Changes in physical properties of a soil
.......~ ' ~ : ~
Forest
.
Ecology
and
Management
E LS EV l E R
Forest Ecology and Management 70 ( 1994 ) 215-229
Changes in physical properties of a soil associated with logging of
Eucalyptus regnans forest in southeastern Australia
M.A. Rab
Department of Conservation and Natural Resources, Catchment and Land Management Division,
Keith Turnbull Research Institute, Ballarto Road, Frankston, Vic. 3199, Australia
Accepted 23 May 1994
Abstract
Logging operations can cause soil profile disturbance and compaction. Soil profile disturbance and compaction
change soil physical properties, which may reduce site productivity, increase soil erosion and degrade catchment
water quality. This study was undertaken to measure the effect of logging on physical properties of the 0-100 mm
surface soil in the Victorian Central Highlands, southeastern Australia. Soil physical properties were measured in
the snig tracks, log landings, general logging areas (disturbed areas which were not occupied by snig tracks or log
landings) and undisturbed areas. Within the general logging areas, measurements were made for three levels of
soil profile disturbance: litter disturbed, topsoil disturbed and subsoil disturbed.
The results indicated that logging significantly increased bulk density and decreased organic carbon and organic
matter content, total porosity and macroporosity on over 72% of the coupe area. However, on 35% of the coupe
area, the snig tracks, log landings and subsoil disturbed areas of the general logging area, bulk densities and macroporosities reached critical levels where tree growth could be affected. On these areas, organic carbon decreased
between 27 and 66%, bulk density increased between 39 and 65% and macroporosity decreased between 58 and
88%.
Saturated hydraulic conductivities decreased to critical levels for runoffto occur on over 72% of the coupe area
(topsoil and subsoil disturbed areas of the general logging area, snig tracks and log landings). On this area, the
reduction in saturated hydraulic conductivity varied between 60 and 95%.
Keywords: Soil compaction; Soil disturbance; Saturated hydraulic conductivity; Timber harvesting
I. Introduction
Logging operations cause soil profile disturbance including removal of the forest litter layer,
mixing of forest litter with mineral topsoil, mixing of topsoil with subsoil, removal of topsoil and
exposure of subsoil, removal of subsoil and exposure of parent material, and even in some situations partial removal of parent material. Logging also causes soil compaction. The level and
extent of soil profile disturbance and compaction vary with soil moisture content at the time
of operations, inherent soil physical properties,
slope of the site, the number of times a vehicle
passes over the site and machine weight (Greacen and Sands, 1980; Howard et al., 1981; Butt
and Rollerson, 1988; Wronski et al., 1989; Soane,
1990; Rab, 1992; Ghuman and Lal, 1992 ).
Soil profile disturbance and compaction may
change soil physical properties to such an extent
0378-1127/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved
SSD10378-1127(94)03430-3
216
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
that the resulting land surface may be more susceptible to soil erosion (Johnson and Beschta,
1980; Mackay et al., 1985; Farrish et al., 1993),
impede root growth (Heilman, 1981; Mitchell et
al., 1982), impede early tree growth (Minko,
1975; Donnelly and Shane, 1986; Farrish, 1990;
King et al., 1993 ) and decrease site productivity
(Perry, 1964; Wert and Thomas, 1981; Lockaby
and Vidrine, 1984). Soil disturbance and compaction increases bulk density (Gent et al., 1983,
1984; Jussofand Majid, 1987; Incerti et al., 1987;
Ole-Meiludie and Njau, 1989; Malmer and Grip,
1990; Rab et al., 1992), decreases macroporosity (Gent et al., 1983, 1984; Incerti et al., 1987;
Rab et al., 1992), reduces/redistributes organic
matter (Sands et al., 1979; Ole-Meiludie and
Njau, 1989; Anderson et al., 1994; Ryan et al.,
1992), reduces infiltration (Ole-Meiludie and
Njau, 1989; Malmer and Grip, 1990) and saturated hydraulic conductivity (Gent et al., 1983,
1984; Incerti et al., 1987). As a consequence,
surface runoff of water may increase and tree
growth may be impaired because of reduced
water supply, restricted root space and poor aeration (Greacen and Sands, 1980; Incerti et al.,
1987; Rab, 1992).
Rab et al. (1992) studied the impact of logging in southeastern Australia on the extent and
degree of soil profile disturbance. They found
that on about 73% of the coupe area the soil profile was disturbed. The majority of this disturbance resulted in topsoil disturbed areas followed by subsoil disturbed areas. They also found
that about 15% of the coupe area was compacted. The majority of the compacted area was
contributed by snig tracks followed by log landings. (Snig tracks are formed by towing a tree by
a tractor or dozer from the stump to the log processing area, known as log landing.) There is a
dearth of information on the impact of soil profile disturbance and compaction on soil physical
properties during logging in southeastern Australia (but see Incerti et al., 1987; Williamson,
1990). This information is important for greater
understanding of the physical processes, for predicting consequences of soil profile disturbance
and compaction on tree growth and soil erosion.
