Typographus Infestation Research Articles

Root rot increases the vulnerability of Norway spruce trees to Ips typographus infestation

Norway spruce (Picea abies) is one of the most economically important tree species in Northern and Central Europe. Root rot caused by Heterobasidion annosum s.l. and the European spruce bark beetle (Ips typographus) are major disturbance agents of Norway spruce and are expected to increasingly affect spruce-dominated forests as the climate warms. This study investigated the direct interaction between root rot and I. typographus, with the aim of examining whether root rot and the stress it causes to a tree increases the risk of subsequent bark beetle attack.In total, 442 Norway spruce trees from nine different mature, even-aged forest stands were studied. First, symptoms caused by I. typographus were evaluated before final felling from each tree based on visual assessments of crown and stem conditions. After the felling, the sample plots were relocated from the clearcut areas, and the stumps of sampled trees were reassessed for root rot. Exploratory analysis and binomial Generalized Linear Mixed Model (GLMM) were used to analyze relationships between explanatory variables and their effect to I. typographus infestation.The best predictors for I. typographus infestation at individual tree level were presence of root rot and to a lesser extent, tree diameter at breast height. Seventy-five percent of root rot-infected trees were also infested with I. typographus, and most of those trees were either dead or severely infested. Results suggest that root rot weakens trees, making them more vulnerable to subsequent I. typographus infestation, especially early in outbreaks when bark beetle population densities are low.

İşletilen ve işletilmeyen doğu ladini (Picea orientalis (L.) Link) meşcerelerindeki Ips typhographus L. saldırılarının yetişme ortamı ve meşcere özelliklerine göre değerlendirilmesi

This study aimed at investigating the effectiveness of management practices for reducing the negative impacts of Ips typographus L. on Oriental spruce (Picea orientalis (L.) Link.) forests, and to review the best site factor(s) associated with Ips typographus infestation. Two sites, Hatila Valley National Park (HVNP-unmanaged site) and Saçinka Forest Sub-District Directorate (SFSD-managed site) were chosen to compare the stand characteristics (mean age, height, bark thickness, basal area, stand density and tree diameter) and soil properties (pH, organic matter-OM, soil texture, and nutrients). At both sites, the sampling plots were taken from the north and south-slope aspects (NSA and SSA) and from upper and lower-slope positions (USP and LSP) on each site. In general, the results showed that in HVNP, Picea orientalis stands had higher stand age, bark thickness, basal area, and tree diameter, but lower soil pH, OM, nutrients, percent clay and silt content than those in SFSD. Among the stand characteristics, the stand age was positively correlated (r = 0.916) to the mortality rates in HVNP. Besides, Picea orientalis stands on SSA and at USP were more damaged than on NSA and at LSP. In conclusion, the results indicate that forest management practices including thinning, pruning, and cleaning can have a significant favorable influence on Picea orientalis forests to minimize the risk of Ips typographus attacks.

The potential of dual-wavelength terrestrial lidar in early detection of Ips typographus (L.) infestation – Leaf water content as a proxy

Climate change is causing novel forest stress around the world due to changes in environmental conditions. Forest pest insects, such as Ips typographus (L.), are spreading toward the northern latitudes and are now able to produce more generations in their current range; this has increased forest disturbances. Timely information on tree decline is critical in allowing forest managers to plan effective countermeasures and to forecast potential infestation areas. Field-based infestation surveys of bark beetles have traditionally involved visual estimates of entrance holes, resin flow, and maternal-gallery densities; such estimates are prone to error and bias. Thus, objective and automated methods for estimating tree infestation status are required.In this study, we investigated the feasibility of dual-wavelength terrestrial lidar in the estimation and detection of I. typographus infestation symptoms. In addition, we examined the relationship between leaf water content (measured as gravimetric water content and equivalent water thickness) and infestation severity. Using two terrestrial lidar systems (operating at 905 nm and 1550 nm), we measured 29 mature Norway spruce (Picea abies [L.] Karst.) trees that exhibited low or moderate infestation symptoms. We calculated single and dual-wavelength lidar intensity metrics from stem and crown points to test these metrics' ability to discriminate I. typographus infestation levels using regressions and linear discriminant analyses.Across the various I. typographus infestation levels, we found significant differences (p < 0.05) in gravimetric water content, but not in equivalent water thickness due to the latter statistic's high correlation with leaf density. The results show correlations between the lidar intensity metrics and several infestation symptoms: defoliation, discoloration and resin flow. The intensity metrics explain 50% of the variation in the infestation severity (as determined in the field based on canopy and stem symptoms). The overall accuracy with three infestation classes (no, low, or moderate) was 66%, but the overall accuracy with two infestation classes (not infested, or infested) was 90%. The classifiers combine lidar intensity metrics from the stem and the canopy to allow for the detection of bark-beetle infestations in the early, so called green-attack stage. The intensity metrics explain part of the variations in tree-level gravimetric water content and equivalent water thickness, with adjusted R2 values of 0.48 and 0.68, respectively. Terrestrial dual-wavelength lidar shows potential for providing objective tree-decline measurements at tree level: this method can be further used to enhance forest inventories and automate tree-vigor data collection, which has traditionally required expert knowledge.

