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Abstract With rapid climate warming, some coastal high‐latitude ecosystems are experiencing more frequent tidal floods. Yet little is known about tundra plant‐community responses to flooding, and whether Arctic warming may modulate such responses.In a 2‐year, full‐factorial field experiment in coastal tundra wetlands of the Yukon‐Kuskokwim (Y‐K) Delta (western Alaska), we simulated periodic tidal flood events at two severities under both ambient and warmed summer conditions and measured above‐ground plant‐community responses. Low‐severity flooding represented overbank flooding 1 day per month, which is consistent with projections in the next 5 years. High‐severity flooding represented a more impactful flooding regime (three consecutive days per month) that is projected to occur in the next 10 years. Our warming treatment (+1°C) also represented a change projected in the next 10 years.Regardless of temperature, high‐severity flooding increased graminoid biomass by >45%, in turn increasing live plant‐community biomass by >18%. Low‐severity flooding had similar, though weaker, effects. Flooding had overall negative effects on both forb and shrub biomass, though shrub responses were weaker. Only during the second summer, warming increased graminoid biomass by 20% and tended to increase shrub biomass, regardless of flooding. Concurrently, warming enhanced standing‐dead graminoid biomass by 20%, while high‐severity flooding decreased it by 15%. Therefore, wet tundra that was both flooded and warmed had the greatest proportion of graminoids and total live biomass, but standing‐dead biomass comparable to that of unmanipulated wet tundra.Synthesis. While our manipulations simulated flooding and warming regimes expected in the wetlands of the Y‐K Delta over the same, near‐future (5‐to‐10 years) time frame, flooding had stronger effects than warming. What is striking is the rate at which graminoid increases occurred, becoming apparent after only two monthly flood events in the first experimental year. Flooding‐induced decreases in standing‐dead biomass suggests that the incorporation of dead plant material into the litter layer might be facilitated by tidal floods. These rapid increases in plant biomass and potentially biomass turnover, especially of graminoids, which are characterized by high‐quality litter, may have major implications for carbon and nutrient cycling of more frequently flooded coastal ecosystems in a warmer Arctic.
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Coastal tundra heath responses to experimental flooding and warming, Yukon-Kuskokwim Delta (western Alaska, United States), 2022-2024
While the Arctic warms rapidly, several coastal tundra regions face increasing threats from altered flooding regimes. Yet, how flooding shapes coastal tundra ecosystems remains largely unknown. We experimentally examined how increased tidal flooding, under both ambient and elevated temperatures, influences key drivers of ecosystem functioning: micro-environment, vegetation, and organic matter decomposition. Data were collected across three summers (2022-2024) in a low-Arctic coastal tundra heath of the Yukon-Kuskokwim Delta (Alaska) – one of the largest high-latitude riverine deltas in North America. In May 2022, soon after snowmelt, we selected seven blocks within the focal tundra heath. Each block contained six plots, for a total of 42 plots. Plots within blocks were randomly assigned to a factorial combination of experimental monthly tidal floods (three levels: no-flooding, low-severity flooding, and high-severity flooding) and experimental warming (two levels: ambient and higher temperatures). We focused on three response categories: (1) micro-environmental changes, including air and soil temperatures, soil active layer thickness, redox potential, salinity, potential of hydrogen (pH), and chemistry; (2) vegetation responses, such as aboveground community composition and biomass, plant height, and root production; and (3) responses of organic matter decomposition (mass loss, decomposition rate, and stabilization factor).
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- Award ID(s):
- 2113641
- PAR ID:
- 10647390
- Publisher / Repository:
- NSF Arctic Data Center
- Date Published:
- Subject(s) / Keyword(s):
- Decomposition Ecosystem shift Micro-environment Permafrost thaw Soil Tea bag index (TBI) Tidal flooding Transient plant community Vegetation Warming Yukon-Kuskokwim Delta (Alaska)
- Format(s):
- Medium: X Other: text/xml
- Sponsoring Org:
- National Science Foundation
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