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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


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