The research unit (RU) “Forest Resources and Management” holds a colloquium four times a year. Besides an update on organisational news, this event allows the exchange of cutting edge forest research, useful skills and advantageous techniques used for excellent science.
Abstract of presentations given at the FOREMA Quarterly Colloquia
Arun Bose (Brigitte Rohner, Alessandra Bottero, Marco Ferretti, David I. Forrester)
Did the 2018 megadrought change the partitioning of growth between tree sizes and species? A Swiss case-study.
By killing or weakening trees, drought could change the partitioning of growth between tree sizes or species, thereby altering stand structure. Growth partitioning, often quantified as growth dominance coefficient (DC) or the shape of individual tree size vs. growth relationships (SGR), indicates the relative contribution of differently sized trees to the total stand growth. Changes in growth partitioning due to droughts are rarely examined but provide valuable information that links tree- and stand-level responses to droughts. The objective of this study was to test whether DC or SGR can be calculated from small sample sizes of trees, and if so, to use such indices to examine whether the 2018 European megadrought altered the growth partitioning among tree sizes and species. DC, and particularly SGR, were sensitive to sample size, forest types (even-aged and uneven-aged), the target variables (tree diameter, basal area, or stem mass) and the range of tree sizes within the sample. SGR could therefore not be used for our analyses. We found no differences in DC prior to and during the 2018-drought. However, when considering only beech (Fagus sylvatica)-dominated stands, DC was lower during post-drought years than during the 2018-drought. Growth of larger trees, especially beech, was more negatively affected during post-drought years. Therefore, an extreme drought event can indeed alter the growth partitioning within forest stands. The DC indicates such changes in partitioning and hence which trees can be selected for commercial thinning, or released from competition, to minimize potential impacts of droughts.
Lars Waser, Nataliia Rehush (Marius Rüetschi, Achileas Psomas, David Small)
Mapping dominant leaf type based on combined Sentinel-1/-2 data – challenges for mountainous countries
Precise and regularly updated information on the state, change and distribution of forest attributes for entire countries is essential for the forestry sector and beyond. Forest attribute maps such as dominant leaf type (DLT) based on remote sensing techniques, are a reliable and complementary information source to existing National Forest Inventory (NFI) estimates.
In this presentation we show a novel approach to map DLT with the thematic classed broadleaved and coniferous for the whole of Switzerland based on countrywide winter and summer Sentinel-1 (S1) backscatter data, cloud-free summer Sentinel-2 (S2) images, an Airborne Laser Scanning (ALS)-based Digital Terrain Model (DTM) and reference data from aerial image interpretation. Two machine learning approaches, i.e. Random Forest (RF) and deep learning (UNET) for the whole country with three sets of predictor variables were applied. The reference data consists of aerial image interpretation and was split into training, validation and test data sets and was spatially stratified using a 25 km regular grid.
Model accuracies of both RF and UNET were generally highest with Kappa (K) around 0.95 when predictors were included from both S1/S2 and the DTM. While on countrywide level RF and UNET performed overall similarly, substantial differences in model performances, i.e. higher variances and lower accuracies, were found in subareas with northwest to northeast orientations. The combined use of S1/S2 and DTM predictors mitigated these problems related to topography and shadows and was therefore superior to the single use of S1 and DTM or S2 and DTM data. The comparison with independent NFI plot data demonstrated precisions of K around 0.6 in the predictions of DLT and indicated a trend of increasing deviations in mixed forests. A comparison with the Copernicus High Resolution Layer (HRL) DLT 2018 revealed overall higher map accuracies with the exception of pure broadleaved forest. Although, spatial patterns of DTL were overall similar, UNET performed better than RF in areas with a distinct DLT on forest stand level, with the largest differences occurring when only S1 and DTM data was used.
With this study, we go beyond the case study level and meet the requirements of countrywide data sets, in particular regarding repeatability, updating, costs and characteristics of training data sets. The 10 m countrywide DLT maps add complementary and spatially explicit information to the existing NFI estimates and are thus highly relevant for forestry practice and other related fields. The new DLT map is now available as Geobasisdatensatz Waldmischungsgrad LFI 2018 or downloadable (on request by email) in EnviDat as Forest Type NFI 2018.
Modelling of potential natural forest communities across Switzerland based on NFI-Data: Challenges, opportunities and potential applications
The potential natural forest communities (PNC; Deutsch: Standorttypen) are an expert based classification system for forests representing idealised compositions of tree and understory plant species considered as natural on a given site. The PNCs are determined based on local site conditions (e.g., climate, topography, understory vegetation) and, therefore, can be different from the current tree species composition, as a result, of past or current management decisions (e.g., spruce plantations in the lowland). Based on a recently finished project (NaiS-LFI) mapping the PNCs on all LFI4 sample plots and a large number of environmental predictors the PNCs across Switzerland were modelled under current and future environmental conditions. While the modelling of PNCs is very challenging and has severe limitations the continuous spatial information on the PNCs in combination with LFI data and remote sensing products also offers great potential for several risk assessments. (1) Forest areas where the current tree species composition strongly deviates from the expected composition based on the PNCs can be identified and analysed regarding their vulnerability towards drought, insect outbreaks or other disturbances. (2) Forest areas where the current tree recruitment deviates from the expected future PNC can be identified and the need for management intervention assessed. (3) Forest areas where the PNCs are expected to drastically change under future conditions can be identified and analysed regarding their ability to provide continued ecosystem services (i.e. protection function).
Leo Bont, Laura Ramstein, Fritz Frutig, Janine Schweier
Neue Grundlagen für eine effiziente Seillinienplanung zur Bereitstellung von Ökosystemleistungen
Wälder erbringen bedeutende Ökosystemleistungen wie Bereitstellung von Holz, Schutz vor Naturgefahren, Erhaltung der Biodiversität, Erholungsraum, Kohlenstoffspeicherung sowie Trinkwasserfilterung und -speicherung. Damit die Wälder diese Dienstleistungen nachhaltig erbringen können, sind waldbauliche Lenkungsmassnahmen erforderlich. Im Schutzwald, muss zur Sicherstellung einer kontinuierlichen Waldverjüngung regelmässig eingegriffen werden. Ausserdem sind viele Pflanzen-, Insekten- und Vogelarten auf gezielte Eingriffe angewiesen, wodurch eine vielfältige Waldstruktur mit einem Nebeneinander sowohl von Altholz- als auch von Pionierwaldphasen geschaffen wird. Auch um einen konstant hohen Zuwachs und damit eine hohe Assimilation von CO2 aus der Luft zu erreichen, sind regelmässige Verjüngungshiebe notwendig. Eine maximale Kohlenstoffsenkenwirkung wird erreicht, wenn das geschlagene Holz für langlebige Holzprodukte verwendet wird, welche den assimilierten Kohlenstoff speichern und energieintensive Baumaterialien wie Stahl und Beton ersetzen. Die Förderung von Baumarten, die an künftige Klimaverhältnisse angepasst sind, sowie die Schaffung von störungsresistenteren und -resilienteren Bestandesstrukturen erfordern ebenfalls entsprechende Lenkungsmassnahmen.
