Dr. Frank Krumm

Purpose of review: We are amid a historical momentum encouraging forest restoration, yet the translation of ambitious targets into reality is hindered by poor documentation and understanding of the success and failure of past restoration efforts. This review aims to evaluate the ecological, social, political and economic characteristics of forest restoration across Europe, their development over time and key lessons learned to guide future restoration initiatives. The analysis is based on the synthesis of expert assessments from 18 European countries.
Recent findings: Early restoration initiatives in central and southern Europe were largely reactive to natural disasters or timber shortages, and while effective in erosion control and timber production, their ecological benefits were often limited due to monoculture plantations and short-rotation systems. Geopolitical crises intensified timber production, with nationalized and centrally managed forests in several countries, but often at the cost of biodiversity. Since the 1990s, a shift toward multifunctionality has emerged driven by the convergence of environmental, social, political and economic events.
Summary: Forest restoration in Europe has transitioned from disaster reduction and production-driven efforts to a more multifunctional approach that promotes biodiversity. Changes have been driven by a combination of environmental (e.g., catastrophic consequences following natural disasters), political (e.g., wars, forest nationalization and management centralization), legal (e.g., strict and ambitious national and international policies), social (e.g., rural abandonment and changes in societal values) and economic (e.g., new funding mechanisms or market fluctuations) events. Despite the development, conflicting goals, insufficient funding, climate change and short-term thinking persist as key barriers.

Tree-related Microhabitats (TreMs) are of prime concern for biodiversity since they host thousands of taxa. TreMs are discrete habitat patches borne by trees and cover a wide range of lifespans, from days to decades to centuries. The taxa associated with such discrete and sometimes highly ephemeral habitat patches are likely to be sensitive to spatial distribution because they need to search for new habitats after the occupied one disappears. Although many studies have recently been dedicated to TreMs, only very few have investigated their spatial distribution. Focusing on European beech-dominated forests, we used a European TreM database with 12,362 trees and 296 plots (ranging from local (0.1–1 ha) to landscape scale (10,000 ha)) to assess TreM spatial distribution patterns in long unmanaged forests. Then, with a TreM sub-database with 6828 trees and 21 plots, we assessed whether and if so, how harvesting changes spatial patterns at the plot scale. In long unmanaged forests, most TreMs showed a regular pattern at the plot scale and an aggregated pattern at larger scales. Tree diameter was the most influential factor for spatial patterns in TreMs. Spatial patterns at the plot scale in harvested forests differed slightly from those observed in unmanaged forests. To favor TreM-dwelling taxa in harvested stands, our results suggest retaining habitat trees in a regular spatial pattern to mimic the natural pattern. However, some TreMs should be conserved in an aggregate pattern; we specify the spatial scale at which this should be done.

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.

Qua o là sta amo ün tal eroe plain fideltà sün seis post, cun büst sfrattamà, e stenda il bratsch our da spelm e grava, sco üna sgür pronta pel cumbat, o ch'el sta ingramüschà sco ün vegliet cha la burasca da la vita ha fat sgobar sün sias crotschas.

Understanding the dynamics of treeline ecotones under global change requires long-term ecological and environmental data. The Stillberg ecological treeline research site in the Swiss Alps was established in 1975 by planting 92,000 seedlings of Larix decidua, Pinus cembra and Pinus mugo ssp. uncinata, and has been continuously monitored since then. Here, we present curated long-term data acquired over almost 50 years at the Stillberg site, and we synthesise the major research findings. The long-term datasets comprise 6.5 million ecological and environmental records from the 40-year afforestation experiment, as well as from a 9-year free-air CO₂ enrichment experiment crossed with a 6-year soil warming experiment, a 12-year nutrient addition experiment and an 8-year multifactorial tree seedling recruitment experiment. Our datasets further include 38 million records of 25 meteorological parameters measured at an hourly resolution from 1975 to 1996, and at a 10 min resolution since 1997. We provide all datasets and the corresponding metadata as open research data. Almost five decades of research in this treeline ecotone showed high mortality after tree establishment that was closely related to microclimatic variability. The two Pinus species survived at a much lower rate than L. decidua, due to indirect pathogen interactions. Furthermore, CO₂ enrichment only increased growth of L. decidua, while warming increased growth of P. mugo ssp. uncinata and two Vaccinium shrub species. Enhanced nutrient availability stimulated growth in tree and understorey shrub species. In addition, soil warming and CO₂ enrichment stimulated microbial activity and decreased soil carbon stocks. These findings improve our understanding of ecological processes in the treeline ecotone under global change and confirm the importance of tree growth and establishment limitations. The enhanced availability and quality of these long-term data are expected to foster whole-system approaches and transdisciplinary research syntheses, supporting the development of effective global change adaptation strategies.

Europe's semi-natural grasslands support notably high levels of temperate biodiversity across multiple taxonomic groups. However, these ecosystems face unique conservation challenges. Contemporary agricultural practices have replaced historical traditional low-intensity agriculture in many regions, resulting in a spectrum of management intensities within these ecosystems, ranging from highly intensive methods to complete abandonment. Paradoxically, both extremes along this spectrum of management intensity can be detrimental to biodiversity of semi-natural grasslands. Moreover, while anthropogenic climate change is an overarching threat to these ecosystems, rapid changes in land use and its intensity often present more immediate pressures. Often occurring at a faster rate than climate change itself, these land-use changes have the potential to rapidly impact the biodiversity of these grasslands. Here, we divide the ecological processes, threats, and developments to semi-natural grasslands into three sections. First, we examine the different impacts of agricultural intensification and abandonment on these ecosystems, considering their different consequences for biodiversity. Second, we review seminal works on various evidence-based management practices and offer a concise summary that provides support for various conservation and management strategies. However, the socio-economic factors that drive both abandonment and intensification in semi-natural grasslands can also be used to develop solutions through strategic governmental and non-governmental interventions. Accordingly, we conclude with a way forward by providing several key policy recommendations. By synthesizing existing knowledge and identifying research gaps, this essay aims to provide valuable insights for advancing the sustainable management of semi-natural grasslands.