This information is also important for develop-
ing strategies that minimise impacts of logging
on soil and water values. This study was undertaken to measure the effect of soil profile disturbance and compaction on organic carbon and organic matter content, bulk density, pore-size
distribution and saturated hydraulic conductivity in the Victorian Central Highlands forests,
southeastern Australia.
2. Methods
2.1. Study area description
The study area is located 150 km east of Melbourne, situated near Tanjil Bren, in the Victorian Central Highlands (30 °2'S, 146 ° 15'E).
Two clearfelled coupes, Old Mill (4 ha) and Deception Spur ( 10 ha) in the Rowleys forest block
were selected for this study. The parent material
of both coupes is granitic rock. The landform is
mainly steep hills to moderately steep rolling hills
(McDonald et al., 1990). The major soil type of
the area is red gradational with a small percentage of yellow brown gradational soil (Northcote
et al., 1975 ). The average depth of the topsoil is
250 m m with up to 400 mm along drainage lines.
The depth of the subsoil varies between 650 and
1200 mm. The climate of the study area is cool
temperate and average annual rainfall is approximately 1900 mm. Average monthly temperature
ranges from 0°C in July to 20°C in February. Elevation ranges from 615 to 950 m. The slopes
vary from 0 to 20 °. The vegetation of the forest
is predominantly 1939 regrowth Mountain Ash
(Eucalyptus regnans), with occasional overmature and regrowth Grey Gum (Eucalyptus cypellocarpa). Stands are of moderate density with top
heights of 50 m. The understorey comprises three
distinct strata. The upper stratum is generally
sparse and consists of wattles (Acacia dealbata
and Acacia obiquinervia) and occasional Myrtle
Beech (Nothofagus cunninghamii) in damp locations. The middle stratum is dense and contains many shrubs and small trees, including
Blanket Leaf (Bedfordia arborescens), Musk
Daisy Bush (Olearia argophylla), Hazen Pomaderris (Pomaderris aspera) and tree ferns
(Dicksonia antarctica and Cyathea australis).
M.A. Rab / Forest Ecology and Management 70 (I 994) 215-229
The ground stratum is generally sparse and consists of various species of fern. The forest also
contains many standing and fallen, fire-killed,
overmature trees.
2.2. Logging
Logging involved three separate operations:
harvesting of timber, preparation of seed-bed and
ripping of log landings. Harvesting was carried
out during 13 February to 27 March 1989 in Old
Mill and 31 October 1988 to 23 March 1989 in
Deception Spur. Harvesting involved chainsaw
felling of 50-year-old Mountain Ash and mechanical snigging of logs to a landing using a rubber tyre skidder (CAT 518 Cable) in Old Mill
and a flexible steel track skidder (FMC 210) in
Deception Spur. In both logging coupes, the log
landings were constructed using a fixed track
crawler tractor (D7G) and the debarking and
loading of logs on landings were done by an excavator. The seed-bed was prepared on 20 May
and 23 May 1989 in Old Mill and Deception Spur
respectively. The seed-bed preparation involved
redistribution of logging slash and scarification
of surface soils over the entire coupe using a D7G
CAT fixed track crawler tractor in both logging
coupes. The log landings were also ripped using
a D7G CAT crawler tractor in both logging
coupes.
217
each grid point sample was classified for predominant soil horizon, litter and mineral soil
mixing a n d / o r removal. Each grid point sample
was then assigned to one of the following soil
profile disturbance categories.
(1) Undisturbed. No machine or log has
passed. Litter on the surface and intact. O~ horizon is predominant.
(2) Litter disturbed. Machine or log has
passed. Litter on the surface or partially removed. Some mineral soil may be visible in noncontinuous patches. 02 horizon is predominant.
If 02 is naturally thin, root mat stills binds the
surface A~.
(3) Topsoil disturbed. Machine or log has
passed. Litter (O~ and O2) removed or mixed
with topsoil. Topsoil mixed with subsoil. Mineral topsoil is predominant. (Topsoil consists of
A~, A2 and A3 horizons except where A2 is conspicuously bleached (McDonald et al., 1990),
w h e r e b y A 2 and A3 are regarded as subsoil. )
(4) Subsoil disturbed. Machine or log has
passed. Topsoil removed or mixed with subsoil.
Subsoil removed or mixed with C-horizon. Mineral subsoil or C-horizon is predominant. Subsoil includes B1 and B2 horizons and conspicuously bleached A 2 horizon (and any other Ahorizon below the A2. )
2.4. Measurements of soil physical properties
2.3. Characterisation of soil disturbance
2.4. I. Experimental design
About 2 months after timber harvesting and
seed-bed preparation, the experimental coupes
were surveyed using a systematic grid sampling
technique for assessing level of soil profile disturbance. The size of the grids were 20 m × 20 m
for Old Mill and 20 m × 40 m for Deception Spur
which resulted in 144 and 122 sampling points
respectively. At each grid point a 1 m 2 quadrat
was studied to identify the level of soil disturbance. Each grid point sample was assigned in
terms of one of the following operational categories: snig track, log landing, general logging area
(disturbed areas which were not used for the
above purposes) or undisturbed area.
