My role: Collaborator
PI: Karen H. Beard (Utah State University)
co-PIs: A. Joshua Leffler (South Dakota State University), Katharine C. Kelsey (University of Colorado Denver)
Funding: U.S. National Science Foundation (NSF)

Keywords: Alaska; Arctic; CH₄ fluxes; CO₂ fluxes (GEP, ER, NEE); Geese; Herbivory; High-tide floods; International Tundra Experiment (ITEX); Litter decomposition (Tea Bag Index); Micro-environment; Open-top chambers (OTCs); Plant community composition; Plant functional traits; Plant functional types (PFTs); Roots; Summer warming; Tundra; ex-typhoon Merbok; Yukon-Kuskokwim (Y-K) Delta; Wetlands

Overview

Over the past four decades, coastal high-latitude regions have experienced some of the most dramatic effects of climate change. The Arctic has warmed nearly four times faster than the global average, while its coastal zones are increasingly threatened by altered flooding regimes. Melting sea and land ice, combined with relative sea-level rise, land subsidence, and more frequent storm surges, are exposing low-lying deltaic plains to recurrent inundation. Yet, the extent to which flooding alters these ecosystems and its ecological consequences remain poorly understood.

This project investigates how increased high-tide flooding, alone and in combination with warming and herbivory, influences plant functional traits, community composition, and key ecosystem processes such as CO₂ and CH₄ fluxes and decomposition in the Yukon-Kuskokwim (Y-K) Delta (Alaska), one of the largest river deltas in North America. The research contributes to a broader understanding of how multiple interacting stressors – flooding, temperature, and grazing – shape community and ecosystem responses in Arctic coastal landscapes.

Approach

This project integrates large-scale field experiments, mesocosm studies, laboratory manipulations, and landscape-scale observations to disentangle the effects of flooding and its components – such as changes in soil salinity, soil moisture, and sediment deposition – as well as warming and herbivory, on coastal tundra ecosystems. Fieldwork was conducted over three summer campaigns (2022-2024).

A large-scale field experiment simulating flooding and warming was conducted in two contrasting plant communities: a lowland wetland prone to flooding and an upland tundra less frequently inundated. A complementary mesocosm experiment simulated flooding, warming, and goose herbivory in two lowland wetlands at slightly different elevations, both flood-prone but differing markedly in plant-community composition.

A series of laboratory experiments further isolated specific mechanisms by manipulating salinity, moisture, temperature, goose feces deposition, and sediment load, using both bare soil cores and intact vegetation-soil turfs transported from the field.

Finally, landscape-scale surveys were established after ex-typhoon Merbok (2022), which caused extensive inland inundation up to 30 km from the coast, providing a rare opportunity to assess the ecological consequences of a natural flooding event.

Selected findings by 2025

Published research as of 2025 primarily derives from the factorial field experiment simulating flooding and warming in lowland wetland plant communities. Results indicate that these drivers modify plant-community composition by increasing the abundance of the already dominant graminoids while reducing the accumulation of standing dead biomass (Petit Bon et al., 2024), with cascading effects on CO₂ and CH₄ exchange (Kelsey et al., 2025). Such rapid increases in biomass production and turnover, particularly among graminoids with high-quality litter, have important implications for carbon and nutrient cycling in increasingly flood-prone Arctic coastal ecosystems.

One landscape, many responses: how Arctic soils react to climate change

The Arctic is warming rapidly, sea levels are rising, and flooding is becoming more frequent in many coastal regions. At the same time, changes in the abundance and distribution of migratory geese are altering the flow of nutrients across the landscape. Together, these changes have the potential to reshape how Arctic soils store and release carbon and nitrogen, yet their combined effects remain poorly understood.

We examined how warming, flooding, and goose-derived nutrients influence carbon and nitrogen cycling in soils from the Yukon–Kuskokwim Delta of western Alaska. Rather than focusing on a single habitat, we compared four distinct soil types spanning a coastal elevation gradient, from frequently flooded grazing lawns and wetlands to rarely flooded upland tundra. Using a controlled laboratory experiment, we measured carbon dioxide (CO₂) and methane (CH₄) emissions, as well as changes in soil nitrogen availability.

We found that both warming and goose feces increased carbon release from soils, although their effects varied among soil types. Flooding, however, produced strikingly different outcomes depending on the soil. In some cases, flooding reduced carbon dioxide emissions, while in others it increased methane production. The strongest response occurred in tundra soils, where flooding substantially suppressed methane emissions despite warmer temperatures. Nitrogen cycling also responded differently across the four soil types, revealing that soils with different flooding histories can react in fundamentally different ways to the same environmental change.

These findings highlight an important challenge for predicting Arctic ecosystem responses to climate change. Coastal landscapes are mosaics of wetlands, tundra, and transitional habitats, each with its own environmental history. As a result, there is no single response of Arctic soils to warming, flooding, or changing nutrient inputs from herbivores. Instead, future carbon and nutrient cycling will depend on where a soil sits on the landscape and how it has been shaped by past environmental conditions.

Reference:
Ross, J. M., et al. (2026). Climate change-related effects on carbon emissions and net ammonification across lowland to upland soils from a high-latitude coastal ecosystem. Biogeochemistry: 169, 42. [Link to paper]

Posted: June 12, 2026

Flexible plants in changing high-latitude wetlands: trait plasticity under warming, flooding, and herbivory

High-latitude coastal wetlands are among the ecosystems changing most rapidly under climate change. Rising temperatures, more frequent flooding, and shifts in herbivore populations are reshaping these landscapes, yet we still know relatively little about how plants adjust their functional traits to these simultaneous environmental pressures.

In this study, we examined phenotypic plasticity in responses to warming, flooding, and herbivory in the Yukon–Kuskokwim Delta of western Alaska, one of the largest Arctic coastal wetland systems in North America. Using a full-factorial mesocosm experiment, we measured key plant functional traits, including vegetative height, leaf area (LA), specific leaf area (SLA), and leaf dry matter content (LDMC). These traits capture how plants balance growth, resource acquisition, and structural investment under changing environmental conditions.

Plant traits responded rapidly to environmental change, with shifts detectable within a single growing season. Herbivory had the most consistent effects across species, generally reducing plant size while promoting leaf traits associated with rapid regrowth. Flooding also reshaped trait expression, but in a more context-dependent way: it promoted more acquisitive traits in the flood-tolerant sedge Carex rariflora, while shifting the deciduous dwarf-shrub Salix fuscescens toward more conservative traits. Warming, in contrast, generally increased size-related traits, although its effects varied among species and wetland types.

These findings highlight the importance of phenotypic plasticity in plant functional traits under multiple environmental drivers. Rapid trait adjustments such as those observed here may influence how Arctic coastal wetland vegetation responds to ongoing warming, altered hydrology, and herbivore pressure.

Reference:
Chirvasa, C., et al. (2026). Rapid plant functional trait responses to warming, flooding, and herbivory in high-latitude coastal wetlands. Oecologia: 208, 40. [Link to paper]

Posted: March 15, 2026