Publications of the NFI

  • Abegg M., Bösch R., Kükenbrink D., Morsdorf F. (2023) Tree volume estimation with terrestrial laser scanning - Testing for bias in a 3D virtual environment Agric. For. Meteorol. 331, 109348 (16 pp.).

    Tree volume is a key feature in forest monitoring, delivering information, such as wood availability or forest carbon balance. To date, tree volume, i.e. the total volume of the above ground woody parts of a tree, cannot be measured directly with conventional tools. Terrestrial laser scanning (TLS) offers the potential to directly measure tree volume. However, its application in forest monitoring requires a profound understanding of the precision and accuracy of retrieval approaches. In this study, we present a simulation environment for evaluating TLS application in forest inventories. We investigate the influence of understorey density, scanner placement and TLS sensor type on volume estimation of tree parts of varying diameters. Using information from 30 sample plots from the Swiss NFI to simulate 197 sample trees, we evaluate three understorey densities, five scanner locations and their combinations and three realistic and one hypothetic (geometric scanning) TLS sensor types. We show that tree volume estimates from point clouds are biased to certain extent: from about 25% for small trees to a few percent for larger trees above 40 cm diameter at breast height (DBH). Especially small tree parts (diameters 7 cm) lack accurate and precise estimation. In small trees with 12 cm DBH they are overestimated by 110% in average with a high variation, whereas they are underestimated in large trees, i.e. with DBH 75 cm, by 50% in average. Volume estimation of small tree parts is subject to physical limits of TLS, however the estimation of volume of large tree parts could be feasible with appropriate TLS settings and field protocols. Nevertheless, tree volume estimation using TLS must be understood in greater depth before it can be applied regularly in forest inventories.

    DOI: 10.1016/j.agrformet.2023.109348

  • Adler P., Beckschäfer P., Hoffmann K., Jütte K., Kirchhöfer M., Koukal T., … Zielewska-Büttner K. (2023) Produkte für die Fernerkundung richtig nutzen durch Validierung AFZ Wald 78(13), 38-41.

    Vermehrt auftretenden Waldveränderungen begegnet man mit einer Vielzahl an fernerkundungsbasierten Produkten wie Waldschadenskarten. Für die Nutzung dieser Produkte ist es wichtig, deren Anwendbarkeit für einen bestimmten Verwendungszweck richtig einschätzen zu können. Dabei helfen Angaben zur Genauigkeit, die aus der Validierung mit Referenzdaten abgeleitet werden. Welche gängigen Validierungsverfahren und Genauigkeitsmaßzahlen genutzt werden, was sie aussagen und warum sie essenziell sind, wird in diesem Artikel erklärt.

  • Allgaier Leuch B., Fischer C. (2023) Zwischenergebnisse des LFI veröffentlicht – wichtige Trends in Kürze Infoblatt Arbeitsgr. Waldplan. manag. (1) (2 pp.).

    Die Wetterextreme der letzten Jahre haben im Schweizer Wald deutliche Spuren hinterlassen. Es gibt mehr geschädigte und tote Bäume. Ausserdem wachsen weniger junge Bäume nach. Dies zeigen die Zwischenresultate über die Erhebungsjahre 2018 bis 2022 des laufenden fünften Landesforstinventars (LFI5), die am 30. Mai 2023 veröffentlicht worden sind. Die Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft (WSL) und das Bundesamt für Umwelt (BAFU) führen das Inventar gemeinsam durch.

  • Beloiu M., Heinzmann L., Rehush N., Gessler A., Griess V.C. (2023) Individual tree-crown detection and species identification in heterogeneous forests using aerial RGB imagery and deep learning Remote Sens. 15(5), 1463 (17 pp.).

    Automatic identification and mapping of tree species is an essential task in forestry and conservation. However, applications that can geolocate individual trees and identify their species in heterogeneous forests on a large scale are lacking. Here, we assessed the potential of the Convolutional Neural Network algorithm, Faster R-CNN, which is an efficient end-to-end object detection approach, combined with open-source aerial RGB imagery for the identification and geolocation of tree species in the upper canopy layer of heterogeneous temperate forests. We studied four tree species, i.e., Norway spruce (Picea abies (L.) H. Karst.), silver fir (Abies alba Mill.), Scots pine (Pinus sylvestris L.), and European beech (Fagus sylvatica L.), growing in heterogeneous temperate forests. To fully explore the potential of the approach for tree species identification, we trained single-species and multi-species models. For the single-species models, the average detection accuracy (F1 score) was 0.76. Picea abies was detected with the highest accuracy, with an average F1 of 0.86, followed by A. alba (F1 = 0.84), F. sylvatica (F1 = 0.75), and Pinus sylvestris (F1 = 0.59). Detection accuracy increased in multi-species models for Pinus sylvestris (F1 = 0.92), while it remained the same or decreased slightly for the other species. Model performance was more influenced by site conditions, such as forest stand structure, and less by illumination. Moreover, the misidentification of tree species decreased as the number of species included in the models increased. In conclusion, the presented method can accurately map the location of four individual tree species in heterogeneous forests and may serve as a basis for future inventories and targeted management actions to support more resilient forests.

    DOI: 10.3390/rs15051463

  • Bont L.G., Schweier J., Temperli C. (2023) Effect of labour costs on wood harvesting costs and timber provision Eur. J. For. Res.

    Efficient forest operations are essential for forest enterprises, who provide wood and numerous ecosystem services for the society. Important factors influencing the efficiency of forest operations, and thus the harvesting costs, are the level of mechanization, the harvesting method applied, the forest road network, and the training of the labourers. The cost of labour, i.e. salaries, is another important driver of harvesting costs. However, its effect on and relative importance for overall harvesting costs is poorly described in the scientific literature. Thus, this study aims to analyse the influence of labour costs in more detail, especially on the country-wide wood harvesting potentials. In addition, we aimed to cross-compare the effect of labour costs with the effect of switching to a more efficient harvesting method. For this purpose, we calculated timber harvesting costs with varying salaries for all sample plots of the Swiss National Forest Inventory (NFI) for both, the currently applied harvesting method recorded in the NFI, and the potential best suitable harvesting method. A 1% change in labour costs affects harvesting costs by 0.33–0.77%, depending on the harvesting method applied. The influence is larger for systems that involve a large share of motor-manual work and for cable-based methods. Changing labour costs by ± 30% affects the number of plots for which timber harvesting is economically feasible, by 5 to 15 percent points. The effect of switching from the current to the best suitable harvesting method is comparable to that of reducing labour costs by 15–30%. These results indicate that the efficiency of wood harvesting can be increased with further mechanization and does not require cutting salaries of forestry personnel. In that, our results may inform forestry planning and policy making at regional to national level.

    DOI: 10.1007/s10342-023-01621-5

  • Bornand A., Rehush N., Morsdorf F., Thürig E., Abegg M. (2023) Individual tree volume estimation with terrestrial laser scanning: evaluating reconstructive and allometric approaches Agric. For. Meteorol. 341, 109654 (13 pp.).

    Accurate estimates of above-ground tree biomass within forest inventories are essential for calibration and validation of biomass mapping products based on Earth observation data. Terrestrial laser scanning (TLS) enables detailed and non-destructive volume estimation of individual trees, which can be converted to biomass with wood basic density. Existing TLS-based approaches range from simple geometrical features to virtual 3D reconstruction of entire trees. Validating such approaches with weight measurements is a key step before the integration of TLS or other close-range technologies into operational applications such as forest inventories. In this study, we firstly evaluate individual tree volume estimation approaches based on 3D reconstruction through quantitative structure models (QSM) against destructive reference data of 60 trees and compare them to operational allometric scaling models (ASM). Secondly, we determine the explanatory power of TLS-derived geometric parameters regarding total wood, stem, coarse wood and fine branch volume. We observe similar accuracy in merchantable (>7 cm) wood compartments for ASMs (NRMSE = 25 %) and QSMs (NRMSE = 29 %), with QSMs showing better results for broadleaves than conifers and generally overestimating fine branch volume. Feature selection shows that a combination of stem diameters and volume of convex hulls around tree crowns has the most potential to model the entire tree volume including branches, especially for conifers. In cases where the quality of available point clouds is insufficient for QSMs, 3D information can thus still be utilised by deriving geometric parameters. The integration of crown dimension parameters into new allometric models could substantially improve the estimation of branch wood volume.

