Abstract Barrier islands are highly dynamic coastal landforms that are economically, ecologically, and societally important. Woody vegetation located within barrier island interiors can alter patterns of overwash, leading to periods of periodic‐barrier island retreat. Due to the interplay between island interior vegetation and patterns of barrier island migration, it is critical to better understand the factors controlling the presence of woody vegetation on barrier islands. To provide new insight into this topic, we use remote sensing data collected by LiDAR, LANDSAT, and aerial photography to measure shrub presence, coastal dune metrics, and island characteristics (e.g., beach width, island width) for an undeveloped mixed‐energy barrier island system in Virginia along the US mid‐Atlantic coast. We apply decision tree and random forest machine learning methods to identify new empirical relationships between island geomorphology and shrub presence. We find that shrubs are highly likely (90% likelihood) to be present in areas where dune elevations are above ∼1.9 m and island interior widths are greater than ∼160 m and that shrubs are unlikely (10% likelihood) to be present in areas where island interior widths are less than ∼160 m regardless of dune elevation. Our machine learning predictions are 90% accurate for the Virginia Barrier Islands, with almost half of our incorrect predictions (5% of total transects) being attributable to system hysteresis; shrubs require time to adapt to changing conditions and therefore their growth and removal lags changes in island geomorphology, which can occur more rapidly.
term population dynamics of 13 herbivore species in this unique national park in northern Tanzania.While population densities of some species have increased over the past 58 year, losses in megaherbivores (African elephant, black rhinoceros, African buff alo) some 30 years ago led to an overall 40% reduction in herbivore biomass with cascading eff ects on vegetation structure and other animal species.
Abstract Coastal dunes are important protective features against sea level rise and coastal storms. Interactions between dune plant aboveground structures and sediment trapping that allow for dune building and maintenance are well established. More recently, studies documenting belowground biomass for promoting erosion resistance in dominant dune species have been conducted, yet a knowledge gap remains regarding species‐specific characterization of whole plants, specifically with respect to roots, rhizomes, and belowground stems. Our objective was to quantify above‐ and belowground traits of four dominant dune grasses to document the potential for species‐specific effects on dune growth, maintenance, and erosion resistance. We examined above‐ and belowground traits among four prominent dune grasses of the Atlantic and Gulf Coasts of North America: Ammophila breviligulata , Panicum amarum , Spartina patens , and Uniola paniculata . Whole plant samples of each species were collected from the foredune at the US Army Engineer Research and Development Center's Field Research Facility in Duck, North Carolina, USA, and quantified for several above‐ and belowground traits (e.g., stem height, rhizome number and length, root surface area by diameter class, root tensile strength, and mycorrhizal percent infection). Belowground factors known to impact important dune processes, such as rhizome length, mycorrhizal percent infection, and root traits, differed substantially among species. When visualized in multivariate space, all species significantly differed in suites of above‐ and belowground traits. When considering belowground only, Ammophila and Spartina were similar, despite differences in biomass allocation. Species separated along axes related to mycorrhizal association, biomass allocation, and root construction. The four co‐occurring dune grass species were dissimilar in suites of plant traits. Belowground trait differences were driven by those describing root construction, biomass allocation, and mycorrhizal infection. Dissimilarity in above‐ and belowground suites of traits may demonstrate different approaches for surviving the dune environment. Incorporating belowground traits into modeling will enhance predictions of dune response to climate change through interactions between vegetation and dune dynamics that facilitate coastal resistance and resilience.
Abstract Shrubs are common – and presently expanding – across coastal barrier interiors (the land between the foredune system and back‐barrier bay), and have the potential to influence barrier morphodynamics by obstructing cross‐shore overwash flow. The ecological and geomorphological consequences of ecomorphodynamic couplings of the barrier interior, however, remain largely unexplored. In this contribution, we add an ecological module of shrub expansion and mortality to a spatially‐explicit exploratory model of barrier evolution (Barrier3D) to explore the effects of shrub‐barrier feedbacks. In our model simulations, we find that the presence of shrubs significantly alters barrier morphology and behavior. Over timescales of decades to centuries, barriers with shrubs (relative to those without) tend to be narrower, migrate landward more slowly, and have a greater proportion of subaerial volume distributed toward the ocean‐side of the barrier. Shrubs also tend to increase the likelihood of discontinuous barrier retreat, a behavior in which a barrier oscillates between periods of transgression and relative immobility, because shrubs induce prolonged periods of barrier immobility by obstructing overwash flow. However, shrubs can increase barrier vulnerability to drowning by preventing periods of transgression needed to maintain barrier elevation relative to rising sea levels. Additionally, physical barrier processes influence shrub expansion in our simulations; we find that greater dune erosion and overwash disturbance tends to slow the rate of shrub expansion across the barrier interior. Complementing recent observational studies of barrier islands in Virginia, USA, our results suggest that interior ecology can be a key component of barrier evolution on annual to centurial timescales.
found that years with regional conditions predicted by continued climate change showed a loss of diversity in both microclimate and phenological events, with a more rapid advancement in bud break occurring at higher elevation sites.
Bissett, S.N.; Zinnert, J.C., and Young, D.R., 2014. Linking habitat with associations of woody vegetation and vines on two mid-Atlantic barrier islands. Coastal habitats are inherently vulnerable to global change, as they are the first areas impacted by sea level rise and to experience more frequent and intense storms. Shrubs and vines dominate the climax communities in these environments, and with comparatively long regeneration periods, they are highly vulnerable to shifting topography and climate. We investigated abiotic and biotic components of two barrier island landscapes with similar plant communities but different site histories to clarify relationships among physical factors, woody plants, and vines. On Hog Island, Virginia and at Duck, North Carolina, intrasite comparisons with reference to distance from shoreline and elevation were made to evaluate relationships between woody and vine communities, as well as edaphic characteristics. Elevation was significantly related to woody species presence, and vine presence was significantly related to presence of woody structure, indicating an indirect association of the climbing species to elevation. Differing histories of management and development at the two sites have resulted in varying degrees of both topographic complexity and stability. Greater topographic complexity has resulted in similar species richness values for the two sites, despite the considerable difference in total area. Presumably, stabilization and prior management efforts at the Duck site have enabled a community assemblage comparable to that of the much larger Hog Island; however, the Duck site may be more vulnerable because of a decreased potential to migrate in response to continued sea level rise and storm impacts.
Using plants as phytosensors could allow for large-scale detection of explosives and other anthropogenic contamination. Quantifying physiological, photosynthetic, and hyperspectral responses of plants to hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) contamination provides the basis for understanding plant signals for remote detection. Plants of the woody shrub Baccharis halimifolia (a generalist species common on many military installations) were potted in soil concentrations of RDX ranging from 100 to 1500 mg kg−1. Physiological measurements of stomatal conductance and photosynthesis were significantly affected by RDX exposure at all treatment levels, with no overall effect on water potential. However, declines in photosynthesis and stomatal conductance were markedly different from those that occur under natural stress. Quantum use efficiency () and electron transport rate indicated that photosystem II (PSII) of RDX-treated plants was functional, with active photosynthetic reaction centers. Thus, declines in photosynthesis resulted from biochemical dysfunction in light-independent processes. Reflectance indices in the near-infrared region (, , and derivative indices) were most affected and may reflect the pathway on which RDX is contained within plants by being compartmentalized in the vacuole, cell wall, or lignin. These results demonstrate the potential for using plants as phytosensors to identify explosives exposure at remote distances.
