Connectivity in coastal systems: Barrier island vegetation influences upland migration in a changing climate

Abstract

Due to their position at the land–sea interface, barrier islands are vulnerable to both oceanic and atmospheric climate change‐related drivers. In response to relative sea‐level rise, barrier islands tend to migrate landward via overwash processes which deposit sediment onto the backbarrier marsh, thus maintaining elevation above sea level. In this paper, we assess the importance of interior upland vegetation and sediment transport (from upland to marsh) on the movement of the marsh–upland boundary in a transgressive barrier system along the mid‐Atlantic Coast. We hypothesize that recent woody expansion is altering the rate of marsh to upland conversion. Using Landsat imagery over a 32 year time period (1984–2016), we quantify transitions between land cover (bare, grassland, woody vegetation, and marsh) and the marsh–upland boundary. We find that the Virginia Barrier Islands have both gains and losses in backbarrier marsh and upland, with 19% net loss from the system during the timeframe of the study and increased variance in marsh to upland conversion. This is consistent with recent work indicating a shift toward increasing rates of landward barrier island migration. Despite a net loss of upland area, macroclimatic winter warming resulted in 41% increase in woody vegetation in protected, low‐elevation areas, introducing new ecological scenarios that increase resistance to sediment movement from upland to marsh. Our analysis demonstrates how the interplay between elevation and interior island vegetative cover influences landward migration of the boundary between upland and marsh (a previously underappreciated indicator that an island is migrating), and thus, the importance of including ecological processes in the island interior into coastal modeling of barrier island migration and sediment movement across the barrier landscape.

Interaction of seed dispersal and environmental filtering affects woody encroachment patterns in coastal grassland

“…The success of Morella could be due to advantages at the germination stage of development over tree species when salinity has increased (unpublished data). Morella expansion continues in stable portions of the island that are slower to erode, accounting for the increased encroachment as islands decline in size (Zinnert et al 2019). Morella is expanding into grassland and forested habitat in coastal areas throughout the Mid-Atlantic and Gulf coast regions with undetermined consequences for species richness and coastal stability.…”

Topography and disturbance influence trait‐based composition and productivity of adjacent habitats in a coastal system

“…This study focuses on two islands, Hog Island and Metompkin Island, within the Virginia Coast Reserve (VCR) Long‐Term Ecological Research site that represent different geomorphology classes based on various geographic variables (i.e., shape, size, disturbance regime, and topographic complexity) and long‐term response to disturbance (Zinnert et al 2019).…”

“…This results in dune and swale habitats similar in how they are influenced by environmental factors such as wind, sea spray, and flooding (Fig. 1a; Young et al 2011, Zinnert et al 2017, 2019, Stallins and Corenblit 2018). If disturbance influences the difference in inter‐ and intra‐island topographic and environmental factors, we would expect to see plant communities differ in overall trait‐based community composition and/or site‐to‐site variability of dune/swale habitat types (Chase 2007).…”

“…Barrier islands are unique systems and are rarely used to study interactions among disturbance, environment, and trait‐based community composition, as well as feedbacks with ecosystem function. However, recent research suggests that barrier islands respond individualistically to similar disturbances due to topographic heterogeneity, making them ideal systems for studying disturbance response across multiple scales (Zinnert et al 2017, 2019). Relationships between plant presence and coastal topography have been documented, but these are largely species‐based (Stallins 2006, Monge and Stallins 2016, Goldstein et al 2017, Hacker et al 2019).…”

“…In this study, we address a knowledge gap by investigating how topographic heterogeneity influences environmental factors and trait‐based community composition in terrestrial barrier island systems that differ in long‐term disturbance response (Stallins 2006, Zinnert et al 2019). Where trait‐based composition differences exist, we determine how those differences influence ecosystem productivity.…”