    DOI: 10.1016/j.agrformet.2023.109654

  • Cioldi F., Conedera M., Giudici F., Herold A. (2023) Dinamica evolutiva dei boschi al Sud delle Alpi Forestaviva (90), 6-8.

  • Didion M., Haeni M., Schmatz D.R., Zappa M., Zellweger F. (2023) Ein Vergleich von räumlichen Klimadaten mit unabhängigen LWF-Messungen für die Schweiz Schweiz. Z. Forstwes. 174(3), 170-173.

    Gegitterte Klimadaten mit einer regelmässigen räumlichen Auflösung sind eine wichtige Grundlage für Umweltstudien. Sie werden mithilfe statistischer Methoden aus Punktdaten von Messstationen erzeugt und haben insbesondere in topografisch komplexen Gebirgsregionen wie den Schweizer Alpen eine limitierte Genauigkeit. Dieser Artikel vergleicht vier für die Schweiz entwickelte gegitterte Datensätze unterschiedlicher Temperatur- und Niederschlagsvariablen mit unabhängigen Messdaten von 14 Dauerbeobachtungsflächen der Langfristigen Waldökosystemforschung (LWF) über einen Zeitraum von 20 Jahren. Die Resultate dienen als Entscheidungshilfe zur Wahl eines für eine grossflächige Anwendung zuverlässigen und homogenen Datensatzes. Die untersuchten Datensätze mit individuellen Stärken und Schwächen kommen für Anwendungen in der Schweiz infrage.

    DOI: 10.3188/szf.2023.0170

  • Dumollard G., Thomas M., Rosset C., Cioldi F., Pauli B. (2023) Ökonomische Bewertung von waldbaulichen Strategien zur Anpassung an den Klimawandel im Schweizer Mittelland Schweiz. Z. Forstwes. 174(2), 92-99.

    Der Klimawandel wirkt sich bereits stark auf die Waldökosysteme der Schweiz aus und dürfte dies zukünftig noch viel stärker tun. Die Veränderung der Standortbedingungen und das erhöhte Risiko von Störungen (Trockenheit, Stürme, Borkenkäfer) haben erhebliche nachteilige Auswirkungen auf das waldbauliche Potenzial der Wälder. Diese Auswirkungen können durch die Wahl geeigneter Baumarten und Produktionszeiträume reduziert werden. Der Klimawandel erfordert daher eine vorausschauende Änderung der waldbaulichen Strategien, damit die Waldökosysteme vital und resilient bleiben und alle ihre Ökosystemleistungen nachhaltig erbringen können. Die Anpassungen müssen von den Waldbesitzenden durch die Inwertsetzung der verschiedenen Waldleistungen, von denen die Holzvermarktung ein wichtiger Bestandteil bleibt, finanziert werden können. Im vorliegenden Artikel werden vier unterschiedliche waldbauliche Strategien («Weiter wie bisher», «Sanfte Lenkung », «Ertragsorientiert», «Starke Anpassung») und die daraus resultierenden ökonomischen Konsequenzen vor dem Hintergrund unterschiedlicher Klimaszenarien beschrieben. Die ökonomischen Konsequenzen der Strategien wurden mithilfe eines Modells simuliert. Die ökonomischen Ergebnisse zeigen, dass eine aktive Anpassung der Wälder an den Klimawandel möglich und aus wirtschaftlicher Sicht sogar wünschenswert ist. Sie zeigen aber auch die hohe Bedeutung von öffentlichen Beiträgen für die künftigen Waldanpassungsstrategien.

    DOI: 10.3188/szf.2023.0092

  • Düggelin C., Abegg M., Allgaier Leuch B., Bischof S., Bont L., Cioldi F., … Thürig E. (2023) Schweizerisches Landesforstinventar. Anleitung für die Befragung der Forstdienste im Rahmen der fünften Erhebung 2018-2026. WSL Berichte: Vol. 141. Birmensdorf: Eidg. Forschungsanstalt für Wald, Schnee und Landschaft WSL. 76 p.

    DOI: 10.55419/wsl:35032

  • Fol C.R., Kükenbrink D., Rehush N., Murtiyoso A., Griess V.C. (2023) Evaluating state-of-the-art 3D scanning methods for stem-level biodiversity inventories in forests Int. J. Appl. Earth Obs. Geoinf. 122, 103396 (12 pp.).

    Monitoring biodiversity in forests is crucial for their management and preservation, especially in light of increasing climatic disturbances. However, traditional methods of surveying forest biodiversity, such as the inventory of tree-related microhabitats (TreMs), are costly and time-consuming. For many years, terrestrial laser scanning (TLS) was the main method for producing highly accurate 3D models of forests. However, with recent advancements in 3D scanning technologies, there are now numerous alternatives available on the market. The aim of this study was to evaluate the performance of four different 3D data acquisition methods, i.e. close-range photogrammetry (CRP), fish-eye photogrammetry (FEP), mobile laser scanning (MLS), and mixed reality depth camera (MRDC), in terms of accuracy and ability to measure biodiversity (TreMs) at tree-stem level, in comparison to TLS. Analysis was performed based on geometric accuracy and point neighbourhood relevance. CRP was the most accurate alternative to TLS for TreM measurement with a median error of 1.5 cm, while FEP provided a good balance between accuracy (median error 1.4 cm) and speed of data collection. Although MLS showed promising results (median error 1.6 cm), noise in the point cloud limited its ability to identify TreMs. MRDC, on the other hand, had lower quality (median error 3.6 cm) and lower point density, making it unsuitable for TreM segmentation. Nevertheless, the study demonstrated the feasibility of augmenting the real world with virtual content at single-tree-stem level using mixed reality technology. Overall, the 3D scanning technologies presented hold great promise for recording the evolution of biodiversity at stem level.

    DOI: 10.1016/j.jag.2023.103396

  • Forzieri G., Dutrieux L.P., Elia A., Eckhardt B., Caudullo G., Taboada F.Á., … Beck P.S.A. (2023) The Database of European Forest Insect and Disease Disturbances: DEFID2 Glob. Chang. Biol. 29(21), 6040-6065.

    Insect and disease outbreaks in forests are biotic disturbances that can profoundly alter ecosystem dynamics. In many parts of the world, these disturbance regimes are intensifying as the climate changes and shifts the distribution of species and biomes. As a result, key forest ecosystem services, such as carbon sequestration, regulation of water flows, wood production, protection of soils, and the conservation of biodiversity, could be increasingly compromised. Despite the relevance of these detrimental effects, there are currently no spatially detailed databases that record insect and disease disturbances on forests at the pan-European scale. Here, we present the new Database of European Forest Insect and Disease Disturbances (DEFID2). It comprises over 650,000 harmonized georeferenced records, mapped as polygons or points, of insects and disease disturbances that occurred between 1963 and 2021 in European forests. The records currently span eight different countries and were acquired through diverse methods (e.g., ground surveys, remote sensing techniques). The records in DEFID2 are described by a set of qualitative attributes, including severity and patterns of damage symptoms, agents, host tree species, climate-driven trigger factors, silvicultural practices, and eventual sanitary interventions. They are further complemented with a satellite-based quantitative characterization of the affected forest areas based on Landsat Normalized Burn Ratio time series, and damage metrics derived from them using the LandTrendr spectral-temporal segmentation algorithm (including onset, duration, magnitude, and rate of the disturbance), and possible interactions with windthrow and wildfire events. The DEFID2 database is a novel resource for many large-scale applications dealing with biotic disturbances. It offers a unique contribution to design networks of experiments, improve our understanding of ecological processes underlying biotic forest disturbances, monitor their dynamics, and enhance their representation in land-climate models. Further data sharing is encouraged to extend and improve the DEFID2 database continuously. The database is freely available at

    DOI: 10.1111/gcb.16912

  • Hegetschweiler K.T., Maidl E., Wunderli J.M., Stride C.B., Fischer C., Wunderli L., … Hunziker M. (2023) Influence of perceptual experiences, especially sounds, on forest attractiveness In L. Koegst, O. Kühne, & D. Edler (Eds.), RaumFragen: Stadt-Region-Landschaft. Multisensory landscapes. Theories and methods. Wiesbaden: Springer VS. 255-277.

