Modeling Habitat Change in Salt Marshes After Tidal Restoration

Salt marshes continue to degrade in the United States due to indirect human impacts arising from tidal restrictions. Roads or berms with inadequate provision for tidal flow hinder ecosystem functions and interfere with self‐maintenance of habitat, because interactions among vegetation, soil, and hydrology within tidally restricted marshes prevent them from responding to sea level rise. Prediction of the tidal range that is expected after restoration relative to the current geomorphology is crucial for successful restoration of salt marsh habitat. Both insufficient (due to restriction) and excessive (due to subsidence and sea level rise) tidal flooding can lead to loss of salt marshes. We developed and applied the Marsh Response to Hydrological Modifications model as a predictive tool to forecast the success of management scenarios for restoring full tides to previously restricted areas. We present an overview of a computer simulation tool that evaluates potential culvert installations with output of expected tidal ranges, water discharges, and flood potentials. For three New England tidal marshes we show species distributions of plants for tidally restricted and nonrestricted areas. Elevation ranges of species are used for short‐term (<5 years) predictions of changes to salt marsh habitat after tidal restoration. In addition, elevation changes of the marsh substrate measured at these sites are extrapolated to predict long‐term (>5 years) changes in marsh geomorphology under restored tidal regimes. The resultant tidal regime should be designed to provide habitat requirements for salt marsh plants. At sites with substantial elevation losses a balance must be struck that stimulates elevation increases by improving sediment fluxes into marshes while establishing flooding regimes appropriate to sustain the desired plants.     

Determinants of species‐area relationships for marsh‐nesting birds

ABSTRACT To clarify the underlying causes of the species‐area relationship in marsh‐nesting birds, I studied eight freshwater tidal marshes of the Connecticut River that differed in area, degree of isolation, mudflat cover, water cover, tidal regime, and extent of individual plant communities. I measured these habitat variables on aerial infrared photos, and surveyed bird populations by mapping the distribution of all birds in marshes under 5 ha in area and establishing 50‐m radius plots in marshes over 5 ha. From surveys, I determined species richness, population densities, and total populations. Analysis revealed a positive relationship between species richness and area, but no correlation between area and habitat heterogeneity. Other habitat variables were poor predictors of species richness. The lack of a relationship between habitat and species richness appeared to be a consequence of most vegetation types present not being sufficiently distinct for birds to differentially associate with them. I also found no relationship between bird population density and area, suggesting that habitat quality in marshes did not improve with increasing size, and species evenness declined with increasing richness because greater richness was associated with the presence of more rare species. Larger marshes had more rare species, species with larger populations, and species with a minimum threshold area for occurrence. Thus, my results are consistent with theoretical predictions that larger populations are less prone to local extinction and, as individuals are added to a community, more rare species are present.     

Bird species richness is associated with phylogenetic relatedness,plant species richness,and altitudinal range in Inner Mongolia

Bird species richness is mediated by local, regional, and historical factors, for example, competition, environmental heterogeneity, contemporary, and historical climate. Here, we related bird species richness with phylogenetic relatedness of bird assemblages, plant species richness, topography, contemporary climate, and glacial‐interglacial climate change to investigate the relative importance of these factors. This study was conducted in Inner Mongolia, an arid and semiarid region with diverse vegetation types and strong species richness gradients. The following associated variables were included as follows: phylogenetic relatedness of bird assemblages (Net Relatedness Index, NRI), plant species richness, altitudinal range, contemporary climate (mean annual temperature and precipitation, MAT and MAP), and contemporary‐Last Glacial Maximum (LGM) change in climate (change in MAT and change in MAP). Ordinary least squares linear, simultaneous autoregressive linear, and Random Forest models were used to assess the associations between these variables and bird species richness across this region. We found that bird species richness was correlated negatively with NRI and positively with plant species richness and altitudinal range, with no significant correlations with contemporary climate and glacial–interglacial climate change. The six best combinations of variables ranked by Random Forest models consistently included NRI, plant species richness, and contemporary‐LGM change in MAT. Our results suggest important roles of local ecological factors in shaping the distribution of bird species richness across this semiarid region. Our findings highlight the potential importance of these local ecological factors, for example, environmental heterogeneity, habitat filtering, and biotic interactions, in biodiversity maintenance.     

