Swiss Forest Research Articles

Fruit production in three masting tree species does not rely on stored carbon reserves

Fruiting is typically considered to massively burden the seasonal carbon budget of trees. The cost of reproduction has therefore been suggested as a proximate factor explaining observed mast-fruiting patterns. Here, we used a large-scale, continuous (13)C labeling of mature, deciduous trees in a temperate Swiss forest to investigate to what extent fruit formation in three species with masting reproduction behavior (Carpinus betulus, Fagus sylvatica, Quercus petraea) relies on the import of stored carbon reserves. Using a free-air CO2 enrichment system, we exposed trees to (13)C-depleted CO2 during 8 consecutive years. By the end of this experiment, carbon reserve pools had significantly lower δ(13)C values compared to control trees. δ(13)C analysis of new biomass during the first season after termination of the CO2 enrichment allowed us to distinguish the sources of built-in carbon (old carbon reserves vs. current assimilates). Flowers and expanding leaves carried a significant (13)C label from old carbon stores. In contrast, fruits and vegetative infructescence tissues were exclusively produced from current, unlabeled photoassimilates in all three species, including F. sylvatica, which had a strong masting season. Analyses of δ(13)C in purified starch from xylem of fruit-bearing shoots revealed a complete turn-over of starch during the season, likely due to its usage for bud break. This study is the first to directly demonstrate that fruiting is independent from old carbon reserves in masting trees, with significant implications for mechanistic models that explain mast seeding.

Waldausdehnung im Berggebiet: Prozesse und Entwicklungen in der Schweizer Waldpolitik

Forest expansion in mountain areas: processes and developments in Swiss forest policy The use and protection of mountain landscapes is steered by several public policies, yet forest and agricultural policies play a particularly crucial role due to the relatively large share of forested and agricultural land in those areas. Both forest and agricultural policy are traditional sectoral policies that went through significant changes over the last years. In this article, we focus on the reform efforts in Swiss forest policy with particular attention to the issue of forest expansion in mountain areas. We first describe the relevant forest policy reform processes over the period from the year 2000 to 2012 using the Actor-Process-Event Scheme (APES), and analyze the underlying policy network. We then refer to other policy developments with potentially significant effects on forested areas, including changes in agricultural policy, and discuss the resulting consequences for the specific situation in Swiss mountain areas. The study shows that not only the goals and instruments of the Swiss federal forest policy gradually changed, but also – at least partly – the decision-making structures. Furthermore, it can be shown that the issue of forest expansion in mountain areas has mainly been discussed in the context of forest policy processes. Solutions to the issue, however, will also require appropriate policy instruments in spatial planning and agricultural policy.

Impacts of salvage-logging on the status of deadwood after windthrow in Swiss forests

Downed and standing deadwood (DW) is a key resource for maintaining forest biodiversity. Although extreme events such as windthrow and fires produce large quantities of DW, this substrate is often drastically reduced by logging activities. To elucidate the respecting consequences of salvage-logging, we assessed both quantity and quality of storm-derived DW (storms Vivian 1990 and Lothar 1999) in Swiss forests using a sample of 90 windthrow sites with ≥3 ha complete windthrow and at elevations ranging from 350 to 1,800 m a.s.l. The majority had been salvage-logged (SL) a few years after the windthrow. On each site, we recorded DW amount and quality on six circular sample plots 20 or 50 m2 in size. DW volume on SL sites was surprisingly high, with 76.4 m3 ha−1 on average 20 years after Vivian and 73.8 m3 ha−1 10 years after Lothar. In comparison, DW volumes on unsalvaged sites, that is, with no post-windthrow intervention (NI), amounted to 270 m3 ha−1. A wide variety of wood decay stages and diameter classes (10 to ≥70 cm) was found on both NI and SL sites, suggesting considerable habitat diversity for DW-associated species irrespective of the treatment. The considerable amounts of DW left after salvage-logging distinctly exceed the minimum DW volumes in forest stands proposed by Müller and Bütler (Eur J For Res 129: 981–992, 2010) in a conservation context, which demonstrates the importance of wind disturbance for biodiversity. Further studies should quantify DW of individual tree species, since habitat requirements are species-specific.

