Search

With the increasing frequencies of extreme weather events caused by climate change, the risk of forest damage from insect attacks grows. Storms and droughts can damage and weaken trees, reduce tree vigour and defence capacity and thus provide host trees that can be successfully attacked by damaging insects, as often observed in Norway spruce stands attacked by the Eurasian spruce bark beetle Ips typographus. Following storms, partially uprooted trees with grounded crowns suffer reduced water uptake and carbon assimilation, which may lower their vigour and decrease their ability to defend against insect attack. We conducted in situ measurements on windthrown and standing control trees to determine the concentrations of non-structural carbohydrates (NSCs), of phenolic defences and volatile monoterpene emissions. These are the main storage and defence compounds responsible for beetle´s pioneer success and host tree selection. Our results show that while sugar and phenolic concentrations of standing trees remained rather constant over a 4-month period, windthrown trees experienced a decrease of 78% and 37% of sugar and phenolic concentrations, respectively. This strong decline was especially pronounced for fructose (-83%) and glucose (-85%) and for taxifolin (-50.1%). Windthrown trees emitted 25 times greater monoterpene concentrations than standing trees, in particular alpha-pinene (23 times greater), beta-pinene (27 times greater) and 3-carene (90 times greater). We conclude that windthrown trees exhibited reduced resources of anti-herbivore and anti-pathogen defence compounds needed for the response to herbivore attack. The enhanced emission rates of volatile terpenes from windthrown trees may provide olfactory cues during bark beetle early swarming related to altered tree defences. Our results contribute to the knowledge of fallen trees vigour and their defence capacity during the first months after the wind-throw disturbance. Yet, the influence of different emission rates and profiles on bark beetle behaviour and host selection requires further investigation. [ABSTRACT FROM AUTHOR]

In a 2‐year field study conducted in the South‐Eastern Alps following a large windthrow disturbance, we tested a large‐scale use of a semiochemical push‐and‐pull strategy to protect susceptible Norway spruce edge trees from the European spruce bark beetle, Ips typographus (Coleoptera: Curculionidae, Scolytinae).Slot traps baited with aggregation pheromones ('pull') and three repellent semiochemicals ('push') were used in both years.In 2020, 26 windthrown areas were classified into three levels of infestation risk, and each was randomly assigned to one of three experimental protocols: eight push‐and‐pull sites; nine trap‐only sites and nine control sites. In 2021, the trials were repeated in 22 clear‐cuts of infested spruce forests, applying two protocols: 16 push–pull and 6 control sites. Fifty traps and 1500 repellent dispensers were used in 2020, and 26 traps and 1500 repellent dispensers were used in 2021.The push‐and‐pull technique performed well in post‐windthrow conditions (2020 trials), especially at high infestation risk, with significantly lower damage to forest edges when compared with untreated sites. The use of pheromone‐baited traps alone was not enough to avoid colonization of forest edges, especially in high‐risk sites.When the push‐and‐pull protocol was applied in clear‐cut areas (2021 trials), the technique was less effective and did not significantly reduce the number of infested trees along the forest edge. Possible interactions with climate conditions are also discussed. [ABSTRACT FROM AUTHOR]