    In most studies, forest attractiveness is determined by visual aspects. However, forest perception is not only influenced by visitors' visual impressions - all sensory dimensions play a role. In order to capture other sensory perceptions, we conducted seven go-along interviews, during which forest visitors were accompanied by an interviewer on their normal route through the forest and prompted to comment on what they saw, smelled, heard and felt. In addition, a pilot survey provided some initial insights on the influence of sounds on visitors' perceived visual attractiveness of forest plots. The pilot study was part of a larger quantitative forest visitor survey across the whole of Switzerland aiming to link forest visitor data to forest characteristics according to the Swiss National Forest Inventory NFI. At a subset of 29 forest plots, sounds were recorded in addition to the questionnaire survey and the data on forest characteristics. This enabled us to link forest visitor data provided in the questionnaires with forest characteristics and sound parameters, in an attempt to explain between-plot variability in the perceived visual attractiveness of forest plots.

    DOI: 10.1007/978-3-658-40414-7_14

  • Hordijk I., Maynard D.S., Hart S.P., Lidong M., ter Steege H., Liang J., … Crowther T.W. (2023) Evenness mediates the global relationship between forest productivity and richness J. Ecol. 11(6), 1308-1326.

    1. Biodiversity is an important component of natural ecosystems, with higher species richness often correlating with an increase in ecosystem productivity. Yet, this relationship varies substantially across environments, typically becoming less pronounced at high levels of species richness. However, species richness alone cannot reflect all important properties of a community, including community evenness, which may mediate the relationship between biodiversity and productivity. If the evenness of a community correlates negatively with richness across forests globally, then a greater number of species may not always increase overall diversity and productivity of the system. Theoretical work and local empirical studies have shown that the effect of evenness on ecosystem functioning may be especially strong at high richness levels, yet the consistency of this remains untested at a global scale.
    2. Here, we used a dataset of forests from across the globe, which includes composition, biomass accumulation and net primary productivity, to explore whether productivity correlates with community evenness and richness in a way that evenness appears to buffer the effect of richness. Specifically, we evaluated whether low levels of evenness in speciose communities correlate with the attenuation of the richness–productivity relationship.
    3. We found that tree species richness and evenness are negatively correlated across forests globally, with highly speciose forests typically comprising a few dominant and many rare species. Furthermore, we found that the correlation between diversity and productivity changes with evenness: at low richness, uneven communities are more productive, while at high richness, even communities are more productive.
    4. Synthesis. Collectively, these results demonstrate that evenness is an integral component of the relationship between biodiversity and productivity, and that the attenuating effect of richness on forest productivity might be partly explained by low evenness in speciose communities. Productivity generally increases with species richness, until reduced evenness limits the overall increases in community diversity. Our research suggests that evenness is a fundamental component of biodiversity–ecosystem function relationships, and is of critical importance for guiding conservation and sustainable ecosystem management decisions.

    DOI: 10.1111/1365-2745.14098

  • Jiang Y., Rüetschi M., Garnot V.S.F., Marty M., Schindler K., Ginzler C., Wegner J.D. (2023) Accuracy and consistency of space-based vegetation height maps for forest dynamics in alpine terrain Sci. Remote Sens. 8, 100099 (15 pp.).

    Monitoring and understanding forest dynamics is essential for environmental conservation and management. This is why the Swiss National Forest Inventory (NFI) provides countrywide vegetation height maps at a spatial resolution of 0.5 m. Its long update time of 6 years, however, limits the temporal analysis of forest dynamics. This can be improved by using spaceborne remote sensing and deep learning to generate large-scale vegetation height maps in a cost-effective way. In this paper, we present an in-depth analysis of these methods for operational application in Switzerland. We generate annual, countrywide vegetation height maps at a 10-m ground sampling distance for the years 2017–2020 based on Sentinel-2 satellite imagery. In comparison to previous works, we conduct a large-scale and detailed stratified analysis against a precise Airborne Laser Scanning reference dataset. This stratified analysis reveals a close relationship between the model accuracy and the topology, especially slope and aspect. We assess the potential of deep learning-derived height maps for change detection and find that these maps can indicate changes as small as 250 m2. Larger-scale changes caused by a winter storm are detected with an F1-score of 0.77. Our results demonstrate that vegetation height maps computed from satellite imagery with deep learning are a valuable, complementary, cost-effective source of evidence to increase the temporal resolution for national forest assessments.

    DOI: 10.1016/j.srs.2023.100099

  • Leiterer R., Milani G., Wegner J.D., Ginzler C. (2023) ExoSilva - ein Multi­-Sensor­-Ansatz für ein räumlich und zeitlich hochaufgelöstes Monitoring des Waldzustandes In Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL (Ed.), WSL Berichte: Vol. 134. Neue Fernerkundungs­technologien für die Umweltforschung und Praxis. Birmensdorf: Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL. 17-22.

    Die Veränderungen der klimatischen Bedingungen sind auch zunehmend in den Waldökosystemen der Schweiz sichtbar. Dies nicht nur in Hinblick auf die langfristigen Auswirkungen auf den Waldzustand durch die zunehmenden Temperaturen und die sich regional verändernden Wasserverfügbarkeiten, sondern auch in Bezug auf das erhöhte Risiko von unmittelbaren Waldschäden durch biotische und abiotische Faktoren. Mit ExoSilva, einem satellitengestützten Ansatz, der zusammen mit der ETHZ, der WSL und dem UZH Spin-off ExoLabs entwickelt wurde, können sowohl langfristige Trends als auch kurzfristige Veränderungen des Waldzustandes in der Schweiz erfasst werden. Dabei ermöglicht, neben der Erfassung des Waldzustandes in einer hohen räumlichen Auflösung von 20 × 20 m Pixelgrösse und einer wöchentlichen Aktualisierung, vor allem der pixel-basierte Abgleich mit der langjährigen Dynamik neue Ansätze für das Waldmonitoring. In diesem Beitrag wird die Datenaufbereitung, die Evaluierung der Ergebnisse sowie das Anwendungspotenzial der entwickelten Methodik präsentiert.

    Changes in climatic conditions are increasingly visible in Switzerland’s forest ecosystems. This is the case not only regarding long-term effects on the condition of the forests caused by increasing temperatures and regionally changing water availability, but also with respect to the increased risk of immediate forest damage due to biotic and abiotic factors. ExoSilva, a satellite-based approach developed collaboratively by ETHZ, WSL and the UZH spin-off ExoLabs, can be used to record both long-term trends and short-term changes in the condition of forests in Switzerland. In addition to recording the forest condition at a high spatial resolution of 20 m × 20 m pixel size and being updated weekly, the pixel-based comparison with the long-term dynamics enables new approaches to forest monitoring. In this paper we present the data preparation, the evaluation of the results, and the application potential of the developed methodology.

    DOI: 10.55419/wsl:33057

  • Madrigal-González J., Calatayud J., Ballesteros-Cánovas J.A., Escudero A., Cayuela L., Marqués L., … Stoffel M. (2023) Global patterns of tree density are contingent upon local determinants in the world's natural forests Comm. Biol. 6, 47 (6 pp.).

    Previous attempts to quantify tree abundance at global scale have largely neglected the role of local competition in modulating the influence of climate and soils on tree density. Here, we evaluated whether mean tree size in the world’s natural forests alters the effect of global productivity on tree density. In doing so, we gathered a vast set of forest inventories including >3000 sampling plots from 23 well-conserved areas worldwide to encompass (as much as possible) the main forest biomes on Earth. We evidence that latitudinal productivity patterns of tree density become evident as large trees become dominant. Global estimates of tree abundance should, therefore, consider dependencies of latitudinal sources of variability on local biotic influences to avoid underestimating the number of trees on Earth and to properly evaluate the functional and social consequences.

    DOI: 10.1038/s42003-023-04419-8

  • Mandl L., Stritih A., Seidl R., Ginzler C., Senf C. (2023) Spaceborne LiDAR for characterizing forest structure across scales in the European Alps Remote Sens. Ecol. Conserv. 9(5), 599-614.

