Long live the forest and all its dead – Succession phases and mortality indices in Austria’s Natural Forest Reserves

89-93

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200210754

Protected Areas facing the Biodiversity Crisis: Conference Volume to the 7th International Symposium for Research in Protected Areas (2022) , 89-93

The natural amount of dead wood in a forest ecosystem is one of the major topics of discussion when it comes to questions concerning the naturalness of forests and sustainable forest management. Especially the time horizon of its dynamics and the corresponding forest succession phase in different forest communities are hard to target in Europe, where large-scale natural forest development is rare. For those specific questions the Natural Forests Reserves (NFR) in Austria can be used as important reference areas. Latest research results deliver information on NFR in different sites and succession phases regarding their stand structure, vegetation types and their dynamics on deadwood enrichment and living wood increment over a long observation period. 80 repeated surveys over around 25 years in 22 different forest communities in Austria show a differentiated picture on the mortality rates in unmanaged forests. An index based on deadwood amounts and volume increment of living trees shows whether the stand is in a phase of accumulation or decomposition of wood biomass or in equilibrium. We assume that this increment-mortality-index (IMI) allows conclusions on the succession phase and thus on stand maturity. A large proportion of the forest association groups investigated in the reserves are in an accumulation phase, where the increment is higher than the mortality rate. It seems like poor and dry sites with permanent associations (e.g. oak-forests) are more likely to be in a decomposition phase since increment is low. We can confirm that the IMI decreases with increasing stand age as one would expect. Furthermore, there is a recognizable trend for differentmanagement intensities at least in oak-hornbeamforests: after former coppice use the recovery time is higher than in forests which have been more intensive managed (e.g. clear cuts). Still there is a need for a larger number of old NFR with longer time since abandonment to generate more data and reliable results on different forest communities.
Keywords: Deadwood, Natural Forest Reserves, Forest communities, Increment Mortality Index