Keryn Gedan

George Washington University | GW · Department of Biological Sciences

Ecological zonation in coastal forests is driven by sea level rise and storm‐surge events. Mature trees that can survive moderately saline conditions show signs of stress when soil salinity increases above its tolerance levels. As leaf burn, foliar damage, and defoliation reduce tree canopy cover, light gaps form within the crown. At the forest‐mar...

The impact of saltwater intrusion on coastal forests and farmland is typically understood as sea-level-driven inundation of a static terrestrial landscape, where ecosystems neither adapt to nor influence saltwater intrusion. Yet recent observations of tree mortality and reduced crop yields have inspired new process-based research into the hydrologi...

Climate‐driven ecosystem shifts occur through turnover in the foundation species which structure the landscape. Therefore, to predict the fate of areas undergoing climate‐driven ecosystem shifts, one approach is to characterize ecological and evolutionary responses of foundation species along dynamic environmental gradients. One such gradient is th...

Rising sea levels lead to the migration of salt marshes into coastal forests, thereby shifting both ecosystem composition and function. In this study, we investigate leaf litter decomposition, a critical component of forest carbon cycling, across the marsh-forest boundary with a focus on the potential influence of environmental gradients (i.e., tem...

Herbivory can hinder restoration success by limiting the recovery of plant biodiversity. This study investigates whether plant-plant interactions, such as associational defenses, can increase the survival of a palatable species in restoration contexts where herbivory inhibits recovery. Specifically, we investigate the potential of associational def...

Sea level rise and storm surges drive coastal forest retreat and salt marsh expansion. Both salinization and flooding control ecological zonation and ecosystem transition in coastal areas. Hydrological variables, if coupled with ecological surveys, can explain the different stages of coastal forest retreat and marsh encroachment. In this research,...

Transferable and mechanistic understanding of cross-scale interactions is necessary to predict how coastal systems respond to global change. Cohesive datasets across geographically distributed sites can be used to examine how transferable a mechanistic understanding of coastal ecosystem control points is. To address the above research objectives, d...

In the original publication [...]

Marsh plants regulate marsh surface elevation through organic matter accumulation and sediment capturing, thus feedback loops and relationships between vegetation and marsh elevation form the basis of numerical models that estimate and predict marsh vulnerability to Sea Level Rise (SLR). However, with interior portions of shallow-sloping microtidal...

Coastal landscapes are naturally shifting mosaics of distinct ecosystems that are rapidly migrating with sea-level rise. Previous work illustrates that transitions among individual ecosystems have disproportionate impacts on the global carbon cycle, but this cannot address nonlinear interactions between multiple ecosystems that potentially cascade...

Saltwater intrusion on coastal farmlands can render productive land unsuitable for agricultural activities. While the visible extent of salt-impacted land provides a useful saltwater intrusion proxy, it is challenging to identify in early stages. Moreover, associated ecological and economic impacts are often underestimated as reduced crop yields in...

Species-specific variation in response to stress is a key driver of ecological patterns. As climate change alters stress regimes, coastal plants are experiencing intensifying salinity stress due to sea-level rise and more intense storms. This study investigates the variation in species' responses to presses and pulses of salinity stress in five gly...

Expansion of shrubs has been observed in a number of biomes and in response to diverse global change drivers. Noting shrub expansion in coastal forests affected by sea level rise, we began to monitor shrub populations in a transgressing loblolly pine forest in coastal Virginia. Forest study plots spanned a gradient of salinity and progression towar...

Recent studies have focused on the effect of large tropical cyclones (hurricanes) on the shore, neglecting the role of less intense but more frequent events. Here we analyze the effect of the offshore tropical storm Melissa on groundwater data collected along the North America Atlantic coast. Our meta‐analysis indicates that both groundwater level...

Experimental results from a multi-year exclosure study (2009–2015) demonstrate strong effects of geese on plant cover and species diversity in an urban, restored tidal freshwater wetland. Access by geese inhibited plant establishment and suppressed plant diversity, particularly of annual plant species. Our experimental results demonstrate that the...

Climate change is driving abiotic shifts that can threaten the conservation of foundation species and the habitats they support. Range shifts are one mechanism of escape, but this requires successful colonization of habitats where interspecific interactions may differ from those to which a species has adapted. For plants with multiple reproductive...

Echinoderms are an ancient deuterostome phylum of marine animals that, under physiological stresses or increases in pathogen populations, often from environmental changes, can be infected and may succumb to diseases in both larvae and adults. Mass die-offs of echinoderms that are keystone species alter their essential functions in maintaining ecosy...

Barrier islands and their backbarrier saltmarshes have a reciprocal relationship: aeolian and storm processes transport sediment from the beaches and dunes to create and build marshes along the landward fringe of the island. In turn, these marshes exert a stabilizing influence on the barrier by widening the barrier system and forming a platform ont...

A paradigm in carbon cycling science predicts that sea-level rise will enhance carbon accumulation in an apparent negative carbon-climate feedback1,2. However, ecosystems exposed to combinations of stressors and subsidies – such as saltwater intrusion and sea-level rise – may adapt, transition to an alternative state, or experience a decline in fun...

