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The Swiss National Forest Inventory dataset «Forest Access Roads 2013» Information on forest accessibility is important for forest management. For example, it helps to determine the potential wood supply and identify areas difficult to access. In 2013–2014, a survey was conducted in Switzerland to update the Forest Access Roads geo-dataset within the framework of the Swiss National Forest Inventory (NFI). The resulting nationwide dataset contains valuable information on truck-accessible forest roads that can be used to transport wood. The survey involved interviewing staff from the approximately 800 local forest services in Switzerland and recording the data first on paper maps and then in digitized form. The data in the NFI on the forest roads could thus be updated and additional information regarding their trafficability for specific categories of truck included. The information has now been attached to the geometries of the Roads and Tracks of the swissTLM3D (release 2012) of the Federal Office of Topography swisstopo. The resulting data are suitable for statistical analyses and modeling, but further (labour-intensive) validation work would be necessary if they are to be used as a basis for applications requiring more spatial accuracy, such as navigation systems. The data are managed at the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and are available for third parties for non-commercial use provided they have purchased a TLM license. In this article, the dataset, as well as its acquisition and potential uses, are described.

Development of tree species in Swiss forests – some methodological considerations Swiss forests have been subject to more stress in recent decades due to increased climatic and biogenic disturbances. Some tree species, such as Norway spruce, have been more severely affected than others. How the tree species composition of the Swiss forest has changed during this time has been assessed with data from the Swiss National Forest Inventory (NFI). The four indicators, presence, dominance, number of stems and basal area, were examined to see: whether the changes in the most important tree species are significant; whether the indicators have developed in the same way in the two diameter classes, D1 (12–36 cm DBH) and D2 (> 36 cm DBH); and how different diameter thresholds (12 or 36 cm DBH) and different circular sample plot sizes (200 m2 or 500 m2) affect the development and significance of the indicators. All the values were estimated for the 5370 NFI forest plots that were accessible in all three inventories, NFI1 (1983–85), NFI2 (1993–95) and NFI3 (2004–06). Only in a minority of tree species did changes in the presence, dominance, number of stems and basal area develop in the same way. Most indicators for the conifer species spruce, fir and pine decreased significantly, whereas for the broadleaf species, maple and ash, as well as larch and the other conifers, they increased significantly. The basal area increased during the period investigated for all tree species except pine and spruce. The different development of the indicators number of stems and basal area can be attributed to a different development within the DBH classes D1 and D2. The inventory diameter threshold strongly affects the development of the indicator number of stems, but not that of the indicator basal area.