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ŠUMARSKI LIST 13/2005 str. 78     <-- 78 -->        PDF

S. Husnjak. N. Pcrnar. R. Pcrnar. I. Kisić: RISK OF WATER-INDUCEU SOIL EROSION IN THE FOREST ... Šumarski list SUPLEMENT (2005). 69-77
Topic andButorac 2004) witnesses the significance
of forest vegetation in soil protection from erosion.


The same author used other interesting research results
to point at the aspects of direct anthropogenetic
impacts caused by the chosen purpose and land use
(Topic, 2000). About one million hectares forests and
forest lands of the Mediterranean and sub-Mediterranean
region are exposed to increased risk of erosion
processes, while forest fires are regularly followed by
erosion in spring and summer months.


As a rule, erosion processes occur as soil loss, i.e.
the removal of the surface humus horizon and, frequently,
the lower horizons, causing degradation, or
complete loss of the individual soil functions. The secondary
effects include increased quantity of powder
particles in canals, rivers, accumulations, and basins
such as seas and lakes, and the covering of the lower
relief locations by erosion sediments. The frequent dry
periods, the loss of forest vegetation, and the desertification
processes are connected with soil erosion, either
as potential, or actual risks (S a s s a 1998, G e e s o n et
al. 2001).


Indices of potential soil erosion risks based on common
criteria are necessary for good valorisation of forest
ecosystems at national and regional levels, and also
for creating economic guidelines according to sustainable
development.


The potential risk of water-induced soil erosion is
defined as the basic susceptibility of the soil to water-
induced soil erosion, regardless of the vegetation cover
and land use, i.e. presuming that the soil is not protected
by vegetation. This means that the estimate of the
potential risks of water-induced soil erosion is based
on the assumption that the whole research area is used
as arable land. By knowing the potential risks, it is possible
to efficiently reduce the real risks and extents of
the existing erosion processes through legal/economic
measures and spatial planning.


The permanent vegetation cover maintains the
structure and increases the water infiltration capacity
of the soil; it also stimulates the run-off of excessive
water. Permeating the soil, the root system prevents its
sudden erosion.


This paper does not deal with direct measurements
and effects of erosion. Instead, it presents the calculated
indices of the predispositions to erosion on the
whole forest area of Croatia.


The first part of the paper presents the estimates of
the potential water-induced risks of soil erosion. The
second suggests the possibilities of applying the model
to the improved estimates of erosion risks.


METHODS


A digital map of potential erosion risks to a scale of
1:300,000 (Husnjak, 2000)3 was used in the research.


The map of the texture, depth and stone contents of
the soil was made according to the data of the mapped
soil units from the Basic pedological map of the Republic
of Croatia, scale 1:50,000, based on the soil texture
data of the dominant systematic soil unit within the
individual cartographic unit of the Practical pedological
map of the Republic of Croatia, scale 1:300,000, as
well as by using the database composed of 1,088 representative
pedological profiles made especially for the
water-induced soil erosion risk estimates. The Soil
erodibility map was made by using the calculated erodibility
index made by the method of integrating the
maps with the classes of texture, depth, and stone contents
of the soil.


The index of precipitation variability was determined
according to the modified Fournier index (FI),
while the aridity index was made on the basis of the
Bagnouls-Gaussen Index (BGI), both for seventy climatologic
stations. According to the mentioned indi


´ The detailed map-making methodology is already presented in
the quoted study, so that we bring it here in a summarised form.


ccs, wc made maps of precipitation variability and climatic
aridity, the integration of which was used with
the index calculation to make the Map of precipitation
erosiveness.


Map of terrain inclination was made by using the
contour lines with an equidistance of 50 m.


Map of potential threat of water-induced soil
erosion was then made by integrating the maps of soil
erodibility classes, precipitation erosiveness, and terrain
inclination, with the calculation of the potential
risk index.


The estimate of the potential water-induced soil
erosion risk was determined for the whole territory of
the Republic of Croatia, according to the programme
CORINE (Coordination of Information on the Environment).
This is a qualitative cartographic method based
on overlapping the individual thematic maps according
to the following scheme:


By overlapping this map with the map of forest distribution
(Husnjak, 1999) the map of potential erosion
risks was made for the forest ecosystem areas in Croatia.
The overlapping and later area inventory were carried
out by using the GIS tools NT Arc Info programme
package.