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Habitatbäume sind eine Schlüsselkomponente der Waldbiodiversität. Seit rund 20 Jahren ist die Bedeutung von Baummikrohabitaten (BMH) als Lebensraum für Tausende teils hochspezialisierte Arten bekannt, und BMH finden zunehmend Eingang ins Waldmonitoring. Mit der Einführung der ersten europäischen Typologie der BMH verfügen das Schweizerische Landesforstinventar (LFI) und die Inventur im Buchenurwald Uholka-Schyrokyj Luh in der Ukraine als erste Grossrauminventuren über repräsentative Referenzdaten. Auch wenn die Reproduzierbarkeit bei einigen BMH-Typen eher schlecht ist, sind nach drei Erhebungsjahren des fünften LFI doch erste aufschlussreiche Vergleiche möglich. Im Schweizer Wald weisen 60% der stehenden lebenden Bäume ab 12 cm Brusthöhendurchmesser mindestens ein BMH auf. Am häufigsten in Stück pro Hektare sind solche mit Flechtenbewuchs (73), Moosbewuchs (67), Stammfusshöhlen (53), Kronentotholz (47) und Harzfluss (37), selten jene mit tiefen Mulmhöhlen (4), Spalten (1), Spechtbruthöhlen (1) und Pilzfruchtkörpern (1). Am geringsten ist die Anzahl BMH-Typen an Tannen (0.6), am grössten an Arven (1.6), Eichen (1.4) und Kastanien (1.3). Generell nimmt die Anzahl verschiedener BMH-Typen mit zunehmendem Baumdurchmesser zu. Die BMH-Dichte variiert je nach Waldfunktion, Waldeigentum, letzter Nutzung, Höhenlage und Geländeneigung. Die tiefen Werte im Mittelland und im östlichen Jura könnten Handlungsbedarf indizieren. Die BMH-Dichte an lebenden Bäumen ist im Schweizer Buchenwald gleich gross wie im Buchenurwald Uholka-Schyrokyj Luh. Allerdings sind tiefe Baumhöhlen, Rindentaschen, Kronentotholz und mehrjährige Pilzfruchtkörper im Buchenurwald häufiger, im Buchenwald dagegen Dendrotelme, Moos- und Efeubewuchs. Der wohl wichtigste ökologische Unterschied liegt im Totholzvolumen, das im Buchenurwald insgesamt fast dreimal so hoch ist wie im Buchenwald, bei den Dürrständern sogar fast sechsmal so hoch.

Der Schweizer Wald spielt für die Erhaltung der biologischen Vielfalt eine zentrale Rolle. Mehr als ein Drittel der bei uns vorkommenden Tiere und Pflanzen sind auf den Wald angewiesen. Die Ergebnisse des LFI4 zeigen, dass der Schweizer Wald ein relativ naturnahes Ökosystem ist. Die Baumarten- und die Strukturvielfalt haben weiter zugenommen, ebenso die dicken Bäume und besonders das Totholz, eine Lebensgrundlage für viele Waldarten. Im Gegensatz zum Mittelland sind die Wälder der Alpen und Alpensüdseite dichter geworden, was dort zur Folge haben kann, dass licht- und wärmeliebende Arten seltener werden. Auch sind viele Waldränder noch eintönig, auch wenn dort die Gehölzartenvielfalt und in geringerem Masse auch die Strukturvielfalt zugenommen haben. Zugenommen hat die Fläche der Waldreservate auf einen Anteil von 5,8 % der Schweizer Waldfläche nach LFI-Definition. Mächtige Bäume sind dort wie auch im übrigen Wald noch immer relativ selten.

Mound-building red wood ants (Formica rufa group) fulfill keystone roles in forest ecosystems, and several species are on the red list of the International Union for Conservation of Nature. Nonetheless, detailed information on their distribution and habitat requirements is lacking, yet needed to evaluate population changes and develop conservation strategies. To assess their status in Switzerland, we studied red wood ant mounds in a nationwide, systematic survey of forests (Swiss National Forest Inventory). We identified key predictors of mound occurrence and mound size related to forest structure, forest composition, climate, and topography. Red wood ants were found to be relatively rare across Switzerland (1.4 mounds per ha of forest), especially at lower elevations (0.16 mounds per ha). Formica lugubris and F. paralugubris were common only in mountainous areas. Few F. rufa and F. polyctena mounds were found countrywide, the latter mostly at lower elevations. Formica aquilonia was restricted to the Engadine region of the Alps. Wood ants mainly depended on slope aspect, climate, forest structure, and conifer abundance, but did not depend on forest fragment size, distance to forest edges, or woody vegetation diversity. Our baseline data will enable population changes of red wood ants to be quantified, to reassess their conservation and protection status. For now, based on their observed rarity, conservation measures for red wood ants seem advisable in Switzerland. Our data suggest that red wood ants are not restricted to large, continuous, or diverse forests. Conservation strategies could thus focus on optimizing the structure of coniferous forests.

