Biologia, Bratislava, 61/Suppl. 19: S261—S265, 2006
S261
Effect of forest and grassland vegetation on soil hydrology in Mátra Mountains (Hungary) Andrea Hagyó1 , Kálmán Rajkai1 & Zoltán Nagy2 1
Research Institute for Soil Science and Agricultural Chemistry of Hungarian Academy of Sciences, Budapest, Hungary; tel.: +36-1-2243652, e-mail:
[email protected] 2 Szent István University, Department of Botany and Plant Physiology, G¨ od¨ ol˝ o, Hungary
Abstract: Water retention characteristics, rainfall, throughfall and soil water content dynamics were investigated in a low mountain area to compare a forest and a grassland. The soil water retention curve of the topsoil has similar shape in both studied areas, however that of the deeper soil layer shows more difference. We determined the precipitation depth, duration and intensity values of rainfall events. The relationship between rainfall and throughfall depth was described in linear regressions. Interception was calculated as the difference between rainfall and throughfall plus stemflow, assuming stemflow to be 3% of rainfall. Soil water content dynamics show a similar trend in the two vegetation types but the drying is more intensive in the forest in the soil layers deeper than 20 cm during the growing-season. Key words: forest, grassland, interception, throughfall, soil moisture dynamics
Introduction Evapotranspiration (ET) and interception are the elements of the water cycle of the soil-plant-atmosphere system that are determined principally by vegetation. ET includes both soil evaporation and transpiration. Interception loss refers to the amount of water intercepted and lost by evaporation from the canopy. There are many studies investigating the quantitative importance of it in different vegetation types, but most studies have been conducted in forests, where interception has been found to be a significant or even a dominant element of ET. It can be estimated from canopy characteristics or can be calculated from the difference of the rainfall and throughfall plus the stemflow (Merta et al., 2006). Throughfall is the fraction of rainfall that gets through the plant canopy, directly through the canopy or with delayed dropping from the leaves and branches. Stemflow, the part of precipitation that reaches the forest floor flowing down the trunks, is usually a minor component of the water balance. It can reach 3–10% of the rainfall in foliated deciduous forests (Price & Carlyle-Moses, 2003). The integrated effect of vegetation on the water cycle can be investigated by the analysis of soil moisture dynamics (Štekauerová et al., 2006). The objectives of our study were (1) to compare the water retention characteristics of a Vertisol in a grassland and in a forest stand, (2) to determine the relationship of rainfall measured in open grassland to
throughfall in the forest and forest canopy cover, and (3) to compare the soil water content dynamics in the two vegetation types.
Material and methods 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. Mátra Mountain has a stratovulcanic structure; rhyolite tuff, pyroxene-andesite tuff and lava are characteristic. The experimental site is situated on a nearly flat surface. The studied soil is Haplic Vertisol according to WRB (1998). Soil texture is clay. The depth of humus layer is 35 cm. The potential vegetation is Quercetum petraeae-cerris. We studied a grassland and a forest located next to each other. The forest is dominated by Turkey oak (Quercus cerris) (50% cover). Small leaved lime (Tilia cordata) and field maple (Acer campestre) are present with 20–20% cover, while robinia (Robinia pseudo-acacia), northern red oak (Quercus rubra), scots pine (Pinus sylvestris) and wild pear (Pyrus pyraster) are considered as rare species (1–5% cover). The total canopy cover is 80–100%. The cover of the shrub layer is 10–50%. The studied forestry unit has an area of about 100 by 200 m. The grassland is dominated by Festuca sp., Carex cariophyllea and Poa angustifolia. The main mass of roots is in the 0–20 cm soil layer. The native forest was cleared and the area was converted to cultivation. Later it had been used as a cattle pasture for about 22 years. The grazing was stopped in 2004. The grassland has an area of 13.5 ha. Automated soil moisture measurements have been ongoing in three soil profiles in the forest (soil profiles/sites
