Effect of Repeated Fires on Soil Hydrolo
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Effect of Repeated Fires on Soil Hydrological Properties in a
Mediterranean Forest Environment
O. González1 , V. Andreu, J. Campo, E. Gimeno-García & J. L. Rubio
Unidad de Degradación y Conservación de suelos. Centro de Investigaciones sobre Desertificación-CIDE (CSIC-Universitat
de Valencia-Generalitat Valenciana). Camí de la Marjal, s/n. 46470-Albal (Valencia, SPAIN). Tel.: +34 96 122 05 40 Fax:
+34 96 127 09 67
Abstract
In the Mediterranean basin, the occurrence of repeated forest fires on the same area has
magnified erosion processes, reducing the vegetation recovery periods and modifying soil
hydrological properties.
The aim of this research is to asses the impact of a repeated experimental fire on soil
hydrology and runoff generation in a Mediterranean forest environment. This study was
developed in the Permanent Experimental Field Station of La Concordia (Llíria-Valencia,
Spain), on a set of nine erosion plots (4 x 20 m). In June 1995, a set of experimental fires
were carried out. Three of the plots were burned with high intensity fire, three with moderate
intensity and the remainders were left unaltered. In summer 2003, the same plots were burned
simulating a repeated fire with the vegetation regenerated since 1995. These last fires were
classified of low intensity. Water retention capacity (WRC) and soil water content (SWC)
were analyzed before (BB), immediately after (AB) and a month after (MAB) the fire impact.
Runoff generated from June to December 2003 (the most aggressive period of rains) and
infiltration rate was also analyzed. Data of BB, AB and MAB were compared.
The WRC highest values were obtained by the moderate intensity treatment BB (23.20 %),
but they did not show significant differences respect the others treatments. The major SWC
obtained in this treatment shows significant differences at pF 2 and 3.5 respect to the others.
Just after the fires, the WRC tendency changes. High and moderate intensity treatments
pointed out similar values (23.57 and 22.77 %, respectively), meanwhile the control one
shows the biggest one (25.57 %). The pF curves corroborate these data; at pF 2 and 2.5 the
control treatment shows the highest values obtaining significant differences respect the others
treatments. But MAB, the WRC values of high intensity treatment and control one, have the
similar levels (24.85 and 24.28 %), meanwhile the moderate treatment rise to 26.05 %,
showing the major values on SWC at pF 2, 2.5 and 3.5. Total runoff produced after the
repeated fire was 95% higher than values of control plots during the studied period.
1.-Introduction
In the last years, forest fires in the Mediterranean Europe have been characterized by an
increase in their number (European Commission, 2002). It could mean, in many cases, the
incidence of fire on zones recovering from a previous burning. As a consequence,
hydrological processes such as runoff at the hillslope scale, which are sensitive to changes in
soil surface properties (Johansen et al., 2001) could be altered.
The highly aggressive rains in the Mediterranean are usually concentrated after the dry
summer period, when fires often occurs, resulting in a high potential for surface runoff and
erosion. Through these processes, fire is one of the principal causes of increasing
desertification risk in the area.
1
Corresponding autor: oscar.gonzalez-pelayo@uv.es
1
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
In this context, the aim of this study is to asses the impact of repeated experimental fires on
soil hydrological parameters, and analyzes its response on runoff and infiltration processes
during the critical period of five month after them.
2.-Material and methods
This research was carried out in the Permanent Experimental Station of La Concordia (LlíriaValencia, Spain), 50 km NW of Valencia city. It is 575 m above sea level, on a forested
hillside SSE facing, with a schlerophyllous shrub cover regenerated after a wildfire in 1978.
The soil is a Rendzic Leptosol (FAO-UNESCO, 1988), with variable depth, always less than
50 cm, abundant stoniness (@ 40%) and good drainage. Average annual precipitation in the
area is 400 mm with two maximums, autumn and spring, and a dry period from June to
September. Mean monthly temperatures range from 13.3 to 25.8ºC.
The Experimental Field Station consists on a set of nine erosion plots (20 x 4m) with similar
characteristics such as soil, slope gradient, rock outcrops and vegetation cover. Climatic
parameters, runoff generation dynamics and the intrinsic characteristics of each rainfall event
are continuously monitored.
