Fir (Abies sibirica Ledeb.) in a changing climate hydrothermal regime and effects of the Ussuri polygraph (Polygraphus proximus Blandford)
V. I. KHARUK1,2, S. T. IM1,2,3, I. A. PETROV1,2, D. A. DEMIDKO1,3, M. L. DVINSKAYA1, A. A. KNORRE2,4, A. S. SHUSHPANOV1,3
1Krasnoyarsk Science Centre of the Siberian Branch of Russian Academy of Science, V. N. Sukachev Institute of Forest of SB RAS, Krasnoyarsk, Russia
2Siberian Federal University, Krasnoyarsk, Russia
3Reshetnev Siberian State University of Science and Technology, Krasnoyarsk, Russia
4”Stolby” State Nature Reserve, Krasnoyarsk, Russia
Keywords: conifer mortality, water stress, Siberian fir, Polygraphus proximus, bark-beetle outbreaks, hydrothermal regime, conifer ranges
Abstract
Changing hydrothermal regime together with dendrophages outbreaks, are the main factor that determining the vitality, growth dynamics and changes in the ranges of conifers. The causes of mass dieback of Abies sibirica Ledeb in the taiga of the Eastern Sayan Mountains (the Krasnoyarsk Stolby National Park) and fir trees vitality within the area of fir dieback were studied. The mortality fir was preceded by a chronic decrease in the trees growth index (GI) associated with water stress which was observed since warming start in the 1970s. The unprecedented dieback of the fir forest was triggered by the abnormal drought in 2012, which led to an abrupt increase in water stress and a strong decrease of the GI of trees. The extreme deterioration of the fir forests vitality stimulated the outbreak of the bark beetle Polygraphus proximus Blandford. The trees dieback, the maximum of which was observed in 2013-2018, resulted in the mortality of up to 75 % of fir-dominant forests. The reaction of fir to P. proximus attacks included the formation of a “physic-chemical” barrier in the tree rings, consisting of closed rows of traumatic resin ducts and xylem lignification. Currently, the number of viable fir regeneration (3-10 thousand/ha) is potentially sufficient for the fir restoration in most zone of fir mortality. However, the predicted worsening of hydrothermal regime in fir habitat in synergy with P. proximus outbreaks suggested future cycles of fir mortality and partial restoration in the 21st century. The considered unprecedented fir forests mortality is within the phenomenon of conifer mesophytes health status worsening in the southern parts of their ra range.
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