    The launch of NASA's Global Ecosystem Dynamics Investigation (GEDI) mission in 2018 opens new opportunities to quantitatively describe forest ecosystems across large scales. While GEDI's height-related metrics have already been extensively evaluated, the utility of GEDI for assessing the full spectrum of structural variability - particularly in topographically complex terrain - remains incompletely understood. Here, we quantified GEDI's potential to estimate forest structure in mountain landscapes at the plot and landscape level, with a focus on variables of high relevance in ecological applications. We compared five GEDI metrics including relative height percentiles, plant area index, cover and understory cover to airborne laser scanning (ALS) data in two contrasting mountain landscapes in the European Alps. At the plot level, we investigated the impact of leaf phenology and topography on GEDI's accuracy. At the landscape-scale, we evaluated the ability of GEDIs sample-based approach to characterize complex mountain landscapes by comparing it to wall-to-wall ALS estimates and evaluated the capacity of GEDI to quantify important indicators of ecosystem functions and services (i.e., avalanche protection, habitat provision, carbon storage). Our results revealed only weak to moderate agreement between GEDI and ALS at the plot level (R2 from 0.03 to 0.61), with GEDI uncertainties increasing with slope. At the landscape-level, however, the agreement between GEDI and ALS was generally high, with R2 values ranging between 0.51 and 0.79. Both GEDI and ALS agreed in identifying areas of high avalanche protection, habitat provision, and carbon storage, highlighting the potential of GEDI for landscape-scale analyses in the context of ecosystem dynamics and management.

    DOI: 10.1002/rse2.330

  • Marqués L., Weng E., Bugmann H., Forrester D.I., Rohner B., Hobi M.L., … Stocker B.D. (2023) Tree growth enhancement drives a persistent biomass gain in unmanaged temperate forests AGU Adv. 4(5), e2022AV000859 (19 pp.).

    While enhanced tree growth over the last decades has been reported in forests across the globe, it remains unclear whether it drives persistent biomass increases of forest stands, particularly in mature forests. Enhanced tree growth and stand-level biomass are often linked with a simultaneous increase in density-driven mortality and a reduction in tree longevity. Identifying empirical evidence regarding the balance between these processes is challenging due to the confounding effects of stand history, management, and environmental changes. Here, we investigate the link between growth and biomass via the negative relationship between average tree size and stand density (tree number per area). We find increasing stand density for a given mean tree size in unmanaged closed-canopy forests in Switzerland over the past six decades and a positive relationship between tree growth and stand density across forest plots - qualitatively consistent with our simulations using a mechanistic, cohort-resolving ecosystem model (BiomeE). Model simulations show that, in the absence of other disturbances, enhanced tree growth persistently increases biomass stocks despite simultaneous decreases in carbon residence time and tree longevity. However, the magnitude of simulated biomass changes for a given growth enhancement critically depends on the shape of the mortality functions. Our analyses reconcile reports of growth-induced reductions of tree longevity with model predictions of persistent biomass increases, and with our finding of trends toward denser forests in response to growth - also in mature stands.

    DOI: 10.1029/2022AV000859

  • Mayer M., Rusch S., Didion M., Baltensweiler A., Walthert L., Ranft F., … Hagedorn F. (2023) Elevation dependent response of soil organic carbon stocks to forest windthrow Sci. Total Environ. 857, 159694 (9 pp.).

    Storms represent a major disturbance factor in forest ecosystems, but the effects of windthrows on soil organic carbon (SOC) stocks are poorly quantified. Here, we assessed the SOC stocks of windthrown forests at 19 sites across Switzerland spanning an elevation gradient from 420 to 1550 m, encompassing a strong climatic gradient. Results show that the effect size of disturbance on SOC stocks increases with the size of the initial SOC stocks. The largest windthrow-induced SOC losses of up to 29 t C ha-1 occurred in high-elevation forests with a harsh climate developing thick organic layers. In contrast, SOC stocks of low-elevation forests with thin organic layers were hardly affected. A mineralization study further revealed high elevation forests to store higher amounts of easily mineralizable C in thick organic layers that got lost following windthrow. These findings are supported by a meta-analysis of available windthrow studies, showing an increase of storm-induced SOC losses with the size of the initial SOC stocks. Modelling simulations further indicate longer-lasting SOC losses and a slower recovery of SOC stocks after windthrow at high compared to low elevations, due to a slower regeneration of mountain forests and associated lower C inputs into soils in a harsh climate. Upscaling the experimental findings/observed patterns by linking them to a data base of Swiss forest soils shows a total SOC loss of ∼0.4 Mt. C for the whole forested area of Switzerland after two major storm events, counteracting the forest net carbon sink of decades. Our study provides strong evidence that the vulnerability of SOC stocks to windthrow is particularly high in forests featuring thick and slowly forming organic layers, such as mountain soils. Thus, the risk of losing SOC to more frequent windthrows in mountain forests strongly limits their potential to mitigate climate change.

    DOI: 10.1016/j.scitotenv.2022.159694

  • Mey R., Temperli C., Stillhard J., Nitzsche J., Thürig E., Bugmann H., Zell J. (2023) Deriving forest stand information from small sample plots: an evaluation of statistical methods For. Ecol. Manag. 544, 121155 (16 pp.).

    Most strategic and operational forest management decisions are taken based on stand-level information, and quantitative models of forest dynamics are key for developing sustainable management strategies. However, data on forest stands for the initialisation of such models that are representative at large spatial scales, e.g., countries or ecoregions, are often lacking. National Forest Inventories (NFIs) provide forest data from small sample plots at large spatial scales, yet deriving full stand information based on such data is challenging. Here, we evaluate seven methods of varying complexity for deriving quantitative stand descriptions based on sample data as provided by the Swiss NFI. We selected 271 extensively measured Swiss forests stands with unimodal diameter distributions, classified them as beech- vs. spruce-dominated in five development stages and randomly placed a small sized sample plot in each stand using the Swiss NFI sampling design (i.e., a circular plot of 500 m2). Seven modelling approaches were used to derive diameter distributions and species-specific stem numbers (i.e., tree species composition) from the sample data that are representative for a particular stand (local scale) and for stand types in general (generalised scale). The prediction performance of the modelling approaches was evaluated using 100 random samples per stand to calculate prediction errors. Generalised even-aged diameter distributions were best predicted by the simultaneous parameter prediction method (PPM), i.e. a combined three-step regression approach, with on average 1.3 to 2.5 times lower prediction errors compared to the simple pooling of diameter samples. However, uneven-aged diameter distributions were best predicted by pooling. At the local scale, the simultaneous PPM performed best for data from sample plots with fewer than 17 to 19 trees across all development stages. Prediction performance of the PPMs increased for structurally and spatially diverse local stands with positively skewed diameter distributions. A Random Forest approach was most suitable for predicting species composition at both the generalised and the local scale. Our study evaluates the strengths and weaknesses of methods to model stands based on data from small sample plots. We emphasise terminological pitfalls by consequently distinguishing local accuracy and generalised representativity of the stand descriptions. We demonstrate the feasibility of deriving locally accurate stands using data from small forest sample plots and evaluate the derivation of generalised stands representative at large regions. At both scales, our developments contribute to an improved initialisation of forest models and thus to a more realistic modelling of forest development under future boundary conditions.

    DOI: 10.1016/j.foreco.2023.121155

  • Mo L., Zohner C.M., Reich P.B., Liang J., de Miguel S., Nabuurs G.J., … Crowther T.W. (2023) Integrated global assessment of the natural forest carbon potential Nature 624, 92-101.

    Forests are a substantial terrestrial carbon sink, but anthropogenic changes in land use and climate have considerably reduced the scale of this system 1. Remote-sensing estimates to quantify carbon losses from global forests 2–5 are characterized by considerable uncertainty and we lack a comprehensive ground-sourced evaluation to benchmark these estimates. Here we combine several ground-sourced 6 and satellite-derived approaches 2,7,8 to evaluate the scale of the global forest carbon potential outside agricultural and urban lands. Despite regional variation, the predictions demonstrated remarkable consistency at a global scale, with only a 12% difference between the ground-sourced and satellite-derived estimates. At present, global forest carbon storage is markedly under the natural potential, with a total deficit of 226 Gt (model range = 151–363 Gt) in areas with low human footprint. Most (61%, 139 Gt C) of this potential is in areas with existing forests, in which ecosystem protection can allow forests to recover to maturity. The remaining 39% (87 Gt C) of potential lies in regions in which forests have been removed or fragmented. Although forests cannot be a substitute for emissions reductions, our results support the idea 2,3,9 that the conservation, restoration and sustainable management of diverse forests offer valuable contributions to meeting global climate and biodiversity targets.

