Forestry Studies | Metsanduslikud Uurimused, Vol. 70, Pages 44–57 Research paper Natural regeneration in Siberian fir Abies( sibirica Ledeb.) forests subjected to invasion of the four-eyed fir bark beetle Polygraphus( proximus Blandf.) Nikita Debkov Debkov, N. 2019. Natural regeneration in Siberian fir (Abies sibirica Ledeb.) forests subjected to invasion of the four-eyed fir bark beetle (Polygraphus proximus Blandf.). – Forestry Studies | Metsanduslikud Uurimused 70, 44–57, ISSN 1406-9954. Journal homepage: http://mi.emu. ee/forestry.studies Abstract. This study assessed the potential of natural regeneration (NR) of forests in Western Siberia, dominated by Siberian fir (Abies sibirica Ledeb.) and damaged due to the invasion of the four-eyed fir bark beetle (Polygraphus proximus Blandf.). The leading methods for investi- gating this problem are the sample plot method and the transect method, which allow reveal- ing the features of NR, their morphological structure and spatial distribution. Analysis of the occurrence and structure of NR revealed a correlation between the degree of stand damage and sapling state. The spatial structure was highly heterogeneous, testifying the group loca- tion of NR and the variable density. For 63% of the sample plots, a decrease in saplings was recorded as a result of the impact of the four-eysouthern ed fir bark beetle. Most of the dead saplings were large (95%), and dead saplings accounted for 10–50%. A positive correlation was found between the decrease in saplings and the state of the fir forest. The number of sap- lings varied from 1,233 to 19,200 plants ha-1, with fir being the dominant species. Fir forests of Western Siberia, damaged by the four-eyed fir bark beetle, have the potential for regeneration. Key words: microsites, invaders, forest degradation. Author’s address: Laboratory of Monitoring of Forest Ecosystems, Institute of Monitoring of Climatic and Ecological Systems, Siberian Branch of the Russian Academy of Sciences, Aca- demichesky ave. 10/3, 634055 Tomsk, Russia; e-mail: [email protected] Introduction aridity (Kharuk et al., 2013). Irrespective of the main cause of this large-scale dieback, Since the beginning of the 21st century, the synergism of these factors entails the the degradation of coniferous evergreen weakening of stands and the sensitisation forests in the boreal zone has intensified of trees to various impacts, in particular in- across the globe (Aitken et al., 2008; Allen sect pests, which are often the final factor et al., 2010; Worrall et al., 2010; Yousefpour leading to the death of coniferous forests. et al., 2010; Martinez-Vilalta et al., 2012; An- An increasing number of invasive organ- deregg et al., 2013), mainly as a result of root isms (mainly insects) in forest ecosystems rot and bacteria (Raffa et al., 2008), insect contributes to this problem, which leads to pests (Logan et al., 2003), and increasing a change in the structure of biological diver- DOI: 10.2478/fsmu-2019-0004 © 2019 by the authors. Licensee Estonian University of Life Sciences, Tartu, Estonia. This article is an open access article distributed under the terms and conditions of the Cre- ative Commons Attribution-NonCommercial-NoDerivatives (CC BY-NC-ND) 4.0 Inter- national license (https://creativecommons.org/licenses/by-nc-nd/4.0/). 44 Natural regeneration in Siberian fir (Abies sibirica Ledeb.) forests subjected to invasion of the four-eyed fir bark beetle (Polygraphus proximus Blandf.) sity (Kenis et al., 2009; Straw et al., 2013) and, instructions (Pobedinsky, 1966), modified in extreme cases, even to its loss (Born et al., in accordance with the tasks assigned. De- 2005; Poland & McCullough, 2006). pending on the characteristics of the com- In South Siberia, against the backdrop munities studied (site area, quantitative of these global processes, a phenomenon parameters and NR height), the calculation unique to the Siberian taiga is currently was carried out in continuous transects being observed: the large-scale dieback of with 25 square counting plots of 4 m2 or on Siberian fir (Abies sibirica Ledeb.) as a result intermittent transects in 30 circular plots of of invasion and mass reproduction of the 10 m2. native Far Eastern bark beetle, Polygraphus We determined the parameters com- proximus Blandf. (Krivets et al., 2015). At position, height, diameter, age, number, first, after the beginning of mass reproduc- length and projection of the crown, linear tion of the Far Eastern invader in fir forests growth of the axial shoot and lateral shoot of Siberia, predictions of the possibility of of the I order. Also, model specimens of complete loss not only of the forest-form- saplings were collected (three plants per ing role of Siberian fir, but also of its bio- height group) to determine the morpho- logical status, were frequently voiced. De- logical characteristics and age. spite these forecasts, until recently, little The location of NR sites was estimated attention has been paid to the regenerative with the calculation of occurrence (the ra- functions of the ecosystems disturbed by tio of registration sites with at least one the four-eyed fir bark beetle. sample of sapling the total number of SP). In this regard, the aim of the research To determine the spatial distribution of was to assess the regeneration potential of saplings, the scattering index proposed by fir ecosystems and to predict their succes- R.A. Fisher was calculated (Svalov, 1985). sion dynamics in the West Siberian region The main parameters adopted in the work in the context of four-eyed fir bark beetle to categorise viable saplings (Uspensky, invasion. 