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ŠUMARSKI LIST 11-12/2006 str. 17     <-- 17 -->        PDF

J. Vukelić, D. Baričević, Z. List, M. Šango: PRILOG FITOCENOLOŠKIM ISTRAŽIVANJIMA ŠUMA ... Šumarski list br. 11–12, CXXX (2006), 479-492
It is classified into three subassociations: iridetosum pseudacori occurring in
the wettest sites, where alder forms high cones surrounded with water almost
throughout the year, polygonetosum hydropiperis growing in wet soils with a
highly developed humus layer, and cornetosum sanguineae growing in relatively
drier soils in progression. The floral composition of the community is
given in Table 1, which contains 7 of our own relevés and 13 relevés by Glavač
from 1960 showing a degree of participation.

According to the research, the range of the forest Carici elongatae-Alnetum
glutinosae has decreased manifoldly. Only some fragments have remained
in water-covered depressions smaller than half a hectare from which water
cannot escape. A comparison of the community’s floral composition some
fifty years ago and today (Table 1) reveals changes not only in the size of the
area but also in the composition of the plant species. There are fewer hygrophytes
and species of swampy depressions with long-lasting stagnant water,
such as Carex elongata, Poa palustris, Lythrum salicaria, Valeriana dioica,
Rorippa amphibia, Calystegia sepium, Mentha aquatica, Carex vesicaria, and
Glyceria fluitans, whereas some species, e.g. Spiraea salicifolia, have already
disappeared. The natural syndynamic development has also stopped, so that
only a subassociation with Iris pseudacorus can currently be identified. The
other stands have already been converted to Pruno-Fraxinetum.

The forest of common alder and narrow-leaved ash with birdcherry
(Pruno-Fraxinetum Oberdorfer 1953) is formed by the succession from the
previous association. It grows on drier and elevated terrains. It belongs to the
order Fagetalia due to the lack of hygrophytes and the prevalence of mezophilic
species. The floral composition of the community is given in Table 2. The
first column shows 15 relevés by Glavač and the second 19 relevés from this

A comparison of the phytocoenological relevés shows an increased proportion
of mezophilic species and an absence or a reduced number of the species
that indicate swampy and very wet forests. The species occurring less frequently
are Galium palustre, Ranunculus repens, Lycopus europaeus, Poa trivialis,
Valeriana dioica, and Potentilla reptans, while on the other hand Sambucus
nigra, Corylus avellana, Prunus padus, Mercurialis perennis, Paris
quadrifolia, Anemone nemorosa, Leucojum vernum, Galeobdolon luteum
and Lamium purpureum have grown in number. Some particular sites currently
feature Acer pseudoplatanus and Daphne mezereum, species that are not
typical for the lowland area of Croatia. In the past fifty years, the area under
these associations has increased considerably.

The name and the description of the association originate in Central Europe,
where these stands contain Fraxinus excelsior instead of Fraxinus angustifolia.
For reasons of this and other differences, this community must be analyzed
in detailed and compared with the Central European community. Its position
in the phytocoenological nomenclature and systematics must also be determined.

Changes in the stands of common alder occurring in the past fifty years
are primarily the consequence of the synergy of altered ecological factors and
anthropogenic factors, i.e. stand management. Although the groundwater levels
in the forest stands being investigated are still relatively favourable (Fig.
3), the newly built hydropower stations in Slovenia and Croatia have generally
altered the water regime. The main problem facing the remaining wet areas
of the river Drava in Slovenia and Croatia is the low water level amounting
to only 2.4 % of the average water flow. Additional problems include significant
oscillations of the river and the erosion of the riverbed. In the past
100 years the water surface area has decreased by 65 %, whereas open sites