DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 5-6/2023 str. 10     <-- 10 -->        PDF

During D. micans swarming period solitary females infest trees and construct egg galleries (Grégoire, 1985, 1988). Wounded trees, forked trees and trees at the stand edges are the most infested individuals in the forest (Granet and Perrot, 1977; Alkan Akıncı, 2017). Successful establishment of the beetles to trees with wounds are documented in oriental spruce forests (Alkan Akıncı et al., 2014). In a stand, there may be uninfested trees besides trees with multiple attacks. Also, some trees may have a number of successful and unsuccessful attacks together on their trunk (Bevan and King, 1983; Grégoire, 1984, 1985; Wainhouse et al., 1998). The lack of aggregation pheromone results in solitary attacks on trees but there are also high number of attacks reported by Turkish researchers (Eroğlu, 1995; Alkan Akıncı et al., 2014). Beetles mainly infest root collars (Grégoire, 1984). Almost 70% of the entrances are below 1 m at the trunk of the trees in Turkey. The percentage of the aborted attacks is 25% (Alkan Akıncı et al., 2014). The percentage of the aborted attacks is higher in Europe; in Belgium it is 70% (72-78%) (Grégoire, 1984). Radial and vertical resin ducts are cut by females during the construction of maternal galleries that cause resin flow, and consequently result in aborted attacks by beetles (Lieutier et al., 1992; Lieutier, 2007). D. micans attacks do not kill its host in a short period of time so infested trees are alive throughout different beetle generations (Grégoire, 1988).
In various studies, trees are artificially forced to induce susceptibility to bark beetles (Moeck et al., 1981; Coulson et al., 1986; Miller and Berryman, 1986; Storer and Speight, 1996; Alkan Akıncı, 2016). Freezing the base of the host trees (Moeck et al., 1981), damaging trees by artificial lightning strikes (Coulson et al., 1986) and artificial mechanical wounds (Miller and Berryman, 1986; Storer and Speight, 1996; Alkan Akıncı, 2016) attracted bark beetles on these trees mostly followed by tree death or successful colonization by the bark beetles.
Some tree parameters affect bark beetle brood survival or reproductive success. Wagner et al. (1979) presents data that bark moisture content affects brood survival of Dendroctonus frontalis. Stressed trees such as windthrowns, wounded trees or trees at stand edges have lower host defenses and greater nutritional quality (Reid and Robb, 1999; Alkan Akıncı et al., 2018). When mean annual increment in the last year, phloem thickness and several parameters of recent tree growth rate were studied on freshly dead Pinus banksiana to assess the reproductive performance of Ips pini, the results showed that tree growth rate parameters were positively related to beetle reproductive performance (Reid and Robb, 1999). Relationships between D. micans successful establishment and survival in its host are investigated experimentally in some studies (Alkan Akıncı and Erºen Bak, 2016; Alkan Akıncı et al., 2018). The role of phloem thickness, tree size and recent tree growth rate were used as tree vigor parameters in the study that parental D. micans females were inserted on healthy oriental spruce trees. Parental females were established successfully mostly on thicker phloem and trees that are growing vigorously (Alkan Akıncı and Erºen Bak, 2016). In another experimental study again parental D. micans females were inserted on healthy oriental spruce trees. In the study, periodic growth, phloem thickness, tree size, crown length, phloem moisture and amount of C, N in phloem have been compared between trees that D. micans females successfully established in the host tree or aborted. Results demonstrated that D. micans parental females successfully established on the codominant trees that have grown vigorously and have decreasing growth in the last 10 years, shorter crown length and higher N in the phloem (Alkan Akıncı et al., 2018).
In this study, oriental spruce trees that were naturally infested by D. micans, and uninfested trees in the forest are investigated. Phloem thickness, recent tree growth rates (the mean annual increment in the past five and ten years, and annual increment in the last year until the sampling date, diameter of breast height (DBH) and the average number of xylem cells (tracheids) in a radial file formed in the last year were studied to figure out tree characteristics of naturally infested and uninfested trees in the forest. We have tried to reveal the nature of the D. micans attacks and the characteristics of the naturally infested trees. In addition, we would like to compare our results with the results of the experimental studies that were formerly performed on oriental spruce.
MATERIALS AND METHODS
MATERIJALI I METODE
Field studies were performed at a naturally regenerated pure spruce stand that was at 1683 m a.s.l. and in southwest aspect in Taºlıca Forest Sub-District, Artvin Directorate of Forestry in 2016. In the stand examined, the estimated tree age was 90, the tree heights were about 20 m, slope was 3% and crown closure was about 70%. The stand is located in the Eastern Black Sea Mountains that has a rainy and foggy climate during whole year and also snowy winters. Both naturally infested and uninfested trees were selected in the stand closure. In the infested trees, D. micans was established and broods were developed under the bark. The broods were at the larval or pupal stage or there were young adults under the bark.
Measurements – Mjerenja
To determine the vitality of the naturally infested trees, we designated 30 naturally infested and 30 uninfested oriental spruce trees at the same stand in the field. Diameter of the breast height (DBH) was 33.20 cm ± 0.57 and 33.77 cm ± 0.62 at infested and uninfested trees, respectively. On each tree, cores were extracted. Annual growth ring widths were