Tree regeneration in a Norway spruce snag stand after tree die-back caused by Ips typographus

In a managed Picea abies mountain forest on Gandberg (northern Swiss Pre-Alps), almost all trees were killed by a European spruce bark beetle outbreak in 1993 and left unharvested. As we assumed the large amount of bark litter would have a negative effect on tree regeneration, we investigated natural tree regeneration in 12 permanent plots after bark removal and in 12 control plots with a bark cover of 50%. In half of the plots, 200 Picea abies seeds were sown per plot in 1995. No advance tree regeneration was present. Three Picea abies seedlings m -2 germinated naturally in 1994. 3.8% of the 2400 sown Picea seeds germinated in 1995, resulting in 7.5 seedlings m -2 , with equal numbers in plots with and without bark litter. We assume pieces of bark to have no effect on Picea germination. The mortality of naturally germinated Picea was 25% each year, regardless the age of the saplings (1–7 year). Acer pseudoplatanus saplings were almost as numerous as Picea (0.58 m -2 ) in 2001, but pioneer trees such as Betula pendula (0.29 m -2 ), Sorbus aucuparia (0.16 m -2 ) and Salix caprea (0.04 m -2 ) were rare. These low numbers together with extensive ungulate browsing indicate it is unlikely that a closed pioneer or Acer stand will be formed. We anticipate that a Picea forest will replace the current Rubus idaeus-association on the Gandberg.

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