1987) are the ratio of the current linear growth of the axial shoot and the lateral shoot of the first order, the so-called “eco- Material and Methods logical coefficient of the crown” (more than 0.5 for small saplings, 0.7 for medium sap- Studies were conducted in the Tomsk re- lings and 1 for large saplings), the length gion on 22 sample plots (SPs), established of the crown compared to the trunk (more in 2012–2017 by the Institute for Monitor- than 61%), and the ratio of crown length ing of Climatic and Ecological Systems to width (more than 0.9). The values of the (SB RAS), both in pure fir stands (with a ecological coefficient of the crown adopted share of other species up to 20%) and in in this paper differ from those generally ac- mixed stands with Siberian pine (Pinus cepted in Russian forest science in relation sibirica Du Tour), Siberian spruce (Picea with the features of Siberian fir ontogene- obovata Ledeb.), silver birch (Betula pendula sis (Makhatkov, 1991). In the early and late Roth.), and aspen (Populus tremula L.). The immature ontogenetic states, applicable to examined stands were premature and ma- the small and medium fir saplings, respec- ture-aged and showed varying degrees of tively, the growth of the lateral branches damage – from weakened (average stand exceeding the axial shoot is characteristic. health category 1.6–2.5 points) to severely The structural organisation of micro- weakened (2.6–3.5 points) and degraded sites in forest communities has been stud- (3.6 points or higher). ied and expressed in the formation of a Natural regeneration (NR) studies were specific microrelief in the life and death of performed according to methodological trees (Zaugolnova & Braslavskaya, 2010). 45 N. Debkov This classifi cation was substantially modi- Mann-Whitney U test was used; to deter- fi ed by the author of the present study for mine the relationship between the indices, specifi c research conditions. Accordingly, the Spearman correlation was applied. micro-habitats (microsites) of the fi rst or- der were identifi ed as undercrown plots of living and dead trees (with a division Results into dieback, windbreak and windfall) as well as intercrown plots. Within each mi- The distribution of the four-eyed fi r bark cro-habitat of the fi rst order, second-order beetle in the Tomsk region micro-habitats were further singled out: As of 2014 (Krivets & Baranchikov, 2015), even plots, pans and deadwood locations the invader was noted in six districts of the – stumps and deadwood. Tomsk region (Figure 1): Bakcharsky (3), Statistical analysis was performed via the southern part of Verkhneketsky (4), descriptive statistics (value ± standard er- Krivosheinsky (9), southern part of Pervo- ror) in the program Statistica 10. To assess maisky (12), Teguldetsky (13) and Tomsky signifi cant differences between the two (14). independent variables, the nonparametric Legend: invader occurrence as of 2018; numbers of administrative districts of the Tomsk region (explanations in the text); sample plots. Figure 1. The modern distribution of the four-eyed fi r bark beetle in the Tomsk region and the location of sample plots. 46 Natural regeneration in Siberian fir (Abies sibirica Ledeb.) forests subjected to invasion of the four-eyed fir bark beetle (Polygraphus proximus Blandf.) In 2018, as a result of field studies con- (89–100%) of Siberian fir (Table 1). As ac- ducted by the SB RAS, material of the De- companying species, Siberian spruce (1– partment of Forestry of the Tomsk region 9%) and Siberian pine were most frequent- and a survey conducted by foresters, the ly found (1–4%). Based on morphological presence of the four-eyed fir bark beetle parameters characterising the state of the in seven new districts of the region was assimilative apparatus (crown) of the sap- reliably established, namely: Asinovsky lings, the viability of NR can be concluded. (2), Zyryansky (5), Kozhevnikovsky (7), The species composition of NR sites in Kolpashevsky (8), Molchanovsky (10), fir forests on the left bank of the Ob Riv- Chainsky (15) and Shegarsky (16) admin- er was also characterised by the predom- istrative districts and in the northern part inance (81–98%) of Siberian fir (Table 2).