Soil CO2efflux from mountainous windthrow areas: dynamics over 12 years post-disturbance

[摘要] Windthrow-driven changes in carbon (C) allocation and soil microclimate canaffect soil carbon dioxide (CO₂) efflux (F_soil) from forestecosystems. Although F_soil is the dominant C flux followingstand-replacing disturbance, the effects of catastrophic windthrow onF_soil are still poorly understood. We measured F_soilat a montane mixed-forest site and at a subalpine spruce forest site from2009 until 2012. Each site consisted of an undisturbed forest stand and twoadjacent partially cleared (stem-fraction-harvested) windthrow areas, whichdiffered with regard to the time since disturbance. The combination of chronosequence anddirect time-series approaches enabled us to investigate F_soildynamics over 12 years post-disturbance. At both sites F_soilrates did not differ significantly from those of the undisturbed stands inthe initial phase after disturbance (1–6 years). In the later phase afterdisturbance (9–12 years), F_soil rates were significantly higherthan in the corresponding undisturbed stand. Soil temperature increasedsignificantly following windthrow (by 2.9–4.8 °C), especially in theinitial phase post-disturbance when vegetation cover was sparse. Asignificant part (15–31%) of F_soil from the windthrow areaswas attributed to the increase in soil temperature. According to ourestimates, ~500–700 g C m⁻² year⁻¹ are released viaF_soil from south-facing forest sites in the Austrian CalcareousAlps in the initial 6 years after windthrow. With a high browsing pressuresuppressing tree regeneration, post-disturbance net loss of ecosystem C tothe atmosphere is likely to be substantial unless forest management isproactive in regenerating such sites. An increase in the frequency of forestdisturbance by windthrow could therefore decrease soil C stocks and feed back positively on rising atmospheric CO₂ concentrations.

[学科分类] 地球化学与岩石