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ŠUMARSKI LIST 13/2005 str. 51     <-- 51 -->        PDF

V. Topic. L. Butorac: THE IMPACT OF SCRUB VEGETATION OF ORIENTAL HORNBEAM ... Šumarski list - SUPLEMKNT (2005). 40-50
The soil is predominantly covered with scrub vegetation
of oriental hornbeam, which protects it from
further aquatic and eolian erosion. The rock and stone
coverage analysis in the sample plots showed that 50 to
70 % of the plots were covered with rocks (Figure 4).


The rocks are generally vertical and sloping, while
the cracks are filled with soil suitable for the establishment
of forest trees. The depth of the humus-accumulative
horizon below the scrub varies from 1 to 10
cm. Above the Amo horizon there are 1 to 2-cm thick
Ol and Of sub-horizons. The dry, fallen leaves of the


Surface runoff and soil
The erosive action of precipitation was monitored in
the oriental hornbeam scrub in sample plots Bft and B7
during the period 1999 - 2003. The annual precipitation
quantities in the investigated plots varied from 1,115.4
to 1,422.1 mm, while the mean annual value amounted
to 1,269.2 mm. Runoff and soil losses were caused by
rainfall from 8.9 to 90.0 mm. Of a total of 471 rainy
days, there were 100 erodible days with runoff precipitation.
Data of mean monthly rainfall values and runoff
in plots B6 and B7 for the period 2002 - 2003 are shown
in Figure 1.
It can be concluded from the above data that the
mean monthly surface runoff values are within the
following limits: in plot B6 they vary from 0.08 to


5.86 mm/m2, and in plot B7 from 0.5 to 5.25 mm/m2.
The mean annual surface runoff values are as follows:
in plot B6 with the removed white hornbeam scrub and
with the completely preserved humus-accumulative
horizon - 24.03 mm/m2 (240.3 m3/ha) with the runoff
coefficient of 0.0192; in plot B7 with the preserved oriental
hornbeam scrub - 19.53 mm/m2, (195.3 mVha),
with the runoff coefficient of 0.0156. The maximal surface
runoff coefficient in sample plot B6 is 0.075 and in
sample plot B7 it is 0.0295.
The data indicate that the surface runoff percentage
in the sample plots is low and that interception, evaporation
and water infiltration in the soil amounts to as much
as 98.8 % annually in the oriental hornbeam scrub with


61.14 % of ground cover at an inclination of 26°.
The value of mean monthly soil losses is given in
Figure 2.


The effects of oriental hornbeam scrub on soil protection
against erosion were monitored over a period of
five years. Research was conducted on sample plots B6
and B7 established on the slopes of Moseć near Muć.
All important erosion parameters were observed. The
following may be concluded on the basis of the obtained
results:


oriental hornbeam scrub are evenly distributed below
the crowns (Figure 3). At the moment of plot establishment
the quantity of the forest cover (leaf litter)
ranged from 1.27 to 10.5 t/ha. The weight of the leaf
litter sample at the moment of taking was over 4 times
higher than after it was dried at 105 °C. This is a proof
of the ability of leaf litter to absorb large amounts of
water. In this way, leaf litter not only accumulates atmospheric
waters that reach it, but also regulates their
runoff. All this plays a very significant role in erosion
prevention, particularly on karst.


loss in the sample plots
The erosion losses (the quantity of dry mud removed
from the plots into the collector) range from zero
in March to 0.0014 t/ha in August for plot B6, and from
zero in March to 0.0011 t/ha in August for plot B7. The
mean annual soil loss values in the plots with oriental
hornbeam scrub for the period 2002 - 2003 are as follows:
in plot B6 it is 0.0072 t/ha, and in plot B7 with the
preserved oriental hornbeam scrub it is 0.0056 t/ha.


Table 1 shows surface runoff and soil losses in oriental
hornbeam scrubs per erodible days.


As seen from Table 1, in the year 2003 erosion
occurred 15 times. The highest values of surface runoff
and soil loss were recorded on 4th July and 2n November.
The rain that fell on 4th July had very high intensity
of 50.7 mm/30´ and lasted for 040 hours (from 940
to 1020). Under the protection of oriental hornbeam
scrub, surface runoff in sample plot B7 was 1.50 mm/m
and soil loss was 0.00041 t/ha. The highest amounts of
precipitation in 2003 and the highest surface runoff


(7.34 mm/m2) and soil losses (0.00090 t/ha) were
recorded on 2nd November (a total of 90.0 mm/m2).
The rain, falling for 7 hours, had high intensity of
11.87 mm/hour and very high intensity of 27.6 mm/hour
from 2120 to000 hours.
To sum up, according to the Table, the total soil losses
in sample plots B6 and B7 in the year 2003 were
0.00661 and 0.00446 t/ha respectively, which is below
tolerant annual loss. However, if the soil in sample plot
B6 continues to be without the vegetation cover, the risk
of erosion will be extremely high or even catastrophic.


Oriental hornbeam scrub in the sub-Mediterranean
karst area of Croatia has a very important and distinctly
positive role in protecting the soil against erosion. Surface
runoff under the studied scrub was low and erosion
was excluded.