Development of tree species in Swiss forests - some methological considerations
2011
Duc, Ph. | Brändli, U.-B. | Cioldi, F. | Lanz, A. | Ulmer, U., Eidgenoessische Forschungsanstalt für Wald, Schnee und Landschaft WSL, Birmensdorf (Switzerland)
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.
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