Effects of Long Piers on Birds in Tidal Wetlands

ABSTRACT As human development continues in coastal areas, shoreline properties adjacent to expansive tidal marsh habitat are increasingly used for access to coastal waterways via long piers (>30 m) over marsh habitat. These tidal wetlands provide breeding and foraging habitat for many marsh birds, which may be affected by the human disturbance associated with long piers. Our objectives were to determine the effect of long piers over vegetated tidal marshes on the relative abundance and species richness of marsh birds. We completed combined passive and callback surveys in tidal marsh habitat at 22 sites with long piers and 24 sites without long piers, May-July 2005–2006 in Worcester County, Maryland, USA. Pier sites had lower relative abundance and species richness of obligate marsh birds than nonpier sites. Pier sites had a greater relative abundance of gulls, terns, herons, and egrets than nonpier sites. Pier sites had fewer species of herons and egrets than at nonpier sites. The presence of long piers had no affect on facultative marsh birds. Long pier density was negatively related to obligate marsh bird relative abundance and species richness, and facultative marsh bird species richness, whereas it was positively related to the relative abundance and species richness of gulls and terns. Herons and egrets relative abundance and species richness were not related to long pier density. Obligate marsh birds were negatively affected by long piers, whereas herons, egrets, gulls, and terns appeared to benefit from perching opportunities. Based on the negative effects of long piers on obligate marsh birds, management should focus on reducing the presence and density of long piers in tidal marshes by requiring the removal of existing long piers, or reducing or eliminating permits for construction of new long piers.     

Macro‐Tidal Salt Marsh Ecosystem Response to Culvert Expansion

The purpose of this paper was to examine the vegetative, sedimentary, nekton and hydrologic conditions pre‐restoration and the initial 2 years post‐restoration at a partially restricted macro‐tidal salt marsh site. Replacement of the culvert increased tidal flow by 88%. This was instrumental in altering the geomorphology of the site, facilitating the creation of new salt marsh pannes, expansion of existing pannes in the mid and high marsh zones, and expansion of the tidal creek network by incorporating relict agricultural ditches. In addition, the increase in area flooded resulted in a significant increase in nekton use, fulfilling the mandate of a federal habitat compensation program to increase and improve the overall availability and accessibility of fish habitat. The restoration of a more natural hydrological regime also resulted in the die‐off of freshwater and terrestrial vegetation along the upland edge of the marsh. Two years post‐restoration, Salicornia europea (glasswort) and Atriplex glabriuscula (marsh orache), were observed growing in these die‐back areas. Similar changes in the vegetation community structure were not observed at the reference site; however, the latter did contain higher species richness. This study represents the first comprehensive, quantitative analysis of ecological response to culvert replacement in a hypertidal ecosystem. These data will contribute to the development of long‐term data sets of pre‐ and post‐restoration, and reference marsh conditions to determine if a marsh is proceeding as expected, and to help with models that are aimed at predicting the response of marshes to tidal restoration at the upper end of the tidal spectrum.     

Tidal‐flow restoration provides little nesting habitat for a globally vulnerable saltmarsh bird

Tidal marshes are among the most threatened habitats on Earth because of their limited natural extent, a long history of human drainage and modification, and anticipated future sea‐level rise. Tidal marshes also provide services to humans and support species of high conservation interest. Consequently, millions of dollars have been spent on tidal marsh restoration throughout North America. Southern New England has a long history of tidal marsh restorations, often focused on removal of the invasive plant Phragmites australis. Working in 18 Connecticut marshes, we examined the bird community in 21 plots in restoration sites and 19 plots in reference sites. Restoration plots were divided into those in marshes where management involved restoring tidal flow and those where direct Phragmites control (e.g. cutting, herbicide) was used. Saltmarsh sparrows Ammodramus caudacutus, which are considered globally vulnerable to extinction, were less common where tidal flow had been restored than at reference sites and nested in only one of 14 tidal‐flow restoration plots. No abundance differences were found for large wading birds, willets Tringa semipalmata, or seaside sparrows Ammodramus maritimus. Vegetation at sites where tidal flow had been restored showed characteristics typical of lower‐elevation marsh, which is unsuitable for nesting saltmarsh sparrows. We conclude that, although tidal‐flow restorations in Connecticut control Phragmites and restore native saltmarsh vegetation, they produce conditions that are largely unsuitable for one of the highest conservation priority species found in eastern U.S. salt marshes.     