To assess the level of soil profile disturbance
Sampling for soil physical measurements was
carried out about 5 months after timber harvesting and seed-bed preparation. To study the effect
of soil profile disturbance on physical properties
of soil, plots were established within the general
logging areas of both logging coupes. After characterising soil disturbance, each logging coupe
was stratified into three topographic positions:
upper, middle and lower slopes. Within each
topographic position, areas were located for four
classes of soil profile disturbance: undisturbed,
litter disturbed, topsoil disturbed and subsoil
disturbed. Each class of soil profile disturbance
within each topographic position was represented by five 1-m2 plots giving a total of 20 plots
per topographic position. Within each topo-
218
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
graphic position and for a given soil profile disturbance class one of the five plots was selected
randomly to measure soil physical properties. For
soil texture, organic carbon and organic matter
determination, two samples were taken from each
plot and measurements were made on bulked
samples. Four measurements of bulk density, total porosity, macroporosity and microporosity
and two measurements of saturated hydraulic
conductivity were taken from each of the randomly selected plots and mean values were used
for data analysis. The data were analysed using a
nested analysis of variance (Payne et al., 1989).
The analysis was formulated with soil profile
disturbance nested within topographic position,
and topographic position within coupe. The effect of topographic position was tested against
between topographic position within coupe variance; the effect of soil profile disturbance and
the interaction between soil profile disturbance
and topographic position were tested against between soil profile disturbance with topographic
position variance. The least significant difference (LSD, P < 0.05 ) values were calculated using the appropriate residual from the analysis of
variance, and the mean values of a specific soil
physical parameter for the four classes of soil
profile disturbance were compared (Gomez and
Gomez, 1984).
To study the effect of compaction on soil physical properties, additional plots were established
in the primary (tracks originated from log landing), secondary (tracks branched from primary
tracks) and tertiary (tracks branched from secondary tracks) snig tracks and the ripped log
landing in one logging coupe (Old Mill ). All snig
tracks and log landing plots were classified as
topsoil disturbed. These classes were replicated
three times, each replication consisting of a cluster of five one metre square plots. One of the five
plots was selected randomly to measure soil
physical properties. For a specific soil physical
parameter, the same number of measurements as
the soil disturbance treatments (above) were
taken from each plot and mean values were used
for data analysis. The data were analysed using a
one-way analysis of variance (Snedecor and
Cochran, 1978). The least significant difference
(LSD, P < 0.05 ) values were calculated using the
appropriate residual from the analysis of variance, and the mean values of a specific soil physical parameter for the log landing, and three
classes of snig track, were compared.
2.4.2. Soil texture, organic carbon and organic
matter
From each plot two disturbed soil samples were
taken at 0-100 mm depth using an auger. The
soil samples were bulked, air dried and passed
through a 2 mm sieve. Soil organic carbon content was determined using the Walkley-Black
procedure (Nelson and Sommers, 1989). Organic matter was estimated as a percentage of loss
on ignition of soil (Curts and Post, 1964; Sands
et al., 1979; Huntington et al., 1989) which was
ignited to 450°C for 24 h (Davies, 1974). Soil
particle size analysis was determined using a
plummet balance method (McIntyre and Loveday, 1974). All results are reported on an ovendried ( 105 ° C constant weight) basis.
2.4.3. Bulk density
Intact soil samples were taken at 0-100 mm
depth using a brass core (63 mm long, 72 mm
inside diameter). The cores were driven into the
soil with a falling weight hand corer. Samples
were oven-dried at 105 °C for 24 h and bulk density was determined by dividing the oven-dried
mass of soil with the core volume.
2.4.4. Pore-size distribution
The intact core samples which were used for
bulk density determination were also used for
determining total porosity, macroporosity and
microporosity (pore diameter less than 30/tm).
Intact core samples were saturated using vacuum suction desiccators and volume of water
content at saturation was determined. Saturated
intact core samples were placed on a hanging column tension table and volumetric water content
at - 10 kPa water potential was determined. Total porosity, the total volume of pore space as a
percentage of total volume of soil and pore space,
was obtained as volumetric water content at saturation. Microporosity (pore diameter less than
~a~. Rab / Forest Ecology and Management 70 (1994) 215-229
30/tm) was obtained as volumetric water content at water potential of - 10 kPa.
Macroporosity was obtained as the difference
between volumetric water content at saturation
and at - 10 kPa water potential.
Disturbed samples were used to determine
percentage of pore volume which was occupied
by pores less than 0.2/~m in diameter. This was
obtained by measuring volumetric water content
at water potential of - 1500 kPa using a pressure
plate.
