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Along low-elevation coastlines, sea-level rise (SLR) threatens to salinate ecosystems. To understand the effects of SLR and freshwater management on landscape carbon (C) exchange, we measured the net ecosystem exchange (NEE) of CO2 between subtropical wetland ecosystems and the atmosphere along a dynamic salinity gradient. Ecosystems were representative of freshwater marl prairies, brackish ecotones, and saline scrub mangrove forests in the southeastern Everglades. Patterns in NEE explained the landward movement of coastal wetlands, a process observed over the last 70 years. The capacity to capture C was greatest along the coast in the scrub mangrove (−294 ± 0.02 g C m−2 y−1) and declined inland into marl prairies (−47 ± 0.03 g C m−2 y−1). Low resilience to current conditions was evident in marl prairies, a result of the legacy impacts of water diversion throughout the greater Everglades. Although the southeastern Everglades captured approximately 115 metric tons of C in 2021, if the ecotone continues to advance at 25 m y−1 over the next century, we project a 12 % increase (16 mt C y−1) in net CO2 capture. Results emphasize that initial functional responses to changes in conditions may not accurately represent long-term outcomes and highlight the role of brackish ecotone communities as the frontline for climate- and management-induced shifts in coastal ecosystem structure and function. This is the first study to use disequilibrium dynamics to understand landscape-level transitions and their implications for C capture. 

Plant phenological and growth responses to experimental warming are widely documented, but less is known about warming effects on plant–pollinator interactions. We investigated the effects of short- and long-term passive warming on flowering phenology, insect visitation, fruit production, and floral rewards in the Low Arctic in northern Alaska. To better understand the role of insect visitors in plant reproductive success, we quantified pollen loads on floral visitors and tested for pollen limitation in four species. Long-term warming advanced flowering onset in evergreen shrubs and forbs. Warming, in general, increased the duration of flowering for forbs, evergreen shrubs, and deciduous shrubs. Considering all growth forms together, long-term warming increased floral density. This pattern was primarily driven by deciduous and evergreen shrubs. Dipterans accounted for more visits than Hymenopterans, although Hymenopterans had higher pollen loads. Insect exclusion and warming decreased fruit set in the forb, Bistorta officinalis Delarbre. Nectar volume in the deciduous shrub, Vaccinium uliginosum, was higher in the warmed plots than the control, but nectar quality did not differ. Advanced flowering onset, longer flowering duration, and increased flower density and nectar volume may have important implications for the pollinator community, warranting further research on long-term warming effects on tundra ecosystems. 

ABSTRACT Global climate change phenomena are amplified in Arctic regions, driving rapid changes in the biota. Here, we examine changes in plant community structure over more than 30 years at two sites in arctic Alaska, USA, Imnavait Creek and Toolik Lake, to understand long‐term trends in tundra response to changing climate. Vegetation cover was sampled every 4–7 years on permanent 1 m²plots spanning a 1 km²grid using a point‐frame. The vascular plant canopies progressively closed at both locations. Canopy cover, defined here as an encounter of a vascular plant above the ground surface, increased from 63% to 91% at Imnavait Creek and from 63% to 89% at Toolik Lake. Both sites showed steady increases in maximum canopy height, increasing by approximately 50% (8 cm). While cover and height increased to some extent for all vascular plant growth forms, deciduous shrubs and graminoids changed the most. For example, at Imnavait Creek the cover of graminoids more than tripled (particularly in wet meadow plots), increasing by 237%. At Toolik Lake the cover of deciduous shrubs more than doubled (particularly in moist acidic plots), increasing by 145%. Despite the steady closing of the plant canopy, cryptogams (lichens and mosses) persisted; in fact, the cover of lichens increased. These results call into question the dominant dogma that cryptogams will decline with increases in vascular plant abundance and demonstrate the resilience of these understory plants. In addition to overall cover, the diversity of vascular plants increased at one site (Imnavait Creek). In contrast to much of the Arctic, summer air temperatures in the Toolik Lake region have not significantly increased over the 30+ year sampling period; however, winter temperatures increased substantially. Changes in vegetation community structure at Imnavait Creek and Toolik Lake are likely the result of winter warming. 