A. Hagyó et al.
S262 Table 1. Measurement periods of the soil moisture probes and rain gauges at the 4 sites. Site 1 (forest)
Site 2 (forest)
Site 3 (forest)
Site 4 (grassland)
15 Apr 2005– 5 Apr 2006
15 Apr 2005– 5 Apr 2006
26 June 2005– 5 Apr 2006
15 Apr – 15 June 2005, 2 Aug 2005 – 5 Apr 2006
27 Sept – 24 Oct 2005, 27 March – 4 May 2006
27 Sept – 28 Nov 2005
27 Sept – 28 Nov 2005 27 March – 4 May 2006
27 Sept – 28 Nov 2005, 27 March – 4 May 2006
Soil moisture (SWC) Rainfall/ Throughfall
a)
b) 20-25 cm 70
60
60
Water content (V/V%)
Water content (V/V%)
0-5 cm 70
50 40 30
WC-OBS grass WC-FIT grass WC-OBS forest WC-FIT forest
20 10
1
2
40
WC-OBS grass WC-FIT grass WC-OBS forest WC-FIT forest
30 20 10 0
0 0
50
3
4
5
0
1
2
3
4
5
pF (lg(cm))
pF (lg(cm))
Fig. 1. Water retention curves of the topsoil (a) and of the 20–25 cm soil layer (b) in the grassland and in the forest.
Nos 1, 2 and 3) and in one profile in the grassland (soil profile/site No. 4). Five capacitive soil moisture probes were buried in each profile, between soil depths from 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. One of the probes was calibrated in the laboratory for the studied soil according to the user guide (Decagon Devices, Inc., 2005). The calibration equation is: SWC (V/V%) = 0.0652P (mV) − 50.683, R2 = 0.9544, where P is the output of the moisture probe. Soil water content (SWC) was recorded every 30 minutes by the system. Throughfall was measured with three tipping bucket rain gauges (HOBO Data Logging Rain Gauges) set up next to the three soil profiles in the forest. Measurement resolution is 0.2 mm and data were recorded at each tip. We determined the canopy cover above the gauges using digital photographs. The camera was placed on the rain gauges with the lens facing upwards. The images were analysed with the Adobe Photoshop 7.0 Trial software (Adobe Systems Inc., USA) following a protocol described in ENGELBRECHT & HERZ (2001), changing the protocol when the sky was too clouded, in which case we set the brightness to 0. Using this method, we obtained the percentage of black pixels, which was considered to be the canopy cover. Rainfall was measured with a tipping bucket rain gauge (Campbell ARG 100 Tipping Bucket Raingauge) with a resolution of 0.2 mm, installed at site No. 4 in the open grassland. Data was recorded on a 30-minute interval. The rainfall events were differentiated as separate events if the time between the events exceeded 5 hours. The duration of events was determined as the sum of half-hour intervals when precipitation was recorded. Events of only 0.2 mm precipitation depth (25 events) were excluded from the analysis. There were some breaks of continuity of the measurements because of technical failures with the data loggers and
the cables of the sensors. We summarized the time periods when the different measurements were going on in Table 1. Soil texture characteristics, bulk density, humus content and water retention characteristics (for three soil samples from soil profiles No. 2 and 4.) were determined in the laboratory for two soil layers (0–5cm and 20–25cm). Soil conductivity measurement with CF ec instrument (RISTOLAINEN et al., 2006) showed that there is low spatial variability within the grassland and the forest.
Results The water retention curves of the two layers in the grassland and in the forest are shown on Fig. 1. The saturated and wilting point water contents of the topsoil are similar in the grassland and in the forest. The shape of the two curves is also comparable, but the water content values of the grassland are about 5–7% higher along the curve. The difference can be explained by the lower bulk density in the grassland (1.18 g/cm3 in the grassland vs. 1.26 g/cm3 in the forest). The water retention curve of the deeper soil layer is more different for the two sites. Saturated water content of the grassland is 14% lower than that of the forest. It can be resulted by the higher dry bulk density of this layer in the grassland (1.43 vs. 1.33 g/cm3 ). The higher density may be the result of the former ploughing and cattle trampling, while tree roots loosen the soil in the forest. There is a difference of approximately 10% in the low suction range moisture retention between the forest and the grassland, which is decreasing toward the higher suction range and becomes similar at wilting point. The
Effect of forest and grassland vegetation on soil hydrology
S263 b)
30
Frequency (count)
Frequency (count)
a)
20 10 0 -2
-5
-10
-15
30 20 10 0
15-
-5
Precipitation depth (mm)
-10
-15
-30
Rainfall duration (h)
Frequency (count)
30 20 10 0 -0.5
-1
-1.5
-2
-3
5-
Rainfall intensity (mm/h)
c)
Fig. 2. The frequency distribution of precipitation depth (a), rainfall duration (b) and rainfall intensity (c).