Holzrücken mittels Seilkran ist ein wichtiges Holzernteverfahren in der Schweizer Forstwirtschaft. Etwa die Hälfte der Wälder werden mit seil- und luftgestützten Mitteln erschlossen. Rund ein Viertel der Waldfläche wird mit dem Seilkran bewirtschaftet, wobei konventionelle Seilkräne und Mobilseilkräne in ähnlichem Umfang eingesetzt werden (Brändli et al., 2020).
Im kürzlich abgeschlossenen Projekt «Neue Grundlagen für eine effiziente Seillinienplanung» wurde untersucht, wie wissenschaftliche Erkenntnisse der Seilmechanik, Entwicklungen in der Fernerkundung sowie mathematische Optimierungsalgorithmen in ein modernes Tool für die Seillinienplanung integriert werden können. Die Berechnung der Seillinie wurde an mehreren Fallbeispielen getestet. Die berechneten Durchhänge und Kräfte mittels Kettenlinien-Ansatz (Methode nach Zweifel) lieferten deutlich präzisere Werte als die Ergebnisse der weit verbreiteten Berechnungsmethode nach Pestal. Weiter wurden verschiedene Einzelbaumdetektionsmethoden zur Identifikation von potenziellen Stützenbäumen für Waldflächen im Seilkrangelände verglichen und die besten Methoden mit schweizweit verfügbaren Geodaten getestet. Alle Untersuchungen wurden mit dem QGIS-Plugin Seilaplan durchgeführt, das im Rahmen des Projekts weiterentwickelt und von der Forstpraxis mit grossem Interesse verfolgt und getestet wurde.
Im Referat am Forema Kolloquium wird ein Überblick über das Projekt gegeben, mit dem Schwerpunkt der Validierung der Berechnungen durch Feldmessungen, sowie das QGIS Plugin Seilaplan vorgeführt.
Weitere Informationen zum Thema:
When do trees actually grow?
Surprising but true: We hardly know when exactly trees grow. Yet it is crucial for understanding tree and forest dynamics whether growth occurs uniformly over days and weeks or lasts for only relatively few hours during a growing season. Here we show that radial growth is mainly timed by air dryness, and trees therefore grow mostly in the second half of the night. This suggests that carbon uptake and carbon consumption are temporally decoupled from growth, and that the growth process is more sensitive to air dryness than carbon uptake.
WML – WaMos meets LFI
Since 2014 we have been developing and testing various approaches to link the Swiss socio-cultural forest monitoring WaMos with the National Forest Inventory LFI. LFI assesses the forest from the perspective of forest management and natural science but does not include forest visitors’ recreation attitudes and behaviour, whereas WaMos investigates the social dimension such as forest recreation attitudes and forest-recreation behaviour but does not include physical data about the forest. However, especially regarding forest recreation, both the physical characteristics of the forest in which recreation takes place as well as the social aspects such as visitor preferences and behaviour play an important role. The question arises whether methods and data from LFI and WaMos could be combined to explain and possibly even predict forest recreation patterns from forest-related and visitor-related data. In this talk I will illustrate our research on this topic over the last six years, focusing on perceived visual attractiveness of forests as an indicator for the recreational value of the forest. I will explain our different approaches, show some main results and give a short outlook on future developments.
TBk: a computer tool for producing stand maps for practical uses based on remote sensing data
TBk is a computer tool with which a stand map can be generated based on generally accessible remote sensing data. Stand delimitation is based on the spatial distribution of dominant trees, i.e. the maximum height per unit area (e.g. are) of a vegetation height model (VHM input grid). The dominant height (hdom), the maximum height (hmax) and the degree of cover (DG) are determined for each stand. The delimitation process is based on a set of rules that also apply when delimiting stands manually in the forest, making the results useful for practical uses like silviculture and forest planning. The coarseness of the resulting stand mosaic can be adjusted by the user with different parameters, especially the tolerance range and the pixel size of the input grid used. TBk has been developed at BFH-HAFL and is in use in several Cantons.
3D Forest Structure Assessment using Laser Scanning and Photogrammetry - Possibilities and Limitations
Forest structure is an important parameter for the assessment of forest functioning and productivity as well as light availability within the forest canopy. It gives us a lot of information about how the forest developed over time and how it will develop in the future. However, three-dimensional forest structure assessment is a non-trivial task. Recent advances in the field of laser scanning and photogrammetry allows us to acquire three-dimensional information on the forest structure at ever increasing levels of detail. In this presentation I will talk about recent experiences we made when testing new instruments and methodologies to acquire 3D structural information on a 1 ha large experimental plot in the Rameren Forest next to the WSL in Birmensdorf.
Including soil information in high-resolution distribution modelling of woody species
Species distribution models (SDMs) provide knowledge about the potential distribution of woody species as a function of a set of environmental parameters, which is of high interest for decision making processes in multifunctional forest management in Switzerland. Soil is known to be an important factor determining the distribution of woody species but is only marginally considered in high-resolution SDMs due to insufficient data quality. Recently, high-resolution maps of soil properties were produced for the entire forested area of Switzerland by means of digital soil mapping (DSM) within a research project at the Swiss Federal Institute of Forest, Snow and Landscape Research (WSL). The purpose of this thesis is to test if this data leads to improved prediction capabilities of SDMs for woody species in Swiss forests.
Twelve species were examined whereof six were expected to react sensitively to gradients of soil properties and six were not. For each species, two SDMs were created for the entire forested area of Switzerland: one without soil data and one with soil data. The models without soil data included climatic, topographic and remotely sensed land-surface parameters, models with soil data additionally included soil parameters. The models were created with an ensemble of various model algorithms. The impact of soil data was tested with a mixed-effect model and the TSS model performance measure, a variable-importance test and a variation-partitioning approach. Additionally, distribution maps were created to detect changing spatial patterns by the addition of soil data.
Model performance increased for 10 out of 12 species, including all 6 species that were anticipated to show sensitivity to soil parameters. Improvements of up to 30 % were achieved in those cases. Significant effects were also detected for models of species that were assigned to the not-sensitive group and for the interaction between the two model types and the species groups. The variable-importance test revealed that soil predictors used in models of soil-sensitive species tended to have higher variable importance ranks than predictors in models of the non-sensitive species group. Results of the variation partitioning approach emphasized the considerable added value of soil data to SDMs of certain species. The distribution maps of models with soil data accounted for the small-scale variability of soil properties within the Swiss forested area.
High-resolution soil data derived using DSM was found to have a significant positive effect on many species and mainly on species with a particularly sensitive reaction to gradients in soil properties. The findings of this thesis show that SDM studies can benefit from soil data and suggest it to be included in such models. Distribution maps created with high-resolution soil data are expected to better account for heterogeneous patterns of soil properties and therefore to provide more detailed information for silvicultural decisions in Switzerland.
Query strategies for detection of patient zero
Infectious diseases often spread through human or animal contacts. In some cases, we know the network of contacts (e.g., animal transport networks). After observing one infected individual at some time t, we aim to find a probability distribution over all possible sources (patient zero) of the disease spread. However, the probability distribution over a potentially large number of possible sources can be quite uninformative after only observing one infected individual. Therefore, our goal is to query unobserved nodes in the network and learn their infection state in order to gain as much information as possible about the source of the spread. To do this we leverage ideas from concept learning and active learning.