Natürliche Störungen gehören zu den grössten Herausforderungen für die Erhaltung der Schutzfunktionen unserer Wälder. Die Förderung einer möglichst hohen Resilienz gegenüber solchen Störungen wurde in den letzten Jahrzehnten zu einem immer wichtigeren Bestandteil der Schutzwaldbewirtschaftung. In diesem Artikel geben wir einen Überblick zum Einfluss von natürlichen Störungen auf die Schutzfunktion gegenüber Naturgefahren, wobei wir Resultate aus kürzlich an der WSL und der ETH abgeschlossen Dissertationen aufgreifen. Darauf aufbauend und vor dem Hintergrund der erwarteten weiteren Zunahme von Störungen und Extremereignissen diskutieren wir, wie die zukunftige Resilienz von Schutzwälder gefördert werden kann.

Natural disturbances are among the greatest challenges for the management of forests with a protective role against natural hazards. Promoting the highest possible resilience related to natural disturbances has thus become an increasingly important part of mountain forest management in recent decades. In this article, we present results of recently finalized PhD dissertations and provide an overview on the effect of natural disturbances on the protective function against natural hazards. Based on this overview and an expected further increase in the frequency and intensity of extreme events and natural disturbances in mountain forests, we discuss how the resilience of protective forests to future extreme events may be promoted.

Un arbre hàbitat o portador de microhàbitats es defineix com un arbre que té almenys un dendromicrohàbitat (Fig. 1). Un dendromicrohàbitat (DMH) és una característica morfològica present en un arbre, utilitzada per determinades espècies durant almenys una part del seu cicle de vida. Aquestes singularitats poden servir com a refugis, llocs de reproducció o llocs crucials d'hibernació o alimentació per a milers d'espècies. Les pertorbacions, biòtiques o abiòtiques, poden crear dendromicrohàbitats: per exemple, la caiguda d'una roca podria malmetre l'escorça, un llamp podria caure sobre un arbre i trencar la fusta, o un picot podria crear una cavitat per a la cria en el tronc. Per a alguns dendromicrohàbitats, com els nius de vertebrats o les escombres de bruixa, l'arbre és simplement un suport físic. Només les singularitats que se sap que tenen un vincle directe amb una o més espècies associades es classifiquen com a dendromicrohàbitats (Larrieu et al. 2018). [...]

Een habitatboom wordt gedefinieerd als een boom met ten minste één boommicrohabitat (Fig. 1). Een boommicrohabitat (afgekort TreM, voor 'Tree Related Microhabitat') is een bijzondere morfologische eigenschap van een boom die gebruikt wordt door soms zeer gespecialiseerde soorten tijdens ten minste een deel van hun levenscyclus. Deze elementen kunnen schuilplaatsen, broedplaatsen of cruciale overwinterings- of voedingsplaatsen vormen voor duizenden soorten. Verschillende biotische of abiotische oorzaken kunnen boommicrohabitats creëren. Een vallend rotsblok kan bijvoorbeeld de schors verwonden, de bliksem kan op een boom inslaan en het hout openbreken, of een specht kan een broedholte uithakken in de stam. Voor sommige TreMs, zoals nesten van gewervelden, is de boom slechts een fysieke ondersteuning. Alleen morfologische kenmerken waarvan bekend is dat ze een direct verband hebben met één of meer geassocieerde soorten worden geclassificeerd als TreMs (Larrieu et al. 2018). [...]

Die teilweise stark veränderte oder gar aufgegebene Nutzung der Wälder im Avers hat dazu geführt, dass sich Baumverjüngung etablieren konnte, welche die zahlreichen alten Lärchen und Arven zunehmend bedrängen.

Lärche und Arve, Charakterbaumarten der oberen Höhenstufen der Alpen, zusammen wachsend, ausgedehnte Wälder prägend und doch mit sehr unterschiedlichen Eigenschaften und Strategien und entsprechend differenzierter waldbaulicher Behandlung.

Im Mai 2020 legte die EU-Kommission eine Biodiversitätsstrategie und anschliessend daran eine neue Waldstrategie vor. Deren Ziel ist es, die Resilienz von Wäldern in EU-Ländern zu erhöhen und damit langfristig die Multifunktionalität von Wäldern zu sichern. Ein übergeordnetes Konzept in der Waldstrategie bezüglich der Bewirtschaftung von Wäldern ausserhalb von Schutzgebieten lautet «Closer-to-Nature Forest Management»: Damit soll vermittelt werden, dass die Bewirtschaftung von Wäldern verbessert werden muss, wo immer es nötig und sinnvoll ist. Um diesen Begriff verständlicher zu machen, wurde ein Bericht von Wissenschaftlerinnen und Wissenschaftlern aus ganz Europa erarbeitet und 2022 vom Europäischen Forstinstitut (EFI) publiziert.

Loss of insect biodiversity is widespread, and in forests habitat loss is one of the major drivers responsible. Integrative forest management must consider the preservation and promotion of key habitat features that provide essential microhabitats and resources to conserve biodiversity alongside ecosystem functions and services.

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.