2.4.5. Saturated hydraulic conductivity (Ks)
The saturated hydraulic conductivity (Ks) was
measured in the field using a disc permeameter
(Perroux and White, 1988) with a suction of 10
mm. Intact soil samples were taken at 0-100 mm
depth using a brass core (73 mm long, 100 mm
inside diameter). The cores were driven into the
soil with a falling weight. One-dimensional vertical flow of water was determined on the intact
core samples. The values of Ks were calculated
using the following equation (Philip, 1957)
219
area had some soil disturbance (see Fig. 1 ).
About two-thirds of this was disturbed by general logging. Snig tracks and log landings disturbed about 25% and 5% of the coupe area respectively. The most common type of disturbance
was topsoil disturbance. On average, topsoil disturbance accounted for 65% of the coupe area.
3.2. Soil texture
Soil texture analysis of the top 100 mm from
the undisturbed and disturbed sites within the
logged area showed that the soil texture varied
from clay loam to silty loam in the experimental
area (Table 1).
3.3. Soil organic carbon and organic matter
Analysis of variance of organic matter content
(see Table 2) indicated that the effect of topo50
[
Old Mill
40
~
Topsoil disturbed
30
1
Subsoil disturbed
I= Sx/ tt+ Ks t
where I is the cumulative flow ( m m ) , S is the
sorptivity (mm d a x / ~ ), t is the elapsed time
(days) and Ks is the saturated hydraulic conductivity (mm d a y - 1).
2.5. Eucalypt growth
] Undisturbed
'r T~'~ Litter disturbed
20
10
c~
)~m
0
Both coupes were operationally sown with E.
regnans seed by helicopter. Each plot was then
individually hand sown with approximately 0.2
g o f E . regnans seed in May 1989 to ensure all
plots received seed. Each plot was surveyed 13
months after sowing. Within each plot the height
and diameter of the tallest eucalypt seedling was
measured at 100 mm above ground level.
50
Deception S p u r
40
30
20
10
3. Results
o
3.1. Characterisation of soil disturbance
Following timber harvesting and mechanical
seed-bed preparation about 87% of the coupe
i
i
L
i
General logging
1
•
Snig track
Operational categories
i
I
J
Log landing
Fig. 1. Distribution of disturbed area by operational categories and level of soil profile disturbance.
220
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
Table 1
Texture of 0-100 m m soil depth (mean _+standard error) for undisturbed and disturbed sites in two logging coupes
Sampling site
Soil component (g per 100 g)
Soil texture
description
Sand
Silt
Clay
48 ± 7
20 ± 6
32 ± 3
Clay loam
48 2 5
53 _+3
49 ± 5
13 ± 2
18 + 5
18 ± 4
39 ± 3
29 _+3
33 ± 3
Clay
Clay loam
Clay loam
51 +
49 ±
53 ±
46 ±
5
3
3
1
25 ± 3
21 ± 6
14 ± 2
22 ± 1
24 + 7
30+2
33 ± 2
32 ± 1
Clay
Clay
Clay
Clay
55 ± 3
26 ± 1
19 ± 4
Silty loam
46 ± 1
49 ± 3
50 _+4
31 ± 2
31 ± 1
31 ± 4
23 ± 3
20 ± 3
19 ± 2
Silty loam
Silty loam
Silty loam
Old Mill
Undisturbed area
General logging area
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Snig tracks
Primary
Secondary,
Tertiary
Log landing
loam
loam
loam
loam
Deception Spur
Undisturbed area
General logging area
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Table 2
Effect of soil profile disturbance on organic carbon, organic matter and bulk density of 0- 100 mm soil depth (mean + standard
error)
Soil profile
disturbance
Organic carbon
content (%)
Organic matter
content (%)
Bulk density
10.7 ± 0.9
8.7 ± 1.4
6.8 ± 1.3
3.2 ± 0.2
24.6 ± 3.0
17.9 ± 0.5
15.5 ± 1.3
I0.0 ± 1.7
0.69 ± 0.08
0.73 ± 0.11
0.90 ± 0.04
1.15 ± 0.12
9.1 ± 0.1
8.4 + 2.2
6.4 ± 0.4
3.5 + 0.4
23.5 ± 0.9
22.9 + 4.0
19.2 ± 0.8
13.6 + 0.5
0.63
0.71
0.85
1.03
(Mg m -3)
Old Mill
Undisturbed
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Deception Spur
Undisturbed
Litter disturbed
Topsoil disturbed
Subsoil disturbed
± 0.05
± 0.09
± 0.04
± 0.07
Table 3
Organic carbon, organic matter and bulk density of 0-100 mm soil depth (mean ± standard error) in snig tracks and log
landing
Sampling site
Organic carbon
content (%)
Organic matter
content (%)
Bulk density
(Mg m -3)
Undisturbed area
Primary snig tracks
Secondary snig tracks
Tertiary snig tracks
Log landing
10.7 + 0.9
5.0 + 0.5
5.2 + 1.3
7.8 + 0.8
6.2 +_0.7
24.6 + 3.0
14.2 + 1.1
14.3 + 1.5
18.0 _+2.7
16.4 ± 1.5
0.69 + 0.08
1.12 ± 0.02
1.13 ± 0.05
0.96 ± 0.05
0.98 ± 0.01
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
10!
i
I
I
-=
•
,
O0
~
o •
"~'"
" 00
•
2~
I
I
221
turbed areas decreased by about 33% and 66%
respectively compared with undisturbed areas.