Habitat size, flora, and fauna: Interactions in a tidal saltwater marsh

Anthropogenic habitat fragmentation is increasingly problematic in both terrestrial and aquatic systems. Fragmentation reduces the size of habitat patches, so examining the effect of patch size on community structure can provide insight into the potential effects of fragmentation. In this study, we examined the effect of habitat size on the density of Spartina alterniflora shoots in tidal saltwater marshes, as well as on the two predominant macrofaunal species, the marsh periwinkle Littoraria irrorata and fiddler crabs Uca spp. We estimated the density of shoots in three different marsh habitats, (1) large island marshes, (2) small island marshes, and (3) large fringing marshes, in Indian Field Creek, York River, Chesapeake Bay. We manipulated shoot density in each of the marsh types to distinguish between the effects of marsh grass density and marsh type on crab and Littoraria densities in the system. We found significant differences in grass density among the three marsh types as well as significant species-specific effects of grass density, marsh type, and distance from edge on faunal abundance. Decreasing the shoot density resulted in a decrease in Littoraria density in the large marshes. Littoraria density increased with distance from edge in the small marshes and in the first 5 m of the fringing marshes, then decreased with distance from edge after 5 m in the fringing marshes. Shoot density had a negative effect on crabs in both the large and small marshes. These results suggest that fragmentation would have a negative effect on the community structure by lowering the densities of both the flora and fauna.     

When species become generalists: on‐going large‐scale changes in bird habitat specialization

Aim Species specialization is often considered as a stable species characteristic over the short term. However, this assumption has hardly been tested, even though it may impair our ability to track the impoverishment of biodiversity induced by the rapid replacement of specialists by generalists. We tested whether species specialization in birds varied over a short period of time, and assessed whether variations in species specialization influence community‐level metrics of biotic homogenization. Location France. Methods We studied the variations in specialization to habitat closure of 94 bird species over the period 2002–08, accounting for species variations in mean density, habitat preference and migratory status. We then quantified the temporal changes in a community specialization index, which measures functional homogenization. Results Specialization decreased over time for 35 species (37%), while 46 (49%) showed non‐significant negative trends and 13 (14%) had null or non‐significant positive trends. The more a species was specialized at the beginning of the study, the more it generalized. We additionally found that changes in the specialization level were density dependent: 34 species (36%) became more generalist in years of higher densities while only one became more specialized. At the community level, accounting for this inter‐annual variability in species specialization accentuated the trend in the functional homogenization of bird communities. Main conclusions Habitat specialization is a labile ecological trait, which may change in the short term following habitat degradation, density dependence and source–sink dynamics. Accounting for short‐term temporal variations in observed habitat specialization of species can increase our understanding of the effects of global changes on species strategies and community dynamics.     

REVISITING WALLACE'S HAUNT: COALESCENT SIMULATIONS AND COMPARATIVE NICHE MODELING REVEAL HISTORICAL MECHANISMS THAT PROMOTED AVIAN POPULATION DIVERGENCE IN THE MALAY ARCHIPELAGO

Sundaland, a biogeographic region of Southeast Asia, is a major biodiversity hotspot. However, little is known about the relative importance of Pleistocene habitat barriers and rivers in structuring populations and promoting diversification here. We sampled 16 lowland rainforest bird species primarily from peninsular Malaysia and Borneo to test the long‐standing hypothesis that animals on different Sundaic landmasses intermixed extensively when lower sea‐levels during the Last Glacial Maximum (LGM) exposed land‐bridges. This hypothesis was rejected in all but five species through coalescent simulations. Furthermore, we detected a range of phylogeographic patterns; Bornean populations are often genetically distinct from each other, despite their current habitat connectivity. Environmental niche modeling showed that the presence of unsuitable habitats between western and eastern Sundaland during the LGM coincided with deeper interpopulation genetic divergences. The location of this habitat barrier had been hypothesized previously based on other evidence. Paleo‐riverine barriers are unlikely to have produced such a pattern, but we cannot rule out that they acted with habitat changes to impede population exchanges across the Sunda shelf. The distinctiveness of northeastern Borneo populations may be underlied by a combination of factors such as rivers, LGM expansion of montane forests and other aspects of regional physiography.     

