Publications of the NFI

• Allgaier Leuch B., Abegg M., Speich S., Cioldi F., Traub B., Meile R., Fischer C. (2024) LFI5.1-5: Ergebnisse nach Forstkreisen online. Infoblatt Arbeitsgr. Waldplan. manag. 2024(1), 1-3.

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• Allgaier Leuch B., Abegg M., Scherrer D., Frehner M., Losey S. (2024) Vegetationshöhenstufen und Standorttypen im LFI: bisherige und neue Angaben im Vergleich. Schweiz. Z. Forstwes. 175(2), 64-71. https://doi.org/10.3188/szf.2024.0064

  Im Rahmen des Projektes NaiS-LFI wurden in den Jahren 2014–2019 die Vegetationshöhenstufen und die Standorttypen auf den zugänglichen Waldprobeflächen des Schweizerischen Landesforstinventars (LFI) bestimmt. Dies geschah in der Systematik der Wegleitung «Nachhaltigkeit und Erfolgskontrolle im Schutzwald» (NaiS). So bietet sich die Möglichkeit zu analysieren, wie hoch die Übereinstimmung des Outputs der bislang im LFI verwendeten Definitionen und Modelle mit den auf den Probeflächen bestimmten NaiS-Vegetationshöhenstufen und -Vegetationseinheiten (= Gruppen von Standorttypen) ist. Bei den Vegetationshöhenstufen betrug die Übereinstimmung 76%. Bei den Vegetationseinheiten war sie mit 36% wesentlich geringer. Die NaiS-Vegetationshöhenstufen und -Vegetationseinheiten sind seit Juni 2023 als Klassifizierungsmerkmale in der LFI-Ergebnisabfrage im Internet verfügbar. Zudem werden in den Ableitungen, die sich auf Vegetationshöhenstufen oder Vegetationseinheiten stützen (z.B. zur Bestimmung der Naturnähe des Nadelholzanteils), neu die NaiS-Angaben verwendet.

  DOI: 10.3188/szf.2024.0064

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• Augustinus B.A., Abegg M., Queloz V., Brockerhoff E.G. (2024) Higher tree species richness and diversity in urban areas than in forests: implications for host availability for invasive tree pests and pathogens. Landsc. Urban Plan. 250, 105144 (10 pp.). https://doi.org/10.1016/j.landurbplan.2024.105144

  Urban and forest trees provide valuable ecosystem services. However, they are increasingly threatened by invasive forest pests and pathogens. Trees in urban areas are often the first potential hosts non-native tree-feeding insects and tree pathogens (“pests”) encounter after introduction in a novel region. If the trees encountered are suitable hosts, these pests can establish and become invasive – eventually also in surrounding forests. Here, we compared tree species and genus composition between urban areas and surrounding forests and examined the implications for host availability for forest pests and potential effects on invasibility. We compiled and standardised 26 urban tree inventories, containing ∼ 500.000 individual trees. We used multivariate analyses to compare urban tree composition with forest tree composition from forests surrounding each municipality (10 km radius), derived from the Swiss National Forest Inventory. With > 1300 different tree species, species richness of urban trees was 17 times higher than species richness in surrounding forests. Linear models and multivariate analyses revealed that host availability for forest quarantine pests is significantly higher in urban areas than in forests, with large differences in host suitability for different quarantine pests between urban and forest tree assemblages. This indicates that differences in species composition in urban and forest trees can result in increased host availability, possibly facilitating the establishment of quarantine forest pests.