In 1995, a random design of two different fire intensity treatments, with three plots each, was
used. These different fire intensities were achieved by the addition of different amounts of
fuel load to the plots of each treatment, 40 t ha-1 to reach high intensity fires and 20 t ha-1 for
the moderate intensity ones. The remaining three plots were maintained unburnt to be used as
control. Statistically significant differences were observed for the mean soil surface
temperatures, between high fire intensity (439 ºC) and moderate fire intensity (232 ºC)
treatments (Gimeno-García et al., 2004). In 2003, after eight years from the fires, the plots
were burned again, but without biomass addition, reaching an average temperature on soil
surface of 170ºC. These repeated fires could be classified as low intensity ones.
For each treatment, Soil Water Content (SWC) was calculated for pF 1, 2, 2.5, 3.5, 4.2, using
the pressure membrane method (Richards, 1947). The pF curves and Soil Water Retention
Capacity (WRC) with field capacity at pF2 and pF2.5 were calculated for each treatment
3.-Results and discussion
3.1.-Rainfall, runoff yield and infiltration evolution
In 2003, the erosive rainfalls reached 324.2 mm in the whole year, and 135.8 mm in the last
five months (July-December), where the most aggressive rains occurred. The average I30
value from July to December (20.22 mm h-1 ) was double than that of January-June period
(8.4 mm h-1 ), and the mean event duration was 8 times lower (2718 min/event for JanuaryJune and 327.5 min/event for July-December), so the most aggressive rainfall conditions
were shown during these last months. The I30 parameter reaches the maximum values of the
whole year in two rain events, meanwhile the event duration reached the minimum ones: (i)
30th July, ten days after fire experience, I30 and rain duration were 65.4 mm h-1 and 30 min,
respectively; and (ii) 17th August, the I30 was 21 mm h-1 and its duration 60 min (Fig. 1). It
means that the most aggressive rains of that year appeared just after fire experience. The short
elapsed time between fire impact and the first rainstorm event after it (ten days), favored the
major runoff produced not only in burned plots but also in control one.
The double runoff yield levels in control plots during July-December respect January-June
period, shows the effect of the Mediterranean climate aggressiveness short after the fires. In
burned plots the runoff amount increases in one order of magnitude in relation to the control
ones (Fig. 2). Furthermore, the soil surface in the moderate intensity treatment could present
2
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Fire impact
70
impact
60
60
50
50
40
40
30
30
20
20
10
10
Rain (mm)
I30(mm/h)
-X
II
11
10
-X
I
-X
26
-X
14
IX
4-
-V
III
22
-V
III
17
-V
II
V
30
-I V
9-
31
17
-I I
-I I
/26
25
20
I
0
-I I
0
I30I30
(mm
h-1)
(mm/h)
Rain (mm)
70
Duration (min x 100)
a higher alteration of its soil physical conditions as it is reflected by the runoff values (11.3 %
more than high intensity treatment).
Figure 1. Erosive rain events occurred during year 2003.
The eight years of soil and vegetation recovery since the 1995 fires, have facilitated that
infiltration rates showed homogeneous values in all treatments during the January-June
period, with not statistical differences between treatments. Quite opposite occurs after fire
impact (July-December), where differences between burned and control plots reach 20.47 %.
This could denote physical changes in soil surface properties.
30
Runoff
Yield
Runoff
yield
(L (L/m2)
m -2)
25
20
I 30 (mm h-1 )
15
10
5
0
Infiltration rate (mm/h) Infiltration
rate (mm h
1
)
14
12
10
8
6
4
2
0
Before fire impact
After fire impact
High
Moderate
Control
Before fire impact
High
After fire impact
Moderate
Control
Figure 2. Runoff yield and infiltration rate values in 2003.
Data reflect that during the two months after the recurrent fire, the soil state is more prone to
runoff generation. In the first rain event occurred after fire (30th July), runoff yield generated
in burned plots were 8.44 L m-2 and 7.88 L m-2 for high and moderate treatments,
respectively, meanwhile in the control plots this value reaches 0.987 L m-2 .
