Tree - soil interactions depend on environmental conditions. Planting trees may affect soil microbial communities and compromise their functioning, particularly in unfavorable environments. To ...understand the effects of tree species composition on soil microbial communities, we quantified structural and functional responses of soil microorganisms to tree species planted in various environments using substrate-induced respiration and phospholipid fatty acid analyses. Five forest types were studied including pure stands of native European beech (Fagus sylvatica), range expanding Norway spruce (Picea abies), and non-native Douglas-fir (Pseudotsuga menziesii), as well as the two conifer - beech mixtures. We found that microbial functioning depends strongly on soil nutrient concentrations in the studied forest sites. At nutrient-poor sites, soil microorganisms were more stressed in pure and mixed coniferous forests, especially in Douglas-fir, compared to beech forests. By contrast, microbial structure and functional indicators in beech forests varied little with site conditions, likely because beech provided ample amounts of root-derived resources for microbial growth. Since soil microbial communities are sensitive to Douglas-fir, planting Douglas-fir may compromise ecosystem functioning, especially at nutrient-poor sites. Overall, root-derived resources are important for determining the structure and functioning of soil microbial communities, so soil microbial responses to tree species will depend upon the provisioning of these resources as well as site-specific environmental conditions.
•Soil microorganisms do not respond to forest types at nutrient-rich sites.•European beech mitigates microbial stress in nutrient-poor forest soils.•Microbial stress in nutrient-poor forest soils is intensified by planting Douglas-fir.•Admixing conifers to beech compromises microbial functioning at nutrient-poor sites.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The combination of drought and heat affects forest ecosystems by deteriorating the health of trees, which can lead to large‐scale die‐offs with consequences on biodiversity, the carbon cycle, and ...wood production. It is thus crucial to understand how drought events affect tree health and which factors determine forest susceptibility and resilience. We analyze the response of Central European forests to the 2018 summer drought with 10 × 10 m satellite observations. By associating time‐series statistics of the Normalized Difference Vegetation Index (NDVI) with visually classified observations of early wilting, we show that the drought led to early leaf‐shedding across 21,500 ± 2,800 km2, in particular in central and eastern Germany and in the Czech Republic. High temperatures and low precipitation, especially in August, mostly explained these large‐scale patterns, with small‐ to medium‐sized trees, steep slopes, and shallow soils being important regional risk factors. Early wilting revealed a lasting impact on forest productivity, with affected trees showing reduced greenness in the following spring. Our approach reliably detects early wilting at the resolution of large individual crowns and links it to key environmental drivers. It provides a sound basis to monitor and forecast early‐wilting responses that may follow the droughts of the coming decades.
We analyze the response of Central European forests to the 2018 summer drought with 10 × 10 m satellite observations. By associating time‐series statistics of the Normalized Difference Vegetation Index with aerial observations of early wilting, we show that the drought led to early leaf‐shedding across 21,500 ± 2,800 km2, in particular in Germany and the Czech Republic. Temperature and precipitation mostly explained these large‐scale patterns, with small to medium‐sized trees, steep slopes, and shallow soils being regional risk factors. Our approach provides a sound basis to monitor and forecast early wilting that may follow the droughts of the coming decades.
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BFBNIB, FZAB, GIS, IJS, KILJ, NLZOH, NUK, OILJ, SBCE, SBMB, UL, UM, UPUK
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•This study uses a novel approach of identifying bark beetle infestation in spruce trees using trained dogs; the traditional approach uses human specialists.•Our study demonstrates ...that trained dogs can detect trees more successfully and efficient than human experts.
One of the most promising techniques for rapid detection of bark beetle-infested trees is the use of specially trained dogs. Due to the novelty of using dogs in detecting bark beetle-infested trees, evaluation of success or comparison with the traditional approaches is lacking. Spruces were pre-treated with a synthetic pheromone at several tree positions in six experimental forest stands of 4–12 ha. The tree positions were selected based on their arrangement in a random scheme or in patches considered suitable for bark beetle colonisation. Three dogs of different ages, sex, and levels of experience in detecting Ipstypographus were compared with three experienced human bark beetle specialists. We used GPS positioning of dog tracks (unleashed), handlers, human experts, and detection points during the search under a blind-test procedure for tracking positions. The potential utility of the search methods was estimated with three aspects: 1) search success: detection of infested trees, 2) search effort: length of route, and 3) search efficiency: trees detected / unit time.