Organic carbon and organic matter content in
the snig tracks and the log landing was also significantly lower than that of undisturbed areas
(Table 3 ). Organic carbon content decreased by
about 53%, 27% and 42% respectively in the primary and tertiary sing tracks and the log landing
respectively compared to undisturbed areas. Organic matter content decreased by about 42%,
27% and 33% respectively in the primary and
tertiary snig tracks and the log landing respectively compared to undisturbed areas.
oI
0.4
0.6
0.8
1.0
1.2
1.4
1.6
3.4. Bulk density
1.2
1.0
0.8
0.6
b
0 ¸ •
•
e.
00
•
0.4
0.2 ~
e~
0.0
0.4
.
•
gO
O ~ "
0.6
0.8
1.0
1.2
]
1.4
1.6
Bulk density (Mg m "3)
Fig. 2. Relationship between bulk density and eucalypt height
a n d d i a m e t e r growth.
graphic position and the interaction between
topographic position and level of soil profile disturbance were not significant but the effect of soil
profile disturbance was significant at the 1%
level. The LSD test showed that organic carbon
and organic matter content in the litter disturbed
areas was not significantly different from that of
undisturbed areas. In contrast, organic carbon
and organic matter content in the topsoil and
subsoil disturbed areas was significantly lower
than that of the undisturbed areas. Mean organic
carbon content in the topsoil and subsoil dis-
Analysis of variance of bulk density data (see
Table 2 ) indicated that the effect of topographic
position and the interaction between topographic position and level of soil profile disturbance were not significant but the effect of soil
profile disturbance was significant at the 1%
level. The LSD test showed that bulk density in
the litter disturbed areas was not significantly
different from that of undisturbed areas. In contrast, bulk densities in the topsoil and subsoil
disturbed areas were significantly greater than
that of the undisturbed areas. Mean bulk density
in the topsoil and subsoil disturbed areas increased by about 33% and 65% respectively
compared to undisturbed areas.
Soil compaction significantly increased bulk
densities in the snig tracks and the log landing
(see Table 3). Bulk density increased by 64%,
64%, 39% and 42% in the primary, secondary and
tertiary snig tracks and the log landing respectively compared with undisturbed areas.
The height and diameter growth of 1-year-old
E. regnans was related to bulk density (Fig. 2).
The height and diameter growth reduced with
increase in bulk density. The regression of height
growth was negative and linear within the range
of data. The diameter growth followed a similar
pattern. However, the bulk density had a larger
effect on the height growth than diameter growth.
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
222
Table 4
Effect of soil profile disturbance on total porosity, macroporosity, microporosity and saturated hydraulic conductivity (Ks) of
0-100 mm soil depth mean +_standard error)
Soil profile
disturbance
Total porosity
(%)
Macroporosity
(%)
Microporosity
(pore diameter
Forest
.
Ecology
and
Management
E LS EV l E R
Forest Ecology and Management 70 ( 1994 ) 215-229
Changes in physical properties of a soil associated with logging of
Eucalyptus regnans forest in southeastern Australia
M.A. Rab
Department of Conservation and Natural Resources, Catchment and Land Management Division,
Keith Turnbull Research Institute, Ballarto Road, Frankston, Vic. 3199, Australia
Accepted 23 May 1994
Abstract
Logging operations can cause soil profile disturbance and compaction. Soil profile disturbance and compaction
change soil physical properties, which may reduce site productivity, increase soil erosion and degrade catchment
water quality. This study was undertaken to measure the effect of logging on physical properties of the 0-100 mm
surface soil in the Victorian Central Highlands, southeastern Australia. Soil physical properties were measured in
the snig tracks, log landings, general logging areas (disturbed areas which were not occupied by snig tracks or log
landings) and undisturbed areas. Within the general logging areas, measurements were made for three levels of
soil profile disturbance: litter disturbed, topsoil disturbed and subsoil disturbed.
The results indicated that logging significantly increased bulk density and decreased organic carbon and organic
matter content, total porosity and macroporosity on over 72% of the coupe area. However, on 35% of the coupe
area, the snig tracks, log landings and subsoil disturbed areas of the general logging area, bulk densities and macroporosities reached critical levels where tree growth could be affected. On these areas, organic carbon decreased
between 27 and 66%, bulk density increased between 39 and 65% and macroporosity decreased between 58 and
88%.
Saturated hydraulic conductivities decreased to critical levels for runoffto occur on over 72% of the coupe area
(topsoil and subsoil disturbed areas of the general logging area, snig tracks and log landings). On this area, the
reduction in saturated hydraulic conductivity varied between 60 and 95%.