3.2.-Hydrogical behavior
Table 1 displays the WRC data. These values showed the WRC homogeneous conditions
before burning, which are reflected in non statistical significant differences between any fire
treatments and control one. The fire treatments values AB were homogenous but slightly
lower than those of control plots, although in the high intensity treatment the total SWC
raised 3.5%, mainly at low pF values, respect to BB values. A month after burning, the fire
treatments WRC values rose to achieve significant statistical differences respect to the control
ones. In the MAB, the burned samples suffered a SWC increase at pF 2 and 2.5, appearing
the major WRC values on burned plots (Fig. 3). These results imply changes in soil surface
physical properties after fire impact (Andreu et al. 2001), mainly in the soil aggregate fraction
that could formed the voids where water is retained at low retention forces.
3
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
The moderate intensity treatment showed the greatest water content variability at low pF
values, probably due to the particle-size distribution and its re-aggregation produced by fire
impact (Giovannini and Lucchesi, 1997). Guber et al (2003), found that larger aggregates
show the greater variation in water content.
60
Water content (%)
Table 1. Water retention capacity (%),
calculated at pF 2 and pF 4.2 (up), and
calculated at pF 2.5 and pF 4.2 (down), for
the different fire treatments. Values not
sharing the same letter in files indicate
significant differences according to Tukey´s
test
BB
50
40
30
20
10
Water
Watercontent
content (%)(%)
0
60 1
Fire treatments
2
2.5
pF
50
High
Moderate
AB
4.2
Control
40
30
20
Sample period
BB
AB
MAB
BB
AB
MAB
High
21.3a
23.6a
24.8ab
14.7a
16.4a
16.7a
Moderate
23.2a
22.7a
26.1b
15.6a
16.0a
18.7b
Control
22.6a
25.6b
24.3a
14.6a
17.0a
16.5a
10
0
60 1
2
2.5
3.5
High
Moderate
4.2
MAB
pF
50
Water content (%)
3.5
Control
40
30
20
10
0
1
2
2.5
3.5
4.2
pF
High
Moderate
Control
Figure 3. SWC (%) measured Before Burned, After Burned, and Month After Burned.
4.-Conclusions
The repeated incidence of fire on a soil in a recovery stage, led to an increase in SWC, mainly
at low water retention forces, where the holding gravitational water is retained. This increase
could indicate structural changes in soil surface which lead to amplify soil erosion rates.
The effect of a new fire impact and the climatic aggressivity showed immediately after it,
produced an increase in runoff yield rates of 1 order of magnitude, meanwhile the infiltration
rate diminishes around 20% respect to control values.
The impact of repeated fires in the Mediterranean zone could be translated in an important
alteration of soil hydrological conditions, which induce a reduction of WRC increasing runoff
generation and soil losses. As a consequence Desertification risk could be enhanced.
5.-References
Andreu, V., Imeson, A. C., and Rubio, J. L. 2001. Temporal changes in soil aggregates and water erosion after a
wildfire in a Mediterranean pine forest. Catena, 44: 69-84.
European Commision, 2002. Forest Fires in Europe: 2001 fire campaign. European Communities, Ispra.
FAO-UNESCO, 1988. Soil map of the world. Revised legend 1:5.000.000. Roma.
Gimeno-García, E., Andreu, V., and Rubio, J. L. 2004. Spatial patterns of soil temperatures during experimental
fires. Geoderma, 118: 17-38.
Giovannini, G., Luchesi, S. 1997. Modifications induced in soil physico-chemical parameters by experimental
fires at different intensities. Soil Science, 162: 479-486.
Guber, A. K., Rawls, W. J., Shein, E. V., and Pachepsky, Ya, A. 2003. Effect of soil aggregate size distribution
on water retention. Soil Science, 168: 223-232.
4
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Johansen, M.P., Hakonson, T.E., Breshers, D.D. 2001. Post-fire runoff and erosion from rainfall simulation:
contrasting forest with shrubland and grasslands. Hydrological Processes, 15 (15): 2953-2965.
Richards, L. A. 1947. Pressure-membrane apparatus, construction and use. Agric Eng., 28: 451-454.