    DOI: 10.1038/s41586-023-06723-z

  • Montoro Girona M., Aakala T., Aquilué N., Bélisle A.C., Chaste E., Danneyrolles V., … Gauthier S. (2023) Challenges for the sustainable management of the boreal forest under climate change In M. Montoro Girona, H. Morin, S. Gauthier, & Y. Bergeron (Eds.), Advances in global change research: Vol. 74. Boreal forests in the face of climate change. Sustainable management. Cham: Springer. 773-837.

    The increasing effects of climate and global change oblige ecosystem-based management to adapt forestry practices to deal with uncertainties. Here we provide an overview to identify the challenges facing the boreal forest under projected future change, including altered natural disturbance regimes, biodiversity loss, increased forest fragmentation, the rapid loss of old-growth forests, and the need to develop novel silvicultural approaches. We specifically address subjects previously lacking from the ecosystem-based management framework, e.g., Indigenous communities, social concerns, ecological restoration, and impacts on aquatic ecosystems. We conclude by providing recommendations for ensuring the successful long-term management of the boreal biome facing climate change.

    DOI: 10.1007/978-3-031-15988-6_31

  • Nasiri V., Beloiu M., Darvishsefat A.A., Griess V.C., Maftei C., Waser‬ L.T. (2023) Mapping tree species composition in a Caspian temperate mixed forest based on spectral-temporal metrics and machine learning Int. J. Appl. Earth Obs. Geoinf. 116, 103154 (12 pp.).

    The tree species composition (TSC) reflects a forest's tree species diversity and is relevant for forest planning, biodiversity conservation, and forest resources management. Yet, accurate information on tree species composition at landscape scale is largely missing, especially for mixed forests and remote areas. One reason being that mapping tree species is time-consuming, and costly, especially in mixed forests and remote areas. Here we develop a robust method for mapping TSC in a mixed temperate forest. Based on forest inventory plots and considering the frequency of dominant tree species in the inventory dataset, five species groups were defined: pure oriental beech, mixed oriental beech, pure common hornbeam, mixed common hornbeam, and mixed deciduous. The classification is based on three-year time series data of Landsat-8 (L8) and Sentinel-2 (S2) derived spectral-temporal features (STMs) and vegetation indices within the long-term, seasonal, and monthly time scales. Model performances of three Machine Learning (ML) algorithms, Random Forest (RF), Support Vector Machine (SVM), and Classification and Regression Tree (CART) were compared and revealed different classification accuracies (overall accuracies (OAs) between ∼ 70 % and 86 %). Highest OA was obtained using SVM regardless of the classification dataset (STMs and satellite time series). The comparisons between different time scales indicated that with both L8 and S2 time series the seasonal STMs produced higher accuracies than monthly and long-term STMs with S2 outperforming L8 across all time scales and with all tested ML algorithms. We conclude that the freely available satellite time series, spectral-temporal features, and ML algorithms are favourable for accurate TSC mapping.

    DOI: 10.1016/j.jag.2022.103154

  • Portier J., Shackleton R.T., Klesse S., Ferretti M., Flury R., Hobi M.L., … Thürig E. (2023) No evidence that coring affects tree growth or mortality in three common European temperate forest tree species Eur. J. For. Res. (11 pp.).

    Tree cores are a highly valuable scientific resource. Annual growth ring data can, for example, improve our understanding of climate change impacts and effects of environmental pollution, allow for better annual estimations of tree growth patterns and carbon storage, and help quantify dynamics and changes in forest ecosystems. The value of coring trees for research has been weighted against concerns around the potential harm coring might cause to trees. To date, there is indeed limited research accurately quantifying the potential effects of coring on tree growth and only a handful of studies assessing its influence on mortality. Consequently, many European long-term forest inventorying and monitoring programs are concerned that tree coring might bias the repeated tree measurements in permanent plots, which they rely on for assessments of states and changes of forests. In this study, we assessed the effects of tree coring on the growth and mortality of three widespread European tree species approximately 10 years after they were cored. We used repeated tree measurements from permanent research sites in Switzerland and Ukraine. In Switzerland, we assessed 35 cored and 159 uncored Norway spruce (Picea abies) trees as well as 147 cored and 332 uncored silver fir (Abies alba) trees. In Ukraine, we assessed 348 cored and 6'611 uncored European beech (Fagus sylvatica) trees. We found no statistical evidence that coring negatively affected the growth or mortality of the three tree species assessed. Although we cannot rule out subtle effects on tree health and wood quality, our findings do not provide any evidence that coring affects or biases repeated measurements (such as DBH measures and recording of mortality) performed on the investigated tree species. Tree coring could therefore be considered more often for routine incorporation, particularly in long-term forest inventorying and monitoring programs and initiatives.

    DOI: 10.1007/s10342-023-01612-6

  • Price B., Huber N., Eggenberg S., Ginzler C. (2023) Die Lebensraumkarte der Schweiz: ein Fernerkundungs­produkt für Planung, Forschung und Praxis In Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL (Ed.), WSL Berichte: Vol. 134. Neue Fernerkundungs­technologien für die Umweltforschung und Praxis. Birmensdorf: Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL. 73-79.

    Lebensraumkarten mit hoher thematischer und räumlicher Auflösung, die weiträumige Gebiete abdecken, sind grundlegende Instrumente für die Planung ökologischer Netzwerke und das Management von Biodiversität. Um eine Lebensraumkarte für die Schweiz zu erstellen, haben wir die besten verfügbaren räumlichen Daten und Verbreitungsmodelle in einer integrierten Methode zusammengeführt. Der Ansatz stützt sich auf die Segmentierung und Klassifizierung von Fernerkundungsdaten mit hoher räumlicher Auflösung, inklusive Orthobilder (1 m Auflösung) und Satellitenbilder von Planet (3 m Auflösung) und Sentinel-1 und -2 (10 m respektive 20 m Auflösung). 84 TypoCH Lebensräume in 32 Gruppen und 9 übergreifenden Klassen wurden schweizweit räumlich explizit mit feiner räumlicher und thematischer Auflösung kartiert. Die erstellte Karte ist im WSL-Datenportal EnviDat und auf frei zugänglich.

    Habitat maps with high thematic and spatial resolution covering broad extents are fundamental tools for planning ecological networks and managing biodiversity. To produce a habitat map for Switzerland, we brought together the best available spatial data and distribution models in an integrated method. The approach is based on the segmentation and classification of remote sensing data with high spatial resolution. 84 TypoCH habitats in 32 groups and 9 overarching classes were mapped in a spatially explicit manner for Switzerland. The map produced is freely accessible on the WSL data portal EnviDat and

    DOI: 10.55419/wsl:33077

  • Price B., Huber N., Nussbaumer A., Ginzler C. (2023) The habitat map of Switzerland: a remote sensing, composite approach for a high spatial and thematic resolution product Remote Sens. 15(3), 643 (24 pp.).

    Habitat maps at high thematic and spatial resolution and broad extents are fundamental tools for biodiversity conservation, the planning of ecological networks and the management of ecosystem services. To derive a habitat map for Switzerland, we used a composite methodology bringing together the best available spatial data and distribution models. The approach relies on the segmentation and classification of high spatial resolution (1 m) aerial imagery. Land cover data, as well as habitat and species distribution models built on Earth observation data from Sentinel 1 and 2, Landsat, Planetscope and LiDAR, inform the rule-based classification to habitats defined by the hierarchical Swiss Habitat Typology (TypoCH). A total of 84 habitats in 32 groups and 9 overarching classes are mapped in a spatially explicit manner across Switzerland. Validation and plausibility analysis with four independent datasets show that the mapping is broadly plausible, with good accuracy for most habitats, although with lower performance for fine-scale and linear habitats, habitats with restricted geographical distributions and those predominantly characterised by understorey species, especially forest habitats. The resulting map is a vector dataset available for interactive viewing and download from open EnviDat data sharing platform. The methodology is semi-automated to allow for updates over time.

    DOI: 10.3390/rs15030643

  • Rohner B. (2023) Dialog über die Baumarten im Schweizer Wald der Zukunft Wald Holz 104(9), 6-7.

    Eine diverse Gruppe von Waldfachleuten versammelte sich am 29. Juni an der ETH Zürich, als das SwissForestLab gemeinsam mit der Konferenz der Kantonsförster (KOK) und Wald-Schweiz zum Dialog über die "Baumarten im Schweizer Wald der Zukunft" einlud.

