Marsh bird occupancy along the shoreline‐to‐forest gradient as marshes migrate from rising sea level

Abstract

One mechanism by which coastal marshes may persist as sea-level rises is to expand landward into existing forest, a process known as marsh migration. Though recent studies highlight the importance of marsh migration to the conservation of birds associated with coastal marshes, marsh bird responses to this transition from forest to marsh are poorly understood. To address this need, we conducted surveys of five focal marsh bird taxa at 92 points distributed across the gradient from the shoreline to the marsh-forest interface in one of the most vulnerable regions to sea-level rise in North America where marshes have been migrating landward for at least several decades. Given this landward movement of the forest-marsh interface, we modeled focal taxa occurrence as a function of distance-to-forest, thereby assuming that marshes closer to the forest were newer than those closer to the shoreline. In addition, we investigated the effects of vegetation conditions and fire frequency. Occupancy probability of marsh birds decreased closer to the forest-marsh interface where woody vegetation was taller and herbaceous cover was dominated by Cladium jamaicense, suggesting migrated marsh may provide limited habitat for these bird species, at least in the short term. Though parameter estimate uncertainty for black rail (Laterallus jamaicensis) was high due to a limited number of detections, occupancy of this species may increase with the conditions associated with migrated marsh, specifically greater C. jamaicense dominance and decreasing distance-to-forest. Clapper/king rail (Rallus crepitans/elegans) occupancy was greater at sites that had burned more frequently over the past decade, and occupancy of all focal taxa was greater in areas with vegetation conditions consistent with the effects of fire in coastal marshes, including reduced herbaceous vegetation density and shorter woody vegetation. As such, prescribed fire may serve as an effective method of facilitating marsh migration and increasing the quality and quantity of habitat for coastal marsh birds as sea-level rises.

Species‐specific responses of a marsh‐forest ecotone plant community responding to climate change

“…Recent research has investigated the ecological dynamics of upland to marsh transition and come up with broad descriptions of the mechanisms and trajectory of change in plant communities (Fagherazzi et al 2019, Kirwan and Gedan 2019, Taillie and Moorman 2019, Tully et al 2019). Within these frameworks, the ecotone or “transition zone” is an ephemeral state.…”

Retreating coastal forest supports saltmarsh invertebrates

“…Future studies should also compare the occupancy and functional use of ghost forest and high marsh by additional taxonomic groups and consider additional functional and behavioral characteristics to determine the overall equivalency of ghost forest and high marsh. Although both saltmarsh species observed here used ghost forest habitat in approximately the same way as high marsh, specialist saltmarsh species may be incapable of migrating into new habitat or unable to use ghost forest habitat as effectively as existing marsh (Taillie & Moorman, 2019). More comprehensive knowledge of the response of critical marsh faunal groups to marsh migration is necessary for accurate evaluation of marsh extent.…”

“…This may include several bird species whose high marsh habitat is expected to decline with sea-level rise (e.g., rails and marsh sparrows; Hunter et al, 2015), most notably the saltmarsh sparrow, which has been predicted to go extinct by 2060 in the absence of effective marsh migration (Field et al, 2017). Certain saltmarsh bird species, however, are known to use newly migrated marsh less than existing high marsh (Taillie & Moorman, 2019). Because this study demonstrates the presence of saltmarsh arthropod prey in the ghost forest, previously observed differences in bird occupancy may be driven by differences in habitat structure between zones (Benoit & Askins, 1999), rather than arthropod prey availability.…”

Biological Flora of Coastal Freshwater and Brackish Marshes: Cladium jamaicense Crantz

“…Sawgrass flowered in the second year following the fire (Davison and Bratton, 1988). Tallie and Moorman (2019) found that a prescribed burn in a sawgrass marsh in North Carolina improved the quality and quantity of habitat for coastal marsh birds. Venne and Frederick (2013) found that great egrets (Ardea alba) and white ibises (Eudocimus alba) selected burned sites and deep sloughs in a sawgrass marsh and avoided dense, unburned sites.…”