Dog-handler pairs were overall more successful in detecting trees attacked by bark beetles than human experts. In particular, the success rate of dogs was higher in plots with random arrangement pre-baited trees and search efficiency was four times higher than that of the human experts.
The most efficient time for the use of dogs for detection would be during the spring flight period, when detection of first attacks and small hot spots could potentially prevent the development of larger infestations. The main advantage of using the dog search method is to amplify the time-window from about one week to one month from the detection to prompt removal of the infested trees from the forest.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Heat-induced weight loss (WL) and chemical and dimensional changes of small specimens of beech (
Fagus sylvatica L.), Scots pine (
Pinus sylvestris L.) and Norway spruce (
Picea abies L.) wood were ...examined after thermal modification in the 190–245 °C temperature range. Treated specimens exhibited reductions in their oven-dry weight in line with the severity of the treatment, with the effect of increasing the temperature of exposure being greater than extending the period of treatment. Wood polysaccharides were found to be distinctly more labile than the lignin constituent; the latter increased possibly as a result of repolymerisation reactions trapping some degradation products in the process. Specimens shrank in the transversal plane in a tangential to radial ratio of 2:1 regardless of the treatment regime, while their length increased marginally for WL < 10–12%. It is proposed that the thermal modification leaves the cell wall material in a permanent strained state.
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The European spruce bark beetle, Ips typographus is the economically most important biotic damaging agent of Norway spruce. Efforts to delimit beetle populations by trapping, application of chemical ...insecticides, or mechanically excluding the beetles from their breeding substrates are often expensive and mostly inadequate. The use of natural enemies and viruses is receiving increased research interest as a potential environmentally healthy approach to control pest insect populations, but practical biocontrol methods against I. typographus are still lacking. To learn more about putative enemies of this pest species, we used high-throughput sequencing to determine its viral community using beetles collected at a Finnish forest site. The analysis revealed a diverse community of RNA viruses associated with I. typographus, including novel viruses that could be affiliated with the classified families Benyviridae, Metaviridae, Narnaviridae, Partitiviridae, Phenuiviridae, Solemoviridae, Virgaviridae, Tombusviridae, and proposed family Spiciviridae, as well as unclassified “quenyaviruses”. Based on phylogenetic analysis, the viruses were distinct from, but resembled, unclassified viruses originating from other arthropods, and many of them were distantly related to previously described viruses. The possibility that the viruses could be hosted by other organisms than the beetle itself (associated fungi, nematodes and protozoa) was addressed by bioinformatic and phylogenetic analyses and is discussed.
•Virome of the European spruce bark beetle was surveyed by high-throughput sequencing of total RNA.•A diverse community of previously unknown RNA viruses was discovered.•Most viruses resembled unclassified viruses originating from other arthropods.•The results enhance understanding of the putative enemies and associates of this pest species.
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The future performance of native tree species under climate change conditions is frequently discussed, since increasingly severe and more frequent drought events are expected to become a major risk ...for forest ecosystems. To improve our understanding of the drought tolerance of the three common European temperate forest tree species Norway spruce, silver fir and common beech, we tested the influence of climate and tree‐specific traits on the inter and intrasite variability in drought responses of these species. Basal area increment data from a large tree‐ring network in Southern Germany and Alpine Austria along a climatic cline from warm‐dry to cool‐wet conditions were used to calculate indices of tolerance to drought events and their variability at the level of individual trees and populations. General patterns of tolerance indicated a high vulnerability of Norway spruce in comparison to fir and beech and a strong influence of bioclimatic conditions on drought response for all species. On the level of individual trees, low‐growth rates prior to drought events, high competitive status and low age favored resilience in growth response to drought. Consequently, drought events led to heterogeneous and variable response patterns in forests stands. These findings may support the idea of deliberately using spontaneous selection and adaption effects as a passive strategy of forest management under climate change conditions, especially a strong directional selection for more tolerant individuals when frequency and intensity of summer droughts will increase in the course of global climate change.