5
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Effect of Repeated Fires on Soil Hydrological Properties in a
Mediterranean Forest Environment
O. González1 , V. Andreu, J. Campo, E. Gimeno-García & J. L. Rubio
Unidad de Degradación y Conservación de suelos. Centro de Investigaciones sobre Desertificación-CIDE (CSIC-Universitat
de Valencia-Generalitat Valenciana). Camí de la Marjal, s/n. 46470-Albal (Valencia, SPAIN). Tel.: +34 96 122 05 40 Fax:
+34 96 127 09 67
Abstract
In the Mediterranean basin, the occurrence of repeated forest fires on the same area has
magnified erosion processes, reducing the vegetation recovery periods and modifying soil
hydrological properties.
The aim of this research is to asses the impact of a repeated experimental fire on soil
hydrology and runoff generation in a Mediterranean forest environment. This study was
developed in the Permanent Experimental Field Station of La Concordia (Llíria-Valencia,
Spain), on a set of nine erosion plots (4 x 20 m). In June 1995, a set of experimental fires
were carried out. Three of the plots were burned with high intensity fire, three with moderate
intensity and the remainders were left unaltered. In summer 2003, the same plots were burned
simulating a repeated fire with the vegetation regenerated since 1995. These last fires were
classified of low intensity. Water retention capacity (WRC) and soil water content (SWC)
were analyzed before (BB), immediately after (AB) and a month after (MAB) the fire impact.
Runoff generated from June to December 2003 (the most aggressive period of rains) and
infiltration rate was also analyzed. Data of BB, AB and MAB were compared.
The WRC highest values were obtained by the moderate intensity treatment BB (23.20 %),
but they did not show significant differences respect the others treatments. The major SWC
obtained in this treatment shows significant differences at pF 2 and 3.5 respect to the others.
Just after the fires, the WRC tendency changes. High and moderate intensity treatments
pointed out similar values (23.57 and 22.77 %, respectively), meanwhile the control one
shows the biggest one (25.57 %). The pF curves corroborate these data; at pF 2 and 2.5 the
control treatment shows the highest values obtaining significant differences respect the others
treatments. But MAB, the WRC values of high intensity treatment and control one, have the
similar levels (24.85 and 24.28 %), meanwhile the moderate treatment rise to 26.05 %,
showing the major values on SWC at pF 2, 2.5 and 3.5. Total runoff produced after the
repeated fire was 95% higher than values of control plots during the studied period.
1.-Introduction
In the last years, forest fires in the Mediterranean Europe have been characterized by an
increase in their number (European Commission, 2002). It could mean, in many cases, the
incidence of fire on zones recovering from a previous burning. As a consequence,
hydrological processes such as runoff at the hillslope scale, which are sensitive to changes in
soil surface properties (Johansen et al., 2001) could be altered.
The highly aggressive rains in the Mediterranean are usually concentrated after the dry
summer period, when fires often occurs, resulting in a high potential for surface runoff and
erosion. Through these processes, fire is one of the principal causes of increasing
desertification risk in the area.
1
Corresponding autor: oscar.gonzalez-pelayo@uv.es
1
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
In this context, the aim of this study is to asses the impact of repeated experimental fires on
soil hydrological parameters, and analyzes its response on runoff and infiltration processes
during the critical period of five month after them.
2.-Material and methods
This research was carried out in the Permanent Experimental Station of La Concordia (LlíriaValencia, Spain), 50 km NW of Valencia city. It is 575 m above sea level, on a forested
hillside SSE facing, with a schlerophyllous shrub cover regenerated after a wildfire in 1978.
The soil is a Rendzic Leptosol (FAO-UNESCO, 1988), with variable depth, always less than
50 cm, abundant stoniness (@ 40%) and good drainage. Average annual precipitation in the
area is 400 mm with two maximums, autumn and spring, and a dry period from June to
September. Mean monthly temperatures range from 13.3 to 25.8ºC.
The Experimental Field Station consists on a set of nine erosion plots (20 x 4m) with similar
characteristics such as soil, slope gradient, rock outcrops and vegetation cover. Climatic
parameters, runoff generation dynamics and the intrinsic characteristics of each rainfall event
are continuously monitored.