Global imprint of historical connectivity on freshwater fish biodiversity

The relative importance of contemporary and historical processes is central for understanding biodiversity patterns. While several studies show that past conditions can partly explain the current biodiversity patterns, the role of history remains elusive. We reconstructed palaeo‐drainage basins under lower sea level conditions (Last Glacial Maximum) to test whether the historical connectivity between basins left an imprint on the global patterns of freshwater fish biodiversity. After controlling for contemporary and past environmental conditions, we found that palaeo‐connected basins displayed greater species richness but lower levels of endemism and beta diversity than did palaeo‐disconnected basins. Palaeo‐connected basins exhibited shallower distance decay of compositional similarity, suggesting that palaeo‐river connections favoured the exchange of fish species. Finally, we found that a longer period of palaeo‐connection resulted in lower levels of beta diversity. These findings reveal the first unambiguous results of the role played by history in explaining the global contemporary patterns of biodiversity.     

Biogeography of salt marsh plant zonation on the Pacific coast of South America

Aim

The aim of this study was to investigate the biogeography of plant zonation in salt marshes on the Pacific coast of South America; to examine whether salt marsh plant zonation varies with latitude; and to explore the relative importance of climatic, tidal, edaphic and disturbance factors in explaining large‐scale variation in salt marsh plant community structure.

Location

A 2,000‐km latitudinal gradient on the Pacific coast in Chile, with a climate shift from hyper‐arid at low to hyper‐humid at high latitudes.

Methods

Plant zonation was quantified in field surveys of ten marshes. Climate, tidal regimes, edaphic factors and disturbances (tsunami and rainfall floods) were determined. We used multivariate analyses to explore their relative importance in explaining large‐scale variation in salt marsh plant community structure.

Results

Across latitude, marshes were dominated by distinct plant communities in different climate regions, especially at the extreme dry and wet latitudes. Intertidal plant species zonation was present in hyper‐arid and semi‐arid climates, but not in arid, humid and hyper‐humid climates. Latitudinal variation in low‐marsh plant communities (regularly flooded at high tide) was largely a function of precipitation, while at high marshes (never flooded at high tide) latitudinal variation was explained with precipitation, temperature, tidal cycles, soil salinity and disturbances.

Main conclusions

Salt marshes on the Pacific coast of South America belong to Dry Coast and Temperate biogeographic types. Salt marsh plant zonation varies across latitude, and is explained by climatic, tidal, edaphic and disturbance factors. These patterns appear to be mechanistically explained by extrapolating experimentally generated community assembly models and have implications for predicting responses to climate change.     

Climate‐driven shifts in the distribution of koala‐browse species from the Last Interglacial to the near future

The koala's Phascolarctos cinereus distribution is currently restricted to eastern and south‐eastern Australia. However, fossil records dating from 70 ± 4 ka (ka = 10³ yr) from south‐western Australia and the Nullarbor Plain are evidence of subpopulation extinctions in the southwest at least after the Last Interglacial (~128–116 ka). We hypothesize that koala sub‐population extinctions resulted from the eastward retraction of the koala's main browse species in response to unsuitable climatic conditions. We further posit a general reduction in the distribution of main koala‐browse trees in the near future in response climate change. We modelled 60 koala‐browse species and constructed a set of correlative species distribution models for five time periods: Last Interglacial (~128–116 ka), Last Glacial Maximum (~23–19 ka), Mid‐Holocene (~7–5 ka), present (interpolations of observed data, representative of 1960–1990), and 2070. We based our projections on five hindcasts and one forecast of climatic variables extracted from WorldClim based on two general circulation models (considering the most pessimistic scenario of high greenhouse‐gas emissions) and topsoil clay fraction. We used 17 dates of koala fossil specimens identified as reliable from 70 (± 4) to 535 (± 49) ka, with the last appearance of koalas at 70 ka in the southwest. The main simulated koala‐browse species were at their greatest modelled extent of suitability during the Last Glacial Maximum, with the greatest loss of koala habitat occurring between the Mid‐Holocene and the present. We predict a similar habitat loss between the present and 2070. The spatial patterns of habitat change support our hypothesis that koala extinctions in the southwest, Nullarbor Plain and central South Australia resulted from the eastward retraction of the dominant koala‐browse species in response to long‐term climate changes. Future climate patterns will likely increase the extinction risk of koalas in their remaining eastern ranges.     