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•Forest disturbance will increase globally with climate change.•Reforestation strategies in a 50,000 ha windthrow landscape in Germany varied.•Bird communities changed dramatically ...after forest loss through windthrow.•Secondary succession hosted more long-distance migratory birds than reforestation.•Future forests and bird communities will be more diverse in Central Europe.
With climate change, the area affected by and the intensity of forest disturbances such as windthrow, insect outbreaks and fire will be increasing. Post-disturbance forest management will be varied, and it is difficult to predict how much natural succession will be allowed in comparison to reforestation. Both, disturbance and reforestation will affect forest biodiversity globally, but potential shifts in species distribution, abundance and community composition are poorly understood.
We studied the response of breeding bird communities to windstorm-induced forest loss (windthrow followed by salvage logging) and different reforestation strategies in one of Central Europe’s largest contiguous windthrow areas created by storm Kyrill in 2007. A decade after the disturbance, we compared bird species diversity, population densities and community composition on plots in replanted beech, replanted conifers and secondary succession (all salvage-logged after the storm), with undisturbed mature (ca. 50–80 years old) Norway spruce Picea abies as a control, in the setting of a natural experiment.
Of the stands blown down, 95% were Norway Spruce. Reforestation strategies varied, with Spruce and non-native conifers planted on twice the area that was replanted with European Beech Fagus sylvestris. Large areas were still dominated by successional tree species a decade after the storm, especially birch Betula spp., mirroring recommendations of sub-national forestry agencies to include secondary succession in future forest development. Birds responded strongly to windstorm-induced forest loss, with a pronounced community turnover. Species associated with high conifer stands reached significantly lower densities on sample plots in disturbed areas. Replanted areas were characterized by mostly ubiquitous bird species. Areas dominated by secondary succession, especially birch, were characterized by high densities of long-distance migrants (often species of conservation concern) and shrubland species, among them several indicator species.
Our results suggest that an increase of forest disturbance across Central Europe will lead to a pronounced reorganisation of biodiversity. Strategies that allow more secondary succession, and avoid replanting allochthonous tree species are likely to benefit populations of depleted bird species, even at salvage-logged and cleared disturbance sites.
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•Pre-commercial thinning strategies simultaneously promote the growth of Norway spruce and provide forage for ungulates.•There was higher amount of forage in stand with no PCT compared to PCT ...stands.•Pre-commercial thinning didn’t influence on birch browsing.•Some version of PCT strategies can be implemented to increase the forage availability in forest landscape.
Mixed stands of Norway spruce and birch have the potential to simultaneously produce timber and provide large ungulates with a significant amount of forage during the regeneration phase. While the growth and yield of such mixtures are well studied, little is known about potential trade-offs between timber and forage production and which management techniques are suitable for meeting both goals. In this study, four different pre-commercial thinning (PCT) strategies were used to study the trade-offs between production and available forage for free-ranging ungulates in a Norway spruce-birch mixture. The four PCT strategies were: 1) retaining 2000 birch stems ha−1 with 2000 Norway spruce ha−1, 2) removing all birches within a 0.75 m radius around Norway spruce stems, 3) removing all birches and other broadleaves, and 4) no PCT (control). Growth of Norway spruce was higher in the 2000 birch ha−1 and full removal treatments compared to the untreated control, but these two treatments did not differ from one another in volume production of Norway spruce. We found a negative effect of PCT on forage availability but no effect on ungulate browsing. Therefore, PCT strategies that provide both sufficient birch forage and maximize volume production of Norway spruce can be implemented.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Increased tropospheric ozone (O3) concentrations in boreal forests affect the emission of biogenic volatile organic compounds (BVOCs), which play crucial roles in biosphere-atmosphere feedbacks. ...Although it has been well documented that BVOC emissions are altered in response to elevated O3, consequent effects on the carbon budget have been largely unexplored. Here, we studied the effects of elevated O3 (80 nmol mol−1) on diurnal variation of BVOC emissions and gas exchange of CO2 from above- and belowground parts of Norway spruce (Picea abies) and Scots pine (Pinus sylvestris) and further investigated effects on the carbon budget. In spring, elevated O3 decreased BVOC emissions and net photosynthesis rate (Pn) from above-ground parts of both species. As BVOC emissions have a causal relationship with dormancy recovery, O3-induced decreases in BVOC emissions indicated the inhibition of dormancy recovery. Contrary to the spring results, in summer BVOC emissions from aboveground parts were increased in response to elevated O3 in both species. Decreases in Pn indicated O3 stress. O3-induced monoterpene emissions from aboveground were the main volatile defense response. Elevated O3 had little effect on BVOC emissions from belowground parts of either species in spring or summer. In spring, elevated O3 decreased the proportion of carbon emitted as BVOCs relative to that assimilated by photosynthesis (the proportion of BVOC-C loss) at the soil-plant system levels in both species. In summer, elevated O3 resulted in a net CO2–C loss at the soil-plant system level of Scots pine. During this process, O3-induced BVOC-C loss can represent a significant fraction of carbon exchange between the atmosphere and Scots pine. In Norway spruce, the effects of O3 were less pronounced. The current results highlight the need for prediction of BVOC emissions and their contributions to the carbon budget in boreal forests under O3 stress.