Rolf Grütter, Meinrad Abegg
Organisation der Begriffe im LFI
Im Schweizerischen Landesforstinventar (LFI) werden seit 1982 zahlreiche Merkmale aufgenommen, mit denen sich der Zustand und die Entwicklung des Schweizer Waldes charakterisieren lassen. Aus diesen Merkmalen werden unterschiedliche Produkte erstellt, seien das die Ergebnisberichte oder Methodenpublikationen in Buchform oder die Resultate im Internet und weitere. In diesen Produkten werden viele Fachbegriffe mit entsprechenden Bedeutungen benutzt, dies, je nach Produkt, auch in mehreren Sprachen.
Das Ziel des LFI ist, diese Begriffe konsistent zu verwenden, inkl. den Übersetzungen und Bedeutungen, und sie möglichst einfach aktuell halten zu können. In den letzten zwei Jahren wurden die Konzepte entwickelt, in welcher Form diese Begriffe organisiert werden können und wie diese effizient zusammengeführt werden können.
Aktuell ist im WSL-Intranet eine Applikation verfügbar, in der die Begriffe der Glossare des Ergebnisberichts LFI4 und der Methodenpublikation schnell und einfach angezeigt, gefiltert und heruntergeladen werden können. In Zukunft sollen so auch weitere Begriffssammlungen verfügbar gemacht werden. Der Unterhalt und die Redaktion besagter Begriffssammlungen wird durch die Produktverantwortlichen wahrgenommen, wobei die Arbeiten über eine Anlaufstelle koordiniert werden.
LFI-Datenbackups - von Null auf Hundert
Notfall! Wie kommt man wieder zu einer Datenbank, wenn alles defekt ist?
Einschätzung des Verbisseinflusses auf die Baumverjüngung: wichtige Faktoren und 2-Baum-Methode
Wildlebende Tiere - besonders Reh, Gämse und Rothirsche - fressen die Triebe junger Bäumchen. Wildlebende Huftiere wählen dabei selektiv einzelne Baumarten und die vitalsten Baumindividuen aus und beeinflussen deshalb das Wachstum der Verjüngung je nach Art unterschiedlich. Dies kann zu Verschiebungen im Konkurrenzgefüge der Arten führen und den Etablierungserfolg einzelner Arten verändern.
Die langfristigen Auswirkungen des Verbisses durch wildlebende Huftiere auf die Baumverjüngung können nur objektiv eingeschätzt werden, wenn mehrere Merkmale betrachtet werden; die Verbissintensität (Verbissprozent) alleine genügt nicht. Insbesondere sind Informationen zu den folgenden Merkmalen nötig zur Einschätzung des Wildeinflusses:
- Endtriebverbiss-Stärke und deren Häufigkeit
- Höhenzuwachs der Bäumchen und damit i) zur Durchwuchszeit und ii) zu den verbissbedingten Änderungen im Höhenzuwachs der Baumarten untereinander
- Reaktionsgeschwindigkeit resp. die zeitliche Verzögerung bis zur Neuausbildung eines Endtriebes
- Dichte und räumliche Verteilung der Verjüngung
- Verbissbedingte Mortalität der Bäumchen
Die meisten dieser Merkmale lassen sich leicht erfassen (ausgenommen Mortalität) und sollten deshalb in Zukunft Eingang in Verbissinventuren finden.
Die Methode mit der Vermessung der 2 zum Probeflächenzentrum nächst gelegenen Bäumchen je Baumart und Höhenklasse passt die abzusuchende Fläche an die Verjüngungsdichte an, ermöglicht das Messen der Höhenzuwächse an einer minimalen Anzahl an Bäumchen je Art und erlaubt die Berechnung von Flächenanteilen, Durchwuchszeiten, und verbissbedingten Änderungen im Höhenzuwachs der Baumarten untereinander. Am Beispiel der Pilotstudie 2018 zur Einschätzung des Einflusses von Verbiss durch wildlebende Huftiere auf die Baumverjüngung in zwei Wildräumen des Kantons St. Gallen wird diese 2-Baum-Methode vorgestellt.
Für mehr Informationen zum Thema Verjüngung:
Kupferschmid, A.D., Brang, P., Bugmann, H., 2020. Einfluss des Verbisses auf die Verjüngung besser beurteilen.
Resultate Pilotstudien St. Gallen:
Kupferschmid, A.D., Gmür, P., 2020. Verbisseinfluss in der Tannenwaldstufe: Zwei unterschiedliche Beispiele aus dem Kanton St. Gallen. Jagd Natur 1, 12-16.
k-Baum Methode zur Einschätzung des Verbisseinflusses:
Kupferschmid, A.D., Gmür, P.A., 2020. Methoden zur Einschätzung des Verbisseinflusses: Vergleich der Messungen an den k nächsten Bäumchen mit Zählungen im Probekreis. Schweiz. Z. Forstwes. 171, 69–78.
Film über die Verjüngungsaufnahme:
Andrea, Kupferschmid; Lachat, Thibault (2020). Einfluss des Wildverbisses auf die Verjüngung : ein Tutorial [Film]. Berner Fachhochschule BFH, Hochschule für Agrar-, Forst- und Lebensmittelwissenschaften HAFL; Eidgenössische Forschungsanstalt für Wald, Schnee und Landschaft WSL. https://arbor.bfh.ch/id/eprint/11872
Mast in European tree species: triggers, inhibitors, and impact on resource dynamics
Weather can be a trigger for years with mass fruit production (i.e. mast years), but can also act as an ‘environmental veto’, thus leading to fruit abortion, the early abandonment of fruit development.
On sites of the International Co-operative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) across Europe, European beech and Norway spruce mast years are triggered by distinct weather conditions in the previous two summers, while pedunculate and sessile oak only depend on favourable conditions during the pollination period.
During the heat wave and prolonged drought in summer 2018, fruit abortion occurred on two out of three LWF beech sites in Switzerland. We found that this most probably is a mechanism to prevent resource loss if environmental conditions are unfavourable for fruit production. Furthermore, we found evidence for a basic biennial mast cycle in European beech which can be interrupted by ‘environmental vetoes’ such as late frost during pollination or heat waves and droughts during fruit development. On ICP Forests sites across Europe, deciduous tree species show variable resource dynamics during mast years. While in European beech stem growth (BAI) is reduced during mast years, pedunculate and sessile oak show a slight increase in BAI.