moisture content at wilting point is high in both layers at both sites because of the high clay content. The total incident precipitation during the periods of 27 September to 28 November 2005 and 27 March to 4 May 2006 was 37.6 mm and 70.8 mm, respectively. A total of 43 precipitation events were studied during the two periods. Mean event incident precipitation input was 3.5 mm and it ranged from 0.4 mm to 22.6 mm. Individual event durations averaged 5.3 h and ranged from 0.5 h to 29.5 h. The mean rainfall intensity was 0.73 mm h−1 ranging from 0.09 mm h−1 to 5.05 mm h−1 . The frequency of precipitation depth, duration and intensity values based on the 43 events are presented in Fig. 2. Canopy cover was similar in October and in May above the same rain gauges, ranging from 78.34% to 92.87%. It was highest above Rain gauge #3 and it was the lowest above Rain gauge #1. We determined the cover of branches without leaves on 20 March 2006 (52.20%, 34.04%, 42.27% above rain gauges 1, 2 and 3, respectively). The total throughfall in the period of 27 September – 28 November 2005 was observed to be 63.79%, 78.2% and 73.9% of rainfall at sites 1, 2 and 3, respectively. It was 68.6% and 65.5% at sites 1 and 3 in the period of 27 March – 4 May 2006. Considering the separate precipitation events the mean throughfall fluxes were 46.6%, 45.05% and 40.47% varying from 8.33 to 80%, 15.56 to 80% and from 9.38 to 80% in percentage of rainfall depths. The relationship between incident rainfall and throughfall was approximated in linear regression (equations 1–4): TF1 = 0.6901P − 0.1539, R2 = 0.9437, N = 24,
(1)
TF2 = 0.7685P − 0.1072, R2 = 0.9862, N = 8,
(2)
TF3 = 0.7495P − 0.2142, R2 = 0.9732, N = 21,
(3)
TFmean = 0.7293P − 0.1946, R2 = 0.9884, N = 29.(4) TF1 , TF2 , and TF3 are the throughfall depths measured with the three rain gauges; TFmean : mean value of throughfall depths; P: precipitation depth. Delayed flow could be observed: delayed dropping from leaves and branches occurred during and after rain events. The delay between the first (start of event) and the last tip (end of event) of recorded rain and throughfall events could be calculated with half-hour resolution. Three periods were distinguished: 29 Sept to 29 Nov 2005 (1), 29 March to 10 Apr 2006 (2) and 11 Apr to 4 May 2006 (3). In the autumn period the mean delay at the start of events is approximately 3 h in case of all the TF measuring plots. The mean delays at the end of the events are 2.2 h, 2.7 h and 3.8 h at the three sites, respectively. The minimum of delay in this period was 1h at all sites for both the start and the end of the events. The maximum delay ranged from 5.5 h to 6.5 h at the start and from 3 h to 7 h at the end of events. In spring the mean delay varied around 2 h at site #1 (variance is 1.06 and 1.70 for start and end). Despite at site #3, mean delay (start: 3.86 h and 2.64 h, end: 4.71 h and 1.90 h) differed in the two periods. We assumed the stemflow to be 3% of rainfall as the lower limit found in the literature (Price & Carlyle-Moses, 2003). Interception – estimated to be the difference between rainfall and throughfall plus stemflow – was 33.21, 18.8 and 23.1% of rainfall (sites 1, 2 and 3, respectively) in the period of 27 September – 28 November 2005. It was 28.4% and 31.5% in the period of 27 March – 4 May 2006 (sites #1 and #3). There were similar trends in soil water content dynamics in the forest and in the grassland (Fig. 3). The 10–20 cm layer was drier than the deeper layers in all
A. Hagyó et al. Soil depth (cm)
S264 -15 -25 -35 -45 -55
0
20
40
60
Soil depth (cm)
Soil Profile 1
-15 -25 -35 -45 -55
0
20
40
60
100 120 140
0
20
160 180
80
100 120 140 160 180
Time (days) Soil depth (cm)
Soil depth (cm)
Soil Profile 2
-15 -25 -35 -45 -55
80
Time (days)
40
Time (days)
-15 -25 -35 -45 -55
60 Soil Profile 4
120
140 160
180
Soil water content (V/V%) 48 44 40 36 32 28 24 20 16 12 10 0
Time (days)
Fig. 3. Soil water content dynamics in Soil Profiles 1, 2 and 4, 14 April (day No. 0) – 11 October (day No. 180) 2005.
