Dr. Marcus Schaub

Premise: Tree structure and function are constrained by and acclimate to climatic conditions. Drought limits plant growth and carbon acquisition and can result in "legacy" effects that last beyond the period of water stress. Leaf and twig-level legacy effects of past water abundance, such as that experienced by trees that established under wetter conditions are unknown.
Methods: In an 18-year forest irrigation experiment, we explored the lasting structural impact of past water richness on leaves and twigs of Pinus sylvestris using synchrotron-based X-ray microscopy. We compared 47 anatomical traits among never-irrigated control trees, trees irrigated for 18 years, and formerly irrigated trees, 7 years after their return to control-level water availability in this naturally dry forest.
Results: We found that legacy effects induced by a period of experimental irrigation continue to shape the structure of new leaves and twigs long after a sharp decrease in water availability. Legacy effects shaping twigs were present but dissipating, while leaf traits displayed long-lasting effects on structural strategy, with extreme values for traits associated with high water stress and low productivity.
Conclusions: Mature trees acclimating to an increasingly dry world may be at a disadvantage compared to young trees that have known only chronic drought. However, these young trees may be capable of thriving in sites of drought-related forest decline especially if planted while larger individuals are still present to support tree establishment. Without a legacy of past water abundance, trees in future forests may be better equipped to cope with our rapidly changing climate.

Springtails (Collembola) and mites (Acari) are soil microarthropods, one of the most diverse animal groups in soils. They play a crucial role in organic matter cycling and are active throughout the food web as decomposers, bacterivores, fungivores, and carnivores. Only little is known about how these groups might respond to shifts in water availability, for example in the context of global change. Here, we investigated how soil microarthropods responded to long-term irrigation in a drought-prone Scots pine (Pinus sylvestris) forest in southern Switzerland. After more than a decade of doubling the annual rainfall, irrigation improved not only tree vitality but also soil quality, and with shifts in bacteria and fungi reflecting changes from oligotrophic to copiotrophic conditions. We assessed soil microarthropods with two approaches: (1) directly by soil DNA metabarcoding and (2) by morphological assessment after extraction of the animals with Macfadyen funnels. Another main aim of that study was to compare the results with the two approaches. The dominant Collembola genus in both assessment approaches was Parisotoma. The dominant Sarcoptiformes genus was Oppiella whereas Geolaelaps was the dominant Mesostigmata genus in both assessment approaches. Only the metabarcoding approach detected Trombidiformes genera, and only one genus, Microtydeus, had a classification confidence >80 %.
The abundance and alpha-diversity of Collembola and Acari did not change significantly as a result of the irrigation treatment, regardless of the assessment approaches applied. In contrast, microarthropod beta-diversity showed significantly shifts for Collembola and Acari, and for the Collembola order Entomobryomorpha and the Acari orders Sarcoptiformes, Mesostigmata, and Trombidiformes. A Procrustes analysis comparing the two assessment approaches indicated a significant effect of the irrigation treatment for the mite order Sarcoptiformes and a nearly significant effect for Collembola.
Using indicator species analysis a Parisotoma species was the only Collembola taxon in the metabarcoding assessment that was strongly associated with the irrigation treatment. With the morphological assessment, Parisotoma notabilis and Lepidocyrtus sp. were significantly associated with irrigation. For Acari, only the morphological approach let to Licnodamaeus pulcherrimus as a negative indicator taxon for irrigation. By using the morphospecies lists as a reference for validation and comparing it with the species list obtained through metabarcoding, we found that only a small percentage of Collembola and Acari morphospecies overlapped. The metabarcoding approach detected taxa that were not observed with the morphological assessment, such as Neelipleona, Symphypleona, or Trombidiformes. Due to the complexity of the taxa and the lack of comprehensive taxonomic identification and reference databases, identification at the species level is hardly possible. Further efforts to enrich the microarthropod reference database are urgently needed.

• Tree net carbon (C) uptake may decrease under global warming, as higher temperatures constrain photosynthesis while simultaneously increasing respiration. Thermal acclimation might mitigate this negative effect, but its capacity to do so under concurrent soil drought remains uncertain.
• Using a 5-yr open-top chamber experiment, we determined acclimation of leaf-level photosynthesis (thermal optimum T_opt and rate A_opt) and respiration (rate at 25°C R₂₅ and thermal sensitivity Q₁₀) to chronic +5°C warming, soil drought, and their combination in beech (Fagus sylvatica L.) and oak (Quercus pubescens Willd.) saplings. Process-based modeling was used to evaluate acclimation impacts on canopy-level net C uptake (A_tot).
• Prolonged warming increased T_opt by 3.03–2.66°C, but only by 1.58–0.31°C when combined with soil drought, and slightly reduced R₂₅ and Q₁₀. By contrast, drought reduced T_opt (−1.93°C in oak), A_opt (c. 50%), and slightly reduced R₂₅ and Q₁₀ (in beech). Mainly because of reduced leaf area, A_tot decreased by 47–84% with warming (in beech) and drought, but without additive effects when combined.
• Our results suggest that, despite photosynthetic and respiratory acclimation to warming and soil drought, canopy-level net C uptake will decline in a persistently hotter and drier climate, primarily due to the prevalent impact of leaf area reduction.