Modelling the predisposition of Norway spruce to Ips typographus L. infestation by means of environmental factors in southern Finland

New measures for effective monitoring and controlling of bark beetle infestations are needed as a response to intensified outbreaks caused by the climate change. Various environmental factors affect tree health and susceptibility, as well as stand predisposition to bark beetles. European spruce bark beetle Ips typographus L. abundance and outbreak frequency in Finland has significantly increased during the last decade. The ability to identify sites under a high risk of infestation would facilitate adaptation to this new situation and help target limited forest health management resources. Accordingly, our goal was to investigate the importance of various stand, soil and topographic characteristics in the assessing predisposition of Norway spruce dominated urban forest in southern Finland to I. typographus infestations. Information on the environmental factors was assessed in the field in 2014 and derived from a digital elevation model. Ips typographus infestation intensity was classified into three infestation index classes based on tree-wise symptoms of resin flow, discoloration and defoliation. Cumulative logit link models were utilized for investigating stand-level infestation probability. The best explanatory factors were aspect, slope, site type and soil texture. Models with the highest cumulative probabilities for severe infestation were linked with eastern aspect, moderate steep slope and rich site type fertility (0.72) and eastern aspect, shallow soil and rich site type fertility (0.71). Higher soil C/N ratios with east aspect and rich site type fertility was associated with an increased risk of severe infestation in a third model. The lowest risk was associated with southern and southwestern aspects, fine soil texture, moderate site fertility and gentle slopes.

How differential management strategies affect Ips typographus L. dispersal

Bark beetle outbreaks have a devastating effect on economically important forests worldwide, thus requiring extensive application of management control strategies. The presence of unmanaged protected areas in close proximity to managed forests can instigate concerns that bark beetle infestations may spread from unmanaged into managed stands. We studied the impact of differential management of forest stands on the dispersal dynamics of the European spruce bark beetle, Ips typographus, making use of inferential population genetics on mitochondrial and nuclear genomes. Bayesian inferences of migration rates and a most parsimonious dispersal tree show that outgoing gene flow was consistently higher from managed to unmanaged areas. Reason for that is likely the thorough removal of potential breeding material in managed forests and thus the dispersal of the base stock beetles from these areas to unmanaged areas where breeding material is available. Our study suggests that the potential threat posed by unmanaged to managed forests in regard to I. typographus infestation needs to be carefully re-considered.

Bark Beetles Increase Biodiversity While Maintaining Drinking Water Quality

Increasing natural disturbances in conifer forests worldwide complicate political decisions about appropriate land management. In particular, allowing insects to kill trees without intervention has intensified public debate over the dual roles of strictly protected areas to sustain ecosystem services and to conserve biodiversity. Here we show that after large scale bark beetle Ips typographus infestation in spruce Picea abies forests in southeastern Germany, maximum nitrate concentrations in runoff used for drinking water increased significantly but only temporarily at the headwater scale. Moreover, this major criterion of water quality remained consistently far below the limit recommended by the World Health Organization. At the same time, biodiversity, including numbers of Red-listed species, increased for most taxa across a broad range of lineages. Our study provides strong support for a policy to allow natural disturbance-recovery processes to operate unimpeded in conifer-dominated mountain forests, especially within protected areas.

Structure and dynamics of temperate lowland natural forest in the Bialowieza National Park, Poland

The world-renowned Bialowiez·a National Park (BNP) in Poland has long been the object of research that provides information on the status and development of the entire, relatively large area of well-preserved lowland forest. For that reason, the aim of the work presented here was to characterize the current structure and dynamics of natural forests in Strict Reserve of BNP (SR-BNP), which covers 4584 ha. The research material encompassed the results of measurements on 460 temporary and 160 permanent sample plots. Results revealed an increase in the level of regeneration, whereas the standing volume is seen to have decreased slightly. Changes occurred in volume of certain tree species, as well as in proportions in given size classes they accounted for. The most marked increase was noted for Carpinus betulus, followed by Alnus glutinosa, Tilia cordata, Betula spp., Acer platanoides and Pinus sylvestris. Only in the case of Picea abies was a significant decrease noted. A decline of P. abies, mainly due to Ips typographus infestation, was revealed. Currently, only 6 of the 17 species of trees growing in the SR-BNP included specimens that were growing from the regeneration layer into the overstorey in more significant numbers. Due to a reduction of species diversity in ingrowth, a gradual depletion of species richness in the SR-BNP stands should be anticipated.