Phragmites australis is a cosmopolitan grass that has transformed tidal wetlands in regions where it is invasive. The position of P. australis at the upland margin of tidal wetlands makes it likely to be among the earliest species to colonize uplands in marshes responding to sea-level rise; P. australis has been spreading in step with transgressive...

Ecotones are responsive to environmental change and pave a path for succession as they move across the landscape. We investigated the biotic and abiotic filters to species establishment on opposite ends of a tidal marsh‐forest ecotone that is moving inland in response to sea level rise. We transplanted four plant species common to the ecotone to th...

The rapid degradation of ecosystems jeopardizes the services they provide. Among the most valuable of these services is protection of coastlines by shoreline ecological communities, such as coral reefs, mangroves and salt marshes. Currently, coastal protection potential of ecosystems is estimated primarily as a function of their spatial extent and...

Interior marsh pond formation has been commonly observed in tidal marshes affected by high rates of relative sea level rise (RSLR). However, it is difficult to conclude whether an accretion deficit (accretion which does not keep pace with RSLR) or natural ice and wrack disturbance has driven pond formation. We propose that marsh deterioration cause...

The impacts of ocean deoxygenation on biodiversity and ecosystem function are well established in temperate regions, and here we illustrate how the study of hypoxia in tropical ecosystems can offer insights of general importance. We first describe how mechanisms of resilience have developed in response to naturally occurring hypoxia across three tr...

Saltwater intrusion (SWI) is the landward movement of seawater, which can salinize coastal farmlands and affect crop yields. Germination is an especially vulnerable life history stage for crops. Salt stress reduces a seed’s ability to absorb water (osmotic stress) and causes an ion imbalance within the seed (ionic stress), ultimately inhibiting ger...

Sea level rise is reshaping the coasts, allowing coastal habitats such as tidal marshes to migrate inland. To predict where changes will occur, it is critical to understand the factors that influence land cover transition. Here, we test the influence of land cover type on land cover transition. We hypothesized that marsh migration may vary by uplan...

Although the effects of persistent hypoxia have been well established, few studies have explored the community-level effects of short-duration and diel-cycling hypoxia, for example on predator–prey interactions. Consumer stress models predict that mobile predators will flee hypoxia, while prey stress models predict that sessile species, unable to a...

An amendment to this paper has been published and can be accessed via a link at the top of the paper.

Resource competition theory (R* theory) predicts that the species with the highest efficiency (lowest resource requirements) will exclude all other species when competing over a single resource. This prediction contrasts the vast diversity in natural systems where there are often few limiting resources. We conjecture that this prediction is derived...

Background & aims: The capacity of dispersal to promote or hinder species' responses to global change remains a major question in ecology. One ecosystem experiencing rapid change is the tidal marsh, which is migrating inland in response to accelerated sea level rise. Few studies to date have investigated the ecological dynamics that impact this la...

Ghost forests created by the submergence of low-lying land are one of the most striking indicators of climate change along the Atlantic coast of North America. Although dead trees at the margin of estuaries were described as early as 1910, recent research has led to new recognition that the submergence of terrestrial land is geographically widespre...

Questions Sea level rise and saltwater intrusion are changing low‐lying coastal landscapes, converting agricultural land and other upland habitats to tidal marsh. Abandoned, saline agricultural fields are affected by a unique combination of environmental filters, those traditionally found in tidal marsh – salinity and flooding – alongside those of...

Saltwater intrusion is the leading edge of sea-level rise, preceding tidal inundation, but leaving its salty signature far inland. With climate change, saltwater is shifting landward into regions that previously have not experienced or adapted to salinity, leading to novel transitions in biogeochemistry, ecology, and human land uses. We explore the...

The potential resilience of biological communities to accelerating rates of global change has received considerable attention. We suggest that some shallow aquatic ecosystems, where temperature, dissolved oxygen (DO), and pH can exhibit extreme variation on short timescales of hours or days, provide an opportunity to develop a mechanistic understan...

To determine factors limiting the distribution of two ecotypes of the annual legume Chamaecrista fasciculata along an abrupt flooding gradient, we quantified the relative importance of tolerance, intra-specific competition, and allocation patterns to vegetative and reproductive functions and their genetic basis. The ecotypes grow in dry upland and...

Interspecific interactions are important structuring forces in ecological communities. Interactions can be disturbed when species are lost from a community. When interactions result in fitness gains for at least one participating organism, that organism may experience reduced fitness as a result of interaction disturbance. However, many species exh...

Mutualisms are important structuring forces in ecological communities, influencing ecosystem functions, diversity, and evolutionary trajectories. New interactions, particularly between native and non-native species, are globally increasing in biotic communities as species introductions accelerate. Positive interactions such as novel mutualisms can...

This pioneering volume provides a blueprint for managing the challenges of ocean conservation using marine historical ecology—an interdisciplinary area of study that is helping society to gain a more in-depth understanding of past human-environmental interactions in coastal and marine ecosystems and of the ecological and social outcomes associated...