Vorgehen zur agentenbasierten Modellierung eines schweizerischen Waldenergieholzmarktes

Procedure to develop an agent-based model of a Swiss forest wood fuel market It is helpful to develop agent-based model based on a structured procedure. The chosen traditional software engineering approach is mainly composed of five phases: 1) the analysis of the observed system; 2) the model development; 3) the detailed design; 4) the actual software implementation; and 5) the model's evaluation. The different phases are briefly described by the respective goals, tasks and expected results. This contribution shows the development of a Swiss forest wood fuel market with specific examples for each phase. The essential work steps and intermediate results are demonstrated from the start to a fully developed agent-based model. Finally it is demonstrated how to carry through scenario analyses for the modeled forest wood fuel market. The simulation example shows first that, as is to be expected, a reduction of the wood supply leads to increasing forest wood fuel prices. Second, it shows how the decision behavior of wood suppliers can additionally modify the price of forest wood fuel in a situation of scarce supply, whereas this effect is smaller in a situation of balanced supply and demand.

Swiss Forest Vegetation Database

The Swiss Forest Vegetation Database (GIVD ID EU-CH-005) contains roughly 14,800 releves located in all parts of Switzerland, and ranging from 200 to 2,480 m a.s.l. Releves were assessed between 1904 and 1995 by 320 different activities with one or more persons involved. A majority of the releves were published in papers, monographs or served for regional mapping projects. A first consistent classification into 71 Swiss forest communities derived from 2,533 of these releves (17%) and equalled the starting point of this collection. During the 1980s and ‘90s, the database was largely extended in order to establish a basis for a revised classification. Meanwhile, many cantons of Switzerland commissioned local forest classifications, which also resulted in an evolution of local expertise on the one hand, and in the difficulty of synthesizing this expertise by means of formal analyses. Eventually, the revision of Ellenberg & Klotzli’s old classification failed. To date, there is no new analysis-based classification of Swiss forests. In contrast, a pragmatic system was established that largely corresponds to the old Ellenberg & Kloztli numbers and may translate between the differing cantonal forest community systems.

Governance approaches in Swiss forest biodiversity policy: Do they really work?

New forms of governance are detected in the Swiss forest reserve policy, a policy in the field of forest biodiversity, and they have helped its implementation. A survey on the implementation status of the Swiss forest reserve concept in the cantons shows that (1) governance elements are clearly favored over traditional command-and-control regulations, (2) 6.6% of the Swiss forest area is delimited forest reserves, (3) large forest reserves are still missing in most of the cantons. Impeding factors can be a lack of conviction of the forest owners, a complicated ownership structure or the weak financial condition of a canton. Improvements may be achieved by increasing consultation and financial incentives or through a purchase of ecologically valuable areas by the Confederation and the cantons.Until now, the Swiss forest reserve policy lacks integration with interacting policies such as climate policy. Climate change could promote forest reserves as sinks for carbon dioxide. Yet this could be counteracted by the support of timber as renewable energy. Integration between forest reserve policy and interacting policies needs to be strengthened, especially with respect to the biodiversity policy (national biodiversity strategy; Convention on Biological Diversity).

Stickstoffeinträge in den Schweizer Wald: Ausmass und Auswirkungen

Inputs of nitrogen to Swiss forests: extent and effects Because of their rough surface forests are an efficient sink for nitrogen compounds emitted by industry, traffic and agriculture. Deposition maps reveal that nitrogen deposition in Swiss forests exceed 30 kg N/(ha × yr) in various regions, which is clearly higher than the critical loads set by the United Nations Economic Commission for Europe (UNECE). The calculated deposition data base on emission inventories, dispersion models, measurements of various deposition components (gaseous, aerosols, wet) as well as on balance calculations. The evaluation of the effects on forests bases on two summary reports: the workshop report of a UNECE meeting on critical loads for nitrogen held in 2010 and a summary of own nitrogen addition experiments published in 2011. The presented data suggest that in Switzerland nitrogen inputs are high enough to cause changes of forest ecosystems.

