engleski

Windthrow resistance of Norway spruce (Picea abies /L./ Karst.) stands - preliminary results

Background and Purpose: Forest damage by wind is an important cause of economic loss in commercial forestry for the Republic of Croatia as well as for many European countries. Thus, mechanical resistence of trees represents a significant issue. Antropogenic spruce cultures showed the lowest resistance to windthrow by now. Nevertheless, there is a weak insight into relatioships of tree and stand resistance to winds in the region. Objectives of the paper are to: (i) provide first evidence of relation between tree characteristics prior to storm event in completely destroyed in comparison to slightly damaged stands, (ii) to evaluate the need to consider tree resistance to winds during thinnings, (iii) to evaluate if there is a need for mechanical stability assessment prior to replacement interventions. Materials and Methods: Paper investigates three individual cases of antropogenic spruce stands on three localities in the hilly part of Central Croatia in the fifth decade of age. Two were completely destroyed by the storm event during the year 2013. The experiment was established in the spring of 2010 using a completely randomised block design with three replications. Based on total tree height (H) and diameter at breast height (DBH) we calculated wood volume (V), basal area (B) and slenderness coefficient. Descriptive statistics and correlation analysis were made in STATISTICA 8.2. Results: Results show overstocking, unfavourable structure and slenderness coefficients (> 80 : 1) in both cultures which were completely blown down. The correlation among variables revealed the significant relationship for all localities (p< 0.05) when slenderness coefficient was compared with B and V (negative), but no correlation with H. Conclusions: Research supported the claim that slenderness coefficient and stand structural analysis can be good predictors of damages caused by wind. In respect to forthcoming increase of frequency and severity of storm events we propose to take evaluation of mechanical resistance of trees to wind into consideration prior to all silvicultural activities (especially high intensity interventions such as replacement/regeneration). Improved mechanical stability of trees against wind should be silvicultural goal already from the first thinning (higher intensity thinnings from below), while in the case of unstable stands canopy cover should be opened cautiously to provide remaining trees opportunity to slowly respond to space increase. It should be noted that these initial findings should be supported by the more extensive research in the future.

general stability, conversion, silvicultural guidance, thinning, afforestation

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