Extreme winter warming events more negatively impact small rather than large soil fauna: shift in community composition explained by traits not taxa

Abstract

Extreme weather events can have negative impacts on species survival and community structure when surpassing lethal thresholds. Extreme winter warming events in the A rctic rapidly melt snow and expose ecosystems to unseasonably warm air (2–10 °C for 2–14 days), but returning to cold winter climate exposes the ecosystem to lower temperatures by the loss of insulating snow. Soil animals, which play an integral part in soil processes, may be very susceptible to such events depending on the intensity of soil warming and low temperatures following these events. We simulated week‐long extreme winter warming events – using infrared heating lamps, alone or with soil warming cables – for two consecutive years in a sub‐ A rctic dwarf shrub heathland. Minimum temperatures were lower and freeze‐thaw cycles were 2–11 times more frequent in treatment plots compared with control plots. Following the second event, A cari populations decreased by 39%; primarily driven by declines of P rostigmata (69%) and the M esostigmatic nymphs (74%). A community‐weighted vertical stratification shift occurred from smaller soil dwelling (eu‐edaphic) C ollembola species dominance to larger litter dwelling (hemi‐edaphic) species dominance in the canopy‐with‐soil warming plots compared with controls. The most susceptible groups to these winter warming events were the smallest individuals ( P rostigmata and eu‐edaphic C ollembola). This was not apparent from abundance data at the C ollembola taxon level, indicating that life forms and species traits play a major role in community assembly following extreme events. The observed shift in soil community can cascade down to the micro‐flora affecting plant productivity and mineralization rates. Short‐term extreme weather events have the potential to shift community composition through trait composition with potentially large consequences for ecosystem development.

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