The 2018 European heatwave led to stem dehydration but not to consistent growth reductions in forests

Publisher Copyright: © 2022, The Author(s).Heatwaves exert disproportionately strong and sometimes irreversible impacts on forest ecosystems. These impacts remain poorly understood at the tree and species level and across large spatial scales. Here, we investigate the effects of the record-breaking 2018 European heatwave on tree growth and tree water status using a collection of high-temporal resolution dendrometer data from 21 species across 53 sites. Relative to the two preceding years, annual stem growth was not consistently reduced by the 2018 heatwave but stems experienced twice the temporary shrinkage due to depletion of water reserves. Conifer species were less capable of rehydrating overnight than broadleaves across gradients of soil and atmospheric drought, suggesting less resilience toward transient stress. In particular, Norway spruce and Scots pine experienced extensive stem dehydration. Our high-resolution dendrometer network was suitable to disentangle the effects of a severe heatwave on tree growth and desiccation at large-spatial scales in situ, and provided insights on which species may be more vulnerable to climate extremes.Peer reviewe

Improvement of Ips typographus catches in pheromone trap barriers by altering of sex assigned pheromone blends

The present study was based on the idea of a pheromone trap barrier with alternating dispensers releasing different pheromone mixtures that affect males and females differently. We tested the possibility of increasing the catch efficacy of pheromone trap barriers by altering the pheromone mixture with low levels of cis-Verbenol (cV, targeting males, BM), the mixture with high levels of cV (targeting females, BF) and the pheromone mixture with intermediate levels of cV (SL). In addition, we were interested in lowering the dispersion of attracted bark beetles, especially males, which reduces the risk of attack on trees in the surroundings. Significant highest absolute and relative catch was found in the catch of the combination BM–BF, which was 2.2-fold higher than the catch of the control barrier treated with commercial IT Ecolure baits (Fytofarm, Slovakia). At the same time, the lowest dispersal in the surroundings of the barrier with the combination BM–BF was found, which was 2.5-fold lower than in the control barrier. The performance of the BM–BF combination of mixtures was proved in a field trial experiment where the total season catch of the part of the barrier treated with BM–BF dispensers caught 1.5-fold more beetles during the season than the control part treated with IT Ecolure dispensers. Furthermore, the results confirm that the performance of the combination of low levels of cV (targeting males) and high levels of cV (targeting females) is complemented by the desired reduced dispersion around the barrier, which reduces the risk of attack on trees in the surroundings

The relationship between potential solar radiation and spruce bark beetle catches in pheromone traps

<span>We analysed the relationship between the amount of potential solar radiation and spruce bark beetle</span><em>Ips typographus</em><span> (L.) catches in pheromone traps in an unmanaged nature reserve in the Carpathians (middle Slovakia region), from 2006 through 2009. This relationship was analysed under outbreak conditions. The number of traps varied in different years from 70 to 92. The traps were installed in spruce-forest-dominated stands affected by a windstorm in 2004. A GPS device was used to mark the position of the pheromone traps. The potential solar radiation was calculated with GIS tools for three different time periods in each year: with entire year, for main flight season of the spruce bark beetle and the spring swarming period. The relationship between the amount of potential solar radiation and the spruce bark beetle catches was statistically significant for each year and each time period except for the spring warming in 2007, when the pheromone traps were not set up on time. </span

Contrasting Norway spruce disturbance dynamics in managed forests and strict forest reserves in Slovakia