  • Rohner B. (2023) Dialogue sur les essences de la forêt suisse de demain Forêt 76(9), 4-5.

    De nombreux spécialistes du secteur forestier ont participé le 29 juin dernier, à l'ETH Zurich au Dialogue sur les essences de la forêt suisse de demain, organisé conjointement par SwissForestLab, la Conférence des inspecteurs et inspectrices cantonaux des forêts (CIC) et ForêtSuisse.

  • Scherrer D., Baltensweiler A., Bürgi M., Fischer C., Stadelmann G., Wohlgemuth T. (2023) Low naturalness of Swiss broadleaf forests increases their susceptibility to disturbances For. Ecol. Manag. 532, 120827 (8 pp.).

    The tree species composition of Swiss forests is influenced by both environmental conditions and centuries of forest management, resulting in varying degrees of naturalness. Here, we estimate the naturalness of Swiss forests by comparing the tree species composition (i.e., dominance and presence/absence of tree species) recorded by the national forest inventory with the idealised species composition of the potential natural forests. We aimed to (1) evaluate the naturalness of different forest types, (2) identify the main drivers of low naturalness and (3) investigate the influence of naturalness on the susceptibility to disturbances. Based on our analysis, 45 % of Swiss forests had a tree species composition classified as ‘not natural’ while 42 % were classified as ‘natural’ or ‘close to natural’. The vast majority (65 %) of the forests classified as ‘not natural’ were potential European beech (Fagus sylvatica L.) and other broadleaf forests which are currently dominated by conifers. In addition, at higher elevations, forests often showed a higher proportion of European larch (Larix decidua Mill.) than expected, based on the potential natural forest. Overall, forests classified as ‘natural’ had a significantly lower risk of being affected by stand-level disturbance events. Potential natural European beech and other broadleaf forests were significantly less affected by disturbances, namely insect outbreaks and wind throw, when comparing ‘natural’ to ‘not natural’ (i.e., afforested with conifers). The observed dieback and associated loss of ecosystem function of conifer afforestations (mainly Norway spruce; Picea abies (L.) H. Karst.) in the Swiss plateau is likely a combination of climatic stress and higher pathogen/parasite pressure. These Norway spruce afforestations already experience a significantly elevated temperature of about 2.5 °C compared to their climatic optimum (i.e., primary natural distribution within Switzerland), representing a large-scale, long-term transplantation experiment. We discuss the question of whether similar diebacks and problems of maladaptation are to be expected for many other species, including European beech, due to accelerated climate warming during the 21st century and the slow transformation of long-lived systems such as forests. Consequently, an adaptation of current management practices might be needed to allow a faster transition of forests minimizing the risk of large-scale diebacks.

    DOI: 10.1016/j.foreco.2023.120827

  • Scherrer D., Allgaier Leuch B., Fischer C., Frehner M., Wohlgemuth T. (2023) Maintaining the protective function of mountain forests under climate change by the concept of naturalness in tree species composition Front. For. Glob. Change 6, 1191639 (12 pp.).

    In Swiss mountain areas, the protective function of forests is the predominant ecosystem service having high cultural and economic significance. It is assumed that natural forests or close-to-natural forests, i.e., forests being in the equilibrium with environmental conditions are the most resilient and resistant in regard to disturbances and hence best protecting people and assets on the long run. Here, we estimated the naturalness of the tree species composition by comparing Swiss National Forest Inventory (NFI) data with current and future potential Natural forest Site Types (NST). Based on this analysis, we identified species that are under or over-represented in protective mountain forests and derived the subsequent potential for management interventions. The urgency of management interventions is expected be small if all predominant tree species of the idealized potential natural forests are present and only their relative portions in the stand need adjustment. In contrast, interventions are advisable, if predominant tree species of the current and future potential natural forests are absent. Based on NFI data, the tree species composition of 47% of the protective mountain forests were classified as "natural" or "close-to-natural," while the remaining 53% were classified as "not natural" or "partly natural." Norway spruce [Picea abies (L.) H. Karst.] and European larch (Larix decidua Mill.) were the two most over-represented species under current and even more so under predicted future climatic conditions. To date, silver fir (Abies alba Mill.) and European beech (Fagus sylvatica L.) were the two species most frequently absent in protective mountain forests, in which they should prevail. Apart from European beech, the most prominent increase in prevalence is predicted for oak (sessile oak and pubescent oak; Quercus petrea Liebl., Q. pubescens Willd.) and small-leaved lime (Tilia cordata Mill.). These species were currently missing from more than 75% of the stands, in which they are expected to be dominant under future conditions. Our analysis indicates the need to transform tree species compositions of protective mountain forests to optimize fitness under future climates. Some of these transformations will take place naturally, incited by disturbances, others - the majority of them - will need active management interventions.

    DOI: 10.3389/ffgc.2023.1191639

  • Soffianian A.R., Toosi N.B., Asgarian A., Regnauld H., Fakheran S., Waser L.T. (2023) Evaluating resampled and fused Sentinel-2 data and machine-learning algorithms for mangrove mapping in the northern coast of Qeshm island, Iran Nat. Conserv. 52, 1-22.

    Mangrove forests, as an essential component of the coastal zones in tropical and subtropical areas, provide a wide range of goods and ecosystem services that play a vital role in ecology. Mangroves are globally threatened, disappearing, and degraded. Consequently, knowledge on mangroves distribution and change is important for effective conservation and making protection policies. Developing remote sensing data and classification methods have proven to be suitable tools for mapping mangrove forests over a regional scale. Here, we scrutinized and compared the performance of pixel-based and object-based methods under Support Vector Machine (SVM) and Random Forest (RF) algorithms in mapping a mangrove ecosystem into four main classes (Mangrove tree, mudflat, water, and sand spit) using resampled and fused Sentinel-2 images. Additionally, landscape metrics were used to identify the differences between spatial patterns obtained from different classification methods. Results showed that pixel-based classifications were influenced heavily by the effect of salt and pepper noise, whereas in object-based classifications, boundaries of land use land cover (LULC) polygons were smoother and visually more appealing. Object-based classifications, with an excellent level of kappa, distinguished mudflat and sand spit from each other and from mangrove better than the pixel-based classifications which obtained a fair-to-good level of kappa. RF and SVM performed differently under comparable circumstances. The results of landscape metrics comparison presented that the classification methods can be affected on quantifying area and size metrics. Although the results supported the idea that fused Sentinel images may provide better results in mangrove LULC classification, further research needs to develop and evaluate various image fusion approaches to make use of all Sentinel's fine resolution images. Our results on the mapping of mangrove ecosystems can contribute to the improvement of management and conservation strategies for these ecosystems being impacted by human activities.

    DOI: 10.3897/natureconservation.52.89639

  • Speich S., Abegg M., Ahles P., Allgaier Leuch B. (2023) Neuste Ergebnisse des Landesforstinventars auf der aufgefrischten LFI-Website Infoblatt Arbeitsgr. Waldplan. manag. (1).

    Seit dem 30. Mai 2023 können neue Ergebnisse des Landesforstinventars (LFI) auf abgefragt werden. Es handelt sich um Zwischenergebnisse über die ersten fünf Jahre (2018–2022) der laufenden fünften Inventur. Im Hinblick auf die Ergebnispublikation im Internet wurde zudem der Webauftritt des LFI technisch, inhaltlich und optisch weiterentwickelt.

  • Temperli C., Nikolova P., Brang P. (2023) Zukunftsfähigkeit der Baumartenzusammensetzung des Schweizer Waldes Schweiz. Z. Forstwes. 174(2), 76-84.

