Dr. Jonas Glatthorn

Estimating growing stock is one of the main objectives of forest inventories. It refers to the stem volume of individual trees which is typically derived by models as it cannot be easily measured directly. These models are thus based on measurable tree dimensions and their parameterization depends on the available empirical data. Historically, such data were collected by measurements of tree stem sizes, which is very time- and cost-intensive. Here, we present an exceptionally large dataset with section-wise stem measurements on 40'349 felled individual trees collected on plots of the Experimental Forest Management project. It is a revised and expanded version of previously unpublished data and contains the empirically derived coarse (diameter ≥7 cm) and fine branch volume of 27'297 and 18'980, respectively, individual trees. The data were collected between 1888 and 1974 across Switzerland covering a large topographic gradient and a diverse species range and can thus support estimations and verification of volume functions also outside Switzerland including the derivation of whole tree volume in a consistent manner.

The biggest challenge for forest management in the near future will be the silvicultural adaptation of forests on sites where climate change will increase the risk for drought induced tree mortality and for a decrease of the growth performance. One management option is the diversification by promoting climate change adapted non-native tree species. Currently, we have in depth experience with only a few non-native tree species in Central Europe. Other tree species that may complement the species pool in Central Europe need to be carefully selected by a range of criteria. Before establishing larger silvicultural experiments at stand-level, the suitability of species to grow well with a low risk of failure under expected future climatic conditions as well as a good performance already today should be tested, amongst other aspects. We present results of a multi-site common garden experiment where growth and survival of five non-native tree species (Abies bornmuelleriana, Cedrus libani, Fagus orientalis, Tilia tomentosa, and Tsuga heterophylla) and one climate adapted local native species per site are tested in five field trials in Austria, Germany and Switzerland along a temperature (7.9–10.4 °C mean annual Temperature) and precipitation (490–1147 mm annual precipitation) gradient. Each species was replicated on three plots per site using a block-wise design. Lower survival and growth of the non-native species as the native reference on most sites indicate that the studied non-native species are today not as well adapted to current climatic conditions as native species. However, the performance of the non-native species was sufficiently high to justify further trials. Survival and growth rates were mostly equally high on the two sites at the opposing ends of the temperature and humidity gradient and lower on all other sites. Height growth and survival were only marginally affected by the strong summer drought in 2018 in all except one site, presumably due to the low water storage capacity of the sandy soils on this site. This indicates that the tested non-native tree species grow well in the wide range of climatically changing weather conditions from our transnational study sites across Central Europe. So far, the tested tree species did not reach their climatic growth limitation. However, edaphic site conditions may have influenced the performance of the tested non-native species as well and must be considered when discussing the suitability of these tree species.

Eine der grössten waldbaulichen Herausforderungen der nächsten Jahrzehnte wird es sein, Waldbestände gegenüber häufigeren Trocken- und Hitzeereignissen und daraus resultierenden Kalamitäten anzupassen. Eine Option ist es, nicht-heimische Baumarten auf geeigneten Standorten anzubauen. Momentan besteht lediglich für wenige nicht-heimische Baumarten mit längerer Nutzungsgeschichte in Mitteleuropa, wie etwa der Douglasie, ausreichend Wissen zu ihrer Anbaueignung. Weitere nicht-heimische Baumarten, die möglicherweise im Zuge einer unterstützten Wanderung (assisted migration) für eine forstliche Nutzung in Mitteleuropa infrage kommen, sollten sorgsam nach festgelegten Kriterien ausgewählt und in Anbauversuchen getestet werden. Insbesondere sollte dabei geprüft werden, ob diese Arten sowohl unter zukünftigen als auch unter heutigen Klimabedingungen eine ausreichende Überlebensrate und Wuchsleistung haben. Um dies zu testen, wurden im Rahmen eines transnationalen Verbundprojekts (KLIP-18) im Jahr 2012 Versuche mit sechs bisher wenig erforschten, nicht-heimischen Baumarten entlang eines Klimagradienten an fünf Standorten in Deutschland, in der Schweiz und in Österreich angelegt (Abies bornmuelleriana, Cedrus libani, Thuja plicata, Tsuga heterophylla, Fagus orientalis, Tilia tomentosa). Zur Referenz wurde jeweils eine zusätzliche standorts- und klimawandelangepasste heimische Baumart gepflanzt. In den ersten Jahren nach der Pflanzung kam es artabhängig zu teilweiser hoher Mortalität. Das Wachstum und Überleben der Versuchsbäume zwischen 2017 und 2022 war stark baumarten- und standortsabhängig. Der Unterschied der Performance der Baumarten zwischen dem feuchtesten und dem trockensten Standort war dabei unerwartet klein, während die Standorte in der Mitte des Klimagradienten vermutlich aufgrund der dort vorliegenden Bodeneigenschaften eine hohe Mortalität und ein niedriges Wachstum hatten. Die Ergebnisse dieser Studie zeigen auf, dass einige bisher teilweise in Mitteleuropa wenig forstlich genutzte Baumarten aufgrund ihrer aktuellen Performance für weitere Testanbauten auf geeigneten Standorten in Frage kommen könnten.