  DOI: 10.1016/j.landurbplan.2024.105144

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• Avitabile V., Pilli R., Migliavacca M., Duveiller G., Camia A., Blujdea V., … Thürig E. (2024) Harmonised statistics and maps of forest biomass and increment in Europe. Sci. Data. 11, 274 (17 pp.). https://doi.org/10.1038/s41597-023-02868-8

  Forest biomass is an essential resource in relation to the green transition and its assessment is key for the sustainable management of forest resources. Here, we present a forest biomass dataset for Europe based on the best available inventory and satellite data, with a higher level of harmonisation and spatial resolution than other existing data. This database provides statistics and maps of the forest area, biomass stock and their share available for wood supply in the year 2020, and statistics on gross and net volume increment in 2010–2020, for 38 European countries. The statistics of most countries are available at a sub-national scale and are derived from National Forest Inventory data, harmonised using common reference definitions and estimation methodology, and updated to a common year using a modelling approach. For those counties without harmonised statistics, data were derived from the State of Europe's Forest 2020 Report at the national scale. The maps are coherent with the statistics and depict the spatial distribution of the forest variables at 100 m resolution.

  DOI: 10.1038/s41597-023-02868-8

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• Bont L.G., Temperli C., Schweier J. (2024) Auswirkungen der Personalkosten auf die Holzerntekosten. Infoblatt Arbeitsgr. Waldplan. manag. 2024(1), 1-10.

  Je nach Erntemethode beeinflusst eine Veränderung der Personalkosten um 1 % die Erntekosten um 0,33-0,77 %. Erwartungsgemäss ist der Einfluss größer bei Systemen mit einem hohen Anteil an motormanueller Holzerei und bei seilgestützten Verfahren. Eine Änderung der Personalkosten um +30 % wirkt sich um 5 bis 15 Prozentpunkte auf den Anteil der Waldflächen aus, für die eine Holzernte wirtschaftlich machbar ist. Eine konsequente Anwendung des Best-Verfahrens hat ähnliche wirtschaftliche Auswirkungen, als wenn Personalkosten um 15 bis 30 % gesenkt würden. Das deutet darauf hin, dass die Effizienz der Holzernte bei gleichen Löhnen durch weitere Mechanisierung gesteigert werden könnte oder bei konsequenter Anwendung des Bestverfahrens, bei gleicher Effizienz, die Löhne erhöht werden könnten.

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• Bont L.G., Schweier J., Temperli C. (2024) Effect of labour costs on wood harvesting costs and timber provision. Eur. J. For. Res. 143, 393-418. https://doi.org/10.1007/s10342-023-01621-5

  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

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• Bouchard E., Searle E.B., Drapeau P., Liang J., Gamarra J.G.P., Abegg M., … Paquette A. (2024) Global patterns and environmental drivers of forest functional composition. Glob. Ecol. Biogeogr. 33(2), 303-324. https://doi.org/10.1111/geb.13790

  Aim: To determine the relationships between the functional trait composition of forest communities and environmental gradients across scales and biomes and the role of species relative abundances in these relationships.
  Location: Global.
  Time period: Recent.
  Major taxa studied: Trees.
  Methods: We integrated species abundance records from worldwide forest inventories and associated functional traits (wood density, specific leaf area and seed mass) to obtain a data set of 99,953 to 149,285 plots (depending on the trait) spanning all forested continents. We computed community-weighted and unweighted means of trait values for each plot and related them to three broad environmental gradients and their interactions (energy availability, precipitation and soil properties) at two scales (global and biomes).
  Results: Our models explained up to 60% of the variance in trait distribution. At global scale, the energy gradient had the strongest influence on traits. However, within-biome models revealed different relationships among biomes. Notably, the functional composition of tropical forests was more influenced by precipitation and soil properties than energy availability, whereas temperate forests showed the opposite pattern. Depending on the trait studied, response to gradients was more variable and proportionally weaker in boreal forests. Community unweighted means were better predicted than weighted means for almost all models.
  Main conclusions: Worldwide, trees require a large amount of energy (following latitude) to produce dense wood and seeds, while leaves with large surface to weight ratios are concentrated in temperate forests. However, patterns of functional composition within-biome differ from global patterns due to biome specificities such as the presence of conifers or unique combinations of climatic and soil properties. We recommend assessing the sensitivity of tree functional traits to environmental changes in their geographic context. Furthermore, at a given site, the distribution of tree functional traits appears to be driven more by species presence than species abundance.