    Der Klimawandel verändert die Wuchsbedingungen der Waldbäume, weshalb langfristig markante Verschiebungen in der Baumartenzusammensetzung des Schweizer Waldes zu erwarten sind. Die TreeApp ist ein Werkzeug für die Forstpraxis zur Ermittlung von Baumarten, die für das zukünftige Klima wahrscheinlich geeignet sind. In dieser Arbeit vergleichen wir Empfehlungen der TreeApp mit der im 4. Landesforstinventar (LFI4) beobachteten Artenzusammensetzung der Bäume (≥12 cm Brusthöhendurchmesser [BHD]) und der Verjüngung (<12 cm BHD), wobei wir auch die Präsenz von potenziellen Samenbäumen berücksichtigten. Wir stellen ein einfaches Bewertungsschema vor, mit dem wir die Stichprobenflächen des LFI in drei Stufen der Zukunftsfähigkeit (Grad der Anpassung an das Klima am Ende dieses Jahrhunderts) einteilen konnten. Schweizweit wurde der Wald auf 57% der Stichprobenflächen als zukunftsfähig, auf 23% als bedingt zukunftsfähig und auf 17% als nicht zukunftsfähig beurteilt. Dabei zeigte sich eine Häufung von nicht zukunftsfähigen Flächen in Fichtenwäldern in den Kantonen Graubünden und Wallis. Im Schutzwald der Voralpen, der Alpen und der Alpensüdseite wurde die Verjüngung auf 25% der Stichprobenflächen als nicht zukunftsfähig eingeschätzt, und auf 22% wurde keine Verjüngung beobachtet. Mit steigendem Fichtenanteil nahm der Anteil des Baumbestands ohne Zukunftsfähigkeit zu. Im Mittelland und im Jura wurde die Verjüngung auf einem grösseren Flächenanteil als zukunftsfähig eingeschätzt als der Baumbestand. Wenn Samenbäume berücksichtigt wurden, war der Stichprobenflächenanteil mit zukunftsfähiger Bestockung um bis zu 16 Prozentpunkte (Voralpen) höher, als wenn nur die Verjüngung betrachtet wurde. Diese Resultate unterstreichen die Notwendigkeit der Förderung einer zukunftsfähigen Verjüngung im Gebirgswald, bieten nützliche Grundlagen für die strategische Waldplanung und tragen so zur Anpassung des Waldes an den Klimawandel bei.

    DOI: 10.3188/szf.2023.0076

  • Thrippleton T., Temperli C., Krumm F., Mey R., Zell J., Stroheker S., … Schweier J. (2023) Anwendung eines Entscheidungssystems für die Anpassung an Klimawandel und Störungen im Gebirgswald Schweiz. Z. Forstwes. 174(2), 85-91.

    Klimawandel und Störungsereignisse stellen eine grosse Herausforderung für die Bewirtschaftung von Gebirgswäldern dar. Im Rahmen der naturnahen Waldbewirtschaftung könnte eine Erhöhung der Bewirtschaftungsintensität (INC-Strategie) die Störungsanfälligkeit verringern, jedoch ist wenig zu den Zielkonflikten mit der Biodiversitätsförderung und der Bereitstellung von Ökosystemleistungen auf Ebene des Forstbetriebes bekannt. In dieser Studie wurden die Auswirkungen verschiedener Bewirtschaftungsintensitäten auf die Störungsanfälligkeit gegenüber Windwurf und Borkenkäfer mit einem Entscheidungsunterstützungssystem (Decision Support System, DSS) untersucht. Dies erfolgte im Dischmatal bei Davos (1350 ha, Teil des Forstbetriebes Davos), für das Simulationen der Waldentwicklung über einen Zeitraum den 2010 bis 2100 unter historischem Klima und Klimawandelszenarien (RCP4.5, RCP8.5) durchgeführt wurden. Zudem wurden Indikatoren für die Biodiversität sowie für Ökosystemleistungen einbezogen. Die Ergebnisse der Fallstudie zeigten, dass die INC-Strategie die Störungsanfälligkeit gegenüber Windwurf und Borkenkäfer verringerte. Der Effekt auf die Borkenkäferanfälligkeit war jedoch relativ gering verglichen mit dem verstärkenden Effekt des Klimawandels unter dem RCP8.5-Szenario. Die INC-Strategie führte zu einer Erhöhung der Erholungsfunktion und der Holzproduktion und zu Zielkonflikten mit der Kohlenstoffspeicherung und der Schutzwirkung. Ausserdem zeigte sich ein positiver Zusammenhang zwischen der Verbesserung der Biodiversitätsindikatoren und dem Rückgang der Störungsanfälligkeit. Unsere Ergebnisse weisen auf eine starke Zunahme der Störungsanfälligkeit unter einem RCP8.5-Klimawandelszenario hin, welche die forstliche Planung vor grosse Herausforderungen stellt. Entscheidungsunterstützungssysteme können helfen, in solch komplexen Planungssituationen die Anpassung an den Klimawandel und die Störungsanfälligkeit mit der Biodiversitätsförderung und der Bereitstellung von Ökosystemleistungen in Einklang zu bringen.

    DOI: 10.3188/szf.2023.0085

  • Thrippleton T., Temperli C., Krumm F., Mey R., Zell J., Stroheker S., … Schweier J. (2023) Balancing disturbance risk and ecosystem service provisioning in Swiss mountain forests: an increasing challenge under climate change Reg. Environ. Chang. 23, 29 (16 pp.).

    Climate change severely affects mountain forests and their ecosystem services, e.g., by altering disturbance regimes. Increasing timber harvest (INC) via a close-to-nature forestry may offer a mitigation strategy to reduce disturbance predisposition. However, little is known about the efficiency of this strategy at the scale of forest enterprises and potential trade-offs with biodiversity and ecosystem services (BES). We applied a decision support system which accounts for disturbance predisposition and BES indicators to evaluate the effect of different harvest intensities and climate change scenarios on windthrow and bark beetle predisposition in a mountain forest enterprise in Switzerland. Simulations were carried out from 2010 to 2100 under historic climate and climate change scenarios (RCP4.5, RCP8.5). In terms of BES, biodiversity (structural and tree species diversity, deadwood amount) as well as timber production, recreation (visual attractiveness), carbon sequestration, and protection against gravitational hazards (rockfall, avalanche and landslides) were assessed. The INC strategy reduced disturbance predisposition to windthrow and bark beetles. However, the mitigation potential for bark beetle disturbance was relatively small (- 2.4%) compared to the opposite effect of climate change (+ 14% for RCP8.5). Besides, the INC strategy increased the share of broadleaved species and resulted in a synergy with recreation and timber production, and a trade-off with carbon sequestration and protection function. Our approach emphasized the disproportionally higher disturbance predisposition under the RCP8.5 climate change scenario, which may threaten currently unaffected mountain forests. Decision support systems accounting for climate change, disturbance predisposition, and BES can help coping with such complex planning situations.

    DOI: 10.1007/s10113-022-02015-w

  • Thrippleton T., Blattert C., Bont L.G., Mey R., Zell J., Thürig E., Schweier J. (2023) Forstplanung in Zeiten von Klimawandel und Multifunktionalität: ein neues Werkzeug für Schweizer Forstbetriebe Schweiz. Z. Forstwes. 174(1), 32-39.

    Eine nachhaltige Waldbewirtschaftung ist für die Bereitstellung von Waldleistungen von zentraler Bedeutung. Für die Forstbetriebe ist dies jedoch eine komplexe Planungsaufgabe, da eine Vielzahl an Waldleistungen und die Biodiversität berücksichtigt werden müssen. Zudem stellt der wachsende Einfluss des Klimawandels eine besondere Herausforderung dar. Im Projekt SessFor wurde der Prototyp eines Entscheidungs-Unterstützungssystems (Decision Support System, DSS) für die strategische und langfristige Planung von Forstbetrieben entwickelt. Das DSS simuliert die Waldentwicklung unter verschiedenen Bewirtschaftungs- und Klimaszenarien und bewertet die Bereitstellung von Waldleistungen mittels einer multikriteriellen Entscheidungsanalyse. Das DSS wurde in drei Fallstudien im Mittelland und den Voralpen über einen Zeitraum von 50 Jahren angewandt. Dabei wurden die Auswirkungen von unterschiedlichen Bewirtschaftungsstrategien auf die Waldleistungen Holzproduktion, Erholung (visuelle Attraktivität), Schutzfunktion und Kohlenstoffspeicherung sowie auf die Biodiversität (v.a. Strukturvielfalt und Baumartendiversität) bewertet. Der höchste Gesamtnutzen für die betrachteten Waldleistungen unter gegenwärtigem und zukünftigem Klima ergab sich in fast allen Fällen unter der aktuellen Bewirtschaftungspraxis. Eine Ausnahme bildete eine Fallstudie im Mittelland, bei der der höchste Gesamtnutzen unter einer reduzierten Holznutzung resultierte. Die untersuchten Klimaszenarien hatten eine relativ geringe Auswirkung auf den Gesamtnutzen. Einzelne Waldleistungsindikatoren zeigten jedoch negative Auswirkungen des Klimawandels für die Betriebe im Mittelland und positive Auswirkungen für den höher gelegenen Forstbetrieb in den Voralpen. Insgesamt zeigte die Studie auf, wie mithilfe des DSS die langfristige Entwicklung von Waldleistungen und Biodiversitätsindikatoren unter verschiedenen Bewirtschaftungsstrategien und Klimabedingungen untersucht werden kann. Die Stärken des DSS liegen insbesondere in der grossen Anzahl berücksichtigter Waldleistungen und in der breiten empirischen Datengrundlage. Die multikriterielle Entscheidungsanalyse unterstützt zudem eine wissenschaftlich fundierte und transparente Entscheidungsfindung für die langfristige Planung.