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•O3 effects on BVOC emissions and carbon budget of two conifer species was studied.•O3 decreased aboveground BVOC emissions in spring but increased them in summer.•O3 had little effect on belowground BVOC emissions in spring or summer.•O3 decreased net photosynthesis rate in both species in spring and summer.•The effect of O3 on the proportion of BVOC-C loss varies over species and season.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Bark beetle disturbances increasingly threaten structure and functionality of temperate and boreal forests globally. The early detection of bark beetle-infested trees, i.e. before beetles’ emergence ...from the breeding tree, is essential for an effective outbreak mitigation. Terrestrial control surveys as traditionally employed for infestation detection, however, are resource-intensive and approach their limits in difficult terrain and during mass outbreaks. Developments in remote sensing and detection algorithms are increasingly giving hope that early-infested trees will be detectable remotely, thereby improving control success and management efficacy. Yet, a comprehensive quantitative evaluation of the approaches currently being developed is lacking to date. This review synthesises the state-of-the-art of recent research on early infestation (or green-attack) detection by remote sensing, and places it in the context with underlying biological constraints, technical opportunities and potential management applications. Since each bark beetle-host tree system has specific characteristics and detectability, we focus on the system with the greatest impact on European forests, the European spruce bark beetle (Ips typographus), which attacks Norway spruce (Picea abies). By screening research published within the period 2000–2022, we included 26 early detection studies in our analyses. All studies reviewed were purely exploratory, testing a variety of data and/or classification algorithms with a relatively limited spatial and temporal coverage. Among tested platforms and sensor types, satellite and multispectral imagery were most frequently investigated. Promising spectral wavelength range or index highly varied among studies and regions. Timeliness and accuracy of detection were found to be insufficient for efficient management, regardless of the tested platform, sensor type, and spatial resolution applied. The main reasons preventing better performance include the rapid development of I. typographus in combination with the delayed and highly variable vitality response of the spruce crown, and frequent cloud cover in spruce-dominated regions across Europe. In conclusion, current remote sensing survey methods cannot yet replace terrestrial control surveys for timely bark beetle management. Nevertheless, they might be supportive either as a back-up to regular and frequent terrestrial surveys, or in specific situations, e.g. to detect hibernation trees, in terrain with difficult accessibility, or in extensively managed forests without sufficient survey capacity. We suggest that the term ‘early detection’ be used consistently as a synonym for ‘pre-emergence detection’ to avoid ambiguity. Finally, we provide recommendations for future research based on the lessons learned from the studies analysed, namely to use a more rigorous and targeted study design, to ensure interdisciplinarity, and to communicate research results explicitly.
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•Accuracy of early-attack detection is insufficient for timely sanitation of trees.•Remote sensing can complement but not replace terrestrial control surveys.•Studies typically lack a large sample size, dense time series and ground truthing.•Cloud cover strongly restricts passive satellite-based approaches across Europe.•Standardised criteria for result validation are recommended in future studies.
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