For more information see:
Anita Nussbaumer, Peter Waldner, Vladislav Apuhtin, Fatih Aytar, Sue Benham, Filippo Bussotti, Johannes Eichhorn, Nadine Eickenscheidt, Petr Fabianek, Lutz Falkenried, Stefan Leca, Martti Lindgren, María José Manzano Serrano, Stefan Neagu, Seppo Nevalainen, Jozef Pajtik, Nenad Potočić, Pasi Rautio, Geert Sioen, Vidas Stakënas, Celal Tașdemir, Iben Margrete Thomsen, Volkmar Timmermann, Liisa Ukonmaanaho, Arne Verstraeten, Sören Wulff, Arthur Gessler. 2018. Impact of weather cues and resource dynamics on mast occurrence in the main forest tree species in Europe. Forest Ecology and Management 429: 336-350. doi: 10.1016/j.foreco.2018.07.011
Anita Nussbaumer, Katrin Meusburger, Maria Schmitt, Peter Waldner, Regula Gehrig, Matthias Haeni, Andreas Rigling, Ivano Brunner, Anne Thimonier. 2020. Extreme summer heat and drought lead to early fruit abortion in European beech. Scientific Reports 363: 10.5334. doi:10.1038/s41598-020-62073-0
Forest microclimate dynamics drive plant responses to warming
Climate warming is causing a shift in biological communities in favor of warm-affinity species (i.e., thermophilisation). Species responses often lag behind climate warming, but the reasons for such lags remain largely unknown. Here we analyze multidecadal understorey microclimate dynamics in European forests and show that thermophilisation and the climatic lag in forest plant communities are primarily controlled by microclimate. Increasing tree canopy cover reduces warming rates inside forests, but loss of canopy cover leads to increased local heat that exacerbates the disequilibrium between community responses and climate change. Reciprocal effects between plants and microclimates are key to understanding the response of forest biodiversity and functioning to climate and land-use changes.
For more Information see: Zellweger, F., De Frenne, P., Lenoir, J., Vangansbeke, P., Verheyen, K., Bernhardt-Römermann, M., … Coomes, D. (2020). Forest microclimate dynamics drive plant responses to warming. Science, 368(6492), 772-775. https://doi.org/10.1126/science.aba6880
Decision support systems (DSS) for forestry by the the research unit forest resources and management
The research unit Forest Resources and Management develops and maintains a broad variety of decision support systems (DSS) for forestry. The here presented website provides an overview. Sustainable forest management aims at balancing societal, ecological and economic interests on forest resource use. However, the complexity of forest systems, the long-term impact of management actions and the uncertain effects of climate change, economic trends, as well as changes in the demand for forest resources hamper finding appropriate management decisions. So called decision support systems (DSS) may support decision-making in complicated forest planning situations. A DSS is any interactive, usually computer-driven tool that helps decision makers to solve complex problems. The WSL Research Unit FOREMA makes available a variety of software packages that support decision-making in different sectors of forestry in Switzerland. Some of the presented DSS feature a fully developed graphical user interface and are at the most part self-explanatory, while others consist of spread sheets, R-packages or java-code and need more training. Accordingly, the scope and the targeted user group vary between DSS. Some are designated to support decisions in operational forestry while others are better suited in research applications.
Sustainable Forestry in a climate change affected environment
Foresters have to tackle various challenges that are caused by climate change and have direct impact on the forest management. For example, more rain during winter season and fewer frost periods leading to an increased use of cable yarding systems in lowlands for harvesting; and high shares of unpredictable wood use demand focusing more on organizational activities. Current silvicultural management strategies respond to the changes caused by climate change and aim to increase forests resistance and resilience. However, they also lead to challenges: for example, mixed forests can hardly be harvested with fully mechanized systems. Another aspect of increasing importance is the question which ecosystem services should be provided and can be brought on the market as valuable product. A modern forestry needs to address these challenges and should thereby address economic, environmental and societal dimensions in order to support a sustainable forest management that is accepted by different stakeholders and thus, successful.
Design-based improvements in change estimation in the Swiss National Forest Inventory through integration with external monitoring networks and sources
Model-assisted estimation is commonplace for improving the precision of estimates in forest inventories as it can produce unbiased results regardless of model misspecification. As it is most frequently applied to estimating some form of timber volume, auxiliary information typically consists of remote sensing based on either satellite imagery or a vegetation height model (VHM). However, as more potential sources of auxiliary information become available, a central question arises concerning which sources of information best complement each other in the model-assisted framework. A case study is presented here in the context of change estimation rather than volume estimation. A wide variety of potential auxiliary variables are assigned to one of five categories: spatial, satellite, topographical, VHM and mechanistic. All combinations of categories are then passed through a variable selection algorithm and their precisions are assessed. A new technique for combining plots from external sources directly into the estimation procedure is also presented. The main findings were that each individual category can provide a moderate increase in precision and the highest increase occurs when including all the categories together. However, remote sensing from satellite imagery or the VHM showed the highest potential for variance reduction.
Linking forest growth with stand structure: tree size inequality, tree growth or resource partitioning and the asymmetry of competition
Stand structure can strongly influence forest growth and other processes, such as the water balance, carbon partitioning, nutrient cycling and light dynamics. However, individual structural variables can be positively or negatively correlated with growth. This is the case for variables such as size inequality and those that describe resource partitioning, such as the degree of symmetric/asymmetric competition and growth dominance. Contrasting growth-structure correlations appear to converge when they are examined using a simple framework where stand growth is a function of three variables as opposed to any one of the variables alone; stand density, size distributions and size-growth relationships. The size distributions quantify how the stand density is distributed between the different sizes while the size-growth relationships quantify how growth is partitioned between different sizes. Size inequality may not often be a useful explanatory variable and instead it appears to sometimes correlate with growth because it can be correlated with other variables that influence growth. The simple framework of three variables could be used to separate the effects of structure and functioning when comparing mixed and monospecific forests, as well as to design silvicultural interventions or to determine whether past management interventions have achieved their goals.
On automatic detection of locations with high/low average values
In the context of regression modeling, we discuss some ideas of detecting points in space &/or time where a certain derivative of the regression function is too high or too low compared to a given threshold. The chosen order (j) of the derivative will depend on the question at hand. For example, for time series data, taking j=1, we are able to detect time points when the speed of change is above a given threshold, i.e. rapid change points. For spatial data, we may be interested in finding locations where the mean (j=0) itself may be high, e.g. finding forest stand locations with high mean DBH. Considering large scales in space and time that we are dealing with, we make flexible assumptions about our regression model and use kernel smoothing for curve/surface estimation. We will discuss the main ideas, highlighting principles and computational issues, along with some data examples. This talk is partially based on joint work with Gabi Moser (guest, Statistics Lab) as well as collaborations with several other colleagues. References to published & ongoing research will be mentioned during the talk.
Characterisation of tree volume for the Swiss NFI using terrestrial laser scanning
The rapid methodological and technological development of portable terrestrial laser scanning (TLS) devices and their applications in the context of forest inventories in recent years, lead to the question whether they can be used for national forest inventories (NFI) to improve their explanatory power, especially where direct measurements are very expensive or impossible. Notably, tree volume, one of the most important tree variables in an NFI cannot be measured directly. To date, volume estimation has to rely on allometric models. TLS hast the potential to overcome issues of allometric models, such as a lack of representativeness or being up-to-date, by measuring tree volume directly on sample plots. However, still little is known on the interaction of TLS field protocols, TLS devices, tree and stand properties on the quality of TLS measurements.
In order to evaluate TLS applicability an NFI, the 3D content creating suite Blender, is used to simulate TLS in forested environments to address the following questions: What are suitable scanner placement patterns on sample plots for a best TLS coverage in forests? What are the properties of three state-of-the-art TLS devices in terms of triggering signals and how can they be integrated in a simulation environment? What is the influence of signal triggering and laser beam diameter on the quality of TLS point clouds in forest areas? And, what problems are encountered when estimating tree volume with TLS?