  DOI: 10.1111/geb.13790

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• Ferretti M., Fischer C., Gessler A., Graham C., Meusburger K., Abegg M., … Shackleton R.T. (2024) Advancing forest inventorying and monitoring. Ann. For. Sci. 81(1), 6 (25 pp.). https://doi.org/10.1186/s13595-023-01220-9

  Forests are under pressure and going through rapid changes. However, current inventorying and monitoring (IM) programs are often either disjointed, too narrow in their scope and/or do not operate at fine enough temporal resolutions, which may hinder scientific understanding, the timely supply of information, fast decision making, and may result in the sub-optimal use of resources. For these reasons, there is an urgent need for Advanced Forest Inventorying and Monitoring (AIM) programs to (i) achieve expanded relevance (by augmenting data/information across ecosystem properties and trophic levels), (ii) have increased temporal resolution (by tailored data collection frequency), and (iii) make use of technological advances (by incorporating novel tools and technologies). The Advanced Inventorying and Monitoring for Swiss Forests (SwissAIM) initiative was launched in 2020 to address these needs. SwissAIM builds upon the foundation offered by the existing programs (e.g., national forest inventory, long-term forest ecosystem research, biodiversity monitoring). It aims to offer a collaborative and adaptive framework to enable integrated data collection, evaluation, interpretation, analysis, and modeling. Ideally, it will result in a more responsive system with respect to current and predicted biotic/abiotic stressors that will challenge Swiss forests. Developing such a system implies identifying the information needs of different stakeholders (e.g., science, policy, practice), related technical requirements, and governance frameworks. Here, we present (i) the main features of the SwissAIM initiative (vision, scientific questions and variables, governance and engagement), (ii) the main outcomes of the participatory design process (measurements, sampling, and plot design), (iii) the potential transferability of AIM initiatives outside Switzerland (timing, relevance, practicability), and (iv) the key messages that emerged (i.e., need for advancement, integration and transdisciplinarity, statistical underpinning). Since similar needs related to forest inventorying and monitoring are emerging throughout Europe and elsewhere, the objective of this opinion paper is to share our experience and promote a dialog with those interested in developing AIM initiatives in other countries and regions.

  DOI: 10.1186/s13595-023-01220-9

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• Flury R., Portier J., Rohner B., Baltensweiler A., Di Bella Meusburger K., Scherrer D., … Stadelmann G. (2024) Soil and climate‐dependent ingrowth inference: broadleaves on their slow way to conquer Swiss forests. Ecography. e07174 (14 pp.). https://doi.org/10.1111/ecog.07174

  Forests provide essential ecosystem services that range from the production of timber to the mitigation of natural hazards. Rapid environmental changes, such as climate warming or the intensification of disturbance regimes, threaten forests and endanger forest ecosystem services. In light of these challenges, it is essential to understand forests' demographic processes of regeneration, growth, and mortality and their relationship with environmental conditions. Specifically, understanding the regeneration process in present-day forests is crucial since it lays the foundation for the structure of future forests and their tree species composition. We used Swiss National Forest Inventory (NFI) data covering vast bio-geographic gradients over four decades to achieve this understanding. Trees that reached a diameter at breast height of 12 cm between two consecutive NFI campaigns were used to determine regeneration and were referred to as ingrowth. Employing three independent statistical models, we investigated the number, species, and diameter of these ingrowth trees. The models were subsequently implemented into a forest simulator to project the development of Swiss forests until the mid-21st century. The simulation results showed an ingrowth decrease and a shift in its species composition, marked by a significant reduction in Norway spruce Picea abies and concurrent increases in broadleaves. Nevertheless, the pace of this change towards climatically better adapted species composition is relatively slow and is likely to slow down even further as ingrowth declines in the future, in contrast to the fast-changing climatic conditions. Hence, support through adaptive planting strategies should be tested in case ingrowth does not ensure the resilience of forests in the future. We conclude that since the regeneration of forests is becoming increasingly challenging, the current level at which ecosystem services are provided might not be ensured in the coming decades.

