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ŠUMARSKI LIST 13/2005 str. 79     <-- 79 -->        PDF

S. Husnjak. N. Pernar, R. Pernar, 1. Kisić: RISK OF WATER-INDUCED SOIL EROSION IN THE FOREST ... Šumarski list - SUPLEMENT (2005). 69-77
RESULTS AND DISCUSSION


The potential risks of soil erosion is defined as the
basic susceptibility of the soil to water-induced erosion
in a given constellation of pedogenic factors, regardless
of the vegetation cover and land use. The potential
risk is the worst possible case, where the estimate of
the potential risk of water-induced erosion is based on
the assumption that the whole research area has no vegetation
cover. Under such presumption, the crucial
factors are soil erodibility, precipitation erosiveness,
and terrain inclination. By overlapping the thematic
maps of these factors within the space of forest ecosystems
(Figure 1), we developed a map the areas of
which were indexed in relation to the potential risks of
erosion processes (Figure 2).


This research revealed that under such presumptions


44.8 % of forest ecosystems in Croatia would be exposed
to high potential risks of erosion, while 26.5 % of
the area would be exposed to moderate risks (Table 1).
The lowland areas and those with mild inclinations
belong to the low risk class. Even on such areas, where
there is no vegetation, some erosion processes take place,
primarily as torrential or splash erosion caused by
the effect of "bombing" or "shattering" the soil by raindrops.
Such processes are slow and difficult to recognise.
Over the slopes with higher inclination than 3 %,
where the soil is "naked", sheet erosion takes place.


The total forest area with high and moderate erosion
risk amounts to 1,677,070 ha, or 71.3 %, indicating
a high potential threat of water-induced soil erosion
and the great significance of stable forest ecosystems
for sustainable management, particularly related
to agriculture and water management.


Considering that soil is a conditionally renewable
nature´s asset, and also a significant natural resource,


any exploitation of forests aimed at their reduction leads
to intensified runoffs and potential erosion processes.
Today we witness massive encroachments on the
forest, either by opening the corridors for roads,
oil/gas/electric lines, or the mineral raw material mines.
The supervision of the design, construction and
manangement of such developments should be carried
out by applying high security factors, because erosion
processes occur to various extents, intensities and degrees
of recognition. Soil protection is an imperative
with any modern project made for terrestrial ecosystems.
We should bear in mind what Gračanin said:
"Croatian soils are the greatest national riches. To
know them means to understand the foundations on
which Croatia lies". The land use and the responsibility
of land management are most drastically illustrated by
the Mediterranean region (K o s m a s etal. 2002), with
the forest fires the high frequency of which corresponds
with irresponsible management methods (neglected
areas with dominant weed vegetation and unorganised
watch-information service) and inadequate
ways of land use.


The frequent fires are the objects of some methodological
issues related to this research. The factor of the
most destructive erosion processes on the Mediterranean
forest areas, fire should be included into the model
of estimating the real erosion risk. In addition, sustainable
management should be supported by developing
a map of potential erosion risks, based on updated and
high-resolution data on the ways of land use and land
cover. The map of land cover should include the attributes
of the CORINE Land Cover programme. On the
other hand, the application of the model to the Mediterranean
and sub-Mediterranean areas presumes the assessment
of both potential and real risks of erosion.


CONCLUSION


Croatian forest ecosystems arc mainly limited to the
areas of moderate to high degrees of erodibility according
to soil properties and relief/climate characteristics.
The research has shown that 71 % of the forest
ecosystem area is exposed to moderate and potentially
high erosion risk. This requires more careful valorisation
of forest ecosystems as priceless natural assets, indispensable
for sustainable management of the whole


Croatian territory, and the application of this model at
regional level. Considering that the 90 % of the karst
area is under potential erosion risk, this region should
be regarded as a priority in the process of developing
the updated high-resolution data on the land cover. The
Mediterranean and sub-Mediterranean regions should
be treated in relation to forest fires and their estimated
characteristics.