‘Silent reserves’- A hidden treasure in National Forest Inventories
In a Europe shaped by centuries of forest management, characterising, understanding and modelling natural forests is highly challenging. In addition to forests reserves that can represent hardly comparable case studies, National Forest Inventories (NFIs) can provide large national datasets with a valuable representativeness as they are composed of systematically distributed plots with a variable time since the last management intervention. We define ‘silent reserves’ as NFI plots free of human influence for at least 50 years. We propose to use ‘silent reserves’ to conduct large-scale studies on near-natural forests, and test this original concept in Switzerland. We characterise compositional and structural attributes of silent reserves and compare them to those of managed forests. As an example of scientific application, we analyse the tree- and stand-level factors affecting tree mortality in ‘silent reserves’.
11.2% of Swiss NFI plots fulfilled the criteria of ‘silent reserves’, mostly located in the Alps and Southern Alps where road accessibility for forest operations is lower. ‘Silent reserves’ presented a higher naturalness than managed forests through a higher proportion of broadleaves and slightly higher mortality rates than managed forests, although diameter distributions were similar in both forest types. These results suggest that 50 years without management might not be sufficient for forests to be fully detached from the effect of past management, and this threshold could be adjusted based on regions or site conditions. Species-specific tree mortality probabilities were negatively related to tree growth, and presented a typical U-shaped response to tree size where small trees died from competition and large trees from senescence or diseases.
Our study demonstrates the potential of NFIs to study near-natural forests at the national scale, with opportunities for broader-scale international collaborations. ‘Silent reserves’ represent a first step towards a greater understanding of such forests using large, existing datasets.
Open Science in Environmental Data Publication - An EnviDat Perspective
The scientific community currently faces a “reproducibility crisis”. Methods or computer code that are not being made transparently available, missing data and incomplete metadata have been recognized as major factors for irreproducible results, hampering open science, including in the area of Earth and Environmental research. Fortunately however, activities are underway worldwide to address the issue. WSL, for example, invests in the development of EnviDat, an institutional environmental data portal and repository. EnviDat represents a platform for making curated, quality-controlled and reusable research data accessible, in accordance with the WSL data policy. EnviDat provides researchers with the technical means to publish and document research datasets with formal metadata, accompanied by proper citation information and Digital Object Identifiers (DOIs). Furthermore, EnviDat encourages researchers to complement data publications with descriptions of research methods as well as with open code using Juypter Notebooks or Singularity containers. A proof of concept for open code and software has been tested in collaboration with members of the research unit FOREMA members (M. Fraefel, L. Bont). Finally, thanks to the collaboration with the WSL IT, both Juypter Notebooks and Singularity containers are now readily available to use in Hyperion, WSL's high performance computing (HPC) Linux cluster. Open science covers many other aspects and it would be beyond the capabilities of EnviDat to address all aspects comprehensively. However, the developments presented here are expected to strengthen WSL’s research position, advance open science and support knowledge sharing and reproducibility of published research.
European forests have been monitored since the 1980s to evaluate their condition in response to abiotic and biotic agents. The main attribute assessed is the deviation of foliage density on tree crowns as compared to a given reference assumed to hold full foliage. Such a deviation is almost universally (and incorrectly) termed “defoliation”, and has been subject to a number of criticisms originated from concerns on data quality and relationship with meaningful assessment endpoints (e.g. growth).
I will briefly present case studies from France, Trentino (Italy), and Switzerland to show that, besides justified criticisms, crown density can display regularities in relationship with growth and response to climate drivers across species and regions. This may open interesting perspectives to better understand forest condition dynamics and feedbacks on climate change.
Modeling ingrowth for empirical forest prediction systems
Accurate and representative prediction of ingrowth is essential for modeling forest development. Besides the number of ingrowth trees, the basic tree attributes diameter and species are also important. In this study, these three characteristics were modeled based on data from the Swiss National Forest Inventory (NFI). The study covered large gradients of stand conditions and climate variables, making the models suitable to predict ingrowth under climate change. As the number of ingrowth trees per plot included more zeros than is expected for a Poisson distribution, we used three alternative probability distributions: zero-inflated Poisson distribution (ZIP), negative binomial distribution (NB) and zero-inflated negative binomial distribution (ZINB). Models with each of the three variants were fitted with and without random effects, resulting in six different model types. Model selection was performed backward using the BIC criterion. Of the final models, ZIP showed the best predictions of independently observed number of ingrowth trees. Our results indicate that the number of ingrowth trees strongly depended on the development stage of forests and on stand basal area, while temperature and precipitation, nitrogen deposition and water holding capacity each had a lower but still significant and plausible effect. The Weibull function was used to describe the probability distribution of the diameter of ingrowth trees and parameters were estimated using the Likelihood approach. The diameter of ingrowth trees was larger where there was a better site index and decreased with increasing stand density. Further, twelve species groups of ingrowth trees were fitted with a multinomial regression approach and showed clear dependence on climate: the probability of spruce and larch ingrowth clearly decreased with increasing temperature, whilst all other tree species profited from warmer conditions. The probability of fir, beech and ash ingrowth increased with increasing basal area, demonstrating the relevance of shade tolerance. The most important variable for predicting the species of ingrowth was the leading tree species group in a plot.
For more Information see: Zell, J., Rohner, B., Thürig, E., & Stadelmann, G. (2019). Modeling ingrowth for empirical forest prediction systems. Forest Ecology and Management, 433, 771-779. https://doi.org/10.1016/j.foreco.2018.11.052
Defining near-optimal harvesting techniques using Swiss National Forest Inventory data
In Switzerland, the competitiveness of the Swiss forestry sector is currently under discussion. The cost-effectiveness could be increased through the application of up-to-date harvesting and transportation techniques The Swiss National Forest Inventory (NFI) delivers a wide range of information on forests using a combination of field assessments and interview surveys. Through the interview survey, including all local foresters of Switzerland (about 830), the Swiss NFI is one among few NFIs able to assess the currently applied harvesting technique and calculate timber harvesting costs for each field plot. Using available NFI data and derived information, we can thus contribute to the current discussion.
In order to evaluate the suitability of the currently applied harvesting techniques, we developed a method to derive the technical feasibility of a variety of potential harvesting techniques. Additionally, we also compared their transportation routes for cost estimations. To identify the technically feasible harvesting techniques we used various wall-to-wall, spatially explicit (topography, forest map), as well as field (NFI plot) data (obstacles for harvesting operations, mean DBH, species composition) and interview data (applied harvesting techniques) from the NFI.
The allocation of the optimal harvesting technique is still being implemented (work in progress) but will be done using expert-defined rules for each NFI field plot. For the allocation, the technical feasibility as well as the harvesting cost of each alternative will be taken into account. We will then compare the optimal harvesting technique with the currently implemented harvesting technique at each sample plot. The transportation cost on the forest road network will be evaluated with regard to its geometrical dimensions (e.g. road width, bearing capacity).