Saline and freshwater wetlands store large amounts of carbon, which has driven interest in their role as nature-based climate solutions. Because these ecosystems can be both sinks and sources of carbon to the atmosphere as environmental conditions and human influence change, the net climate mitigation potential of wetlands at regional to global scales remains uncertain. We used a data-driven approach to measure ground-based and airborne fluxes to upscale carbon dioxide (CO₂) and methane (CH₄) fluxes using satellite-based surface reflectances at 500-m resolution across a gradient of saline to freshwater wetlands in Southern Florida, USA. Daily time series of CO₂and CH₄fluxes from 2000 to 2024 integrated surface properties related to vegetation productivity, flooding, and disturbance, and captured 80% and 91% of the variability in annual fluxes of CO₂and CH₄, respectively. Long-term (23-y) patterns in the fluxes of CH₄, CO₂, and their CO₂-equivalent (CO₂eq) are represented as Global Warming Potential 100 (GWP100) and were shown to vary spatially with wetland management, revealing higher carbon uptake in mangroves susceptible to hurricane damage and coastal hydrology, and greater carbon emissions in freshwater sawgrass marshes where freshwater hydrology is managed for restoration. Regional net annual CO₂eq uptake in coastal and freshwater wetlands increased by 18% from −7.0 ± 3.3 MMT CO₂eq y⁻¹in ~2003 to −8.4 ± 3.8 MMT CO₂eq y⁻¹in ~2020 at an uptake rate of −0.06 ± 0.01 MMT CO₂eq y⁻². Annually, roughly 43% of CO₂uptake was offset by CH₄emissions from all wetlands in the region (from 16% in mangroves to 82% in freshwater marshes). 

The essential oils of the widely distributed boreal/Arctic dwarf shrub, Rhododendron tomentosum ssp. subarcticum (Harmaja) G.D. Wallace, have important ecological, cultural, medicinal, and commercial roles. To understand the relationship between resource limitation and essential oil content of this species we measured the amount and diversity of terpenes from shoots of plants exposed to a 14-year ecosystem resource manipulation experiment in Arctic Alaska. Treatments tested interactive effects of nitrogen (N) and phosphorus (P) addition, warming and N + P fertilization, and shading and N + P fertilization. The controls and NP fertilization had the highest essential oil content, whereas shading and P addition had less than 20% of the control content. Warming reduced essential oil content to <65% of that of the controls. Essential oil components varied greatly among the treatments, with significant differences in the expression of specific essential oil components. Large changes in plant community composition and ecosystem structure in response to treatments likely played a large role in the response of R. tomentosum. Our data suggest that resource changes in response to climate warming and its secondary effects on light and nutrient availability have the potential to change the profiles of essential oils in R. tomentosum, with important ecological and cultural impacts. 

Plot-level photography is an attractive time-saving alternative to field measurements for vegetation monitoring. However, widespread adoption of this technique relies on efficient workflows for post-processing images and the accuracy of the resulting products. Here, we estimated relative vegetation cover using both traditional field sampling methods (point frame) and semi-automated classification of photographs (plot-level photography) across thirty 1 m2 plots near Utqiaġvik, Alaska, from 2012 to 2021. Geographic object-based image analysis (GEOBIA) was applied to generate objects based on the three spectral bands (red, green, and blue) of the images. Five machine learning algorithms were then applied to classify the objects into vegetation groups, and random forest performed best (60.5% overall accuracy). Objects were reliably classified into the following classes: bryophytes, forbs, graminoids, litter, shadows, and standing dead. Deciduous shrubs and lichens were not reliably classified. Multinomial regression models were used to gauge if the cover estimates from plot-level photography could accurately predict the cover estimates from the point frame across space or time. Plot-level photography yielded useful estimates of vegetation cover for graminoids. However, the predictive performance varied both by vegetation class and whether it was being used to predict cover in new locations or change over time in previously sampled plots. These results suggest that plot-level photography may maximize the efficient use of time, funding, and available technology to monitor vegetation cover in the Arctic, but the accuracy of current semi-automated image analysis is not sufficient to detect small changes in cover. 