Responses of Salt Marsh Ecosystems to Mosquito Control Management Practices along the Atlantic Coast (U.S.A.)

Open marsh water management (OMWM) of salt marshes modifies grid‐ditched marshes by creating permanent ponds and radial ditches in the high marsh that reduce mosquito production and enhance fish predation on mosquitoes. It is preferable to using pesticides to control salt marsh mosquito production and is commonly presented as a restoration or habitat enhancement tool for grid‐ditched salt marshes. Monitoring of nekton, vegetation, groundwater level, soil salinity, and bird communities before and after OMWM at 11 (six treatment and five reference sites) Atlantic Coast (U.S.A.) salt marshes revealed high variability within and among differing OMWM techniques (ditch‐plugging, reengineering of sill ditches, and the creation of ponds and radial ditches). At three marshes, the dominant nekton shifted from fish (primarily Fundulidae species) to shrimp (Palaemonidae species) after manipulations and shrimp density increased at other treatment sites. Vegetation changed at only two sites, one with construction equipment impacts (not desired) and one with a decrease in woody vegetation along existing ditches (desired). One marsh had lower groundwater level and soil salinity, and bird use, although variable, was often unrelated to OMWM manipulations. The potential effects of OMWM manipulations on non‐target salt marsh resources need to be carefully considered by resource planners when managing marshes for mosquito control.     

Divergent selection and drift shape the genomes of two avian sister species spanning a saline–freshwater ecotone

The role of species divergence due to ecologically based divergent selection—or ecological speciation—in generating and maintaining biodiversity is a central question in evolutionary biology. Comparison of the genomes of phylogenetically related taxa spanning a selective habitat gradient enables discovery of divergent signatures of selection and thereby provides valuable insight into the role of divergent ecological selection in speciation. Tidal marsh ecosystems provide tractable opportunities for studying organisms' adaptations to selective pressures that underlie ecological divergence. Sharp environmental gradients across the saline–freshwater ecotone within tidal marshes present extreme adaptive challenges to terrestrial vertebrates. Here, we sequence 20 whole genomes of two avian sister species endemic to tidal marshes—the saltmarsh sparrow (Ammospiza caudacutus) and Nelson's sparrow (A. nelsoni)—to evaluate the influence of selective and demographic processes in shaping genome‐wide patterns of divergence. Genome‐wide divergence between these two recently diverged sister species was notably high (genome‐wide F_ST = 0.32). Against a background of high genome‐wide divergence, regions of elevated divergence were widespread throughout the genome, as opposed to focused within islands of differentiation. These patterns may be the result of genetic drift resulting from past tidal march colonization events in conjunction with divergent selection to different environments. We identified several candidate genes that exhibited elevated divergence between saltmarsh and Nelson's sparrows, including genes linked to osmotic regulation, circadian rhythm, and plumage melanism—all putative candidates linked to adaptation to tidal marsh environments. These findings provide new insights into the roles of divergent selection and genetic drift in generating and maintaining biodiversity.     

Salt marsh elevation is a strong determinant of nest‐site selection by Clapper Rails in Georgia,USA

As sea levels rise, birds nesting in coastal marshes will be particularly vulnerable to increased tidal inundation. Understanding how marsh birds select their nesting habitat along the elevational gradient of these marshes will provide insight into how these species might be affected by rising sea levels. Clapper Rails (Rallus crepitans) are coastal marsh‐nesting birds whose nests are vulnerable to flooding, but it is not clear if they select for habitat along the elevational gradient or only use other habitat cues. Our objective was to determine if Clapper Rails select higher‐elevation nest sites, while also controlling for selection of other habitat variables at both landscape and territory levels, by comparing nest habitat to habitat in other areas of territories and at random points in the marsh landscape. At the landscape level, Clapper Rails did not exhibit selection for the elevational gradient, with nests and random points at similar elevations. At the territory level, however, nest‐site selection was most influenced by elevation and plant height, with Clapper Rails selecting nest sites with higher elevations and in areas with taller plants. However, the strength of the elevation effect was uncertain, suggesting the importance of precise elevation measurements in the field. Given this selection for higher‐elevation nest sites, Clapper Rails may be somewhat resilient to increased tidal inundation. However, the potential for increased intra‐ and interspecific competition for high‐elevation marshes should make conservation of these habitats a priority.     