The appropriate role of historical information in ecosystem restoration is a topic of debate within restoration ecology, as the discipline and the practice of restoration adapt to keep up with the increasing demands and challenges of multiple human impacts and global climate change. Whereas historical data have traditionally been used to define res...

An age-old conflict around a seemingly simple question has resurfaced: why do we conserve nature? Contention around this issue has come and gone many times, but in the past several years we believe that it has reappeared as an increasingly acrimonious debate between, in essence, those who argue that nature should be protected for its own sake (intr...

Estuaries and coastal seas provide valuable ecosystem services but are particularly vulnerable to the co-occurring threats of climate change and oxygen-depleted dead zones. We analyzed the severity of climate change predicted for existing dead zones, and found that 94% of dead zones are in regions that will experience at least a 2 °C temperature in...

Invasive species threaten biodiversity and incur costs exceeding billions of US$. Eradication efforts, however, are nearly always unsuccessful. Throughout much of North America, land managers have used expensive, and ultimately ineffective, techniques to combat invasive Phragmites australis in marshes. Here, we reveal that Phragmites may potentiall...

Many coastal habitat restoration projects are focused on restoring the population of a single foundation species to recover an entire ecological community. Estimates of the ecosystem services provided by the restoration project are used to justify, prioritize, and evaluate such projects. However, estimates of ecosystem services provided by a single...

Currently, coastal protection potential of ecosystems is estimated primarily as a function of its spatial extent and type. The degree to which coastal protection depends on aspects of biodiversity within these ecosystems is, however, less explored. Here, we provide a short summary of classical coastal protection strategies and the current state of...

Salt marsh plant communities have long been envisioned as dynamic, resilient systems that quickly recover from human impacts and natural disturbances. But are salt marshes sufficiently resilient to withstand the escalating intensity and scale of human impacts in coastal environments? In this study we examined the independent and interactive effects...

Variation in physical factors, such as slope, orientation, and wind exposure, shapes thermal conditions. Variation in substrate size is common in many habitats, but its thermal consequences for organisms are not well characterized. Larger substrates should remain more thermally stable and act as thermal refuges for associated organisms during short...

Foundation species structure environments and create refuge from environmental stress. In New England high salt marsh, the grass Spartina patens is a foundation species that reduces salinity, anoxia, desiccation, and thermal stresses through canopy shading and root proliferation. In a factorial S. patens-removal and warming field experiment, founda...

For more than a century, coastal wetlands have been recognized for their ability to stabilize shorelines and protect coastal communities. However, this paradigm has recently been called into question by small-scale experimental evidence. Here, we conduct a literature review and a small meta-analysis of wave attenuation data, and we find overwhelmin...

Salt marshes are frequently exposed to storm overwashes resulting in large deposits of sand and wrack at the margin of the high marsh and sand dune communities. On Cape Cod, MA, these disturbance-generated areas are dominated by burrows of the crab Uca pugilator and by nest entrances of the ants Formica subsericea and Tetramorium caespitum. We mimi...

The cordgrass Spartina alterniflora Loisel is a foundation species critical to the establishment and maintenance of western Atlantic salt marshes. Although the factors regulating cordgrass growth along sheltered, fine-sediment shorelines have been exhaustively studied, less is known about the mechanisms that maintain cordgrass production in high-en...

Background/Question/Methods Summer temperatures can impose lethal stresses on rocky intertidal organisms and are influenced by substrate characteristics such as orientation and slope. Here, we show that rock size plays an even more important role than these other factors in determining rock temperatures and influencing the distribution of intertid...

Anthropogenic climate change is predicted to cause widespread biodiversity loss due to shifts in species' distributions, but these predictions rarely incorporate ecological associations such as zonation. Here, we predict the decline of a diverse assemblage of mid-latitude salt marsh plants, based on an ecosystem warming experiment. In New England s...

Secondary succession is impacted by both biotic and abiotic forces, but their relative importance varies due to environmental drivers. Across estuarine salinity gradients, physical stress increases with salinity, and biotic stresses are greater at lower salinities. In southern New England tidal marshes spanning a landscape-scale salinity gradient,...

Salt marshes are among the most abundant, fertile, and accessible coastal habitats on earth, and they provide more ecosystem services to coastal populations than any other environment. Since the Middle Ages, humans have manipulated salt marshes at a grand scale, altering species composition, distribution, and ecosystem function. Here, we review his...

Analyses of habitat loss are often restricted to the past 75 years by the relative youth of aerial photography and remote sensing technologies. Although photographic techniques are highly accurate, they are unable to provide measurements of habitat loss prior to the 1950s. In this study, historical maps from the late 1700s and early 1800s covering...

In the recently radiated genus Inga (Fabaceae), few nucleotide substitutions have accumulated among species, yet large divergences have occurred in defensive phenotypes, suggesting strong selection by herbivores. We compared herbivory and defenses of young leaves for I. goldmanii, a more derived species that follows a "defense" strategy, and I. umb...