EFFECTS OF FOREST AND GRASSLAND VEGETATION ON SOIL HYDROLOGY IN MÁTRA
MOUNTAINS (HUNGARY)
Andrea Hagyó1, Zoltán Nagy2, Kálmán Rajkai1
1Research
Institute for Soil Science and Agricultural Chemistry of HAS, Hungary, H-1022, Budapest,
Herman O.u.15. ahagyo@rissac.hu
2 Szent István University, Department Botany and Plant Physiology, Hungary.
Abstract
Forests have a great effect on soil hydrology. Forest vegetation moderate soil freezing, tree roots
loosen the soil, therefore infiltration conditions for water into the soil are better. Tree canopy protects
the soil against intensive rainfall. In the study area the potential native vegetation is deciduous forest.
However, because of deforestation the hydrophysical properties of the soil has probable become less
favourable and the risk of soil erosion increased so the study of soil hydrology in these areas is
relevant.
The objective of this study was to identify the effect of forest and grassland vegetation on soil
hydrology of a forest soil. We compared the hydrophysical properties and water content dynamics of
the soil at two sites next to each other where the potential native vegetation is forest, but now covered
by forest and grassland, respectively. The texture of the studied soil is clay. Heavy texture soils have
unfavourable hydrophysical properties so the effect of vegetation can be very important in the area.
The study is carried on in the Mátra Mountains, Northern Hungary (N 4750’37,6”, E 1943’16.5”).
Elevation is 278 m a.s.l. The studied soil is Haplic Vertisol according to WRB, where the depth of
humus layer is 35 cm. The forest and grassland fields are situated next to each other, on a nearly flat
surface.
The forest stand is dominated by Turkey oak (Quercus cerris), its mixture ratio is 50 %. Small leaved
lime (Tilia cordata) and field maple (Acer campestre) are present with 20-20% mixture ratio, while
robinia (Robinia pseudo-acacia), northern red oak (Quercus rubra), scots pine (Pinus sylvestris) and
wild pear (Pyrus pyraster) are considered as rare species (mixture ratio: 2-4 %). The canopy cover is
80-100 %. The most dominant species of the shrub layer: saplings of the deciduous tree species of
the canopy layer and Crataegus monogyna, Rubus caesius, Ligustrum vulgare, Rosa canina. Their
average cover is 10-50%. The herb layer is rather poor; its total cover is about 1-5 %.
The grassland has come through more land use changes. After deforestation it was functioning as a
plough-land. Later it has been used as a cattle pasture for about 22 years. Grazing was stopped in
2003. The grass vegetation is now homogeneous. The dominant species in it is a Carex sp.
We measured the bulk density, humus content, detailed particle-size distribution and water retention
characteristics of the 0-5 cm topsoil and the 20-25 cm soil layer for both sites in laboratory. Soil water
content has been measured continuously since 15 April 2005 in both sites. We use ECH2O soil
moisture probes. Five-five ECH2O probes were buried into soil profiles between soil depths of 15 cm
to 55 cm with 10 cm vertical distance between the sensors. The probes were placed parallel to the soil
surface, orienting the flat side perpendicular to the surface of the soil. There are three soil profiles in
the forest and one in the grassland. The soil moisture probe was calibrated for the studied soil.
Records of soil water content in each layer were taken in every 30 minutes.
The water retention curves of the two studied sites are shown in Fig.1. The saturated and wilting point
water contents of the topsoil are similar at the two sites. The water retention curves of the two sites
are also similar, but the water content values of the grassland are about 5-7 % higher along the curve.
The water retention curve of the 20 cm soil layer is more different for the two sites. The saturated
water content of the grassland is 14% lower than that of the forest. It can be resulted by the higher
compactness of this layer in the grassland soil. The origin of the compaction may remained from
former ploughing and cattle trampling. The significant (approx. 10 %) difference between the the low
suction range moisture retention of the 20-25 cm soil layer is decreasing toward the higher suction
range and becoming similar at the wilting point at the two sites. The wilting point moisture content is
high in both layers at both sites because of the high clay content.
0-5 cm
20-25 cm
70
Water content (V/V%)
Water content (V/V%)
70
60
50
40
30
WC-OBS grass
WC-FIT grass
WC-OBS forest
WC-FIT forest
20
10
0
0
1
60
50
40
WC-OBS grass
WC-FIT grass
WC-OBS forest
WC-FIT forest
30
20
10
0
2
3
pF (lg(cm))
4
5
0
1
2
3
4
5
pF (lg(cm))
a.
b.
Figure 1. Water retention curves of the topsoil and of the 20 cm soil layer (a.) in the grassland and (b.)
in the forest.
There were similar trends in soil water dynamics of the forest and the grassland. The main difference
is the more intensive drying in the layers below 20 cm soil depth in the drying periods. The 10-20 cm
layer was dryer than the deeper layers in all profiles in spring. In the summer soil water content
decreased with different intensity in the profiles. The 10-20 cm layer in one of the soil profiles in the
forest showed lower water content values in the dry summer period than the other two. This could be
resulted by shrinking and later crack formation in the soil.
Keywords: forest, grassland, Vertisol, soil hydrology, soil hydrophysical properties