Droughts Are Not the Likely Primary Cause for Abies sibirica and Pinus sibirica Forest Dieback in the South Siberian Mountains
Droughts Are Not the Likely Primary Cause for Abies sibirica and Pinus sibirica Forest Dieback in the South Siberian Mountains
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DOI：
10.3390/f13091378
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发表时间：
2022-08
期刊：
影响因子：
2.9
通讯作者：
N. Tchebakova;E. Parfenova;E. Bazhina;A. Soja;P. Groisman
中科院分区：
文献类型：
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作者：
N. Tchebakova;E. Parfenova;E. Bazhina;A. Soja;P. Groisman
背景。自20世纪中叶以来，北美和欧亚大陆北部的温带和寒带地区出现了大规模的针叶林枯死现象。解释森林枯死的第一个假设与工业空气污染（酸雨）有关。本世纪末，出现了新的假设，支持关键的气候引起的干旱化来解释森林枯死。许多研究都是基于 SPEI（标准化降水蒸散指数）干旱指数。我们的目标是调查 SPEI 干旱指数是否是反映南西伯利亚山脉 (Mts) 湿润暗针林干旱状况的合适指标，以及干旱是否会引发这些森林的枯死。方法。我们计算了 1961 年至 2019 年期间南西伯利亚山脉四个样带的 SPEI 干旱指数、年湿度指数 AMI、潜在蒸散量 PET 和水平衡动态。现场发现暗针西伯利亚松林和冷杉林的衰退/枯死。来自位于每个样带较低和较高海拔的九个气象站的气候数据被用来计算1961-2019年期间的气候指数动态，以确定该时期的干燥和湿润阶段。结果。我们的研究结果表明，在过去 60 年（1961 年至 2019 年）中，气候湿度/干燥指数很少降至高风险水平。 AMI 未达到临界限值 2.25，这是暗针针叶林下边界的特征。 SPEI值<-1.5代表下边界暗针针叶树的干旱胁迫条件，并且这些条件在60年期间发生了3-4次。然而，在中高海拔湿润森林中，这些年的年水平衡保持正值。众所周知，树木偶尔能在 (1-2) 年干旱中存活。我们发现，暗针针叶树顶枯病通常发生在雨水充沛的潮湿年份，而不是干旱年份。我们发现森林枯死与西风带有关，西风带从西边带来北纬 50-56 度的大气污染，那里的气团穿过拥有广泛工业园区的人口稠密地区。结论。我们得出的结论是，观察到的南西伯利亚山脉中高海拔地区黑针叶树的减少是由几个可能的原因造成的，其中空气污染似乎比干燥的气候条件更可信，正如文献中引用的那样。随着地球的变化，结果对于了解这些生态系统和其他生态系统至关重要。其他原因和机制应进一步研究，这将需要创建支持植物生理学家、林业工作者、化学家等团队合作的基础设施。
Background. Since the mid-20th century, massive dieback of coniferous forests has been observed in the temperate and boreal zones across North America and Northern Eurasia. The first hypotheses explaining forest dieback were associated with industrial air pollution (acid rain). At the end of the century, new hypotheses emerged that supported critical climate-induced aridization to explain forest dieback. Many studies were based on the SPEI (Standardized Precipitation Evapotranspiration Index) drought index. Our goals were to investigate if the SPEI drought index was a suitable metric to reflect drought conditions in wet and moist dark-needled forests in the South Siberian Mountains (Mts) and if droughts trigger the dieback of those forests. Methods. We calculated the SPEI drought index, the annual moisture index AMI, potential evapotranspiration PET, and water balance dynamics for the period 1961–2019 for four transects in the South Siberian Mts. where decline/dieback of dark-needled Siberian pine and fir forests were identified in situ. Climate data from nine weather stations located at lower and upper elevations of each transect were used to calculate climatic index dynamics for the 1961–2019 period to identify dry and wet phases of the period. Results. Our findings showed that climatic moisture/dryness indices have rarely gone down to high risk levels during the last 60 years (1961–2019). AMI did not reach the critical limit, 2.25, characteristic of the lower border for the dark-needled taiga. SPEI values < −1.5 represent drought stress conditions for dark-needled conifers at the lower border, and these conditions occurred 3–4 times during the 60-year period. However, the annual water balance stayed positive in those years in wet and moist forests at mid-to-high elevations. Trees are known to survive occasional (1–2) dry years. We found that dark-needled conifer dieback often occurs in wet years with plentiful rain rather than in drought years. We found forest dieback was associated with the westerlies that bring atmospheric pollution from the west at 50–56 N latitudes, where the air masses cross populated regions that have widespread industrial complexes. Conclusions. We concluded that the observed decline of dark-needled conifers at middle-to-high elevations across South Siberia’s Mts was conditioned by several plausible causes, among which air pollution seems to be more credible than dry climatic conditions, as cited in the literature. Results are essential for understanding these ecosystems and others as our planet changes. Other causes and mechanisms should be further investigated, which would necessitate creating infrastructure that supports the teamwork of plant physiologists, foresters, chemists, etc.