Soil carbon pools in Swiss forests show legacy effects from historic forest litter raking

Globally, forest soils contain twice as much carbon as forest vegetation. Consequently, natural and anthropogenic disturbances affecting carbon accumulation in forest soils can alter regional to global carbon balance. In this study, we evaluate the effects of historic litter raking on soil carbon stocks, a former forest use which used to be widespread throughout Europe for centuries. We estimate, for Switzerland, the carbon sink potential in current forest soils due to recovery from past litter raking (‘legacy effect’). The year 1650 was chosen as starting year for litter raking, with three different end years (1875/1925/1960) implemented for this forest use in the biogeochemical model LPJ-GUESS. The model was run for different agricultural and climatic zones separately. Number of cattle, grain production and the area of wet meadow have an impact on the specific demand for forest litter. The demand was consequently calculated based on historical statistical data on these factors. The results show soil carbon pools to be reduced by an average of 17 % after 310 years of litter raking and legacy effects were still visible 130 years after abandonment of this forest use (2 % average reduction). We estimate the remaining carbon sink potential in Swiss forest due to legacy effects from past litter raking to amount to 158,000 tC. Integrating historical data into biogeochemical models provides insight into the relevance of past land-use practices. Our study underlines the importance of considering potentially long-lasting effects of such land use practices for carbon accounting.

Wald und Recht (Essay)

Forest and Law (essay) The forests of Switzerland are afforded special legal protection. Since 1902, the year in which the first piece of forestry legislation was enacted, Swiss forestry law is governed by the principle of conservation and the interdiction to clear forest land. Hence, during the 20th century Swiss forests were able to recover from past exploitation as well as to remain unscathed, at least in the main. Swiss forest protection is a success story. Recent developments have, however, given cause for concern. The fact that the ban on building outside of building zones has been considerably watered down during the last fifteen years – an end to this trend is unfortunately not yet in sight – could, before long, have a substantial bearing on the forests. Indeed, the Swiss legislator recently amended the Forest Act of 1991, and its next amendment is already in the pipeline. The politics of unsustainable settlement expansion are doing enough damage to the Swiss landscape as it is. We must be vigilant in order to ensure that our forests do not become their next victim.

Sind Naturwaldreservate naturnäher als der Schweizer Wald?

Do strict forest reserves feature more naturalness than the Swiss forest? In natural forest reserves (NFR), forests develop in the absence of direct human interference, primarily management. This increases their naturalness and should – in the long run – allow forests to regain primeval attributes. Based on stand structural data from the third National Forest Inventory (NFI) and 25 NFR in Switzerland, we investigate 1) whether NFR feature more naturalness than managed forests, 2) whether the naturalness of Swiss forests increases with the time elapsed since the cessation of management, and 3) to what extent NFR differ from Swiss forests that have not been managed during several decades. Thereby, we focus on the four main forest types beech, silver fir-beech, silver fir-Norway spruce and Norway spruce forests, and furthermore group the data according to the time since the last intervention (0–20, 21–50 and > 50 years.). The structural features investigated differ only slightly between NFR and managed forest (0–20 years). NFR feature a higher abundance of “giant” trees (dbh ≥ 80 cm), higher stem numbers and greater basal area, and thus a higher growing stock. The abundance of snags, however, is indistinguishable between the two types of forests. Naturalness in Swiss forests increases only slightly with time since the last intervention, indicated by a higher abundance of small snags and a slightly higher number of giant trees. By contrast, clear differences can be seen between NFR in which no intervention has taken place for at least 50 years, and other forests abandoned for a similarly long time, with NFR showing lower stem numbers, greater basal area and higher numbers of giant trees. Many of the investigated reserves are still affected by former management and are – from the point of view of primeval forest dynamics – still quite “young”. According to their naturalness, the NFR range between managed and primeval forests, although to date they are still closer to the former. Nevertheless, the differences found in our study indicate a steady development of the NFR towards stand structures that are characteristic of primeval forests.

Fourmis des bois en Suisse: état de la situation et perspectives de monitoring

Wood ants in Switzerland: situation and outlook of a monitoring The authors summarise their state of knowledge about wood ants and their role in the forest ecosystem. They also describe the situation in Switzerland, their past development and their conservation status. In several regions, mainly in the Plateau, wood ants seem to diminish, despite their total protection since 1966. The reasons for this regression are not well known, but the fragmentation of forest habitats in the Plateau region and direct damage to ant nests seem to play a certain role. A new project in which the development of wood ant nests is monitored in Swiss forest reserves (Formica-Forêts-CH) was recently started in the Swiss national park. It is to be extended, in collaboration with the forest services, over the whole of Switzerland.

