Von wegen tot: Leben im Totholz ¶

• The deadwood volume across Switzerland has increased to 32 cubic metres per hectare in the past decade, meaning that this forest policy objective has been achieved in most regions. On the Plateau, however, there is less than 20 cubic metres of deadwood per hectare in some regions.
• Both values are sufficient only for species with low deadwood requirements. Old trees with a wide variety of microhabitats and large-diameter deadwood are still too scarce. Measures are needed to promote large-diameter deadwood and old trees that complete their entire life cycle.
• The growing demand for wood could jeopardise the positive trend towards higher deadwood volumes.

• Das Totholzvolumen hat sich in der letzten Dekade schweizweit auf 32 Kubikmeter pro Hektare erhöht.  Somit ist dieses waldpolitische Ziel in den meisten Regionen erreicht. Im Mittelland gibt es aber in gewissen Regionen weniger als 20 Kubikmeter Totholz pro Hektare.
• Beide Werte reichen nur für Arten mit niedrigen Totholzansprüchen aus. Alte Bäume mit grosser Vielfalt an Mikrohabitaten und dickes Totholz sind noch zu selten. Es besteht ein Bedarf an Massnahmen zur Förderung von dickem Totholz und alten Bäumen, die den vollständigen Lebenszyklus durchlaufen.
• Die steigende Nachfrage nach Holz könnte den positiven Trend zu höheren Totholzvolumen gefährden.

Von wegen tot! Nichts ist lebendiger als Totholz. Kaum ist ein Baum abgestorben, beginnt sein Abbau. Dabei wirken Insekten, Pilze und Bodenlebewesen in vielfältiger Weise zusammen.

Background: Gradients in local environmental characteristics may favour the abundance of species with particular traits, while other species decline, or favour species with different traits at the same time, without an increase in average species abundances. Therefore, we asked: do variations in species and traits differ along gradients of deadwood variables? Do species abundance and trait occurrence change with species richness within or between functional groups? Thus, we analysed the beetle assemblages of five forest sites located in Italy, along the Apennines mountains.
Methods: From 2012 to 2018 we sampled beetles and five deadwood types in 193 plots to characterise the deadwood gradient: standing dead trees, snags, dead downed trees, coarse woody debris, and stumps. We modelled beetle species relative abundances and trophic traits occurrences against the deadwood variables using joint species distribution models.
Results: Out of 462 species, only 77 showed significant responses to at least one deadwood type, with a weak mean response across species. Trophic groups showed mostly negative responses to deadwood variables. Species abundance increased with species richness among sites only for phytophagous and saproxylophagous. Trait occurrence did not increase with species richness among sites, except for phytophagous and saproxylophagous. However, trait occurrence changed significantly with species richness of several trophic groups within some sites. We found that increases in species richness do not result in decreases in species abundance of a given trophic group, but rather null or positive relationships were found suggesting low interspecific competition.
Conclusions: Our findings suggest that in Mediterranean mountain forests there is still room for increasing the level of naturalness, at least for what concerns deadwood management. On one side, our findings suggest that competition for deadwood substrates is still low, on the other side they indicate that increasing deadwood volume and types to improve overall beetle richness may increase also beetle abundances.

Totholz erscheint in ästhetisch kunstvollen Skulpturen, ist Lebensraum, Nahrungsquelle, Keimbett, Sinnbild für Werden und Vergehen, Steinschlagschutz, Brennholz. Totholz ist vielgestaltig und alles andere als tot. Tausende von Tieren, Pflanzen und Pilzen leben von toten Bäumen.