New (a)biotic conditions, resulting from climate change, are expected to change disturbance dynamics, e.g., wind throw, forest fires and insect outbreaks, and their interactions. Unprecedented natural disturbance 30 dynamics might alter the capability of forest ecosystems to buffer atmospheric CO2 increases in the atmosphere, even leading to the risk that forests transform from sinks into sources of CO2. This study aims to enhance the capability of the ORCHIDEE land surface model to study the impacts of climate change on bark beetle dynamics and subsequent effects on forest functioning. The bark beetle outbreak model is based on previous work by Temperli et al. 2013 for the LandClim landscape model. The new implementation of this model in ORCHIDEE r7791 35 accounts for the following differences between ORCHIDEE and LandClim: (1) the coarser spatial resolution of ORCHIDEE, (2) the higher temporal resolution of ORCHIDEE, and (3) the pre-existing process representation of wind throw, drought, and forest structure in ORCHIDEE. Qualitative evaluation demonstrated the model's ability to simulate a wide range of observed post-disturbance forest dynamics: (1) resistance to bark beetle infestation even in the presence of windthrow events; (2) slow transition (3-7 years) from an endemic into an epidemic bark beetle population following medium intensity window events at cold locations; and (3) fast transition (1-3 years) from endemic to epidemic triggered by strong windthrow events. Although all simulated sites eventually recovered from disturbances, the time needed to recover varied from 5 to 10 years depending on the disturbance dynamics. In addition to enhancing the functionality of the ORCHIDEE model, the new bark beetle model represents a fundamental change in the way mortality is simulated as it replaces a framework in which mortality is conceived as a continuous process by one in which mortality is represented by abrupt events. Changing the mortality framework provided new insights into carbon balance estimates, showing the risk of overestimating the short-term sequestration potential under the commonly used continuous mortality framework. [ABSTRACT FROM AUTHOR]

In November 2004 a large windstorm affected forests dominated by Norway spruce (Picea abies (L.) H. Karst, 1881) in the High Tatras National Park, Slovakia, and was followed by a wildfire (2005) and bark beetle outbreak. In this study we investigate temporal changes of breeding bird community (their species richness, density and diversity) as well as different nest-position guilds, in relation to disturbance type. Bird species composition was surveyed in two periods (2006 and 2007, and 2017 and 2018) using the point count method on four plots differing by disturbance type – undisturbed forest, unlogged windthrow, salvage logged windthrow and burnt salvage logged windthrow. A total of three visits per point and breeding season were performed at forty point count sites. We also assessed the successional shift in habitat characteristics between the two monitored periods. In total, 55 bird species and 2059 individuals were recorded on the plots during the study. We observed no effect of disturbance type on mean species richness, abundance and Simpson's diversity per point; however, those characteristics did significantly increase over the study duration. While differently disturbed points had previously differed in their (nest-position) guild number and diversity, the differences between them disappeared over time. We found different trajectories of temporal change in the composition of the species communities and guild diversity in relation to disturbance type, but in a similar direction. During the first period, the greater the initial differences in the severity of disturbance among the disturbance types, the greater the differences were in the composition of bird communities; however, the differences gradually diminished as the forests regenerated. Alterations in habitat structure caused by natural and anthropogenic disturbance and by subsequent succession were the most probable reasons for the altered bird communities and observed patterns of recovery. [ABSTRACT FROM AUTHOR]

Intensifying natural disturbance regimes are driving changes in turbulent forest‐atmosphere exchange of energy and carbon dioxide (CO 2 ), which are affecting the atmosphere at local to global scales. In the European Alps, windthrow and bark beetle infestations have been increasing in severity and intensity; however, studies employing eddy covariance to investigate net ecosystem‐atmosphere exchange of sensible ( H ) and latent heat ( LE ), and CO 2 ( NEE ) along forest disturbance chronosequences in this ecoregion have yet to emerge. This paper presents the first eddy covariance measurements at windthrow sites in the European Alps. Despite the complex terrain, turbulent flux data quality at the sites was high, as indicated by the near‐100% energy balance closures and the large proportion of data satisfying strict quality criteria. Seasonal datasets (15th May–15th October) from the two sites (disturbed in 2009 and 2007, respectively) were subsequently combined in a time series‐chronosequence approach to investigate H , LE , and NEE over the 2nd to 8th growing seasons post‐windthrow. While varying weather conditions strongly influenced energy partitioning, post-disturbance vegetation recovery coincided with a general decrease in median summer Bowen ratios ( H/LE ), although the decline was most pronounced between the 2nd and 3rd summers. Net CO 2 emissions on the other hand demonstrated a clear and consistent post‐disturbance decline, though the seasonal fluxes point toward large losses of ecosystem carbon (C) after disturbance. In the 3rd season post‐windthrow, a net total of 405 ± 15 g C m −2 was lost to the atmosphere, while the seasonal net ecosystem production of −4 ± 16 g C m −2 observed at the 2007 windthrow site indicates that 8 years after disturbance the site remains an annual net C source. This study therefore demonstrates that eddy covariance can provide robust and valuable insights into forest disturbance impacts on H , LE , and NEE in the European Alps. [ABSTRACT FROM AUTHOR]