With our results, we hope to show that cheaper, optimised, harvesting techniques could be applied in various parts of Switzerland, thus substantially reducing costs for forest owners.
Analysing timber harvesting and transport options for the entire Swiss forest
Forest accessibility from an existing road network is often assessed using average values such as road densities or simple spatial descriptors such as buffers. However, these methods do not take into account the heterogeneity of the terrain or soil properties. Moreover, because both the hauling of wood to a nearby road and the on-road transport contribute to the total timber production costs, information on the whole logging process should be used to find combinations of possible harvesting techniques and transport routes. Our approach allocates the most suitable harvesting technique – cable, ground-based or aerial systems – to every forest parcel (pixel), and identifies the corresponding landings on a road. In a second step, the best transport route out of the forest is determined using the topological NFI forest road network. For each forest parcel, the corresponding harvesting and transport costs are then estimated, and the most economic harvesting technique and transport route can be found. The main result is a country-wide, 10-m-resolution map of forest accessibility, indicating the suitability for economic wood production. The model results can also be compared to the currently practised methods identified in the NFI.
Optimizing the layout of an existing forest road network in steep terrain
Most existing forest road networks in Switzerland were built between the 1950s and the 1980s, so they were planned for different conditions that we find today (different harvesting and hauling technology as well different financial restriction). At latest when reaching the end of the life cycle, those road networks need to be redesigned. For example some road segments will not be required anymore, some need an upgrade and some road pieces need to be new constructed.There are few methods that consider redesigning of existing road networks. Henningson et al. 2007 presented a model for redesigning forest road networks. They considered road upgrades to reduce the losses due to road closures caused by heavy rains or thawing. As this model is hard to solve, Flisberg et al. 2014 presented an easier-to-solve implementation for this problem. But however this model is still large and hard to solve as it integrates harvest and logistic planning into the model. Integrating harvesting and logistic planning is not necessary in our case, as there are different silvicultural restrictions in the alps.Based on an existing road network, our model aims to identify a harvesting and road network layout that minimizes concurrently the cost for the road network (construction, upgrade and maintenance), the wood harvesting and the hauling operations over an entire life cycle. This is accomplished by selecting road segments that are necessary, assigning them a certain road standard, determining which parcels are to be harvested by what harvesting technology and to detect the hauling route. We require to harvest all timber parcels.We present an Mixed Integer Linear Programming Model, which was applied to optimize the road network of the entire Poschiavo Valley in the Swiss Alps. The valley was split into 7 catchments for which the optimization was done. Computation time for these areas was between few minutes up to 30 minutes, which allows also to do some sensitivity analysis. The harvesting methods were mainly cable based, the hauling was mainly done by truck, but also, as a particularity by railway.When doing such simulations, a particular attention must be paid to an accurate cost estimation of road building or upgrading, or the uncertainty must be considered trough sensitivity analysis.The results were evaluated and discussed with the forest service and road planning specialists. Results seemed to be very realistic and comprehensible. The represents of the forest service decided to consider the outcome of the project, before doing further investments in road networks.
For more Information see: Bont, L.G.; Church, R.L., (2018). Location set-covering inspired models for designing harvesting and cable road layouts. European Journal of Forest Research, 137 (6), 771-792. doi: 10.1007/s10342-018-1139-7
Bont, L.G.; Fraefel, M.; Fischer, C., (2018). A spatially explicit method to assess the economic suitability of a forest road network for timber harvest in steep terrain. Forests, 9 (4), 169 (21 pp.). doi: 10.3390/f9040169
Bont, L.G.; Heimimann, H. R.; Church, R.L., (2015). Concurrent optimization of harvesting and road network layouts under steep terrain. 232 (41), 41-64. doi: 10.1007/s10479-012-1273-4
MoGLI – Modellierung der potentiellen Verbreitung von Gehölzarten im Schweizer Wald
Das Hauptziel dieses Projektes ist, die aktuelle Verbreitung der häufigsten Gehölzarten des Schweizer Waldes flächendeckend zu modellieren. Gute Kenntnisse zur Verbreitung von Arten in Schweizer Wäldern sind nicht nur für die Grundlagenforschung (z.B. zur Überprüfung ökologischer Theorien), sondern auch für angewandte Fragen rund um die Nutzung und den Schutz natürlicher Ressourcen wichtig. Das MoGLI-Projekt entwickelt dafür Verbreitungskarten in hoher räumlicher Auflösung (25m) und stellt sie der Forschung und Praxis zur Verfügung. Dieser Vortrag führt die verwendete Methodik ein und zeigt einige Resultate; Verbreitungskarten von Gehölzen. Der Fokus liegt dabei darauf, die Möglichkeiten und Limitierungen der erstellten Karten aufzuzeigen.
Marco Ferretti, Fabrizio Cioldi
RapiDbeeCH - Rapid survey on short-term effects of 2018 Drought on beech forests in Switzerland - CH
RapiDbeeCH is a spontaneous FOREMA Research Initiative. FOREMA field crews will (re)visit NFI plots to evaluate the impact of 2018 drought on beech forests. Besides data for ad-hoc scientific analyses, this will provide guidance for a concept on how NFI and other FOREMA infrastructures can be used for future assessment of effects of sudden, acute, adverse, extreme events on Swiss forests, also in co-ordination / co-operation with other Swiss forest monitoring programs and projects. Here, some information is provided about the way in which RapiDbeeCH was made operational.
Spherical images on NFI plots
In addition to the data collection, the NFI documents its sample plots using various means. This ensures e.g. the retrieval of the sample plots in future inventories or subsequent clarifications in the office are facilitated. Since the start of NFI5 in 2018, a spherical photo of each visited sample plot has been created. The camera RICOH THETA V is used to take this picture. The camera is very compact and priced at around CHF 400. The operation is via an app on the smartphone and the time required for taking a photo is about 1-2 minutes. Besides to the two possible uses already mentioned above, it would also be conceivable to use the photos by means of virtual reality glasses at the periodic interview survey with the local foresters. The camera allows versatile application possibilities with little effort and could therefore also be useful for other WSL projects.
Data assimilation in forest ecosystems using forest inventories and processes growth model (Preliminary results)
Data assimilation, a process of incorporating observations into a forecast model, helps to improve our understanding of forest dynamics. Existing models of forest ecosystems dynamics include large uncertainties, which ramify and lead to divergence in forecasts how climate change will impact the future terrestrial carbon cycle. To reduce these uncertainties, it is necessary to extend and combine assessments of current observation networks using novel analytical approaches and data sources.
We applied a data assimilation technique, widely used in numerical weather prediction, to estimate Swiss forest net ecosystem productivity (NEP) at monthly resolution in order to relate biomass changes over time with global drivers. In particular, we link permanently monitored sample plots data of high spatial but low temporal resolution with 3-PG (physiological processes predicting growth) model. We first conduct a Bayesian calibration to estimate a set of posterior parameter probability distribution, and then propagate the estimated uncertainty.
I will present a conceptual framework along with preliminary results aiming to establish NEP data assimilation system hoping to learn from long experience of data assimilation techniques used in numerical weather prediction. The preliminary results are based on subset of National Forest Inventory plots with dominance of Norway Spruce.
