Effects of Ips typographus (L.) and sanitation logging disturbance on organic matter decomposition and carbon in the humus layer in boreal Picea abies (L.) H. Karst. stands

Abstract Key message Sanitation logging, aimed at mitigating the spread of European spruce bark beetle ( Ips typographus L.) outbreaks in boreal stands, was associated with increased decomposition and loss of carbon from the humus layer, measured 10 years post-disturbance. We encourage forest managers to take such ecological side-effects into consideration when planning intervention strategies against bark beetle attacks. Context The disturbance due to the European spruce bark beetle ( Ips typographus L.)—often managed with sanitation logging—is predicted to increase in European forests, with unclear potential consequences for soil carbon (C). Aims We examined the impact of I. typographus and sanitation logging on organic material decomposition and C content of the humus layer together with the drivers of such changes in boreal stands. Methods Humus-layer C and N concentrations, C stocks, decomposition of Green and Rooibos tea material (labile and more recalcitrant, respectively), and soil temperature were compared between (i) undisturbed sites, (ii) sites disturbed by I. typographus , and (iii) sites sanitized (clear-cut) and replanted due to I. typographus risk). Observations were done circa 10 years after the disturbances. Results Humus-layer C and N concentrations and remaining mass of Rooibos tea were lower and C/N ratio and soil temperature were higher at the sanitized sites in comparison to undisturbed sites. A similar, but milder pattern was observed between the sites disturbed by I. typographus (ii) and undisturbed sites(i)i. C concentrations and stocks as well as relative remaining mass of Rooibos tea across plots correlated negatively with soil temperature, and positively with the number of remaining trees. Conclusion Sanitation loggings appeared to increase decomposition and C loss from the humus layer. Such ecological effects should be considered when planning silvicultural interventions to mitigate insect damage.