Regeneration of Picea abies in high-elevation mountain forests often depends on the presence of coarse woody debris (CWD), as logs provide sites with more favorable conditions for spruce regeneration compared to the forest floor. However, there is little quantitative knowledge on the factors that are conducive to or hindering spruce establishment on CWD. We examined spruce regeneration on CWD by sampling 303 plots (50 cm × 50 cm each) on 56 downed logs in a virgin forest in the Swiss Alps. Variables describing microsite conditions were measured, and fungi were isolated from wood samples. To investigate the relationship between the ecological factors and establishment success, two models were fitted with seedling and sapling density as response variables, respectively. Besides log diameter, the models identified different ecological factors as significant for seedling and sapling establishment, i.e., regeneration depends on different factors in different development stages. Seedling density depended on the type of rot, log inclination, and decay stage. Sapling density depended mainly on light availability, cover by bark and moss, the time of tree fall, and the distance between the log surface and the forest floor. A total of 22 polypore fungi were isolated from the wood samples, four of them being threatened species. White-and brown-rot fungi were found in all decay stages. The visual assessment of the type of rot in the field corresponded in only 15% of cases to the type of rot caused by the isolated fungi; hence caution is needed when making field assessments of rot types.
Which factors determine regeneration on nurse logs in the Scatlè virgin forest? Harsh environmental conditions in subalpine forests render Norway spruce regeneration difficult, limiting germination and establishment to a few microsites such as decaying logs. In 2002, spruce regeneration was studied on coarse woody debris (CWD) in the Swiss virgin forest Scatlè. In 2012, regeneration status and the factors characterizing environmental conditions were re-assessed. The statistical model that had been parameterized with the 2002 data also performed well with the explanatory variables measured in 2012, indicating that regeneration on CWD is a non-random, complex process resulting from the interaction of several ecological factors. A 5.5-fold increase of regeneration density was observed over the past ten years, which is most likely attributable to a higher abundance of suitable microsites on CWD: 1) an increase of moderately and strongly decayed wood, 2) average sunshine duration in June of 50 to 120 minutes per day, 3) a decrease of the plot-to-ground distance with little competition by the surrounding ground vegetation, 4) an increase of the thickness of moss cover. The mast years of 2009 and 2011 certainly were influential for the increase of regeneration density. Establishment of regeneration may start as early as six years after tree death, but logs older than 23 years were most suitable. Natural regeneration on rotten wood thus is a slow and long-lasting process, and the sustainability of regeneration requires a continuous supply of dead wood of different decay stages. Besides the important role of dead and dying trees for spruce regeneration, we also found an important role of CWD for biodiversity, as fifteen species of decay fungi were detected, two of them having the status of endangered species.
How light emissions have been lighting up the Swiss forest since 1992 Light emissions increasingly light up the night sky. Worldwide and in Switzerland, there has been a marked increase over the last 20 to 30 years. This is problematic for biological-ecological and health reasons as well as for cultural reasons. At federal and cantonal level, there are various laws and technical standards governing light emissions. In order to monitor the success of these regulations, it is important to observe night-time brightness over longer periods and within larger areas. In Switzerland, this is done within the framework of the Swiss Landscape Observatory (LABES), which provides time series for night-time observations for the years 1992 to 2012. The present work uses satellite images to investigate the extent to which the Swiss forests are lighted up by nocturnal emissions from surrounding residential areas and infrastructures. It also examines the differences between the forest and open land (meadows, fields and remote areas far away from settlements above the treeline) and how the forested area without any detectable artificial light developed between 1992 and 2012. It is shown that the Swiss forests are more and more lighted up by surrounding light sources. With the exception of the Jura, night-time brightness in forest areas is even higher than in open land, which in the present study is dominated by areas above the treeline. The results can be explained by the relative proximity of the forest to residential areas. On the Plateau the last patch of forest without any detectable artificial light during the night disappeared in 2001, and in the Jura mountains in 2010: in the Alps there are still between 4% (Western Central Alps) and 16% (Southern Alps) forest areas without any detectable artificial light during night time. The last large dark areas are, however, not found in the forested area, but in the areas above the treeline. They should be given adequate protection against illumination, for example with large protection areas (“dark sky parks”).
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