DEForScen - Understanding canopy defoliation of European forests under recent climate changes to predict future adaptation scenarios
There is increasing interest to identify patterns of current plastic and evolutionary response of plants to climate change. Since plasticity can be reflected by tree health, one possible investigation approach is the analysis of tree health (canopy defoliation) data collected on ca. 6000 plots across Europe since the 1980s and for which a fully convincing evaluation is still missing. We will investigate if changes and trends in defoliation permit to identify species-specific response to climate change, also in view of future adaptation scenarios. We will do it according to novel methods, including Fast Fourier Transforms, selection of candidate variables, grouping of sites, optimal spectra (time window) and offset (time lag) for each variable, and response in relation to predictors within moving windows.
Ansätze zur Schutzwaldanalyse mittels terrestrischem Laserscanning
In dieser Präsentation berichte ich über verschiedene Ansätze zur Analyse von Schutzwäldern mit Daten von terrestrischem Laserscanning (TLS). Mithilfe dieser Methoden soll im Rahmen des LFI-Projektes ‘Beurteilung von Schutzwäldern mittels Fernerkundung‘ geprüft werden, inwieweit sich die Verjüngung in Schutzwäldern automatisiert erkennen und quantifizieren lässt. Die Einzelmethoden umfassen grundlegende Techniken wie die radiometrische Korrektur der Intensität von Laserscanningsignalen sowie verschiedene Teilanwendungen. Zu letzteren gehören beispielsweise die automatisierte und dreidimensionale Isolierung von Baumstämmen aus den Gesamtdaten, die Bestimmung des BHD sowie ein Ansatz zur Erkennung von Einzelbäumen. Letztendlich wird getestet inwieweit mit Hilfe der Teilmethoden die Verjüngung auf Probeflächen ähnlich derer der Forstinventur bestimmbar ist.
For more Information see: Heinzel, J.; & Huber, M. O., 2017: Detecting tree stems from volumetric TLS data in forest environments with rich understory. Remote Sensing, 9(1), 9 (17 pp.). http://doi.org/10.3390/rs9010009
Heinzel, J.; Huber, M. O., 2017: Tree stem diameter estimation from volumentric TLS image data. Remote Sensing, 9(6), 614 (11 pp.). http://doi.org/10.3390/rs9060614
Heinzel, J.; Huber, M.O., 2016: TLS field based intensity correction for forest environments. In: The International Archives of the Photogrammetry, Remote Sensing and Spatial Information Sciences, XLI-B8, Prague, Czech Republic, 643-649. http://doi.org/10.5194/isprsarchives-XLI-B8-643-2016
Marielle Fraefel, Ionut Iosifescu Enescu
Using the SWITCHengines computing and storage services
Integrated into the academic network of SWITCH, SWITCHengines offers a cloud infrastructure for researchers where access to storage and virtual machines can be adapted to the individual's needs. It provides users with a total of 2.5 petabytes storage and a total of 2000 CPU cores. Users set up their own virtual machines and pay for the items they need for as long as they need them. All SWITCH member institutes can subscribe to SWITCHengines. WSL is currently in an evaluation phase. In our presentation, we give some background information on SWITCHengines, an overview of the steps necessary to set up a virtual machine, and a short account of our experience with the process. We have tested the SWITCHengines infrastructure, using configurations with up to 128 GB RAM or up to 100 TB storage on both Windows and Linux. We found the set-up relatively easy, support was readily available, and no serious problems were encountered. Users should however be aware that no backup or monitoring services are included.
Laserscanning für Forstwanwendungen auf der SilviLaser 2017 Konferenz
Im Oktober 2017 fand die 15. SilviLaser Konferenz in Blacksburg (VA), USA statt. Die SilviLaser Konferenzen werden regelmässig seit 2002 durchgeführt, momentan im zweijährigen Turnus. Sie ist die grösste Fachtagung zum Einsatz von Laserscanning (LiDAR) basierter Fernerkundung für Forstanwendungen und Forstwissenschaft. Im vergangen Jahr stand sie unter dem Motto „Anwendung von LIDAR und verwandter Technologien zur Beurteilung und zum Management von Waldökosystemen“. Dabei zielte sie zum einen auf ein besseres Verständnis der Waldstruktur und Waldfunktion, als auch auf die Nachhaltigkeit der Forstwirtschaft. Diese Präsentation soll einen Überblick über die wichtigsten behandelten Themen und den aktuellen Stand der Forschung geben.
Esther Frei, Peter Brang, Kathrin Streit
A large-scale research infrastructure testing tree species adapted to future climates
In a warmer climate with drier summers many tree species, which currently provide important forest ecosystem services, may become maladapted and will eventually be replaced by species that are better adapted to the changed climate. Some species, pre-adapted to future climate conditions, grow already at their future optimal locations whereas others are currently completely absent. Consequently, planting tree seedlings adapted to future climates (assisted migration) or provenances adapted to future climates (assisted gene flow) are proposed strategies to mitigate climate change impacts on forest health and productivity. However, it is not known whether tree species and provenances adapted to future climatic conditions can already be successfully established today at their future growing locations. To close this research gap we plan to establish a network of about 50 experimental plantations in Switzerland in collaboration with FOEN, cantonal forest services, foresters, forest owners and nurseries. This network will allow to test and compare a set of tree species and several provenances per species along large environmental gradients. The project also aims at establishing a long-term research infrastructure, which allows to conduct application-relevant studies about adaptation of forests to future climate conditions during the next 30 to 50 years. We will present the current state of the pilot project, which aims at establishing a network of collaborating partners, defining the experimental design, and selecting tree species and provenances.
Comparing growth of Norway spruce and European beech in pure and mixed stands in Switzerland
Whether mixtures are more productive than monocultures is an ongoing debate considering the wide range of variables and methods used for the growth comparison. Using Swiss National Forest Inventory (SNFI) data, this study assesses whether mixed stands of Picea abies and Fagus sylvatica are more productive than pure stands, and whether the mixture effect depends on site- or stand characteristics. The species proportions were estimated using species proportion by area which depends on the maximum stand basal area (BAmax). Three different methods and 2 different versions of parameters of the self-thinning rule were used to estimate BAmax and the effect of differing methods and parameters on the estimated mixture effect was also investigated. On average, the growth of Picea abies suffered from the mixture. However, this pattern decreased as the site quality increased. Fagus sylvatica grew better in mixtures and its productivity increased with site quality. A significant interaction between proportions and stand age was also found for Fagus sylvatica: a slight negative mixture effect occurred on young stands whereas the mixture had a positive effect in medium and old stands. Overyielding was predicted for 167 out of the 185 SNFI mixed sites. The method employed to estimate BAmax and the version of the self-thinning rule parameters both modulated the estimated mixture effect.
For more Information see: Houpert, L.; Rohner, B.; Forrester, D.; Mina, M.; Huber, M., 2018: Mixing effects in Norway spruce – European beech stands are modulated by site quality, stand age and moisture availability. Forests, 9, 2: 83 (19 pp.). http://doi.org/10.3390/f9020083
Measuring trees with terrestrial Laserscanning
Considering the rapid development of portable terrestrial laser scanning devices (TLS) in the recent years, their applicability for forest research has received increased attention, especially where direct measurements are very expensive or impossible. Its ability for fast and precise measurements of inaccessible parts of trees makes it a technique promising new insights in forests properties. This talk presents potential and limitations of TLS regarding potential forest research applications.