Keywords: Soil compaction; Soil disturbance; Saturated hydraulic conductivity; Timber harvesting
I. Introduction
Logging operations cause soil profile disturbance including removal of the forest litter layer,
mixing of forest litter with mineral topsoil, mixing of topsoil with subsoil, removal of topsoil and
exposure of subsoil, removal of subsoil and exposure of parent material, and even in some situations partial removal of parent material. Logging also causes soil compaction. The level and
extent of soil profile disturbance and compaction vary with soil moisture content at the time
of operations, inherent soil physical properties,
slope of the site, the number of times a vehicle
passes over the site and machine weight (Greacen and Sands, 1980; Howard et al., 1981; Butt
and Rollerson, 1988; Wronski et al., 1989; Soane,
1990; Rab, 1992; Ghuman and Lal, 1992 ).
Soil profile disturbance and compaction may
change soil physical properties to such an extent
0378-1127/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved
SSD10378-1127(94)03430-3
216
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
that the resulting land surface may be more susceptible to soil erosion (Johnson and Beschta,
1980; Mackay et al., 1985; Farrish et al., 1993),
impede root growth (Heilman, 1981; Mitchell et
al., 1982), impede early tree growth (Minko,
1975; Donnelly and Shane, 1986; Farrish, 1990;
King et al., 1993 ) and decrease site productivity
(Perry, 1964; Wert and Thomas, 1981; Lockaby
and Vidrine, 1984). Soil disturbance and compaction increases bulk density (Gent et al., 1983,
1984; Jussofand Majid, 1987; Incerti et al., 1987;
Ole-Meiludie and Njau, 1989; Malmer and Grip,
1990; Rab et al., 1992), decreases macroporosity (Gent et al., 1983, 1984; Incerti et al., 1987;
Rab et al., 1992), reduces/redistributes organic
matter (Sands et al., 1979; Ole-Meiludie and
Njau, 1989; Anderson et al., 1994; Ryan et al.,
1992), reduces infiltration (Ole-Meiludie and
Njau, 1989; Malmer and Grip, 1990) and saturated hydraulic conductivity (Gent et al., 1983,
1984; Incerti et al., 1987). As a consequence,
surface runoff of water may increase and tree
growth may be impaired because of reduced
water supply, restricted root space and poor aeration (Greacen and Sands, 1980; Incerti et al.,
1987; Rab, 1992).
Rab et al. (1992) studied the impact of logging in southeastern Australia on the extent and
degree of soil profile disturbance. They found
that on about 73% of the coupe area the soil profile was disturbed. The majority of this disturbance resulted in topsoil disturbed areas followed by subsoil disturbed areas. They also found
that about 15% of the coupe area was compacted. The majority of the compacted area was
contributed by snig tracks followed by log landings. (Snig tracks are formed by towing a tree by
a tractor or dozer from the stump to the log processing area, known as log landing.) There is a
dearth of information on the impact of soil profile disturbance and compaction on soil physical
properties during logging in southeastern Australia (but see Incerti et al., 1987; Williamson,
1990). This information is important for greater
understanding of the physical processes, for predicting consequences of soil profile disturbance
and compaction on tree growth and soil erosion.
This information is also important for develop-
ing strategies that minimise impacts of logging
on soil and water values. This study was undertaken to measure the effect of soil profile disturbance and compaction on organic carbon and organic matter content, bulk density, pore-size
distribution and saturated hydraulic conductivity in the Victorian Central Highlands forests,
southeastern Australia.
2. Methods
2.1. Study area description
The study area is located 150 km east of Melbourne, situated near Tanjil Bren, in the Victorian Central Highlands (30 °2'S, 146 ° 15'E).
Two clearfelled coupes, Old Mill (4 ha) and Deception Spur ( 10 ha) in the Rowleys forest block
were selected for this study. The parent material
of both coupes is granitic rock. The landform is
mainly steep hills to moderately steep rolling hills
(McDonald et al., 1990). The major soil type of
the area is red gradational with a small percentage of yellow brown gradational soil (Northcote
et al., 1975 ). The average depth of the topsoil is
250 m m with up to 400 mm along drainage lines.
The depth of the subsoil varies between 650 and
1200 mm. The climate of the study area is cool
temperate and average annual rainfall is approximately 1900 mm. Average monthly temperature
ranges from 0°C in July to 20°C in February. Elevation ranges from 615 to 950 m. The slopes
vary from 0 to 20 °. The vegetation of the forest
is predominantly 1939 regrowth Mountain Ash
(Eucalyptus regnans), with occasional overmature and regrowth Grey Gum (Eucalyptus cypellocarpa). Stands are of moderate density with top
heights of 50 m. The understorey comprises three
distinct strata. The upper stratum is generally
sparse and consists of wattles (Acacia dealbata
and Acacia obiquinervia) and occasional Myrtle
Beech (Nothofagus cunninghamii) in damp locations. The middle stratum is dense and contains many shrubs and small trees, including
Blanket Leaf (Bedfordia arborescens), Musk
Daisy Bush (Olearia argophylla), Hazen Pomaderris (Pomaderris aspera) and tree ferns
(Dicksonia antarctica and Cyathea australis).