Ecological responses to tidal restorations of two northern New England salt marshes

Efforts are underway to restore tidal flow in New England salt marshes that were negatively impacted by tidal restrictions. We evaluated a planned tidal restoration at Mill Brook Marsh (New Hampshire) and at Drakes Island Marsh (Maine) where partial tidal restoration inadvertently occurred. Salt marsh functions were evaluated in both marshes to determine the impacts from tidal restriction and the responses following restoration. Physical and biological indicators of salt marsh functions (tidal range, surface elevations, soil water levels and salinities, plant cover, and fish use) were measured and compared to those from nonimpounded reference sites. Common impacts from tidal restrictions at both sites were: loss of tidal flooding, declines in surface elevation, reduced soil salinity, replacement of salt marsh vegetation by fresh and brackish plants, and loss of fish use of the marsh. Water levels, soil salinities and fish use increased immediately following tidal restoration. Salt-intolerant vegetation was killed within months. After two years, mildly salt-tolerant vegetation had been largely replaced in Mill Brook Marsh by several species characteristic of both high and low salt marshes. Eight years after the unplanned, partial tidal restoration at Drakes Island Marsh, the vegetation was dominated bySpartina alterniflora, a characteristic species of low marsh habitat. Hydrologic restoration that allowed for unrestricted saltwater exchange at Mill Brook restored salt marsh functions relatively quickly in comparison to the partial tidal restoration at Drakes Island, where full tidal exchange was not achieved. The irregular tidal regime at Drakes Island resulted in vegetation cover and patterns dissimilar to those of the high marsh used as a reference. The proper hydrologic regime (flooding height, duration and frequency) is essential to promote the rapid recovery of salt marsh functions. We predict that functional recovery will be relatively quick at Mill Brook, but believe that the habitat at Drakes Island will not become equivalent to that of the reference marsh unless the hydrology is further modified.     

Ecological responses to tidal restorations of two northern New England salt marshes

Efforts are underway to restore tidal flow in New England salt marshes that were negatively impacted by tidal restrictions. We evaluated a planned tidal restoration at Mill Brook Marsh (New Hampshire) and at Drakes Island Marsh (Maine) where partial tidal restoration inadvertently occurred. Salt marsh functions were evaluated in both marshes to determine the impacts from tidal restriction and the responses following restoration. Physical and biological indicators of salt marsh functions (tidal range, surface elevations, soil water levels and salinities, plant cover, and fish use) were measured and compared to those from nonimpounded reference sites. Common impacts from tidal restrictions at both sites were: loss of tidal flooding, declines in surface elevation, reduced soil salinity, replacement of salt marsh vegetation by fresh and brackish plants, and loss of fish use of the marsh.Water levels, soil salinities and fish use increased immediately following tidal restoration. Salt-intolerant vegetation was killed within months. After two years, mildly salt-tolerant vegetation had been largely replaced in Mill Brook Marsh by several species characteristic of both high and low salt marshes. Eight years after the unplanned, partial tidal restoration at Drakes Island Marsh, the vegetation was dominated bySpartina alterniflora, a characteristic species of low marsh habitat.Hydrologic restoration that allowed for unrestricted saltwater exchange at Mill Brook restored salt marsh functions relatively quickly in comparison to the partial tidal restoration at Drakes Island, where full tidal exchange was not achieved. The irregular tidal regime at Drakes Island resulted in vegetation cover and patterns dissimilar to those of the high marsh used as a reference. The proper hydrologic regime (flooding height, duration and frequency) is essential to promote the rapid recovery of salt marsh functions. We predict that functional recovery will be relatively quick at Mill Brook, but believe that the habitat at Drakes Island will not become equivalent to that of the reference marsh unless the hydrology is further modified.Corresponding Editor: R.E. Turner Manuseript     

Does National Wetland Inventory class consistently identify vegetation and edaphic differences in Oregon tidal wetlands?

