Nature-Near Forest Management and its Effects on the Forest Ecosystem: Conversion from Age Class Systems to Selective Harvesting Systems under Mountainous Conditions

Forestry "near to nature" (by structure and texture) is, generally valued as a possibility to sustain the forests´ natural stability and resilience by only minor silvicultural operations. This shall also better correspond to a broadened understanding of "sustainability" - like defined in Rio or Helsinki.

Such a naturalness is understood as an appropriate tree species mixture (site-corresponding), oriented largely on the "potentially natural forest ecosystems" (in German: potentiell natürliche Waldgesellschaft PNWG). But nature-near forestry is understood also as an economic harvesting (and rejuvenation) strategy which fullfills (on the stand or even property scale) sustainability criteria through abandonment of the (still prevalent) clear-cutting system and instead a far-reaching selective cutting of single (for instance target-sized) stems or small groups of stems (cf. irregular shelterwood system; group selection felling; selection thinning/ preharvest o. o. - cf. in German: "Schirmschlag", "Plentern", "Femeln"). One version in this context is a permanent forest, or "Dauerwald", which does not include major rejuvenation or reforestation areas but consists of a permanent forest cover of elder ages in the leading stand trees. A research programme at BOKU was initiated in the Hebalm area (in southern Austria) which shall be visited on 8th Sept. and where the conversion issues shall be demonstrated and discussed in some detail.

This research programme was a multidisciplinary one, focussing on aspects of forest ecology and silviculture, of forest yield and tree growth (as a basis for nutrients cycle conclusions), on technical aspects of harvesting and its economic assessment for both the forestry alternatives, and also on socio-economic considerations/ expectations of involved forestry enterprises towards a more "natural" forestry. The final goal of the project was to define an operational framework for implementing the planning and control efforts for those forestry enterprises which are already active in permanent forestry management, or try to convert to it.

This study came to the following conclusions:

• The studied permanent forest enterprise resulted - in comparison to the clear cut/ age class forest area - in economic advantages while positive ecological effects were rather overrated. Only structural diversity is more pronounced (cf. bhd-distribution and height differentiation).
• Nitrogen loss differences appear not very pronounced and its amounts likewise high.
• Harvesting impacts on and damages of the natural rejuvenation are of such a magnitude that sufficient rejuvenation remains undamaged. Damages to the remaining old trees as well as to the soil conditions were comparatively low or modest. (The use of a forwarder could reduce these damages further).
• Annual yields in shelterwood or selective felling systems were superior (ca. 1,5 x) to the clear-cut system. Investigations as well as interviews agree that in a permanent forest higher yields and lower operative costs are to be expected.

Excursion Programme "Hebalm" (8th Sept)

Forest owner: Malteser Ritter-Orden
Montane forests of ca. 1600 ha in size

Silvicultural field trip/schedule:

• basics of the Hebalm-Forest ·
• reasons and motivation for a change in the silvicultural system
•  

  requirements

  for age class system

  for selective cutting system

• clearcut versus selective cutting - an interdisciplinary study (Bodenkultur, 1999, see above)
  visit of some of the research plots
  results of the study: growth and yield economics
• marking practice for different silvicultural systems at study sites of
  thinning phase
  regeneration phase
  (the course participants will work in small groups)
• final discussion and summary