To log or not to log: Salvaging bark-beetle affected spruce stands results in direct losses of leaf litter C, stable topsoil C stocks, and shifts in enzyme stoichiometry

Abstract

Disturbances by bark beetles and subsequent salvage logging affect forest carbon (C) stocks. Although deadwood retention is recognised to maintain soil organic C (SOC), the effects of standing deadwood vs. salvage logging on soil properties are poorly understood. This study examines C stocks and soil biochemistry at 21 low-elevation Norway spruce forests 1–3 years after disturbance in the Czech Republic. One third of the stands served as undisturbed control, one third remained dead standing, and one third was salvage logged. The litter C stocks of salvaged plots were immediately reduced to 2.8 ± 0.8 Mg C ha⁻¹, whereas the litter and topsoil C stocks of dead standing plots decrease from 26.8 and 43.8 Mg C ha⁻¹ to 4.4 and 24.9 Mg C ha⁻¹, respectively, over the first three years. Consequently, the topsoil C stocks were ∼24 % lower at the dead than those of the salvaged plots. NH₄-N contents increased two- to three-fold following dieback but decreased to the level of control within the third year. Extracellular enzyme stoichiometry indicated lower organic topsoil C and P microbial limitations at salvaged plots. Our results highlight the rapid dynamics of SOC pools following spruce forest dieback and a marked redistribution of SOC towards topsoil layers when salvaged. Thus, the incorporation of harvest residues and/or changes in soil microbial processes prevented a significant decrease in SOC stocks due to logging. Although deadwood retained higher ecosystem C stocks at the unlogged plots, detailed data on SOC dynamics are required for managing forests to maximise C stocks.