Totholzvolumen und -qualität in ausgewählten Schweizer Naturwaldreservaten

Deadwood volume and quality in selected swiss natural forest reserves Deadwood is structurally and functionally important for forest ecosystems. To date, there are hardly any data on the amount of deadwood in Swiss natural forests which can serve as reference value for deadwood management in managed forests. In this study, deadwood volumes and qualities (sizes, broadleaf/conifer ratios, decomposition stages) from six natural forest reserves were analysed and compared with data from managed forests as well as from natural and virgin forests. An average of 69 m3/ha with a broadleaf proportion of 66% was calculated for the six reserves. Deadwood volume in relation to the total volume was 12% on average. Overall the volume of lying deadwood was double the volume of standing deadwood. The average proportion of large deadwood (diameter >30 cm) was 48% and was higher in snags (52%) than in lying deadwood (46%). Advanced stages of decomposition made up 53% of the lying deadwood. The volumes, sizes and decomposition stages varied greatly within the reserves. In comparison, in the Swiss forests altogether, there is less deadwood (21.5 m3/ha, 5% of total volume), the deadwood is thinner (35% large deadwood proportion) and less decayed (proportion of advanced stages of decomposition 10%). However, deadwood volumes in the reserves are considerably lower than those in European natural beech forests and beech virgin forests. The investigated reserves are therefore, 40 to 92 years after the last silvicultural intervention, only at the beginning of the process of acquiring a virgin forest character.

Waldpolitischer Jahresrückblick 2011

Annual review of Swiss forest policy 2011 The revision of the Forest Act, the adoption of the Forest Programme 2020 by the Federal Council as well as the preparation of the second contribution period of the New System of Financial Equalisation and Division of Tasks between the Confederation and the Cantons (NFE) shaped, in addition to the routine business, the forest policy of 2011. The parliamentary initiatives on forest and forest policy issues remained of about the same amount as in previous years, while the Federal Court decisions on forest legislation have declined significantly. In various forest-related sectoral policies, the government and parliament made important decisions. In climate policy, the Parliament adopted the CO2 Law. However, this has not yet happened to the revision of the Spatial Planning Act. In nature and landscape policy, the administration has prepared the Swiss biodiversity strategy so far that the Federal Council could send it out for consultation. The revision of the Hunting Regulation, with changes in the management of large carnivores, is nearing adoption. At the international level, the Federal Council has submitted the European Landscape Convention to the Parliament for ratification, and the European forestry ministers have agreed to the preparation of a European Forest Convention.

Stem exclusion and mortality in unmanaged subalpine forests of the Swiss Alps

Understanding the causes and consequences of spatiotemporal structural development in forest ecosystems is an important goal of basic and applied ecological research. Most existing knowledge about the sequence and timing of distinct structural stages following stand origin in unmanaged (not actively managed in >50 years) forests has been derived from forests in North America, which are characterized by particular topographic, climatic, biotic and other environmental factors. Thus, the effects on structural development remain poorly understood for many other forest systems, such as the dense, unmanaged, subalpine Norway spruce forests of the Swiss Alps. Over the past century, land abandonment and reductions in active forest management have led to a substantial increase in the density of these forests types. Consequently, many stands are entering the stem exclusion stage and are currently characterized by associated self-thinning mortality. However, the environmental influences on the rate of this structural development as well as this structural stage itself have not yet been examined. We studied stem exclusion processes based on forest inventory data (National Swiss Forest Inventory; NFI) over three survey periods (1983–1985, 1993–1995 and 2004–2006) using repeated measures statistics. To complement these analyses, we also collected and analysed 3,700 increment cores from 20 field plots within dense subalpine Norway spruce forests dispersed across the Swiss Alps. Over the past decades, basal area (BA) has generally increased, particularly on N-facing and steeper slopes, and within 300 m of potential treeline. The number of dead trees was higher on N-facing compared with S-facing slopes, but the BA of dead wood was higher on S-facing slopes. Tree ring analysis confirmed important differences in growth patterns between N- and S-facing slopes and verified the results of the NFI analysis. This study provides a detailed example of how environmental heterogeneity and management history can influence the spatiotemporal structural development of forest ecosystems.

