Sanitary State Dynamics of Spruce Forests Under Culminating <i>Ips typographus</i> Reproduction and Efficiency of Forest-Protection Measures
In the Bryansk Region, spruce is located on the southern boundary of its range in the area of recurrent reproduction of eight-dentated bark beetle and large-scale spruce drying. Since 2010, Central Russia has seen a new wave of spruce forests drying and bark beetle reproduction, which was caused by severe droughts. The draughts supplied the pest with plentiful nutrients, favouring their rapid superabundance. The bark beetle became an independent factor contributing to trees’ weakening and drying. The research aimed to define more exactly the pest’s phenology in the region and check the comparative effectiveness of the traditionally recommended sanitary and protection measures during pandemic reproduction of Ips typographus. The research was conducted in 80-120-year-old spruce forests having trees with different intensity of drying. On 6 sites we studied changes in the state of trees during the vegetation period and the influence of various combinations of sanitary and protection measures on the bark beetle quantity and on the state of spruce. We applied standard methods of forest pathology research, monitoring, entomological analysis of trees, and pheromone control. Phenological stages of the pest’s development were determined by means of pheromone traps. In 2010 and 2011, the beetle had two generations with one sister generation. Hibernation started in mid-September. The majority of beetles hibernated in insect holes under the bark of the under-crown part of the tree trunk along the drying zones line. Pheromone traps caught 5-11 thousand beetles per season, which is enough to colonize 1-3 trees. Trap trees, depending on their diameter, are colonized by 8-22 thousand beetles. Pheromone traps are less efficient than trap trees. The maximum effect was obtained in those forests where we used both traps and trap trees. Different combinations of sanitary and protection measures aimed to preserve weakened spruce forests have proved that: pheromone traps in recommended quantity are efficient to control and reduce the pest’s quantity in less weakened forests if tree drying occurs in groups or in limited areas. In case of large-scale drying, they have no effect on the bark beetle quantity and cannot stop the drying; in case of tree drying in groups or in limited areas, trap trees help save the spruce from colonization along the lines of drying zones. A greater effect was obtained at simultaneous use of pheromone traps and trap trees; selective forest cutting, when done in two steps (at the end of May and September) before young beetles leave, has a positive protective effect; in case of spruce drying in limited areas, no positive effect is produced even by complex measures. When the bark beetle is in the phase of quantity culmination and spruce forests are weak, clear-cutting should be done throughout the entire territory of mature spruce forests contiguous to the territory of drying.