Biodiversity loss and its potential threat on ecosystem functions call for a critical evaluation of human impacts on forest ecosystems. Management practices based on stand diversification offer a possible solution to biodiversity loss due to monoculture plantations, and these practices often involve planting introduced tree species. Although introduced non-native tree species may provide high economic returns, they may also form novel ecosystems and threaten local biodiversity, but this has been little studied. Here, we combined a taxonomic and trait-based approach and investigated communities of oribatid mites (Oribatida, Acari) across forest types of both native and introduced tree species in Northern Germany. Both trophic and life-history traits of oribatid mites were evaluated using native European beech (Fagus sylvatica) as reference, compared to native Norway spruce (Picea abies), introduced Douglas fir (Pseudotsuga menziesii) and beech-conifer mixtures. The abundance and diversity of oribatid mites were generally similar among monocultures of European beech, Norway spruce and Douglas fir. By contrast, species and trait compositions of oribatid mite communities were shifted to include more primary decomposers and more surface-living oribatid mites in Douglas fir, resulting in a trophic reorganization with less predators than in European beech forests. These results suggest that oribatid mites maintain a similar level of trait diversity regardless of forest type, but the changes in trophic guild composition and vertical distribution indicate greater availability of litter-based resources in Douglas fir than in European beech forests. The similar abundance and diversity of oribatid mite communities in Douglas fir mixed stands as in native European beech forests points to mixed forests as a promising management option for future forestry. Overall, our trait-based analyses provided insights into the changes of soil biota composition, revealing the impact of introduced tree species on the structure and functions of soil animal communities.

Enriching tree species-poor and less productive forests by introducing economically valuable species is a strategy proposed for achieving multipurpose forest management. However, empirical evidence from managed and mature forests on the impact of this enrichment on ecological (multidiversity and ecosystem multifunctionality) and economic dimensions remains scarce, particularly when nonnative species are used. Here, we propose and test a framework that integrates economic multifunctionality, encompassing timber production-oriented goals and resistance against disturbances, with multidiversity and ecosystem multifunctionality in European beech forest stands enriched with conifers. Our results show that enriched beech forest stands (~80 years old) can provide high levels of economic multifunctionality without compromising multidiversity and ecosystem multifunctionality. In comparison to pure beech stands, enriched stands with Douglas-fir supported win-win-win situations for these three dimensions. Our findings contribute to the discussion of integrating biodiversity, ecosystem, and economic functions, providing empirical evidence for future forest management.

Ziel des adaptiven Waldbaus ist es, die Waldbewirtschaftung nach Bedarf an die sich ändernden Umweltbedingungen anzupassen, damit Waldleistungen und Biodiversität angesichts der durch den Klimawandel immer häufigeren und auch extremeren Störungsereignisse erhalten bleiben. Dieser Artikel fasst die Kernaussagen der in dieser Schwerpunktausgabe vorgestellten Beispiele aus Forschung und Praxis zum aktuellen Stand des adaptiven Waldbaus zusammen. Und er zeigt auf, dass der adaptive Waldbau in der Praxis voranschreitet. Gleichzeitig müssen sowohl Praxis als auch Forschung weiter und zusammen daran arbeiten, bestehende Unsicherheiten im Hinblick auf die zukünftige Klimaentwicklung und die Eignung verschiedener waldbaulicher Anpassungsmassnahmen zu reduzieren.

The objective of adaptive forest management is a directed adjustment of silvicultural measures wherever necessary to ensure provision of forest services and biodiversity in the face of more frequent and more intense disturbance events due to climate change in the future. This paper synthesises the main points of the examples from practitioners and scientists that are presented in this special issue and shows that there is good progress towards the adaptation of forest stands to climate change. At the same time, forest practitioners and scientists need to further collaborate to reduce existing uncertainties regarding the future development of the climate and the effectiveness of specific silvicultural adaption measures.

Cultivation of non-native tree species is a promising option to adapt managed forests to climate change. However, consequences of non-native tree species on flora, fauna, and microorganisms that occur in forest ecosystems (forest associates) need to be considered when managing forests. We lack a solid understanding of how cultivating non-native tree species in pure stands and in mixture with native tree species impacts abundance and species diversity of forest associates. We compared abundance, alpha-, beta- and gamma-diversity of eight forest-floor-associated taxa that are relevant for ecosystem functioning (including fungi, plants, arthropods, and small mammals) between different forest ecosystems. We addressed pure stands of non-native coniferous Douglas-fir (Pseudotsuga menziesii) and two native species, broad-leaved European beech (Fagus sylvatica) and coniferous Norway spruce (Picea abies), as well as mixed stands of European beech with each conifer in two regions with differing site conditions in temperate Northwest Germany. Diversity indices revealed differences among species groups. Gamma-diversity and alpha-diversity of forest associates in Douglas-fir and spruce stands were usually higher than in beech stands. Estimates of species diversity of mixed stands are intermediate between estimates for the respective pure stands. Differences in the diversity between the two study regions were highly taxon specific with no clear support for a general trend toward a higher or lower species diversity of forest associates depending on site quality. Abundance values show a pattern similar to our diversity estimates, but with a higher statistical uncertainty. Non-native Douglas-fir stands provided habitats to support associated species communities of equally high or higher diversity than stands of native beech or spruce. Mixed stands of non-native and native tree species may be a management option to achieve different goals, that is, to provide habitats for species that are strictly associated with beech and to increase resilience to climate change. However, the overall diversity of forest-floor-associated biota is not improved by cultivating Douglas-fir or spruce in mixture with beech.