  DOI: 10.1111/ecog.07174

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• Gschwantner T., Riedel T., Henning L., Adame P., Adolt R., Aguirre A., … Westerlund B. (2024) Improved large-area forest increment information in Europe through harmonisation of National Forest Inventories. For. Ecol. Manag. 562, 121913 (14 pp.). https://doi.org/10.1016/j.foreco.2024.121913

  Consistent knowledge about the increment in European forests gained amplified importance in European policies and decision processes related to forest-based bioeconomy, carbon sequestration, sustainable forest management and environmental changes. Until now, large-area increment information from European countries was lacking international comparability. In this study we present a harmonisation framework in accordance with the principles and the approach established for the harmonisation of National Forest Inventories (NFIs) in Europe. 11 European NFIs, representing a broad range of increment measurement and estimation methods, developed unified reference definitions and methods that were subsequently implemented to provide harmonised increment estimates by NUTS regions (Nomenclature of territorial units for statistics of the European Union), main forest types and tree species groups, and to rate the impact of harmonisation measures. The main emphasis was on gross annual increment (GAI), however, also annual natural losses (ANL) and net annual increment (NAI) were estimated. The data from the latest available NFI cycles were processed. The participating countries represent a forest area of about 130 million ha, and 82% of the European Unions’ (EU) forest area, respectively. The increments were estimated in terms of volume (m³ year⁻¹, m³ ha⁻¹ year⁻¹) and above-ground biomass (t year⁻¹, t ha⁻¹ year⁻¹). The harmonised GAI volume estimates deviate in a range of +12.3% to −26.5% from the estimates according to the national definitions and estimation methods. Within the study area, the harmonised estimates show a considerable range over the NUTS regions for GAI, from 0.6 to 12.3 m³ ha⁻¹ year⁻¹, and 0.8–6.4 t ha⁻¹ year⁻¹, of volume and above-ground biomass, respectively. The largest increment estimates are found in Central Europe and gradually decrease towards the North, South, West and East. In most countries coniferous forests show larger increment estimates per hectare than broadleaved forests while mixed forests are at an intermediate level. However, in some instances, the differences were small or mixed forests revealed the largest increment estimates. The most important tree species groups in the study area are Pinus spp. and Picea spp., contributing 29% and 26% of the estimated total GAI volume, respectively. The shares of the prevalent broadleaved species are smaller with contributions of 9%, 7% and 6% by Quercus spp., Fagus sylvatica and Betula spp. The results underline the importance of harmonisation in international forest statistics. Looking ahead, harmonised large-area increment estimation is pivotal for accurate monitoring and evidence-based policy decisions in the changing context of future forest ecosystems dynamics, management strategies and wood availability.

  DOI: 10.1016/j.foreco.2024.121913

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• Hordijk I., Bialic-Murphy L., Lauber T., Routh D., Poorter L., Rivers M.C., … Crowther T.W. (2024) Dominance and rarity in tree communities across the globe: patterns, predictors and threats. Glob. Ecol. Biogeogr. https://doi.org/10.1111/geb.13889

  Aim: Ecological and anthropogenic factors shift the abundances of dominant and rare tree species within local forest communities, thus affecting species composition and ecosystem functioning. To inform forest and conservation management it is important to understand the drivers of dominance and rarity in local tree communities. We answer the following research questions: (1) What are the patterns of dominance and rarity in tree communities? (2) Which ecological and anthropogenic factors predict these patterns? And (3) what is the extinction risk of locally dominant and rare tree species?.
  Location: Global.
  Time period: 1990–2017.
  Major taxa studied: Trees.
  Methods: We used 1.2 million forest plots and quantified local tree dominance as the relative plot basal area of the single most dominant species and local rarity as the percentage of species that contribute together to the least 10% of plot basal area. We mapped global community dominance and rarity using machine learning models and evaluated the ecological and anthropogenic predictors with linear models. Extinction risk, for example threatened status, of geographically widespread dominant and rare species was evaluated.
  Results: Community dominance and rarity show contrasting latitudinal trends, with boreal forests having high levels of dominance and tropical forests having high levels of rarity. Increasing annual precipitation reduces community dominance, probably because precipitation is related to an increase in tree density and richness. Additionally, stand age is positively related to community dominance, due to stem diameter increase of the most dominant species. Surprisingly, we find that locally dominant and rare species, which are geographically widespread in our data, have an equally high rate of elevated extinction due to declining populations through large-scale land degradation.
  Main conclusions: By linking patterns and predictors of community dominance and rarity to extinction risk, our results suggest that also widespread species should be considered in large-scale management and conservation practices.