Statistical evaluation of Ips typographus population density: a useful tool in protected areas and conservation-oriented forestry

Ips typographus (Col., Curculionidae, Scolytinae) occurring on Picea abies stems is a species characterised by large fluctuations in population numbers and causing frequent outbreaks. In protected areas, I. typographus is regarded as a sensitive bioindicator responsive to changes in forest health and vitality. In conservation-oriented forestry, attention is being paid to the ecological value of I. typographus beetles as ecosystem engineers and keystone species, driving forest natural regeneration and conversion. Despite many publications devoted to I. typographus, no accurate method for estimating the population density of this species has been developed. The objective of this study was to develop a statistical method for estimating I. typographus population density that enables calculation of estimation errors. The proposed method consists of two parts: tree-level analyses and stand-level analyses. Part one allows calculation of the total density of I. typographus infestation of each of P. abies selected stem (after selecting sample windfalls), part two allows estimation of the mean total infestation density of the stem in the area investigated. Linear regression functions were applied to part one and survey sampling to part two. The method is only marginally invasive because it involves debarking of one 0.5 m-long stem section on maximum 50 P. abies windfalls (trap trees can optionally be used). The developed method was employed to assess I. typographus population density in the Świetokrzyskie Mountains in Central Poland in an area of ca. 4,000 ha. In 2010, in the area investigated, the mean total I. typographus infestation density of the P. abies stem was 440.6 maternal galleries/m2 (from 358.7 to 522.6 maternal galleries/m2 with α = 0.05; the relative error of estimation was 18.6%). The examined I. typographus population was in a progradation phase. The proposed method can be used in nature reserves, national parks and managed forests, mainly for scientific purposes.

Forest decline and pedobiological characteristics of humus forms in the Šumava National Park

Humus forms dynamics and characteristics of different forest sites were studied in the area of Smrčina Mt. in the Šumava National Park territory. The study was performed in vital Norway spruce forest, dead Norway spruce forest (bark beetle Ips typographus infestation) and on a clear-cut area (site conditions were comparable for all three plots). The amount of surface organic matter was not affected by forest decline or by clear-cut (95.5 t/ha, 73.1 t/ha and 100.2 t/ha, respectively), pH being comparable (between 2.3 and 3.2 pH KCl). A slight favourable effect of grass litter on pH increase was obvious; higher leaching of bases occurred in lower horizons. Nitrogen losses were detected from the L + F horizons, falling from 1.93–1.83% (living stand) to 1.73–1.83% (clear-cut area). Higher ammonia production was documented in substrates (F and H horizons) from the living stand (from 263 and 103 mg/kg before incubation to 610 and 248 mg/kg after incubation – nitrogen content in ammonia form), and higher nitrification rates (nitrogen content in nitrate form) were recorded on the clear-cut area (103 and 80 mg/kg to 153 and 87 mg/kg) and especially in the dead stand (160 and 93 mg/kg to 216 and 139 mg/kg). Respective values for the living stand increased from 52 and 61 mg/kg to 119 and 84 mg/kg. Respiration activity, both potential and basic, was more balanced, indicating more intensive dynamics in the case of dead stand and clear-cut area.

Development and distribution of predators and parasitoids during two consecutive years of an Ips typographus (Col., Scolytidae) infestation

Abstract: The development of the natural enemy complex, its within‐tree distribution and the resulting mortalities imposed on bark beetles were investigated during two consecutive years (1994, 1995) at the peak of an Ips typographus infestation. For this reason bolts from infested spruce trees were incubated until the inhabiting insects had emerged. Some 17 000 antagonists were identified and found to belong to 16 predatory and 14 parasitic insect species. Among the predators the Dolichopodidae (Dip.) were most abundant, while among the parasitoids the Pteromalidae (Hym.) ranked first. Parasitoids preferred the upper tree parts, while predators were more abundant in the lower parts. Total bark beetle mortality was assessed based on the literature data on the per capita consumption of the antagonistic larvae. In the first year, the most destructive group were the dolichopodid flies, killing three to seven times more bark beetle larvae than the second ranking Lonchaeidae (Dip.) and the Pteromalidae. In the second year, the pteromalid parasitoids killed 2.5 times more larvae than the dolichopodids. Total bark beetle survival was assessed to decrease from 46 to 18% in the course of the 2 years.