Fifty years of natural succession in Swiss forest reserves: changes in stand structure and mortality rates of oak and beech

AbstractQuestionWhat are the drivers of structural changes and mortality in oak–beech forests over 50 yrs of natural succession?LocationTwelve unmanaged forest sites, comprising a large environmental gradient in theSwiss lowlands.MethodBy using repeated inventory data from more than 17 600 individually tagged trees, the dynamics of oak–beech stands over the past 50 yrs were analysed. Generalized linear mixed‐effects models were fitted to quantify annual mortality rates of oak and beech based onDBH, stand basal area, precipitation and slope.ResultsStand basal area increased, whereas tree density decreased over time. At most sites, the relative importance of oak decreased gradually compared to beech. Mortality increased over time for both oak and beech, but the increase was stronger for oak. Oak and beech mortality decreased with increasingDBHand tended to increase with precipitation. Additionally, oak mortality increased with stand basal area, whereas no such trend was found for beech.ConclusionOur study indicates that mortality inCentralEuropean oak–beech forests is driven by a combination of stand structures (i.e. tree size and stand basal area) and climate. However, the influence of climate on oak mortality is comparably low. Increasing oak mortality with stand basal area is a plausible consequence of its lower relative competitiveness and higher demand for light. Thus, in forests developing towards higher stand basal area, the ecologically important oak is increasingly outcompeted by beech, unless competition is reduced through management or disturbances.

Dead wood volume to dead wood carbon: the issue of conversion factors

Requirements for emission reporting under the Kyoto protocol demand an estimate of the dead wood carbon pool in forests. The volume of dead wood consists of coarse woody debris, smaller woody debris and dead roots. The measurement of dead wood volume was included in the most recent National Forest Inventory in Switzerland. To convert dead wood volume into carbon two conversion factors are required: (a) carbon (C) concentration and (b) wood density. So far internationally accepted default values for C concentration (50%) and for wood density (density of alive trees) were used as default values to estimate dead wood carbon, since local measurements were lacking. However, in a field study at 34 sites in Switzerland, the C concentration and density of CWD from Picea abies and Fagus sylvatica of four decay classes were measured recently. The results showed that C concentration in CWD differed significantly between species but did not change due to decay class. The density of CWD decreased significantly with an increase in decay class and it also differed between species. The decrease in CWD density was more pronounced for F. sylvatica than for P. abies. We assessed correlations between climate attributes and CWD density using regression analysis. The modeled densities and measured C concentrations were then expanded with the help of CWD volume data from the NFI3. Spruce CWD and thus spruce CWD carbon is much more abundant in Swiss forests than beech CWD carbon. The majority of spruce CWD is located in the Alps and Pre-Alps. The CWD volume from P. abies was 10 times higher than that from F. sylvatica. Thus, changes in conversion factors for P. abies CWD affected the overall estimate of dead wood carbon in Swiss forests much more than changes in conversion factors for F. sylvatica CWD. Current improvements in CWD conversion factors decreased the estimated amount of spruce CWD carbon by 23.1% and that of beech by 47.6%. The estimated amount of CWD carbon in Swiss forests is decreased by 31%. Since improved estimation methods are currently not applied to smaller woody debris and dead root material, the estimated amount of dead wood carbon is only reduced by 15%. Improving conversion factors for all dead wood fractions would presumably decrease the amount of dead wood carbon by additional 16%.

Atmospheric nitrogen deposition and canopy retention influences on photosynthetic performance at two high nitrogen deposition Swiss forests

ABSTRACTPortable chlorophyll fluorometry measurements, providing plant photosynthetic efficiency (PE) data, were carried out at two contrasting Swiss forests experiencing high nitrogen (N) deposition. Fluorometry data were obtained in conjunction with controlled N treatment applications within forest canopies to more realistically simulate deposition of plant-available N species. At the high N deposition Novaggio oak forest, growing season canopy N applications caused increases in PE and other photosynthetic measures. Similar N applications at the Lägeren mixed beech and spruce forest site indicated a possible PE decrease in beech leaves and no effect on spruce needles. N is considered a growth-limiting nutrient in temperate environments where low to moderate N deposition can benefit forest growth; however, high N deposition can have negative effects on forest health and growth due to nutrient imbalances. We conclude that the growth effect dominates at both sites, thereby increasing the potential for carbon sequestration. We found clear evidence of direct leaf-level canopy N uptake in combination with increased PE at the Novaggio oak forest site and no definitive evidence of negative N effects at the Lägeren site. We conclude that PE measurements with chlorophyll fluorometry is a useful tool to quantify N and carbon exchange aspects of deciduous forest dynamics.