Assessing tree microhabitats using terrestrial laser scanning (TLS) - the state of the NFI pilot project
Over the last decade, terrestrial laser scanning (TLS) has become a subject of very high interest in forest research. In the future TLS may become operational in national forest inventories (NFIs), since TLS data have been successfully used to estimate a wide range of tree attributes (stem position, DBH, volume and others) and the scanning instruments are becoming much lighter, more compact and precise.
Estimation of the economic and ecological value of trees or forest stands is one of the core objectives of the Swiss NFI. The ecological value of a tree can be assessed using surveys of microhabitats (i.e. cavities, fungi, epiphytic structures). However, assessing and measuring of microhabitats in the field is very time consuming and the results are difficult to reproduce. TLS can provide detailed and reproducible information on tree stem surfaces and structures, since it acquires data from surrounding objects with a very high level of detail.
The aim of the project is to develop a semi-automated approach to assess tree microhabitats using TLS. To fulfill this aim, habitat trees were scanned in several forest reserves and managed forests across Switzerland using a FARO Focus 3D S120 scanner. The first results show that local geometric features of tree stem point clouds are a powerful tool for assessing tree microhabitats. Applying a machine learning technique allows to distinguish between some microhabitats quite accurately.
The new Cluster at WSL - Opportunities and Challenges
The specifications of HYPERION, the new HPC environment recently provided at WSL are presented. Next to a short introduction to the SLURM submission system (the system that allows you to use HYPERION), possible opportunities and challenges of using HPC for the daily work of a researcher are outlined using examples of how to run parallelized R computations.
“Waldbäume der Schweiz” on lfi.ch
The website of the Swiss NFI www.lfi.ch presents the “forest trees of Switzerland”. There based on a citizen science approach the highest trees in Switzerland can be reported. In addition specific tree species occurring in Switzerland are presented for the populace. This part of the NFI website was recently revised and shows now the up to date dispersion of the tree and shrub species based on NFI data.
Nonlinear mixed models for tree growth: Combining climate, site, stand, management, and nutrient effects
Empirical forest scenario models are used in several contexts, e.g. to evaluate management strategies, to predict potential timber supply, or to estimate carbon sequestration. As key parts of such models, the growth functions are supposed to incorporate a large variety of influencing factors while representing large spatial extents. In recent times, the demand to include effects of climate change into scenario models has increased. Thus, the present study aimed at empirically modelling effects of climate and N-deposition on tree growth, while simultaneously considering effects of stand, management and site properties. Nonlinear mixed-effects models with covariates were fitted to individual-tree basal area increment (BAI) data from the Swiss National Forest Inventory. Data from 1983-2006 were used for model fitting, data from 2009-2013 for model evaluation. A total of 23 potential explanatory variables were included into a variable selection procedure that was performed separately for spruce, fir, pine, larch, further conifers, beech, oak, ash/maple, and further broadleaves. The combinations of selected variables differed among the species, well reflecting their physiological properties. In general, BAI was positively related to DBH, and negatively related to slope, basal area of larger trees, stand density (not so for the shade tolerant beech), mean DBH of the 100 thickest trees per ha, and soil pH. For most species, a positive harvesting effect was identified. Increasing N-deposition resulted in increasing BAI, except for spruce and fir, for which the models indicated an inverse effect. Drought proved to be relevant for most species, except for pine and oak. As a next step, the developed growth functions may be incorporated in empirical forest scenario models and used for nationwide scenario analyses as well as for applications in other parts of central Europe represented in Switzerland’s large environmental gradients.
For more Information see: Rohner, B.; Waldner, P.; Lischke, H.; Ferretti, M.; Thürig, E., 2018: Predicting individual-tree growth of central European tree species as a function of site, stand, management, nutrient, and climate effects. European Journal of Forest Research, 137: 29-44. http://doi.org/10.1007/s10342-017-1087-7
The Swiss-SpeMixMod project: studying mixing effects using forest inventory data
Mixing effects for any given tree species are difficult to generalize because they can vary greatly along gradients of climatic conditions and resource availability. Identifying the conditions where species diversity can positively influence productivity is crucial but to date few studies have examined how complementarity (i.e., competition, facilitation or competitive reduction) across species and mixture types is modulated by stand and environmental factors. Using the Swiss National Forest Inventory and the climate-sensitive functions developed for the forest scenario model Massimo, we investigated how complementarity for several major central European tree species change with climate, edaphic conditions, stand structural characteristics and species composition. Complementarity varied strongly with stand density and stand development as well as with topographic, climatic and soil conditions. This emphasizes the need to account for site-dependent conditions when exploring mixture effects in relation to forest productivity along gradients. We also found that under certain conditions (i.e., increasing drought and temperature) mixed forests can promote individual-tree growth. Careful assessments depending on the species composing the stands are required under changing resource availability as well as under different levels of stand density and development. These outcomes are of high interest in the context of forest management and conservation, as they allow to identify under which set of conditions promoting species diversity can also help in fostering forest productivity.
For more Information see: Mina, M.; Huber, M.O.; Forrester, D.I.; Thürig, E.; Rohner, B., 2018: Multiple factors modulate tree growth complementarity in Central European mixed forests. Journal of Ecology, 106: 1106-1119. http://doi.org/10.1111/1365-2745.12846
Tree allometric relationships for structurally and species diverse forests
Allometric relationships are often required in forest growth models and to quantify the effects of biodiversity or stand structural characteristics on forest growth and functioning. However, many of the available relationships were developed in monocultures, or they are general relationships developed after combining data from different treatments. This can lead to severely biased predictions and conclusions. The aim of this study was to examine how commonly used relationships between stem diameter and biomass (e.g. foliage, stem or root), height or crown dimensions are modified by vertical structure (dominance), stand density or species composition. The analysis included a meta-analysis of nearly 1000 published biomass equations for major European tree species. All stand structural variables significantly influenced the relationships, but their effects differed widely between the target species. The inter-specific variability was often correlated with species traits (wood density, shade tolerance). With this information, single "general" equations were developed for each given species that could be applied to stands with a wide range of stand structures and species combinations. This approach could improve predictions of biomass and carbon stocks in structurally and compositionally diverse forests.
For more Information see: Forrester, D. I.; Tachauer, I. H. H.; Annighoefer, P.; Barbeito, I.; Pretzsch, H.; Ruiz-Peinado, R.; ... Sileshi, G. W., 2017: Generalized biomass and leaf area allometric equations for European tree species incorporating stand structure, tree age and climate. Forest Ecology and Management, 396, 160-175. http://doi.org/10.1016/j.foreco.2017.04.011
Forrester, D. I.; Benneter, A.; Bouriaud, O.; Bauhus, J., 2016: Diversity and competition influence tree allometric relationships - developing functions for mixed‐species forests. Journal of Ecology, 105, 761-774. https://doi.org/10.1111/1365-2745.12704