In 1995, a random design of two different fire intensity treatments, with three plots each, was
used. These different fire intensities were achieved by the addition of different amounts of
fuel load to the plots of each treatment, 40 t ha-1 to reach high intensity fires and 20 t ha-1 for
the moderate intensity ones. The remaining three plots were maintained unburnt to be used as
control. Statistically significant differences were observed for the mean soil surface
temperatures, between high fire intensity (439 ºC) and moderate fire intensity (232 ºC)
treatments (Gimeno-García et al., 2004). In 2003, after eight years from the fires, the plots
were burned again, but without biomass addition, reaching an average temperature on soil
surface of 170ºC. These repeated fires could be classified as low intensity ones.
For each treatment, Soil Water Content (SWC) was calculated for pF 1, 2, 2.5, 3.5, 4.2, using
the pressure membrane method (Richards, 1947). The pF curves and Soil Water Retention
Capacity (WRC) with field capacity at pF2 and pF2.5 were calculated for each treatment
3.-Results and discussion
3.1.-Rainfall, runoff yield and infiltration evolution
In 2003, the erosive rainfalls reached 324.2 mm in the whole year, and 135.8 mm in the last
five months (July-December), where the most aggressive rains occurred. The average I30
value from July to December (20.22 mm h-1 ) was double than that of January-June period
(8.4 mm h-1 ), and the mean event duration was 8 times lower (2718 min/event for JanuaryJune and 327.5 min/event for July-December), so the most aggressive rainfall conditions
were shown during these last months. The I30 parameter reaches the maximum values of the
whole year in two rain events, meanwhile the event duration reached the minimum ones: (i)
30th July, ten days after fire experience, I30 and rain duration were 65.4 mm h-1 and 30 min,
respectively; and (ii) 17th August, the I30 was 21 mm h-1 and its duration 60 min (Fig. 1). It
means that the most aggressive rains of that year appeared just after fire experience. The short
elapsed time between fire impact and the first rainstorm event after it (ten days), favored the
major runoff produced not only in burned plots but also in control one.
The double runoff yield levels in control plots during July-December respect January-June
period, shows the effect of the Mediterranean climate aggressiveness short after the fires. In
burned plots the runoff amount increases in one order of magnitude in relation to the control
ones (Fig. 2). Furthermore, the soil surface in the moderate intensity treatment could present
2
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Fire impact
70
impact
60
60
50
50
40
40
30
30
20
20
10
10
Rain (mm)
I30(mm/h)
-X
II
11
10
-X
I
-X
26
-X
14
IX
4-
-V
III
22
-V
III
17
-V
II
V
30
-I V
9-
31
17
-I I
-I I
/26
25
20
I
0
-I I
0
I30I30
(mm
h-1)
(mm/h)
Rain (mm)
70
Duration (min x 100)
a higher alteration of its soil physical conditions as it is reflected by the runoff values (11.3 %
more than high intensity treatment).
Figure 1. Erosive rain events occurred during year 2003.
The eight years of soil and vegetation recovery since the 1995 fires, have facilitated that
infiltration rates showed homogeneous values in all treatments during the January-June
period, with not statistical differences between treatments. Quite opposite occurs after fire
impact (July-December), where differences between burned and control plots reach 20.47 %.
This could denote physical changes in soil surface properties.
30
Runoff
Yield
Runoff
yield
(L (L/m2)
m -2)
25
20
I 30 (mm h-1 )
15
10
5
0
Infiltration rate (mm/h) Infiltration
rate (mm h
1
)
14
12
10
8
6
4
2
0
Before fire impact
After fire impact
High
Moderate
Control
Before fire impact
High
After fire impact
Moderate
Control
Figure 2. Runoff yield and infiltration rate values in 2003.
Data reflect that during the two months after the recurrent fire, the soil state is more prone to
runoff generation. In the first rain event occurred after fire (30th July), runoff yield generated
in burned plots were 8.44 L m-2 and 7.88 L m-2 for high and moderate treatments,
respectively, meanwhile in the control plots this value reaches 0.987 L m-2 .