A method to derive vegetation distribution maps for pollen dispersion models using birch as an example

Detailed knowledge of the spatial distribution of sources is a crucial prerequisite for the application of pollen dispersion models such as, for example, COSMO-ART (COnsortium for Small-scale MOdeling-Aerosols and Reactive Trace gases). However, this input is not available for the allergy-relevant species such as hazel, alder, birch, grass or ragweed. Hence, plant distribution datasets need to be derived from suitable sources. We present an approach to produce such a dataset from existing sources using birch as an example. The basic idea is to construct a birch dataset using a region with good data coverage for calibration and then to extrapolate this relationship to a larger area by using land use classes. We use the Swiss forest inventory (1 km resolution) in combination with a 74-category land use dataset that covers the non-forested areas of Switzerland as well (resolution 100 m). Then we assign birch density categories of 0%, 0.1%, 0.5% and 2.5% to each of the 74 land use categories. The combination of this derived dataset with the birch distribution from the forest inventory yields a fairly accurate birch distribution encompassing entire Switzerland. The land use categories of the Global Land Cover 2000 (GLC2000; Global Land Cover 2000 database, 2003, European Commission, Joint Research Centre; resolution 1 km) are then calibrated with the Swiss dataset in order to derive a Europe-wide birch distribution dataset and aggregated onto the 7 km COSMO-ART grid. This procedure thus assumes that a certain GLC2000 land use category has the same birch density wherever it may occur in Europe. In order to reduce the strict application of this crucial assumption, the birch density distribution as obtained from the previous steps is weighted using the mean Seasonal Pollen Index (SPI; yearly sums of daily pollen concentrations). For future improvement, region-specific birch densities for the GLC2000 categories could be integrated into the mapping procedure.

Ökosystemleistungen des Waldes im politischen Kontext: Bedeutung und Argumenttypen

Ecosystem services of forests in the political context: importance and types of arguments The majority of ecosystem services can be described as public or semi-public goods, whose utilisation does not follow market principles. From the viewpoint of political science it is interesting to analyse how these services are taken into account in political programmes and processes. The present article investigates which ecosystem goods and services of forests have been considered in the Swiss forest policy, and why and in which form some services have been included in political programmes, while others have not. The analysis is based on a theoretical approach that assigns the arguments in the political decision process to specific types. The study shows that of all forest ecosystem services protection services play the most important role in the Swiss forest legislation. Biodiversity and nature conservation are important, too, while services related to recreation and landscape conservation are of minor importance. Concerning political arguments, those related to the long-term role of forestry as part of the overall economy are more important than arguments in favour of a short-term profit maximisation.

Zur Freizeitnutzung von Schweizer Wäldern: ihre Bedeutung für die regionale Ökonomie

Recreational use of Swiss forests: their importance for the regional economy Forests fulfill conservation, production and welfare functions. If forests are not considered isolatedly, but rather as part of a landscape or a region, their positive impact on regional welfare becomes apparent. The regional economic impact of the recreational use of Swiss forests is investigated in the case study regions of Sihlwald, a typical local recreation area, and Bergell, a destination for nature-based tourism. The relative importance of forests in the decision to visit the case study regions is identified by means of a conjoint analysis that assesses the forest affinity of visitors. Both the regional added value and the employment effects of the recreational use of forests are identified in an economic impact analysis. The results show that although they have a high affinity for forests, visitors to local recreation forests, such as the Sihlwald, spend little and generate rather small regional economic impacts. In contrast, the findings for nature-based tourism destinations, such as the Bergell, show a different picture: although the forest is not the most important criterion when selecting the destination, the regional economy benefits from higher consumer expenditures. The amount of visitor expenditure most notably depends on the variety and quality of tourism services in and around the forest area. Hence, to promote the regional economic importance of the recreational use of forests, tourism services in forest areas would have to be created or enhanced.