  DOI: 10.1111/geb.13889

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• Kaennel Dobbertin M., Allgaier Leuch B., Reich T. (2024) Die Fichte in der Schweiz. In Eidg. Forschungsanstalt WSL (Ed.), Poesie des Vergehens. Vom vielfältigen Leben in einer toten Fichte. Bern: Haupt Verlag. 182-183.

  Von den Alpen bis zum Jura prägt die Fichte unsere Bergwälder und erfüllt dort wichtige Schutzfunktionen. Da die Art fast alle waldfähigen Standorte besiedeln kann und rasch wächst, wurde sie lange Zeit über ihr natürliches Verbreitungsgebiet hinaus angebaut. So ist die Fichte heute auch im Mittelland die häufigste Baumart.

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• Kupferschmid A.D. (2024) Methodischer Vergleich und Zeitreihenanalysen zu Verbiss im Verjüngungskontext des LFI: Schlussbericht. Eidg. Forschungsanstalt für Wald, Schnee und Landschaft WSL. 16 p. https://doi.org/10.55419/wsl:36188

  Die Baumverjüngung ist ein komplexer Prozess der stark von abiotischen und biotischen Faktoren beeinflusst wird wie z.B. dem Verbiss durch wildlebende Huftiere. Mittels der Schweizerischen Landesforstinventare (LFI) werden Aussagen zur zeitlichen Entwicklung des Verbisses in den letzten Jahrzehnten untersucht.
  Da die Methode der Verjüngungserhebung zwischen LFI1 und LFI4 mehrmals gewechselt wurde, wurde im 1 Modul die Änderungen detailliert dokumentiert (1A) und mittels Simulationen deren Auswirkungen auf die Dichte der Verjüngung und des Verbisses aufgezeigt (1B). Es wird empfohlen, nur LFI2 (zusätzliche Reduktion auf nur 1 Subplot) mit LFI4 (bzw. LFI5) zu vergleichen und auch dies nur in einseitigen Test (Zunahme des Verbisses) bzw. Abnahmen im Verbiss müssen grösser als ca. 25% sein, damit sichergestellt ist, dass es kein Artefakt der Methodenänderung der Verbissansprache ist.
  Das Modul 2 befasste sich mit der Ebene der Stratifizierung zur Auswertung des Verbisses im Schweizer Wald. Damit relevante Verbiss-Zu- oder Abnahmen festgestellt werden können, sind minimal 50 bestockte Probeflächen (N = 50) bzw. 100 Bäumchen je Aussageeinheit nötig. Die kantonal ausgeschiedenen Wildräume sind dafür zu klein. Es wird, in Anlehnung an die klassischen LFI-Gliederungen, die Verwendung der Schutzwaldregionen unter Aufteilung der Region «Jura + Mittelland» gemäss der biogeographischen Region «Jura» und den Wirtschaftsregionen «Mittelland West», «Mittelland Mitte» und «Mittelland Ost» vorgeschlagen.
  Im 3. Modul wurden für alle Kantone verschiedene regionale Dichteschätzungen von wildlebenden Huftieren zusammengetragen. Insbesondere wurden Daten zu Abschuss und Fallwild für die Zeitspanne von 1983 bis 2017 aufbereitet und damit unterschiedliche Indexe (z.B. Ungulate Density Index und Faktoren zum Geschlechterverhältnis) berechnet.
  Im Modul 4 wurden statistische Modelle berechnet zur zeitlichen Entwicklung des Verbisses unter Einbezug der Wildtierdichten. Exemplarisch sind die Resultate für die Weisstanne und 5 häufige Baumarten für die Regionen Jura, Mittelland Ost, Mittelland West + Mittelland Mitte, Nordalpen Ost und Nordalpen West vorgestellt. Je höher die Dichte der wildlebenden Huftiere mittels der Abschüsse und des Fallwildes eingeschätzt wurde (UDI), desto mehr Verbiss wurde festgestellt. Die Signifikanz der Faktoren zum Geschlechterverhältnis deuten auf die Wichtigkeit der Managementziele bezüglich Wildtierdichten (Zunahme, Stabilisation oder Abnahme der Wilddichten) hin. Der Verbiss hat im Laufe der Zeit an den (häufigen) Laubbaumarten abgenommen, nicht aber an der Weisstanne. [...]