ABSTRACT Mangrove forests are typically considered resilient to natural disturbances, likely caused by the evolutionary adaptation of species‐specific traits. These ecosystems play a vital role in the global carbon cycle and are responsible for an outsized contribution to carbon burial and enhanced sedimentation rates. Using eddy covariance data from two coastal mangrove forests in the Florida Coastal Everglades, we evaluated the impact hurricanes have on mangrove forest structure and function by measuring recovery to pre‐disturbance conditions following Hurricane Wilma in 2005 and Hurricane Irma in 2017. We determined the “recovery debt,” the deficit in ecosystem structure and function following a disturbance, using the leaf area index (LAI) and the net ecosystem exchange (NEE) of carbon dioxide (CO₂). Calculated as the cumulative deviation from pre‐disturbance conditions, the recovery debt incorporated the recapture of all the carbon lost due to the disturbance. In Everglades mangrove forests, LAI returned to pre‐disturbance levels within a year, and ecosystem respiration and maximum photosynthetic rates took much longer, resulting in an initial recovery debt of 178 g C m⁻²at the tall forest with limited impacts at the scrub forest. At the landscape scale, the initial recovery debt was 0.40 Mt C, and in most coastal mangrove forests, all lost carbon was recovered within just 4 years. While high‐intensity storms could have prolonged impacts on the structure of subtropical forests, fast canopy recovery suggests these ecosystems will remain strong carbon sinks. 

Increases in shrub growth and canopy cover are well documented community responses to climate warming in the Arctic. An important consequence of larger deciduous shrubs is shading of prostrate plant species, many of which are important sources of nectar and berries. Here, we present the impact of a shading experiment on two prostrate shrubs, Vaccinium vitis-idaea L. and Arctous alpina L., in northern Alaska over two growing seasons. We implemented three levels of shading (no shade, 40% shade, and 80% shade) in dry heath and moist acidic tundra. Plots were monitored for soil moisture content, surface temperature, normalized difference vegetation index (NDVI), and flowering. Shading was shown to, on average, lower surface temperature (0.7 °C to 5.3 °C) and increase soil moisture content (0.5% to 5.6%) in both communities. Both species- and plot-level NDVI values were delayed in timing of peak values (7 to 13 days) and decreased at the highest shading. Flower abundance of both species was lower in shaded plots and peak flowering was delayed (3 to 8 days) compared with controls. Changes in timing may result in phenological mismatches and can impact other trophic levels in the Arctic as both the flowers and resulting berries are important food sources for animals. 

The Arctic is warming twice as fast as the rest of the globe. Graminoid, deciduous shrub, and evergreen shrub cover has increased in some regions, but not others. To better understand why plant responses vary across regions, we compared change in plant cover over time with nine functional traits of 12 dominant species in three regions of northern Alaska (Utqiaġvik, Atqasuk, and Toolik Lake). Cover was measured three times from 2008 to 2018. Repeated-measures analysis of variance (ANOVA) found that one species — Carex aquatilis — showed significant change in cover over time, increasing by 12.7% at Atqasuk. Canonical correspondence analysis suggested a relationship between shifts in species cover and traits, but Pearson and Spearman rank correlations did not find a significant trend for any trait when analyzed individually. Investigation of community-weighted means (CWMs) for each trait revealed no significant changes over time for any trait in any region. By comparison, estimated ecosystem values for several traits important to ecosystem functioning showed consistent increases over time in two regions (Utqiaġvik and Atqasuk). Our results indicate that vascular plant community composition and function have remained consistent over time; however, documented increases in total plant cover have important implications for ecosystem functioning. 

This data set is associated with Curasi et al., 2022 (https://doi.org/10.1088/1748-9326/ac6005) it includes detailed survey data for Eriophorum vaginatum spanning sites in the Alaskan, Canadian, and Russian Arctic. The data set includes detailed surveys of tussock density and diameter, shrub basal diameter and abundance, the relationship between tussock size and mass, the relationship between shrub size and mass, tussock chemical properties, soil properties, and bulk density. It also includes outputs and projections from a tussock machine learning ecological niche model. This data was collected to characterize the distribution of this foundation species across the landscape and illustrate its role in the ecosystem. The data collection methods and subsequent analysis are described in detail in https://doi.org/10.1088/1748-9326/ac6005