Motivation: Here, we make available a second version of the BioTIME database, which compiles records of abundance estimates for species in sample events of ecological assemblages through time. The updated version expands version 1.0 of the database by doubling the number of studies and includes substantial additional curation to the taxonomic accuracy of the records, as well as the metadata. Moreover, we now provide an R package (BioTIMEr) to facilitate use of the database.
Main Types of Variables Included: The database is composed of one main data table containing the abundance records and 11 metadata tables. The data are organised in a hierarchy of scales where 11,989,233 records are nested in 1,603,067 sample events, from 553,253 sampling locations, which are nested in 708 studies. A study is defined as a sampling methodology applied to an assemblage for a minimum of 2 years.
Spatial Location and Grain: Sampling locations in BioTIME are distributed across the planet, including marine, terrestrial and freshwater realms. Spatial grain size and extent vary across studies depending on sampling methodology. We recommend gridding of sampling locations into areas of consistent size.
Time Period and Grain: The earliest time series in BioTIME start in 1874, and the most recent records are from 2023. Temporal grain and duration vary across studies. We recommend doing sample-level rarefaction to ensure consistent sampling effort through time before calculating any diversity metric.
Major Taxa and Level of Measurement: The database includes any eukaryotic taxa, with a combined total of 56,400 taxa.
Software Format: csv and. SQL.

Wälder sind eine wichtige Kohlenstoffsenke, stehen jedoch durch sich häufende Klimaextreme wie Hitze und Trockenheit zunehmend unter Druck. Nach 25 Jahren Monitoring an den 19 Standorten des Programms «Langfristige Waldökosystem-Forschung» zeigen sich Veränderungen in der Waldstruktur und im Wachstum. Die Wälder wurden generell dichter und älter. Das Wachstum nahm sowohl in den Tief- als auch in den Hochlagen ab, vor allem bei Fichte, Tanne und Buche. Das Wachstum korreliert auf Einzelbaum- und auf Bestandesebene mit Bestandesstruktur (Bestandesdichte und Alter) und negativ mit Temperatur und Trockenheit. Verglichen mit den 1990er-Jahren weisen die Wälder an den untersuchten Standorten heute eine geringere Produktivität bei gleicher Bestandesdichte auf, was auf eine Abnahme der Standortskapazität hinweist.

25 years of growth development in 19 Swiss forests under increasing drought
Forests are an important carbon sink but are under increasing pressure due to more frequent climate extremes such as heat and drought. After 25 years of monitoring at the 19 sites of the Long-Term Forest Ecosystem Research programme (LWF), changes in forest structure and growth are evident. The forests have generally become denser and older. Growth decreased in both low- and high-altitude sites, especially for spruce, fir and beech. Growth was correlated with stand structure (stand density and age) at individual tree and stand level, as well as negatively with temperature and drought. Compared to the 1990s, the LWF forests today show lower productivity at the same stand density, which indicates a decrease in site capacity.

• Nitrogen deposition exceeds critical loads in almost 90% of forest areas. Increased nitrogen deposition leads to nutrient imbalances in the soil and vegetation and can affect the biodiversity of plants, lichens and soil organisms.
• Ground-level ozone damages the photosynthetic cells in leaves. The ozone dose taken up through the stomata has decreased in beech trees, but it remains above the critical threshold.
• Although nitrogen and ozone pollution has been reduced, it still exceeds the relevant limits in many places and can inhibit forest’s growth and drought resistance.

• In quasi il 90 per cento della superficie forestale gli apporti di azoto sono superiori ai valori limite di contaminazione. Questo fenomeno comporta squilibri nutritivi nel suolo e nella vegetazione e può influire sulla biodiversità di piante, licheni e organismi del suolo.
• L'ozono troposferico danneggia le cellule fotosintetiche delle foglie. Nei faggi la dose di ozono assorbita
attraverso le aperture degli stomi è diminuita, ma rimane superiore al livello critico.
• Sebbene sia stato possibile contenerle, le emissioni di azoto e ozono spesso superano ancora i valori
limite di contaminazione e possono inibire la crescita dei boschi e la loro resistenza alla siccità.