  DOI: 10.55419/wsl:36188

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• Nikolova P.S., Allgaier Leuch B., Frehner M., Wohlgemuth T., Brang P. (2024) Indikatoren der Waldverjüngung und ihre Anwendungsbereiche. Schweiz. Z. Forstwes. 175(3), 108-115. https://doi.org/10.3188/szf.2024.0108

  Bei der Waldbewirtschaftung geht es darum, gewünschte Leistungen mit möglichst wirksamen und kostengünstigen Eingriffen bereitzustellen. Von besonderer Bedeutung sind dabei Eingriffe, die über den Erfolg der Waldverjüngung bestimmen. Entsprechend wird die Verjüngung bei der Planung und Kontrolle von waldbaulichen Eingriffen, in der Waldplanung wie auch in der Jagdplanung regelmässig beurteilt. Allerdings sind Erfassung und Beurteilung der Verjüngung mit einigen Herausforderungen verbunden. In diesem Beitrag stellen wir fünf Indikatoren für die Beurteilung der Verjüngungssituation vor: die Verjüngungsdichte, der Verjüngungsdeckungsgrad, die Distanz zwischen Verjüngungsansätzen, der Flächenanteil ohne Verjüngung sowie die Verjüngungsfläche. Wir diskutieren ihre Eigenschaften und zeigen ihren Einsatzbereich in der Praxis auf. Die verschiedenen Indikatoren unterscheiden sich insbesondere darin, ob sie mithilfe von Messungen oder von Schätzungen erfasst werden, was Folgen für den Erhebungsaufwand und die Reproduzierbarkeit hat. Bei der Planung und Kontrolle von waldbaulichen Eingriffen ist in vielen Fällen eine gutachtliche Beurteilung der Verjüngung durch okulare Schätzung ausreichend. Wo die Verjüngungssituation jedoch unklar ist oder kontrovers beurteilt wird, werden gemessene Daten benötigt. Für den auf Messwerten beruhenden Indikator Verjüngungsdichte sind die Zielvorstellungen (Sollwerte, Bandbreiten) erst noch zu konsolidieren.

  DOI: 10.3188/szf.2024.0108

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• Portier J., Shackleton R.T., Klesse S., Ferretti M., Flury R., Hobi M.L., … Thürig E. (2024) No evidence that coring affects tree growth or mortality in three common European temperate forest tree species. Eur. J. For. Res. 143, 129-139. https://doi.org/10.1007/s10342-023-01612-6

  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

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• Rota F., Scherrer D., Bergamini A., Price B., Walthert L., Baltensweiler A. (2024) Unravelling the impact of soil data quality on species distribution models of temperate forest woody plants. Sci. Total Environ. 944, 173719 (11 pp.). https://doi.org/10.1016/j.scitotenv.2024.173719