M.A. Rab / Forest Ecology and Management 70 (I 994) 215-229
The ground stratum is generally sparse and consists of various species of fern. The forest also
contains many standing and fallen, fire-killed,
overmature trees.
2.2. Logging
Logging involved three separate operations:
harvesting of timber, preparation of seed-bed and
ripping of log landings. Harvesting was carried
out during 13 February to 27 March 1989 in Old
Mill and 31 October 1988 to 23 March 1989 in
Deception Spur. Harvesting involved chainsaw
felling of 50-year-old Mountain Ash and mechanical snigging of logs to a landing using a rubber tyre skidder (CAT 518 Cable) in Old Mill
and a flexible steel track skidder (FMC 210) in
Deception Spur. In both logging coupes, the log
landings were constructed using a fixed track
crawler tractor (D7G) and the debarking and
loading of logs on landings were done by an excavator. The seed-bed was prepared on 20 May
and 23 May 1989 in Old Mill and Deception Spur
respectively. The seed-bed preparation involved
redistribution of logging slash and scarification
of surface soils over the entire coupe using a D7G
CAT fixed track crawler tractor in both logging
coupes. The log landings were also ripped using
a D7G CAT crawler tractor in both logging
coupes.
217
each grid point sample was classified for predominant soil horizon, litter and mineral soil
mixing a n d / o r removal. Each grid point sample
was then assigned to one of the following soil
profile disturbance categories.
(1) Undisturbed. No machine or log has
passed. Litter on the surface and intact. O~ horizon is predominant.
(2) Litter disturbed. Machine or log has
passed. Litter on the surface or partially removed. Some mineral soil may be visible in noncontinuous patches. 02 horizon is predominant.
If 02 is naturally thin, root mat stills binds the
surface A~.
(3) Topsoil disturbed. Machine or log has
passed. Litter (O~ and O2) removed or mixed
with topsoil. Topsoil mixed with subsoil. Mineral topsoil is predominant. (Topsoil consists of
A~, A2 and A3 horizons except where A2 is conspicuously bleached (McDonald et al., 1990),
w h e r e b y A 2 and A3 are regarded as subsoil. )
(4) Subsoil disturbed. Machine or log has
passed. Topsoil removed or mixed with subsoil.
Subsoil removed or mixed with C-horizon. Mineral subsoil or C-horizon is predominant. Subsoil includes B1 and B2 horizons and conspicuously bleached A 2 horizon (and any other Ahorizon below the A2. )
2.4. Measurements of soil physical properties
2.3. Characterisation of soil disturbance
2.4. I. Experimental design
About 2 months after timber harvesting and
seed-bed preparation, the experimental coupes
were surveyed using a systematic grid sampling
technique for assessing level of soil profile disturbance. The size of the grids were 20 m × 20 m
for Old Mill and 20 m × 40 m for Deception Spur
which resulted in 144 and 122 sampling points
respectively. At each grid point a 1 m 2 quadrat
was studied to identify the level of soil disturbance. Each grid point sample was assigned in
terms of one of the following operational categories: snig track, log landing, general logging area
(disturbed areas which were not used for the
above purposes) or undisturbed area.
To assess the level of soil profile disturbance
Sampling for soil physical measurements was
carried out about 5 months after timber harvesting and seed-bed preparation. To study the effect
of soil profile disturbance on physical properties
of soil, plots were established within the general
logging areas of both logging coupes. After characterising soil disturbance, each logging coupe
was stratified into three topographic positions:
upper, middle and lower slopes. Within each
topographic position, areas were located for four
classes of soil profile disturbance: undisturbed,
litter disturbed, topsoil disturbed and subsoil
disturbed. Each class of soil profile disturbance
within each topographic position was represented by five 1-m2 plots giving a total of 20 plots
per topographic position. Within each topo-
218
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
graphic position and for a given soil profile disturbance class one of the five plots was selected
randomly to measure soil physical properties. For
soil texture, organic carbon and organic matter
determination, two samples were taken from each
plot and measurements were made on bulked
samples. Four measurements of bulk density, total porosity, macroporosity and microporosity
and two measurements of saturated hydraulic
conductivity were taken from each of the randomly selected plots and mean values were used
for data analysis. The data were analysed using a
nested analysis of variance (Payne et al., 1989).
The analysis was formulated with soil profile
disturbance nested within topographic position,
and topographic position within coupe. The effect of topographic position was tested against
between topographic position within coupe variance; the effect of soil profile disturbance and
the interaction between soil profile disturbance
and topographic position were tested against between soil profile disturbance with topographic
position variance. The least significant difference (LSD, P < 0.05 ) values were calculated using the appropriate residual from the analysis of
variance, and the mean values of a specific soil
physical parameter for the four classes of soil
profile disturbance were compared (Gomez and
Gomez, 1984).