3.2.-Hydrogical behavior
Table 1 displays the WRC data. These values showed the WRC homogeneous conditions
before burning, which are reflected in non statistical significant differences between any fire
treatments and control one. The fire treatments values AB were homogenous but slightly
lower than those of control plots, although in the high intensity treatment the total SWC
raised 3.5%, mainly at low pF values, respect to BB values. A month after burning, the fire
treatments WRC values rose to achieve significant statistical differences respect to the control
ones. In the MAB, the burned samples suffered a SWC increase at pF 2 and 2.5, appearing
the major WRC values on burned plots (Fig. 3). These results imply changes in soil surface
physical properties after fire impact (Andreu et al. 2001), mainly in the soil aggregate fraction
that could formed the voids where water is retained at low retention forces.
3
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
The moderate intensity treatment showed the greatest water content variability at low pF
values, probably due to the particle-size distribution and its re-aggregation produced by fire
impact (Giovannini and Lucchesi, 1997). Guber et al (2003), found that larger aggregates
show the greater variation in water content.
60
Water content (%)
Table 1. Water retention capacity (%),
calculated at pF 2 and pF 4.2 (up), and
calculated at pF 2.5 and pF 4.2 (down), for
the different fire treatments. Values not
sharing the same letter in files indicate
significant differences according to Tukey´s
test
BB
50
40
30
20
10
Water
Watercontent
content (%)(%)
0
60 1
Fire treatments
2
2.5
pF
50
High
Moderate
AB
4.2
Control
40
30
20
Sample period
BB
AB
MAB
BB
AB
MAB
High
21.3a
23.6a
24.8ab
14.7a
16.4a
16.7a
Moderate
23.2a
22.7a
26.1b
15.6a
16.0a
18.7b
Control
22.6a
25.6b
24.3a
14.6a
17.0a
16.5a
10
0
60 1
2
2.5
3.5
High
Moderate
4.2
MAB
pF
50
Water content (%)
3.5
Control
40
30
20
10
0
1
2
2.5
3.5
4.2
pF
High
Moderate
Control
Figure 3. SWC (%) measured Before Burned, After Burned, and Month After Burned.
4.-Conclusions
The repeated incidence of fire on a soil in a recovery stage, led to an increase in SWC, mainly
at low water retention forces, where the holding gravitational water is retained. This increase
could indicate structural changes in soil surface which lead to amplify soil erosion rates.
The effect of a new fire impact and the climatic aggressivity showed immediately after it,
produced an increase in runoff yield rates of 1 order of magnitude, meanwhile the infiltration
rate diminishes around 20% respect to control values.
The impact of repeated fires in the Mediterranean zone could be translated in an important
alteration of soil hydrological conditions, which induce a reduction of WRC increasing runoff
generation and soil losses. As a consequence Desertification risk could be enhanced.
5.-References
Andreu, V., Imeson, A. C., and Rubio, J. L. 2001. Temporal changes in soil aggregates and water erosion after a
wildfire in a Mediterranean pine forest. Catena, 44: 69-84.
European Commision, 2002. Forest Fires in Europe: 2001 fire campaign. European Communities, Ispra.
FAO-UNESCO, 1988. Soil map of the world. Revised legend 1:5.000.000. Roma.
Gimeno-García, E., Andreu, V., and Rubio, J. L. 2004. Spatial patterns of soil temperatures during experimental
fires. Geoderma, 118: 17-38.
Giovannini, G., Luchesi, S. 1997. Modifications induced in soil physico-chemical parameters by experimental
fires at different intensities. Soil Science, 162: 479-486.
Guber, A. K., Rawls, W. J., Shein, E. V., and Pachepsky, Ya, A. 2003. Effect of soil aggregate size distribution
on water retention. Soil Science, 168: 223-232.
4
14th International Soil Conservation Organization Conference.
Water Management and Soil Conservation in Semi-Arid Environments. Marrakech, Morocco, May 14-19, 2006 (ISCO 2006).
Johansen, M.P., Hakonson, T.E., Breshers, D.D. 2001. Post-fire runoff and erosion from rainfall simulation:
contrasting forest with shrubland and grasslands. Hydrological Processes, 15 (15): 2953-2965.
Richards, L. A. 1947. Pressure-membrane apparatus, construction and use. Agric Eng., 28: 451-454.
5