Search

Due to the scarcity of old-growth forests in much of Europe, there is little quantitative information on disturb- ance processes that influence forest dynamics. However, this information is crucial for forest management that tries to em- ulate patterns and processes in natural forests. We quantified the gap disturbance regime in an old-growth forest dominated by European beech (Fagus sylvatica L.) and silver fir (Abies alba Miller) in the Dinaric Mountains of Bosnia and Herzegovina. We sampled 87 gaps in four stands using line-intercept sampling. The percentages of forest area in can- opy gaps and expanded gaps ranged from 12% to 17.2% and 35.5% to 39.7%, respectively. Although many of the gaps were small ( 1000 m 2 with numerous gapmakers made up a disproportionate amount of the total gap area. More than half the gaps had more than one gapmaker and were often in separate decay classes, indicating gaps had expanded over time during separate disturbance events. Furthermore, 51% of all gapmakers were uprooted or wind-snapped, whereas only 22% died standing. These results suggest that wind disturbance plays an important role in creating intermediate to large canopy openings through both gap formation and gap expansion processes. Resume´ : En raison de la raretedes vieilles forets dans une grande partie de l'Europe, il y a peu d'information quantita- tive sur les processus de perturbation qui influencent la dynamique forestiere. Cependant, cette information est fondamen- tale pour un amenagement forestier qui tente de reproduire les patrons et les processus des forets naturelles. Nous avons quantifiele regime de perturbation par trouees dans une vieille foret dominee par l'hetre commun (Fagus sylvatica L.) et le sapin argente´ (Abies alba Miller) dans les montagnes Dinariques de Bosnie-Herzegovine. Nous avons echantillonne´ 87 trouees situees dans quatre peuplements en utilisant un echantillonnage par transects d'interception lineaire. Le pourcent- age du territoire forestier occupepar des trouees et par des trouees etendues variait respectivement de 12 a 17,2% et de 35,5% a 39,7%. Meme si plusieurs trouees etaient petites (

We studied the immediate effects of two successive storms in 1983 and 2004 in an old-growth Fagus sylvatica L. – Abies alba Mill. forest in the Dinaric Alps, southeastern Slovenia. In the 1983 and 2004 storms the density and basal area of wind-killed trees were 27.4·ha–1 and 5.98 m2·ha–1 and 11.2·ha–1and 4.02 m2·ha–1, respectively. In both storm events, mid-sized to large stems were more prone to wind mortality than small stems, and A. alba was more susceptible than F. sylvatica. In the 2004 storm, 70% of wind-killed trees were uprooted and 30% were snapped. Tree size (diameter at breast height) was more important than species in determining damage type, smaller stems being more prone to uprooting and larger stems to snapping. The combined mortality due to the two storms was similar to a decade of baseline mortality, and wind-killed trees were larger than trees that died from background mortality processes. In both storms, wind-killed trees had a clumped spatial distribution, which resulted in the formation of many multiple-tree-fall gaps up to 1500 m2 in size. We suggest that intermediate wind disturbance occurs at time intervals similar to or less than the life expectancy of most canopy tree species in central Europe, and may play a more important role in forest dynamics than previously thought.