DIGITALNA ARHIVA ŠUMARSKOG LISTA
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ŠUMARSKI LIST 7-8/2001 str. 27 <-- 27 --> PDF |
B. Prpić: UTJECAJ VODOTEHNIČKIH ZAHVATA NA STABILNOST SASTOJINA HRASTA LUŽNJAKA ... SUMMARY: The river valleys of Croatia are home to about 200,000 ha of lowland forests with a larger or smaller proportion of pedunculate oak. In different humid sites of water valleys, pedunculate oak forms forest ecosystems in association with other plant species and the animal community. While these ecosystems differ in the composition of plant species, with a multitude of hygrophytes, their common feature is a considerable participation of pedunculate oak in the tree layer. The direct ecological factor contributing to the growth of pedunculate oak is water which, whether below the minimum or above the maximum, leads to physiological weakening, and frequently to dying of the oak. In the sites of presently stable pedunculate oak middle-aged and older stands, water relations are considered to be optimal. Among the tree species of lowland forests, pedunculate oak is one of the most sensitive. Currently, about 30 % of pedunculate oak trees are endangered in Croatia, and they will desiccate before reaching their economic maturity. Pedunculate oak is capable of surviving climatic excesses, drought and very humid years. However, hydro-technical interventions in the forested area of the valleys resulting in abrupt changes, cause its decline in all forestecosystems. CONCLUSIONS 1. Hydro-technical interventions in the woody areas of lowland forests cause changes in water relations in different sites of forest ecological systems. These changes lead to a disturbed biological balance in forests and the dieback of pedunculate oak and other tree species. The experience of the forestry profession and science is a sum total of the awareness of unfavourable effects of hydro-technical and technical interventions undertaken since the beginning of the 20"´ century up to the present day. Lowland forests represent particularly rich and complex ecological systems with high biological diversity of plant and animal species. The supply of forest trees with water, the dominant ecological factor of forest communities, is especially complex. This factor depends both on the physiological potential of the trees and river dynamics. What is particularly important are the different ways in which the peduncidate oak root systems are supplied with water in varying hydropedological soil units and in their transitions. The supply depends on the level of groundwater and its capillary movement in the ecological soil profile, which is different for almost any tree. It can be assumed with a high degree of certainty that almost every tree, and at least groups of trees, in the lowland forests of Podravina around Koprivnica and Đurđevac have their own way of supply with water, which is mainly in the form of groundwater. In order to maintain lowland forests, it is necessary to maintain the present state of water relations. 2. The 1990 Forest Act of the Republic of Croatia and a 1997 by-law estimated the biological capital of the Koprivnica-Đurđevac lowland forests, comprising both the generally beneficial functions and the raw material and energetic function, at 1,822,613,682 DM. This amount exceeds the total investment of 987,000,000 DM into the hydropower station Novo Virje. The annual increment of these forests amounts to 90,783 m\ which is 5,921,000 DM in market value. This amount does not comprise the value of subsidiary forest products (hunting, forest fruit, mushrooms, medicinal herbs and others), as well as the value of beneficial forest functions (carbon dioxide absorption, water and air cleansing, the influence of forests on the climate, maintenance of biodiversity, conservation of the genofund Šumarski list br. 5-6, CXXV (2001). 379-390 . |