Response of soil chemistry to forest dieback after bark beetle infestation

We evaluated changes in the chemistry of the uppermost soil horizons in an unmanaged spruce forest (National Park Bohemian Forest, Czech Republic) for 3 years after dieback caused by a bark beetle infestation, and compared these changes with a similar undisturbed forest area. The soils below the disturbed forest received 2-6 times more elements via litter fall compared to the unaffected plot. The subsequent decomposition of litter and reduced nutrient uptake by trees resulted in a steep increase in soil concentrations of soluble N (NH4-N, organic-bound N) and P forms in the disturbed plot. The average concentrations of NH4-N and soluble reactive P increased from 0.8 to 4.4 mmol kg(-1) and from 0.04 to 0.9 mmol kg(-1), respectively, in the uppermost soil horizon. Decomposition of litter at the disturbed plot elevated soil concentrations of Ca2+, Mg2+ and K+, which replaced Al3+ and H+ ions from the soil sorption complex. Consequently, soil concentrations of exchangeable base cations increased from 120 to 200 meq kg(-1), while exchangeable Al3+ and H+ decreased 66 and 50 %, respectively, and soil base saturation increased from 40 to 70 %. The Al3+ liberation did not elevate concentrations of ionic Al in the soil solution, because most of the liberated Al3+ was rapidly complexed by dissolved organic carbon (DOC) and transformed to DOC-Al complexes. The chemical parameters investigated at the unaffected plot remained stable during the study.