Forest disturbances are intensifying globally, yet regional drivers of these dynamics remain poorly understood. We investigated recent disturbance intensities in Norway spruce (Picea abies L.) forests in Slovakia (Central Europe) with different management objectives in 2000–2017 based on Landsat imagery. We focused on 122 strict reserves without any management, their actively managed surroundings (500 m and 2000 m buffers), and managed production forests beyond the buffer areas. We used generalized additive mixed models to test for differences in temporal trends of disturbance intensity among these management categories. We found that disturbance intensity was increasing in all management categories during the studied period. The increase was more pronounced in the managed forests (compound annual disturbance rate 1.76% year−1) and the 2000 m buffer (2.21% year−1) than in the strict reserves (0.58% year−1). The predicted cumulative disturbance during the 18-year period was 9.9% in the reserves and 30.5% in the 2000 m buffer. We found that forests in nature reserves can be more resistant to disturbances than forests managed for timber production, despite management efforts to control disturbances in managed forests. Our findings can help reconcile the different perceptions of natural disturbances and their management in Central Europe and support climate-adapted management strategies that consider natural disturbances as an indispensable component of ecosystem dynamics.peerReviewe

Drivers of Spruce Bark Beetle (Ips typographus) Infestations on Downed Trees after Severe Windthrow

Research Highlights: Bark beetles are important agents of disturbance regimes in temperate forests, and specifically in a connected wind-bark beetle disturbance system. Large-scale windthrows trigger population growth of the European spruce bark beetle (Ips typographus L.) from endemic to epidemic levels, thereby allowing the killing of Norway spruce trees over several consecutive years. Background and Objectives: There is a lack of evidence to differentiate how outbreaks are promoted by the effects of environmental variables versus beetle preferences of trees from endemic to outbreak. However, little is known about how individual downed-tree characteristics and local conditions such as tree orientation and solar radiation affect beetle colonization of downed trees. Materials and Methods: To answer this question, we investigated the infestation rates and determined tree death categories (uprooted, broken, and stump) in wind-damaged areas in Western Tatra Mts. in Carpathians (Slovakia) from 2014-2016, following a windthrow in May 2014. In total, we investigated 225 trees over eight transects. For every tree, we measured its morphological (tree height, crown characteristics), environmental (solar radiation, terrain conditions, trunk zenith), temporal (time since wind damage), and beetle infestation (presence, location of attack, bark desiccation) parameters. We applied Generalized Additive Mixed Models (GAMM) to unravel the main drivers of I. typographus infestations. Results: Over the first year, beetles preferred to attack broken trees and sun-exposed trunk sides over uprooted trees; the infestation on shaded sides started in the second year along with the infestation of uprooted trees with lower desiccation rates. We found that time since wind damage, stem length, and incident solar radiation increased the probability of beetle infestation, although both solar radiation and trunk zenith exhibited nonlinear variability. Our novel variable trunk zenith appeared to be an important predictor of bark beetle infestation probability. We conclude that trunk zenith as a simple measure defining the position of downed trees over the terrain can anticipate beetle infestation. Conclusions: Our findings contribute to understanding of the bark beetle's preferences to colonize windthrown trees in the initial years after the primary wind damage. Further, our findings can help to identify trees that are most susceptible to beetle infestation and to prioritize management actions to control beetle population while maintaining biodiversity.peerReviewe

Assessment of Machine Learning Algorithms for Modeling the Spatial Distribution of Bark Beetle Infestation

Machine learning algorithms (MLAs) are used to solve complex non-linear and high-dimensional problems. The objective of this study was to identify the MLA that generates an accurate spatial distribution model of bark beetle (Ips typographus L.) infestation spots. We first evaluated the performance of 2 linear (logistic regression, linear discriminant analysis), 4 non-linear (quadratic discriminant analysis, k-nearest neighbors classifier, Gaussian naive Bayes, support vector classification), and 4 decision trees-based MLAs (decision tree classifier, random forest classifier, extra trees classifier, gradient boosting classifier) for the study area (the Horní Planá region, Czech Republic) for the period 2003–2012. Each MLA was trained and tested on all subsets of the 8 explanatory variables (distance to forest damage spots from previous year, distance to spruce forest edge, potential global solar radiation, normalized difference vegetation index, spruce forest age, percentage of spruce, volume of spruce wood per hectare, stocking). The mean phi coefficient of the model generated by extra trees classifier (ETC) MLA with five explanatory variables for the period was significantly greater than that of most forest damage models generated by the other MLAs. The mean true positive rate of the best ETC-based model was 80.4%, and the mean true negative rate was 80.0%. The spatio-temporal simulations of bark beetle-infested forests based on MLAs and GIS tools will facilitate the development and testing of novel forest management strategies for preventing forest damage in general and bark beetle outbreaks in particular