  Soil properties influence plant physiology and growth, playing a fundamental role in shaping species niches in temperate forest ecosystems. Here, we investigated the impact of soil data quality on the performance of species distribution models (SDMs) of 41 woody plant species in Swiss forests. We compared models based on measured soil properties with those based on digitally mapped soil properties on regional (Swiss Forest Soil Maps) and global scales (SoilGrids). We first calibrated topo-climatic SDMs with measured soil data and plant species presences and absences from mature temperate forest stand plots. We developed further models using the same soil predictors, but with values extracted from digital soil maps at the nearest neighbouring plots of the Swiss National Forestry Inventory. The predictive power of SDMs without soil information compared to those with soil information, as well as measured soil information vs digitally mapped, was evaluated with metrics of model performance and variable contribution. On average, models with measured and digitally mapped soil properties performed significantly better than those without soil information. SDMs based on measured and Swiss Forest Soil Maps showed higher performance, especially for species with an ‘extreme’ niche position (e.g., preference for high or low pH), compared to those using SoilGrids. Nevertheless, if no regional soil maps are available, SoilGrids should be tested for their potential to improve SDMs. Moreover, among the tested soil predictors, pH, and clay content of the topsoil layers most improved the predictive power of SDMs for forest woody plants. In conclusion, we demonstrate the value of regional soil maps for predicting the distribution of woody species across strong environmental gradients in temperate forests. The improved accuracy of SDMs and insights into drivers of distribution may support forest managers in strategies supporting e.g. biodiversity conservation, or climate adaptation planning.

  DOI: 10.1016/j.scitotenv.2024.173719

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• Wunderlich A.C., Salak B., Hegetschweiler K.T., Bauer N., Hunziker M. (2024) How the COVID-19 pandemic changed forest visits in Switzerland: is there a back to normal? Landsc. Urban Plan. 249, 105126 (16 pp.). https://doi.org/10.1016/j.landurbplan.2024.105126

  Lockdown measures implemented during the COVID-19 pandemic led to a rise in people’s visits to forests and urban green spaces. However, as vaccination efforts progressed and infection rates declined, it remained uncertain whether forest visitation levels would return to pre-pandemic norms or even decreased. To explore the post-crisis status of forest visits, we conducted a comprehensive analysis using data from a representative online panel survey conducted in Switzerland. Specifically, we compared data collected one week prior to the lockdown (in March 2020), on visit frequency, duration, activities and locations visited, with data collected two weeks after the lockdown was enforced (2020), and also with data from the summer of 2021. We aimed to determine if forest visitation had returned to normal by the time of the third survey. Our findings indicate that during times of crisis, visitation patterns and recreational preferences in urban green spaces, such as forests, undergo changes, with some of these changes exhibiting greater persistence than others. Meanwhile the activities during a forest visit as well as motivations of forest visits seem to return to their initial levels after the crisis, for example, the changes in the frequency or lengths of the visits appear to be more persistent. Recognizing and understanding these changes are crucial for urban planners and forest management authorities to adapt policies and effectively address the evolving needs of visitors.

  DOI: 10.1016/j.landurbplan.2024.105126

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• Zou Y., Zohner C.M., Averill C., Ma H., Merder J., Berdugo M., … Zo-Bi I.C. (2024) Positive feedbacks and alternative stable states in forest leaf types. Nat. Commun. 15, 4658 (15 pp.). https://doi.org/10.1038/s41467-024-48676-5

  The emergence of alternative stable states in forest systems has significant implications for the functioning and structure of the terrestrial biosphere, yet empirical evidence remains scarce. Here, we combine global forest biodiversity observations and simulations to test for alternative stable states in the presence of evergreen and deciduous forest types. We reveal a bimodal distribution of forest leaf types across temperate regions of the Northern Hemisphere that cannot be explained by the environment alone, suggesting signatures of alternative forest states. Moreover, we empirically demonstrate the existence of positive feedbacks in tree growth, recruitment and mortality, with trees having 4–43% higher growth rates, 14–17% higher survival rates and 4–7 times higher recruitment rates when they are surrounded by trees of their own leaf type. Simulations show that the observed positive feedbacks are necessary and sufficient to generate alternative forest states, which also lead to dependency on history (hysteresis) during ecosystem transition from evergreen to deciduous forests and vice versa. We identify hotspots of bistable forest types in evergreen-deciduous ecotones, which are likely driven by soil-related positive feedbacks. These findings are integral to predicting the distribution of forest biomes, and aid to our understanding of biodiversity, carbon turnover, and terrestrial climate feedbacks.

  DOI: 10.1038/s41467-024-48676-5

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