    DOI: 10.3188/szf.2023.0032

  • Trummer J., Hegetschweiler K.T. (2023) How do forest visitors perceive forest management forms? Public acceptance of coppice-with-standards in urban forests Trees For. People 14, 100439 (19 pp.).

    To mitigate climate change consequences, a shift to more renewable energy sources is necessary. The traditional forest management form coppice-with-standards features efficient harvesting cycles and could therefore provide a reliant biomass source. Particularly forests close to urban settlements are popular destinations for outdoor recreation. Therefore, for a well-functioning interaction between recreation and forest management, forest visitors' preferences need to be considered. Even though, coppice-with-standards have been studied scientifically from various points of view, including its cultural and ecological values, little focus was put on the perceived visual attractiveness of this management form. Therefore, this study aims to investigate how forest visitors perceive different forest management forms with a focus on coppice-with-standards in the case study area in Zurich, Switzerland by performing qualitative Go-Along interviews and a quantitative forest visitor survey. The statistical analysis revealed that forest visitors have divided opinions on this management form and prefer even-aged high forest as well as continuous forest management. Therefore, in case of an increasing use of coppice-with-standards management for biomass production, implementation in recreational forests needs to be weighed against less frequently visited areas. However, addressing the visitors with well-targeted communication strategies could result in increased understanding and acceptance and could therefore support the implementation process also in recreational forests.

    DOI: 10.1016/j.tfp.2023.100439

  • Waser L., Ginzler C. (2023) Landesweite Datensätze zum Wald mittels Fernerkundung - der Beginn einer neuen Ära In Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL (Ed.), WSL Berichte: Vol. 134. Neue Fernerkundungs­technologien für die Umweltforschung und Praxis. Birmensdorf: Eidg. Forschungsanstalt für Wald, Schnee und Landschaft, WSL. 23-30.

    Regelmässig erhobene, aktuelle Informationen zu verschiedenen Waldparametern auf landesweiter Ebene erfuhren in den letzten Jahren eine steigende praktische und wissenschaftliche Relevanz. Neueste Technologien aus der Fernerkundung und dem maschinellen Lernen haben eine neue Ära eingeläutet und ermöglichen eine genaue, reproduzierbare und flächige Erstellung der gewünschten Datensätze. Sie dienen als zuverlässige Basis zur Beschreibung des heutigen Zustandes sowie der zukünftigen Entwicklung des Waldes.
    Im folgenden Artikel werden die im Rahmen des Schweiz. Landesforstinventars (LFI) landesweit verfügbaren Datensätze Vegetationshöhenmodell, Waldmischungsgrad, Gebüschwald und Holzvorrat vorgestellt. Es wird aufgezeigt, was heutzutage mit Fernerkundungs- und Modellierungstechniken möglich ist und wo aber auch die Grenzen liegen. Neben einer kurzen Beschreibung der verschiedenen Datensätze, wird ein spezielles Augenmerk auf die Interpretation der Resultate und deren Anwendung gelegt. Anhand des Waldmischungsgrads LFI wird der Unterschied zwischen Modellgenauigkeit und Produktegenauigkeit erklärt. Ein wichtiger Punkt ist die korrekte und solide Validierung, mit unabhängigen Daten und auch Vor-Ort-Begehungen. Zudem wird aufgezeigt, dass ein Austausch zwischen der Praxis und Forschung wichtiger denn je ist.

    In recent years, up-to-date and regularly provided information on relevant forest parameters on countrywide level have experienced an increasing demand from both research and practice. Cutting edge remote sensing technologies and data sets have opened a new era by providing reliable, reproducible, and wall-to-wall forest parameter data sets. They serve as basis to assess the current state of forest ecosystems and their future developments and add to the existing NFI estimates by providing spatially explicit information.
    This article introduces the four countrywide available forest parameter data sets vegetation height model, dominant leaf type, shrub forest and growing stock which were produced in the framework of the Swiss National Forest Inventory (NFI).
    Besides a detailed description of these approaches, their limitations are critically discussed. In particular, the focus is laid on a correct interpretation and application of these data sets, the need of a proper validation, and the need of a regular exchange between research and practitioners.

    DOI: 10.55419/wsl:33059

  • Zehner M., Dubois C., Thiel C., Schellenberg K., Rüetschi M., Brenning A., … Schmullius C. (2023) Accounting for deciduous forest structure and viewing geometry effects improves Sentinel-1 time series image consistency IEEE Trans. Geosci. Remote Sens. 61, 4407813 (13 pp.).

    Microwave scattering from forests generates pixel geolocation shifts in Synthetic aperture radar (SAR) data that require an adequate representation within digital elevation models (DEM) for preprocessing. We analyze the impact of DEM properties on the radiometry and geolocation of radiometric terrain corrected (RTC) Copernicus Sentinel-1 imagery of forests to improve consistency in backscatter intensities for time series analyses. To account for the penetration depth of the C-Band sensor, we approximate the structure of stands in a temperate deciduous forest using height percentiles from Aerial Laser Scanning (ALS) point clouds in the Hainich National Park, Germany. Comparing the RTC results obtained using DEMs of SRTM, Copernicus, and ALS DEMs, the latter reduces topographically induced errors, resulting in visibly smaller effects from topography and spatially shifted information. Based on the P50 ALS vegetation elevation, results show homogeneous intensities within the same orbit and reduce variance from 2.4 dB2 to 1.2 dB2 in the difference of mid-range data from ascending and descending azimuth directions. Over forest, we observe lower intensities on sensor-facing and increased intensities on away-facing slopes and correlations with the illuminated pixel area (IPA) and local incidence angle. We reduce this bias with linear regressions of intensity on IPA. ALS DEMs in RTC and the proposed regression correction increase the consistency of images across orbits, measured by the inter-orbit range, throughout the selected year at our study site. We suggest the proposed method applies to other areas, requiring further testing under different forest types and topography.

    DOI: 10.1109/TGRS.2023.3310113

  • Zweifel R., Pappas C., Peters R.L., Babst F., Balanzategui D., Basler D., … Sterck F. (2023) Networking the forest infrastructure towards near real-time monitoring - a white paper Sci. Total Environ. 872, 162167 (11 pp.).

    Forests account for nearly 90 % of the world's terrestrial biomass in the form of carbon and they support 80 % of the global biodiversity. To understand the underlying forest dynamics, we need a long-term but also relatively high-frequency, networked monitoring system, as traditionally used in meteorology or hydrology. While there are numerous existing forest monitoring sites, particularly in temperate regions, the resulting data streams are rarely connected and do not provide information promptly, which hampers real-time assessments of forest responses to extreme climate events.
    The technology to build a better global forest monitoring network now exists. This white paper addresses the key structural components needed to achieve a novel meta-network.
    We propose to complement - rather than replace or unify - the existing heterogeneous infrastructure with standardized, quality-assured linking methods and interacting data processing centers to create an integrated forest monitoring network.
    These automated (research topic-dependent) linking methods in atmosphere, biosphere, and pedosphere play a key role in scaling site-specific results and processing them in a timely manner. To ensure broad participation from existing monitoring sites and to establish new sites, these linking methods must be as informative, reliable, affordable, and maintainable as possible, and should be supplemented by near real-time remote sensing data.
    The proposed novel meta-network will enable the detection of emergent patterns that would not be visible from isolated analyses of individual sites. In addition, the near real-time availability of data will facilitate predictions of current forest conditions (nowcasts), which are urgently needed for research and decision making in the face of rapid climate change. We call for international and interdisciplinary efforts in this direction.

    DOI: 10.1016/j.scitotenv.2023.162167