Living, dead, and absent trees - How do moth outbreaks shape small-scale patterns of soil organic matter stocks and dynamics at the Subarctic mountain birch treeline?

Mountain birch forests (B. pubescens Ehrh. ssp. czerepanovii) at the subarctic treeline not only benefit from global warming, but are also increasingly affected by caterpillar outbreaks from foliage-feeding geometrid moths. Both of these factors have unknown consequences on soil organic carbon (SOC) stocks and biogeochemical cycles. We measured SOC stocks down to the bedrock under living trees and under two stages of dead trees (12 and 55 years since moth outbreak) and treeless tundra in northern Finland. We also measured in-situ soil respiration, potential SOC decomposability, biological (enzyme activities, microbial biomass), and chemical (N, mineral N, pH) soil properties. SOC stocks were significantly higher under living trees (4.1±2.1 kg m²) than in the treeless tundra (2.4±0.6 kg m²), and remained at an elevated level even 12 (3.7±1.7 kg m²) and 55 years (4.9±3.0 kg m²) after tree death. Effects of tree status on SOC stocks decreased with increasing distance from the tree and with...