• Die Stickstoffeinträge liegen für knapp 90 % der Waldfläche über den kritischen Belastungsgrenzen. Erhöhter Stickstoffeintrag führt zu Nährstoffungleichgewichten in Boden und Vegetation und kann die Biodiversität von Pflanzen, Flechten und Bodenorganismen beeinträchtigen.
• Bodennahes Ozon schädigt die fotosynthetischen Zellen der Blätter. Die durch die Spaltöffnungen aufgenommene Ozondosis hat bei den Buchen abgenommen,
verharrt aber über dem kritischen Grenzwert.
• Obwohl die Immissionen von Stickstoff und Ozon reduziert werden konnten, überschreiten sie vielerorts immer noch die Belastungsgrenzen und können
das Wachstum des Waldes und seine Resistenz gegen Trockenheit hemmen.

• Les dépôts azotés dépassent les charges critiques sur près de 90% de la surface forestière. Un apport excessif d'azote provoque des déséquilibres nutritifs
dans le sol et la végétation et peut nuire à la biodiversité des plantes, des lichens et des organismes du sol.
• L'ozone troposphérique endommage les cellules photosynthétiques des feuilles. La dose d'ozone absorbée par les stomates a diminué chez le hêtre, mais reste supérieure à la valeur limite.
• Les immissions d'azote et d'ozone ont pu être réduites. Cependant, elles dépassent encore en bien des endroits les charges critiques, et peuvent affecter la croissance de la forêt et sa résistance à la sécheresse.

Die Buche könnte schon Mitte des Jahrhunderts in grossen Teilen der Schweiz verschwunden sein – und kaum jemanden scheint dies zu interessieren.

Der Zustand der Baumkrone ist ein wichtiger Indikator für die Vitalität eines Baumes. In Schweizer Wäldern wird der Kronenzustand seit 1985 im Rahmen der Sanasilva-Inventuren und seit 1994 als Teil des Forschungsprogramms «Langfristige Waldökosystem-Forschung» erhoben. In dieser Periode hat die Vitalität des Waldes deutlich abgenommen. Starke und grossflächige Verschlechterungen zeigten sich insbesondere nach Trockensommern. Der Zustand der Baumkronen ist auch ein Indikator für die Absterbewahrscheinlichkeit eines Baumes in den Folgejahren. Hauptursache für den Vitalitätsverlust des Waldes ist der erhöhte Trockenstress, der sich besonders auf Wälder in tieferen Lagen und trockenen Regionen der Schweiz auswirkt. Ein Extrembeispiel dafür ist die Entwicklung der Waldföhre (Pinus sylvestris L.) im Wallis. Regional starb dort in mehreren Wellen ein grosser Teil der Waldföhren ab. Über die Jahre haben sich die Erkenntnisse zu Ursachen und Prozessen immer klarer abgezeichnet. Die immer längeren und wertvolleren Zeitreihen einer Vielzahl beobachteter Parameter erlauben es uns, auch einzelne Ereignisse und Entwicklungen in einen grösseren Kontext zu stellen und zu interpretieren. Kontinuierliche Langzeitbeobachtungen sind deshalb unersetzlich, um Veränderungen im Wald früh zu erkennen und zu verstehen und daraus entsprechende Empfehlungen an die Politik und Praxis abzuleiten.

Good things take time: findings on forest health from long-term observations

The condition of the tree crown is an important indicator of the vitality of a tree. In Swiss forests, the crown condition has been surveyed since 1985 as part of the Sanasilva inventories and since 1994 as part of the research programme "Longterm Forest Ecosystem Research". During this period, the vitality of the forest has declined significantly. Pronounced and widespread deterioration was particularly evident after dry summers. The condition of the tree crowns is also an indicator of the probability of a tree dying within a few years. The main reason for the loss of vitality in the forest is the increased drought stress, which particularly affects forests at lower altitudes and in dry regions of Switzerland. An extreme example of this is the development of the Scots pine (Pinus sylvestris L.) in Valais. In several waves, a large proportion of the Scots pines there died off regionally. Over the years, the findings on causes and processes have become increasingly clear. The increasingly longer and more valuable time series of a large number of observed parameters also allow us to place and interpret individual events and developments in a wider context. Continuous long-term observations are therefore indispensable for recognising and understanding changes in the forest at an early stage and for making appropriate recommendations to policymakers.