Coniferous forests cover extensive areas of the boreal and temperate zones. Owing to their primary production and C storage, they have an important role in the global carbon balance. Forest disturbances such as forest fires, windthrows or insect pest outbreaks have a substantial effect on the functioning of these ecosystems. Recent decades have seen an increase in the areas affected by disturbances in both North America and Europe, with indications that this increase is due to both local human activity and global climate change. Here we examine the structural and functional response of the litter and soil microbial community in a Picea abies forest to tree dieback following an invasion of the bark beetle Ips typographus, with a specific focus on the fungal community. The insect-induced disturbance rapidly and profoundly changed vegetation and nutrient availability by killing spruce trees so that the readily available root exudates were replaced by more recalcitrant, polymeric plant biomass components. Owing to the dramatic decrease in photosynthesis, the rate of decomposition processes in the ecosystem decreased as soon as the one-time litter input had been processed. The fungal community showed profound changes, including a decrease in biomass (2.5-fold in the litter and 12-fold in the soil) together with the disappearance of fungi symbiotic with tree roots and a relative increase in saprotrophic taxa. Within the latter group, successive changes reflected the changing availability of needle litter and woody debris. Bacterial biomass appeared to be either unaffected or increased after the disturbance, resulting in a substantial increase in the bacterial/fungal biomass ratio. [ABSTRACT FROM AUTHOR]

Windthrows in spruce forests provide a prime substrate for the population build-up of bark beetles. Until now, no information has been available on the population development of associated parasitoids., The development of bark beetle and parasitoid populations was monitored on cleared and uncleared windthrow areas for 4 years, corresponding to the second to fifth growing seasons after the storm., The population level of both groups quickly increased synchronously from the second to the third season, and gradually declined thereafter until the fifth growing season. The parasitoids showed no time lag., At the species level, the same pattern was found for the pest Ips typographus (L.) and its specific parasitoid Dinotiscus eupterus (Walk.)., During the 4 years under study, a succession of different bark beetle and parasitoid species was found., Bark beetles and parasitoids were more abundant on uncleared windthrow areas than on cleared areas, whereas predatory beetles generally preferred the adjacent forest., Once the deteriorated phloem quality precludes further bark beetle development, no more bark beetle-relevant parasitoids are produced in windthrows. [ABSTRACT FROM AUTHOR]

The increasing number of severe storm events is threatening European forests. Besides the primary damages directly caused by storms, there are secondary damages such as bark beetle outbreaks and tertiary damages due to negative effects on the market. These subsequent damages can be minimized if a detailed overview of the affected area and the amount of damaged wood can be obtained quickly and included in the planning of clearance measures. The present work utilizes UAV-orthophotos and an adaptation of the U-Net architecture for the semantic segmentation and localization of windthrown stems. The network was pre-trained with generic datasets, randomly combining stems and background samples in a copy–paste augmentation, and afterwards trained with a specific dataset of a particular windthrow. The models pre-trained with generic datasets containing 10, 50 and 100 augmentations per annotated windthrown stems achieved F1-scores of 73.9% (S1Mod10), 74.3% (S1Mod50) and 75.6% (S1Mod100), outperforming the baseline model (F1-score 72.6%), which was not pre-trained. These results emphasize the applicability of the method to correctly identify windthrown trees and suggest the collection of training samples from other tree species and windthrow areas to improve the ability to generalize. Further enhancements of the network architecture are considered to improve the classification performance and to minimize the calculative costs. [ABSTRACT FROM AUTHOR]

