Sammendrag
Tree mortality from insect infestations can significantly
reduce carbon storage in forest soils. In
subarctic birch forests (Betula pubescens), ecosystem
C cycling is largely affected by recurrent outbreaks
of defoliating geometrid moths (Epirrita autumnata,
Operophtera brumata). Here, we show that soil C
stocks in birch forests across Fennoscandia did not
change up to 8 years after moth outbreaks. We
found that a decrease in woody fine roots was
accompanied by a lower soil CO2 efflux rate and a
higher soil N availability following moth outbreaks.
We suggest that a high N availability and less
ectomycorrhiza likely contributed to lowered heterotrophic
respiration and soil enzymatic activity.
Based on proxies for decomposition (heterotrophic
respiration, phenol oxidase potential activity), we
conclude that a decrease in decomposition is a
prime cause why soil C stocks of mountain birch
forest ecosystems have not changed after moth
outbreaks. Compared to disturbed temperate and
boreal forests, a CO2-related positive feedback of
forest disturbance on climate change might therefore
be smaller in subarctic regions.
Betula pubescens; disturbed subarctic
forests; Epirrita autumnata; heterotrophic soil respiration;
Operophtera brumata; root biomass; soil
carbon sequestration; soil CO2 efflux; soil enzyme
activity; structural equation modelling.
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