• Die Häufung von warmen und trockenen Jahren wird zunehmend zu einer Belastung für den Wald. Selbst Baumarten, die bisher als trockenresistent galten, leiden darunter.
• Zwischenergebnisse des fünften Landesforstinventars zeigen eine Zunahme von geschädigten Bäumen. Hauptursachen sind Insekten und Krankheitserreger sowie Windwurf und Vitalitätsverlust nach Trockenheit.
• Das Bundesamt für Umwelt (BAFU) und die Eidg. Forschungsanstalt für Wald, Schnee und Landschaft (WSL) haben Werkzeuge zur Baumartenwahl im Klimawandel entwickelt. Wichtige Massnahmen sind die Förderung von Mischwäldern und die Erhöhung der genetischen Vielfalt der Wälder.

• As hot, dry years become more frequent, forests are placed under stress. Even tree species previously considered drought-resistant are suffering as a result.
• Interim results of the fifth National Forest Inventory  show an increase in damaged trees. The main causes are insects and pathogens as well as windthrow and loss of vitality after drought.
• The Federal Office for the Environment (FOEN) and the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) have developed tools for selecting tree species in a changing climate. Key measures include promoting mixed forests and increasing the genetic diversity of forests.

• La multiplication d'années chaudes et sèches pèse de plus en plus sur la forêt. Même des essences réputées jusqu'ici résistantes à la sécheresse en souffrent.
• Les résultats intermédiaires du cinquième inventaire forestier national montrent une hausse des arbres endommagés, principalement en raison d'insectes, d'agents pathogènes, de chablis et de pertes de vitalité dues à la sécheresse.
• L'Office fédéral de l'environnement (OFEV) et l'Institut fédéral de recherches sur la forêt, la neige et le paysage (WSL) ont développé des outils pour un choix d'essences adaptées aux changements climatiques. La promotion de forêts mélangées et l'augmentation de la diversité génétique des forêts sont des mesures importantes.

• La frequenza di anni caldi e secchi sta diventando sempre più problematica per il bosco. Ne stanno risentendo anche le specie un tempo considerate resistenti alla siccità.
• I risultati intermedi del quinto Inventario forestale nazionale indicano un aumento degli alberi danneggiati,
soprattutto a causa di insetti e agenti patogeni ma anche per schianti da vento e perdita di vitalità in seguito alla siccità.
• L'Ufficio federale dell'ambiente (UFAM) e l'Istituto federale di ricerca per la foresta, la neve e il paesaggio
(WSL) hanno sviluppato degli strumenti per selezionare specie arboree adatte al cambiamento climatico. Le principali misure consistono nella promozione dei boschi misti e nell’incremento della loro diversità genetica.

Wälder haben eine essenzielle Bedeutung für die Biodiversität, die Klimaregulation und weitere Ökosystemleistungen. Das Programm «Langfristige Waldökosystem-Forschung» der Eidgenössischen Forschungsanstalt WSL hat im Verlauf der vergangenen drei Jahrzehnte wertvolle Erkenntnisse über die komplexen Wechselwirkungen zwischen biotischen, abiotischen und anthropogenen Faktoren gewonnen. Luftverschmutzung und Klimawandel stellen eine erhebliche Belastung für die Wälder dar, was zu Bodenversauerung, Nährstoffungleichgewichten und erhöhter Baumsterblichkeit führt. Technologische Innovationen wie Fernerkundung, Echtzeitüberwachung und Machine Learning machen detaillierte Analysen möglich, die ein verbessertes Verständnis der Waldökosystemprozesse unter verschiedenen Klimaszenarien zulassen. Die Ergebnisse aus drei Jahrzehnten «Langfristige Waldökosystem-Forschung» lieferten wertvolle Leitlinien für Entscheidungsträgerinnen und Waldbesitzer. Angesichts der steigenden Umweltbelastungen ist die Erhaltung resilienter Wälder entscheidend, um ihre Schutz- und Regulierungsfunktionen langfristig zu sichern.

30 years of Long-Term Forest Ecosystem Research: synthesis and outlook
Forests are of vital importance for biodiversity, climate regulation and other ecosystem services. The Long-Term Forest Ecosystem Research (LWF) conducted by the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) over the past three decades has provided valuable insights into the complex interactions between biotic, abiotic and anthropogenic factors. Air pollution and climate change are a significant burden on forests, leading to soil acidification, nutrient imbalances and increased tree mortality. Technological innovations such as remote sensing, real-time monitoring and machine learning allow for detailed analyses that provide an improved understanding of forest ecosystem processes under different climate scenarios. The results from three decades of LWF research provided valuable guidelines for decision-makers and forest owners. In the face of increasing environmental pressures, maintaining resilient forests is crucial to ensure their protective and regulatory functions in the long term.