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Dendroecological analysis of the influence of strong winds and snow accumulation on the growth of trees at the treeline in Vitosha Mountain, Bulgaria

Momchil Panayotov, Steffan Yurukov
University of Forestry, Sofia, Bulgaria
Correspondent e-mail: panayotov.m@ltu.bg

As in other parts of Europe, the treeline position in the Bulgarian mountains has been affected by human action in the past. In certain regions like the highest parts of Vitosha Mountain overuse and fires have destroyed a big part of the coniferous forests. In the 40-s of the 20-th century their restoration has been started by afforestations. The forest authorities have taken the decision to use tree species that were found elsewhere at the Bulgarian subalpine forests - Macedonian pine (Pinus peuce Griseb.), Bosnian pine (Pinus heldreichii Christ), Norway spruce (Picea abies Karst.), Scots pine (Pinus sylvestris L.) and the shrub form of Mountain pine (Pinus mugo Turra ssp. mugo).
At the present moment the state of the trees from those species allows the studying of the differences in their resistibility to limiting factors at the treeline. Since the afforestations in Vitosha Mountain have been made below the potential thermal treeline, the most important limiting factors here are the influence of strong winds and accumulation of big quantities of snow due to wind transportation.
Tree test sites have been chosen in Pinus peuce forests with the aim to collect samples for dendroecological analysis. The sites have been separated in two categories - affected by strong winds and accumulation of big quantities of snow and unaffected.
At the affected sites trees have been separated in categories according to their stem and crown state.
By the means of dendroecological techniques have been compared the growth of trees in affected and unaffected sites, the years in which trees were damaged and the reactions in the wood after such events.
The results from the analysis show that major impact on growth of the trees in the region have stem deformations and damages, caused by accumulation of big quantities of snow and rhyme. Strong winds occasionally break the last several years of vertical increment of the trees, which are situated at the borders of the forest stands. Trees with broken tops do not show serious decrease in radial growth.

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