Mortality rate is thought to show a U-shape relationship to tree size. This shape could result from a decrease of competition-related mortality as diameter increases, followed by an increase of senescence and disturbance-related mortality for large trees. Modeling mortality rate as a function of diameter is nevertheless difficult, first because this relationship is strongly nonlinear, and second because data can be unbalanced, with few observations for large trees. Parametric functions, which are inflexible and sensitive to the distribution of observations, tend to introduce biases in mortality rate estimates. In this study we use mortality data for Abies alba Mill. and Picea abies (L.) Karst. to demonstrate that mortality rate estimates for extreme diameters were biased when using classical parametric functions. We then propose a semiparametric approach allowing a more flexible relationship between mortality and diameter. We show that the relatively shade-tolerant A. alba has a lower annual mortality rate (2.75%) than P. abies (3.78%) for small trees (DBH <15 cm). Picea abies, supposedly more sensitive to bark beetle attacks and windthrows, had a higher mortality rate (up to 0.46%) than A. alba (up to 0.30%) for large trees (DBH ≥50 cm). [ABSTRACT FROM AUTHOR]

The spatial distribution of windthrows and dead-standing trees as well as the occurrence of two bark beetle species, Ips typographus and Tomicus piniperda, were studied at forest-clearcut edges in southern Finland. More than 80% of the recorded dead trees were situated within the first 15 m from the clearcut border. The number of dead-standing spruces attacked by I. typographus did not depend on the amount of windthrows at the same site. According to logistic regression analysis, the distance from a clearcut border had a negative effect on the likelihood of I. typographus being present in the windthrows. The results indicate that windthrows do not necessarily increase bark beetle-induced tree mortality under endemic wind conditions. The accumulation of dead trees at forest-clearcut edges may support the diversity of saproxylic species, but may also maintain populations of harmful bark beetles under non-epidemic conditions. [ABSTRACT FROM AUTHOR]

Forest damage due to storms causes economic loss and requires a fast response to prevent further damage such as bark beetle infestations. By using Convolutional Neural Networks (CNNs) in conjunction with a GIS, we aim at completely streamlining the detection and mapping process for forest agencies. We developed and tested different CNNs for rapid windthrow detection based on PlanetScope satellite data and high-resolution aerial image data. Depending on the meteorological situation after the storm, PlanetScope data might be rapidly available due to its high temporal resolution, while the acquisition of high-resolution airborne data often takes weeks to a month and is, therefore, used in a second step for more detailed mapping. The study area is located in Bavaria, Germany (ca. 165 km2), and labels for damaged areas were provided by the Bavarian State Institute of Forestry (LWF). Modifications of a U-Net architecture were compared to other approaches using transfer learning (e.g., VGG19) to find the most efficient architecture for the task on both datasets while keeping the computational time low. A custom implementation of U-Net proved to be more accurate than transfer learning, especially on medium (3 m) resolution PlanetScope imagery (intersection over union score (IoU) 0.55) where transfer learning completely failed. Results for transfer learning based on VGG19 on high-resolution aerial image data are comparable to results from the custom U-Net architecture (IoU 0.76 vs. 0.73). When using both architectures on a dataset from a different area (located in Hesse, Germany), however, we find that the custom implementations have problems generalizing on aerial image data while VGG19 still detects most damage in these images. For PlanetScope data, VGG19 again fails while U-Net achieves reasonable mappings. Results highlight the potential of Deep Learning algorithms to detect damaged areas with an IoU of 0.73 on airborne data and 0.55 on Planet Dove data. The proposed workflow with complete integration into ArcGIS is well-suited for rapid first assessments after a storm event that allows for better planning of the flight campaign followed by detailed mapping in a second stage. [ABSTRACT FROM AUTHOR]