Sap flow as a function of variables within nested scales: ordinary least squares vs. spatial regression models

Understanding scale-dependent influential drivers of sap flow variability can help managers and policymakers to allocate resources within a particular scale to improve forest health and resiliency against water-stress stimuli such as drought and insects, e.g. bark beetle infestations. We defined a daily measure of sap flow as a function of variables within nested scales of landscape, stand, and tree, using ordinary least squares (OLS), spatial lag and error regression models. Model covariates were elevation, latitude (Y-coordinate), longitude (X-coordinate), neighborhood tree density, tree diameter at breast height, and bark temperature for 40-surveyed Norway spruce ( Picea abies ) in the Czech Republic, Central Europe. Trees were spatially distributed within 19-established subplots across five plots, with distances ranging 2–9 km, at which variations in soil water potential and temperature were limited. The daily measure of sap flow within the regional scale allowed us to avoid the temporal and spatial variability of climate effects on sap flow. A relatively flat terrain across subplots also allowed us to control the effects of slope, aspect, and topography-related solar incidence angle on sap flow. Sap flow was strongly spatially autocorrelated, so OLS models failed to take spatial autocorrelation into account unless to some extent, depending on the spatial distribution of samples, by including latitude and/or longitude in the models. Among spatial regression models, spatial error models performed better than lag models, allowing to capture the effects of unmeasured independent variables. Sap flow variability for the most part (∼70%) was explained by the landscape-level variable of elevation followed by the stand-level variable of tree density, and the remaining part by variables related to tree characteristics; a nested down-scaling function, defined and visualized for the first time. Therefore, thinning forest stands and future plantations with optimum distances, based on the elevation gradients, may be required to counterbalance the allocation of resources, e.g. water, nutrients, and light, among trees, leading to enhance forest health and resiliency against water-stress stimuli

Influence of weather and day length on intra-seasonal growth of Norway spruce (Picea abies L. (Karst.)) and European beech (Fagus sylvatica L.) in a natural montane forest.

Intra-seasonal growth responses of co-occurring European beech (Fagus sylvatica L.) and Norway spruce (Picea abies L. (Karst.)) to weather variability in montane forests can provide useful information on their future growth trends. To improve growth predictions, we aimed to identify: i) the main seasonal windows during which weather variability influences tree-ring growth; ii) species-specific differences in the response to weather fluctuations; and iii) teleconnections to remote sites in the Western Carpathians. We monitored intra-seasonal growth dynamics based on proxies extracted growth signals detected by high-resolution dendrometers in transition zone between beech and spruce altitudinal belt. Within 12 consecutive seasons in the natural montane forest (1350 m a.s.l.), the main part of spruce (68% to 10 July) and beech (95% to 26 August) annual increment was under the prevailing influence of temperature. After this, precipitation pattern (regarding spruce) and day length became the most influential variables during deceleration and cessation of growth. In addition, synchronous patterns with remote sites in the Western Carpathians were found. The results emphasize the importance of studying the influence of shorter-term weather fluctuations during the season. Our findings suggest that montane spruce tends to be less temperature-demanding and more drought-sensitive than beech, which may favor beech over the spruce under the future climate.The accepted manuscript in pdf format is listed with the files at the bottom of this page. The presentation of the authors' names and (or) special characters in the title of the manuscript may differ slightly between what is listed on this page and what is listed in the pdf file of the accepted manuscript; that in the pdf file of the accepted manuscript is what was submitted by the author

Overview of development of an anti-attractant based technology for spruce protection against Ips typographus: From past failures to future success

SCOPUS: ar.jinfo:eu-repo/semantics/publishe