Accurately mapping, modeling, and managing the diversity of wetlands present in estuaries often relies on habitat classification systems that consistently identify differences in biotic structure or other ecosystem characteristics between classes. We used field data from four Oregon estuaries to test for differences in vegetation structure and edaphic characteristics among three tidal emergent marsh classes derived from National Wetlands Inventory (NWI) data: low estuarine marsh, high estuarine marsh, and tidal palustrine marsh. Independently of NWI class, we also evaluated the number and types of plant assemblages present and how edaphic variables, non-native plant cover, and plant species richness varied among them. Pore water salinity varied most strongly across marsh classes, with sediment carbon and nitrogen content, grain size and marsh surface elevation showing smaller differences. Cover of common vascular plant species differed between marsh classes and overall vegetation composition was somewhat distinct among marsh types. High estuarine marsh had the largest species pools. However, plot-level plant diversity was similar among marsh classes. Non-native species cover was highest in tidal palustrine and high estuarine marshes. The marshes in the study contained a large number of plant assemblages with most occurring across more than one marsh class. The more common assemblages occurred along a continuum of tidal elevation, soil salinity, and edaphic characteristics, with varying plant richness and non-native cover. Our data suggest that NWI classes are useful for differentiating several general features of Oregon tidal marsh structure, but that more detailed information on plant assemblages found within those wetland classes would allow more precise characterization of additional wetland features such as edaphic conditions and plant diversity.     

Upslope development of a tidal marsh as a function of upland land use

To thrive in a time of rapid sea‐level rise, tidal marshes will need to migrate upslope into adjacent uplands. Yet little is known about the mechanics of this process, especially in urbanized estuaries, where the adjacent upland is likely to be a mowed lawn rather than a wooded natural area. We studied marsh migration in a Long Island Sound salt marsh using detailed hydrologic, edaphic, and biotic sampling along marsh‐to‐upland transects in both wooded and lawn environments. We found that the overall pace of marsh development was largely unaffected by whether the upland being invaded was lawn or wooded, but the marsh‐edge plant communities that developed in these two environments were quite different, and some indicators (soil salinity, foraminifera) appeared to migrate more easily into lawns. In addition, we found that different aspects of marsh structure and function migrated at different rates: Wetland vegetation appeared to be a leading indicator of marsh migration, while soil characteristics such as redox potential and surface salinity developed later in the process. We defined a ‘hydrologic migration zone’, consisting of elevations that experience tidal inundation with frequencies ranging from 20% to 0.5% of high tides. This hydrologically defined zone – which extended to an elevation higher than the highest astronomical tide datum – captured the biotic and edaphic marsh‐upland ecotone. Tidal inundation at the upper border of this migration zone is highly variable over time and may be rising more rapidly than mean sea level. Our results indicate that land management practices at the upland periphery of tidal marshes can facilitate or impede ecosystem migration in response to rising sea level. These findings are applicable to large areas of tidal marsh along the U.S. Atlantic coast and in other urbanized coastal settings.     

Genomic data reveal ancient microendemism in forest scorpions across the California Floristic Province

The California Floristic Province (CFP) in western North America is a globally significant biodiversity hotspot. Elucidating patterns of endemism and the historical drivers of this diversity has been an important challenge of comparative phylogeography for over two decades. We generated phylogenomic data using ddRADseq to examine genetic structure in Uroctonus forest scorpions, an ecologically restricted and dispersal‐limited organism widely distributed across the CFP north to the Columbia River. We coupled our genetic data with species distribution models (SDMs) to determine climatically suitable areas for Uroctonus both now and during the Last Glacial Maximum. Based on our analyses, Uroctonus is composed of two major genetic groups that likely diverged over 2 million years ago. Each of these groups itself contains numerous genetic groups that reveal a pattern of vicariance and microendemism across the CFP. Migration rates among these populations are low. SDMs suggest forest scorpion habitat has remained relatively stable over the last 21 000 years, consistent with the genetic data. Our results suggest tectonic plate rafting, mountain uplift, river drainage formation and climate‐induced habitat fragmentation have all likely played a role in the diversification of Uroctonus. The intricate pattern of genetic fragmentation revealed across a temporal continuum highlights the potential of low‐dispersing species to shed light on small‐scale patterns of biodiversity and the underlying processes that have generated this diversity in biodiversity hotspots.