Table 2. SWC at the end of drying periods in soil profiles 1, 2, 3 and 4. F = forest, G = grassland. Decrease in SWC
Soil Profile
10–20cm
20–30cm
30–40cm
40–50cm
50–60cm
28 April – 4 May Number of days = 7
1 (F) 2 (F) 4 (G)
–1.24 –1.04 –3.91
–7.50 –0.78 –5.74
–2.67 –3.13 –3.59
0.39 –4.04 0.13
0.20 –3.00 0.20
23 May – 3 June Number of days = 12
1 (F) 2 (F) 4 (G)
–32.27 –1.70 –20.21
–3.85 –2.48 –3.13
–4.50 –4.30 –5.87
–1.24 –5.93 –2.28
0.20 –3.19 0
29 Aug – 10 Sept Number of days = 13
1 (F) 2 (F) 3 (F) 4 (G)
–21.10* –9.13 –10.50 –21.26
–18.26 –29.14 –19.89 –11.67*
–33.32 –19.56 –23.60 –2.67*
–12.13 –15.19 –18.39 –3.91*
–8.22 –25.23 –31.62 –9.71
2 – 11 Oct Number of days = 10
1 (F) 2 (F) 3 (F) 4 (G)
–4.22* –1.24 –1.30 –7.89
–5.48 –23.08 –1.17 –3.06*
–16.76 –5.28 – –1.70*
–7.17 –3.13 –0.33 –3.33
–24.25 –1.17 – –
* decrease in SWC is the smallest in the grassland, – missing data because of sensor failure
profiles in spring. The SWC of the layers below 20 cm are similar in all profiles until the beginning of June, then the SWC in the forest profiles decreased more than in the grassland profile. However, layers 30–40, 40–50 and 50–60 cm are always the wettest in the grassland. We studied the decrease of SWC during four drying periods (Table 2). In the deeper layers it was smaller in the grassland during all the periods. There was minor drying in the two deepest layers in the first period, and in the deepest layer in the second period. The smallest decrease could be observed in the grassland profile in the 20–30, 30–40 and 40–50 cm layers in the third and fourth period. Recorded SWC data decreased below wilting point
during drying periods, therefore data of profile 3 are not shown. The reason can be that the sensors became separated over part of their length when the soil dried and shrank, and therefore false readings were received below SWC of about 10 V/V% in the Vertisol. Thus our next research aims at the sensitivity analysis of the sensors in soil drier than wilting point. Discussion There were differences in soil water retention characteristics between the grassland and the forest (Fig. 1). The relationship between rainfall and throughfall can be described in linear regressions that are similar among the
Effect of forest and grassland vegetation on soil hydrology three sites (equations 1–3). The mean throughfall depth of all the studied events increased with the decrease in canopy cover. In the autumn period the mean and minimum throughfall delay are similar at the three sites; maximum delay increased with the increase in canopy cover. The mean throughfall delay of the two studied sites differed in the spring period, when foliage started to grow. The determined interception losses are within the range (11–36%) given for broadleaved forests in the literature review by Hörman et al. (1996). Soil water content dynamics show similar trend in the forest soil profiles and in the grassland profile (Fig. 3). The main difference is that the soil dried out more in the forest than in the grassland in the layers below 20 cm. It can be the result of the larger water use from the deeper soil layers by trees than the grass vegetation. References ENGELBRECHT, B.M.J. & HERZ, H.M. 2001. Evaluation of different methods to estimate understorey light conditions in tropical forests. J. Tropic. Ecol. 17: 207–224.
S265 HÖRMAN, G., BRANDING, A., CLEMEN, T., HERBST, M. & HINRICHS, A. 1996. Calculation and simulation of wind controlled canopy interception of beech forest in Northern Germany. Agric. For. Meteorol. 79: 131–148. MERTA, M., SEIDLER, C. & FJODOROWA, T. 2006. Estimation of evaporation components in agricultural crops. Biologia, Bratislava 61(Supl. 19): S280–S283. PRICE, A.G. & CARLYLE-MOSES, D.E. 2003. Measurement and modelling of growing-season canopy water fluxes in a mature mixed deciduous forest stand, southern Ontario, Canada. Agr. Forest Meteorol. 119: 69–85. RISTOLAINEN, A., TÓTH, T. & FARKAS, CS. 2006. Measurement of soil electrical properties for the characterization of the conditions of food chain element transport in soils. Cereal Res. Comm. 34: 159–162. ŠTEKAUEROVÁ, V., NAGY, V. & KOTOROVÁ, D. 2006. Soil water regime of agricultural field and forest ecosystems. Biologia, Bratislava 61(Supl. 19): S300–S304. WRB 1998. World reference base for soil resources. 1998. FAO, ISRIC and ISSS. Rome.
