreen leaf habit and, possibly, corticular photosynthesis (CP, i.e. refixation of respired CO 2 , %ref). We quantified seasonal variations in CP characteristics in first through fifth order branches of M. cerifera to determine the extent and relevance of CP to shrub expansion in coastal environments. Maximum mean %ref was 110±39 % of CO 2 efflux in the dark (R D ) in first order branches during winter. Minimum %ref was 18±3 % in fifth order branches during summer. Variations in %ref paralleled changes in incident photosynthetic photon flux density (PPFD). As incident PPFD attenuated with increasing branch order, %ref decreased. A less dense canopy in winter led to increased PPFD and increases in %ref. Total chlorophyll (Chl) content and Chl a/b ratios were consistent with shade acclimation as branch order increased. CP may be a mechanism to enhance M. cerifera shrub expansion because of the potential increase in whole plant carbon use efficiency and water use efficiency attributed to refixation of respired CO 2 .