In this chapter, we discuss several types of quality assurance (QA) and quality control (QC) measures, which are described for the three main stages in the field survey in sequence. This comprises the process of aerial-image interpretation, which is crucial for ensuring the complete coverage of the Swiss forest in the field sample. We also discuss the QA activities applied during fieldwork, including the training of field teams, the maintenance of the field manual, and several organisational measures to prevent mistakes. Finally we describe the additional surveys conducted to assess the quality (reproducibility) of the field assessments in terms of precision (uncertainty) and accuracy, and summarise the quantitative results of selected attributes from the Swiss National Forest Inventory (NFI)’s repeat survey.

Repeat surveys as a quality assurance tool in the Swiss National Forest Inventory The Swiss National Forest Inventory (NFI) repeats surveys to guarantee the quality of fieldwork. To this end, approximately 10% of sample plots are completely surveyed a second time over a field season. Based on the results of the repeat survey, the current investigation focuses on the assessment precision, i.e. the reproducibility of various tree and stand attributes in NFI4. It also investigates whether the change from periodic (NFI1–NFI3) to continuous (NFI4) fieldwork has had a positive effect on the reproducibility of the attributes. The current results of the repeat surveys for NFI4 (2009/2017) are compared with those for NFI3 (2004/2006) to this end. We used statistical measures as well as measurement quality objectives (MQO) set by the NFI instructor team as a reference for evaluating reproducibility. The results vary for tree attributes which are vital for estimating stock. The result for the diameter at breast height (dbh) corresponds to the expected values, while that for upper stem diameter at seven meters height and tree height were approximately 5% below the expected values. With regard to the seven stand attributes also analyzed, four of them exceeded the quality goals (stand age, stand stability, the degree of cover of secured regeneration, and stage of development). The results for the mixture proportion, the stand structure and crown closure were between 5 and 18% below MQO. The result for presence of woody species shows that the recording of larger plants (above 130 cm) is clearly more reproducible than for smaller plants (40–130 cm). In NFI4, the reproducibility for almost all studied attributes was improved. The results suggest that the modified structure of fieldwork (with only three field teams and continuous fieldwork in NFI4) has a positive influence on the reproducibility of the included attributes.

Martijn L. Vandegehuchte, Beat Wermelinger, Marielle Fraefel, Andri Baltensweiler, Christoph Düggelin, Urs-Beat Brändli, Anne Freitag, Christian Bernasconi, Daniel Cherix, Anita C. Risch (2017): Distribution and habitat requirements of red wood ants in Switzerland: Implications for conservation. Biological Conservation 212: 366-375, DOI: 10.1016/j.biocon.2017.06.008

The results of the third National Forest Inventory indicate that shrub forest accounts for 5% of the total forest area in Switzerland. It grows almost exclusively in the subalpine zone and is dominated by the woody species Alnus viridis and Pinus mugo prostrata. As a consequence of global warming and the increasing demand for sustainable energy, there is a national and international interest to quantify wood volume and biomass in shrub forests. Therefore representative coppice shoots were measured in detail to establish allometric volume and biomass functions for Alnus viridis, Pinus mugo prostrata and Salix sp. For each coppice shoot the wood volume, the wet weight, the dry weight and the carbon mass was determined as a function of the base diameter. In the next step all coppice shoots of 49 sample plot areas were measured. A regression analysis shows the relationship between the degree of cover and wood volume, and hence the biomass, in a shrub forest stand. Shrub forest stands which consist of Alnus viridis and which have a degree of cover of 100% contain on average 74 m3/ha of above-ground wood volume. More than twice of that volume, namely 166 m3/ha, is contained in corresponding Pinus mugo prostrata shrub forest stands. In Swiss shrub forests, the average aboveground wood volume amounts to 66 m3/ha, corresponding to around 2 million tons of biomass. Based on the presented volume functions it will be possible to estimate the aboveground wood volume and biomass of shrub forest stands dominated by Alnus viridis and Pinus mugo prostrata with good results. Input variable is the degree of cover of the present woody species, which can be determined efficiently on aerial photography by image interpretation.