Long-term (2009–2019) field studies of the CO2 fluxes over the Valday upland in north-western European Russia were performed in an old-growth spruce-dominated forest subject to the combined effects of climate change, bark beetle attacks and windfall events. The annual carbon uptake within the study area decreased from − 300 g C m−2 yr−1 in 2010–2011 to − 95 g C m−2 yr−1 in 2018 as a result of progressive tree mortality. However, mortality did not cause a significant reduction in specific ecosystem respiration. The respiration of the damaged forest was formed by efflux from soil (64.8%), living vegetation (15.5%), hotspots under dry standing trees (12.1%) and decomposition of woody debris (7.6%). High correlations between net ecosystem exchange and dry standing spruce stocks and average soil CO2 efflux were found. The decrease in the carbon sink was followed by a decline in evapotranspiration from 0.0142 ± 0.0003 g H2O m−2 s−1 for May–October 2010 to 0.0116 ± 0.0002 g H2O m−2 s−1 in 2018. We assumed that the decrease in carbon uptake was due to both the reduction in primary tree production and the decrease in the area of the unaffected stands. Our estimates show that an increase in tree mortality up to 27% of a stand area could turn an old-growth spruce forest into a net source of CO2. This should be taken into account when considering human-induced and climate-related effects on boreal forests.

中文翻译：

---

树木死亡对老生云杉林 CO2 通量的影响

对俄罗斯西北部 Valday 高地的 CO2 通量的长期（2009-2019）实地研究在受气候变化、树皮甲虫袭击和意外事件的综合影响的古老云杉占主导地位的森林中进行. 由于树木不断死亡，研究区域内的年碳吸收量从 2010-2011 年的 - 300 g C m-2 yr-1 下降到 2018 年的 - 95 g C m-2 yr-1。然而，死亡率并没有导致特定生态系统呼吸的显着减少。受损森林的呼吸作用是由土壤（64.8%）、活植被（15.5%）、干立树木下的热点（12.1%）和木屑分解（7.6%）形成的。发现净生态系统交换与干立云杉种群和平均土壤 CO2 流出之间存在高度相关性。碳汇减少之后，蒸散量从 2010 年 5 月至 10 月的 0.0142 ± 0.0003 g H2O m-2 s-1 下降到 2018 年的 0.0116 ± 0.0002 g H2O m-2 s-1。我们假设减少碳吸收的减少是由于初级树木产量的减少和未受影响林分面积的减少。我们的估计表明，树木死亡率增加高达 27% 的林分面积可以将古老的云杉林变成二氧化碳的净来源。在考虑人为和气候相关对北方森林的影响时，应考虑到这一点。我们假设碳吸收的减少是由于初级树木产量的减少和未受影响林分面积的减少。我们的估计表明，树木死亡率增加高达 27% 的林分面积可以将古老的云杉林变成二氧化碳的净来源。在考虑人为和气候相关对北方森林的影响时，应考虑到这一点。我们假设碳吸收的减少是由于初级树木产量的减少和未受影响林分面积的减少。我们的估计表明，树木死亡率增加高达 27% 的林分面积可以将古老的云杉林变成二氧化碳的净来源。在考虑人为和气候相关对北方森林的影响时，应考虑到这一点。