Restoration of high-value timber trees in logged tropical forests is indispensable as a conservation strategy and for the enhancement of ecosystem services. Khaya anthotheca is a mahogany tree species of major restoration importance in Uganda. However, the factors affecting the natural regeneration success of this species are poorly understood. We determined the effect of selected site conditions on the abundance of K. anthotheca regeneration in the Budongo Forest Reserve. Two hundred and four 1,000 m² inventory plots, each nested with four 4 m² subplots, were systematically established in logged and unlogged sites within the study area. All trees greater than or equal to 10 cm DBH and natural regeneration (<10 cm DBH) were identified and recorded in the plots and subplots, respectively. We characterized plots by the density of conspecifics, light availability, ground cover of undergrowth, litter depth, soil pH, and basal area. Regression models were used to evaluate the variables that influenced regeneration abundance and occurrence. The density of adult conspecifics and soil pH were important. Regeneration abundance and occurrence increased with increasing density of adult conspecifics and decreased with increasing soil pH. Our results highlight that in addition to seed availability, soil pH was important for successful regeneration. This is one of the first K. anthotheca-specific studies to evaluate more than a few environmental factors influencing the density of its naturally established seedlings in tropical African forests. The abundance and distribution of adult conspecifics in the canopy and soil pH should be considered in K. anthotheca restoration plans.

Protection from gravitational natural hazards such as snow avalanches and rockfall is among the most important ecosystem services provided by forests in steep mountain terrain such as the European Alps. These so-called "protection forests" often have to be actively managed to ensure a sustainable ecosystem service provision in time and space. For studying these slowly developing ecosystems, dynamic forest models are important tools to assess the effect of management on the protective function. However, existing models focus on the current protective effect and in many cases neglect aspects of stand resistance and resilience to large disturbances, which are important factors for maintaining the long-term protective function. Therefore, we developed ProForM, a new dynamic forest model aimed at (1) reproducing stand dynamics of managed temperate mountain forests and (2) assessing their protective function in detail. ProForM is a structurally simple model that contains mechanistic formulations of basic demographic processes but was developed mainly with empirical data. It is spatially explicit and was developed with a focus on regeneration dynamics. The model is parameterized for four tree species (Picea abies, Abies alba, Fagus sylvatica, and Acer pseudoplatanus) and four elevational zones, ranging from mixed species submontane to spruce-dominated subalpine forests. ProForM was calibrated with and validated against independent data from long-term forest inventories from Switzerland. It exhibited a satisfactory performance in reproducing measured basal area, stem number, diameter distribution and mean crown ratio at the stand level, comparable to the performance of other, typically more complex models. Illustrative example simulations demonstrate the assessment of the protective function of a stand against gravitational hazards according to multiple criteria used in forestry practice in Alpine countries. ProForM is a valuable new tool to study the impacts of management on the protective effect of mountain forests, and to inform forest managers.

1. Recent biodiversity loss has emphasized the necessity to critically evaluate the consequences of human alterations of forest ecosystems. Stand diversification via tree species mixtures and the use of non-native trees are two such alterations currently gaining importance as climate change adaptations. However, the effects of local versus regional tree mixing on associated biodiversity and notably the modifying role of tree species growing outside their natural range remain poorly understood.
2. We assessed how monocultures and mixtures of native and introduced tree species influence the taxonomic and functional diversity of bird communities at stand and landscape scales in north-west Germany. We focused on the dominant natural tree species (Fagus sylvatica) and economically important conifer species planted outside their natural range (the native Picea abies and non-native Pseudotsuga menziesii).
3. We found that bird species richness and functional diversity were generally higher in pure and mixed stands of native F. sylvatica than in pure conifer stands, especially in comparison to non-native P. menziesii. These differences were particularly strong at the landscape scale. Pure conifer stands harboured only a reduced set of functionally similar bird species. Structural diversity based on tree microhabitat availability emerged as a key predictor of bird diversity.
4. Synthesis and applications. Our study suggests that tree species mixtures do not necessarily increase bird diversity compared to pure stands of native trees, but can promote bird diversity relative to pure stands of species planted outside their natural range. Moreover, local mixtures, rather than a mosaic of pure stands, may promote bird diversity also at the landscape scale. By contrast, pure stands of tree species planted outside their natural range can increase biotic homogenization of forest birds. Promoting structural diversity of microhabitats via tree retention and ensuring that non-native trees are planted in mixtures with native trees may alleviate potential limitations of climate change-oriented management for biodiversity.