Health condition and colonization of stem insects in Scots pine after ground fire in Central Polissya

Abstract

Over the past decades, the increase in occurrence of fires has caused degradation of the forest ecosystem and caused impacts to the environment. The aim of this study was to reveal the peculiarities of Scots pine health condition dynamics in the first 2 years after August fire and to estimate the rate of tree colonisation by stem insects in Central Polissya. Scots pine health condition for the first 2 years after summer ground fire in August 2016 and the rate of tree colonisation by stem insects was studied in Zhytomyr region, Western Ukraine. Stem scorch height was measured for every fire-damaged tree, and the index of fire damage severity was calculated. Vital trees health condition worsened more intensively in the sample plot with the lowest relative stocking density and the highest stem scorch by fire. Generally, the forest health condition has worsened in post-fire period in fire damaged stands. However, 23.1% of trees recovered health condition from category 'drying-up' to 'severely weakened'. In fire-damaged stands, the number of species of stem insects has increased from 8 to 11 during the first 2 years of fire damage. Bark beetles were represented by Tomicus piniperda (Linnaeus, 1758), Tomicus minor (Hartig, 1834), Ips acuminatus (Gyllenhal, 1827) and Ips sexdentatus (Boerner, 1767). Jewel beetles included Anthaxia quadripunctata (Linnaeus, 1758), Phaenops cyaneus (Fabricius, 1775), Melanophila acuminata (DeGeer, 1774) and Chalcophora mariana (Linnaeus, 1758). Longhorn beetles included Monochamus galloprovincialis (Olivier, 1795), Pogonocherus fasciculatus (Degeer, 1775) and Acanthocinus aedilis (Linnaeus, 1758). Tree colonisation by stem insects in the year of fire damage was comparable with control stand, because insect swarming completed before this disturbance. Maximal occurrence of stem insects in 2017 in fire-damaged stand increased up to 66.7% (for I. sexdentatus). The percentage of trees colonised by any insect species at fire-damaged and healthy pine stands differed significantly. The occurrence of stem insects depended mainly on the ratio of trees with different health condition. Our results demonstrate data of tree damage from fire and tree health index as a strong predictor of post-fire mortality of Scots pine and bark beetle occurrence.