Demidko Denis A, Trefilova Olga V, Kulakov Sergey S, Mikhaylov Pavel V
Laboratory of Forest Zoology, Sukachev Institute of Forest, Siberian Branch, Russian Academy of Science, 50, Bil. 28, Akademgorodok, 660036 Krasnoyarsk, Russia.
Reshetnev Siberian State University of Science and Technology, Krasnoyarskii Rabochii Ave. 31, 660037 Krasnoyarsk, Russia.
Insects. 2021 Jan 21;12(2):90. doi: 10.3390/insects12020090.
The pine looper is one of the most widespread phyllophagous insect species across Northern Eurasia, defoliating Scots pine forests over vast territories. Since there are not enough long-term documented observations on a series of outbreaks, there is a need for methods allowing them to be reconstructed to study their dynamics patterns. Previously, dendrochronological methods were successfully used to solve such issues. However, the most common approach is not applicable for the Western Siberian forest-steppe since it requires comparison with a non-damaged tree species close to pine in terms of longevity and resistance to rot. In the pine forests of the steppe and forest-steppe zones of Western Siberia, there are no species that are not damaged by the pine looper that meets these requirements. Methods allowing not using control species are also not free from disadvantages (e.g., weak specificity). Therefore, we have developed a new method based on the analysis, not of the tree-ring width but the early- and latewood width to reconstruct past defoliation events. The past defoliation by the pine looper is indicated by the presence of a negative pointer year for latewood, followed by a negative pointer year for earlywood in a subsequent year among the majority of individuals. Linear modeling showed a difference between the climate impact on radial growth and the defoliation one. The obtained reconstruction was compared with the results of other methods (mowing window, OUTBREAK, independent component analysis), literature, and Forest Service data. The developed new method (pointer year method; PYM) showed high efficiency confirmed by results of the tree-ring series analysis (11 revealed outbreaks in the past). Compared with other reconstruction techniques under the given conditions (a favorable combination of heat and humidity; probably low-intense and short defoliation), the proposed method provided more precise results than those proposed earlier. Due to high accuracy, the PYM can be useful for detecting late-summer and autumn past defoliations of tree species with clear difference between early- and latewood even though the damage was weak.
松尺蠖是欧亚大陆北部分布最广的食叶昆虫物种之一，在大片区域使苏格兰松林落叶。由于缺乏一系列虫灾的长期记录观测，需要有方法来重建这些虫灾以研究其动态模式。此前，树木年代学方法已成功用于解决此类问题。然而，最常用的方法不适用于西西伯利亚森林草原地区，因为它需要与在寿命和抗腐性方面与松树相近的未受损树种进行比较。在西西伯利亚草原和森林草原地区的松林中，没有符合这些要求且未受松尺蠖侵害的树种。不使用对照树种的方法也并非没有缺点（例如特异性较弱）。因此，我们开发了一种基于分析早材和晚材宽度而非年轮宽度的新方法来重建过去的落叶事件。松尺蠖过去的落叶情况表现为多数个体中晚材出现负指示年，随后次年早材出现负指示年。线性模型显示了气候对径向生长的影响与落叶影响之间的差异。将得到的重建结果与其他方法（移动窗口法、OUTBREAK法、独立成分分析法）的结果、文献以及林业局数据进行了比较。所开发的新方法（指示年法；PYM）经年轮序列分析结果证实具有高效性（揭示了过去11次虫灾）。与给定条件下（热量和湿度的有利组合；可能是低强度且短暂的落叶）的其他重建技术相比，该方法提供的结果比早期提出的方法更精确。由于准确性高，PYM可用于检测夏末和秋季过去的落叶情况，即使损害较轻，对于早材和晚材有明显差异的树种也适用。