To study the effect of compaction on soil physical properties, additional plots were established
in the primary (tracks originated from log landing), secondary (tracks branched from primary
tracks) and tertiary (tracks branched from secondary tracks) snig tracks and the ripped log
landing in one logging coupe (Old Mill ). All snig
tracks and log landing plots were classified as
topsoil disturbed. These classes were replicated
three times, each replication consisting of a cluster of five one metre square plots. One of the five
plots was selected randomly to measure soil
physical properties. For a specific soil physical
parameter, the same number of measurements as
the soil disturbance treatments (above) were
taken from each plot and mean values were used
for data analysis. The data were analysed using a
one-way analysis of variance (Snedecor and
Cochran, 1978). The least significant difference
(LSD, P < 0.05 ) values were calculated using the
appropriate residual from the analysis of variance, and the mean values of a specific soil physical parameter for the log landing, and three
classes of snig track, were compared.
2.4.2. Soil texture, organic carbon and organic
matter
From each plot two disturbed soil samples were
taken at 0-100 mm depth using an auger. The
soil samples were bulked, air dried and passed
through a 2 mm sieve. Soil organic carbon content was determined using the Walkley-Black
procedure (Nelson and Sommers, 1989). Organic matter was estimated as a percentage of loss
on ignition of soil (Curts and Post, 1964; Sands
et al., 1979; Huntington et al., 1989) which was
ignited to 450°C for 24 h (Davies, 1974). Soil
particle size analysis was determined using a
plummet balance method (McIntyre and Loveday, 1974). All results are reported on an ovendried ( 105 ° C constant weight) basis.
2.4.3. Bulk density
Intact soil samples were taken at 0-100 mm
depth using a brass core (63 mm long, 72 mm
inside diameter). The cores were driven into the
soil with a falling weight hand corer. Samples
were oven-dried at 105 °C for 24 h and bulk density was determined by dividing the oven-dried
mass of soil with the core volume.
2.4.4. Pore-size distribution
The intact core samples which were used for
bulk density determination were also used for
determining total porosity, macroporosity and
microporosity (pore diameter less than 30/tm).
Intact core samples were saturated using vacuum suction desiccators and volume of water
content at saturation was determined. Saturated
intact core samples were placed on a hanging column tension table and volumetric water content
at - 10 kPa water potential was determined. Total porosity, the total volume of pore space as a
percentage of total volume of soil and pore space,
was obtained as volumetric water content at saturation. Microporosity (pore diameter less than
~a~. Rab / Forest Ecology and Management 70 (1994) 215-229
30/tm) was obtained as volumetric water content at water potential of - 10 kPa.
Macroporosity was obtained as the difference
between volumetric water content at saturation
and at - 10 kPa water potential.
Disturbed samples were used to determine
percentage of pore volume which was occupied
by pores less than 0.2/~m in diameter. This was
obtained by measuring volumetric water content
at water potential of - 1500 kPa using a pressure
plate.
2.4.5. Saturated hydraulic conductivity (Ks)
The saturated hydraulic conductivity (Ks) was
measured in the field using a disc permeameter
(Perroux and White, 1988) with a suction of 10
mm. Intact soil samples were taken at 0-100 mm
depth using a brass core (73 mm long, 100 mm
inside diameter). The cores were driven into the
soil with a falling weight. One-dimensional vertical flow of water was determined on the intact
core samples. The values of Ks were calculated
using the following equation (Philip, 1957)
219
area had some soil disturbance (see Fig. 1 ).
About two-thirds of this was disturbed by general logging. Snig tracks and log landings disturbed about 25% and 5% of the coupe area respectively. The most common type of disturbance
was topsoil disturbance. On average, topsoil disturbance accounted for 65% of the coupe area.
3.2. Soil texture
Soil texture analysis of the top 100 mm from
the undisturbed and disturbed sites within the
logged area showed that the soil texture varied
from clay loam to silty loam in the experimental
area (Table 1).
3.3. Soil organic carbon and organic matter
Analysis of variance of organic matter content
(see Table 2) indicated that the effect of topo50
[
Old Mill
40
~
Topsoil disturbed
30
1
Subsoil disturbed
I= Sx/ tt+ Ks t
where I is the cumulative flow ( m m ) , S is the
sorptivity (mm d a x / ~ ), t is the elapsed time
(days) and Ks is the saturated hydraulic conductivity (mm d a y - 1).
2.5. Eucalypt growth
] Undisturbed
'r T~'~ Litter disturbed
20
10
c~
)~m
0
Both coupes were operationally sown with E.
regnans seed by helicopter. Each plot was then
individually hand sown with approximately 0.2
g o f E . regnans seed in May 1989 to ensure all
plots received seed. Each plot was surveyed 13
months after sowing. Within each plot the height
and diameter of the tallest eucalypt seedling was
measured at 100 mm above ground level.
50
Deception S p u r
40
30
20
10
3. Results
o
3.1. Characterisation of soil disturbance
Following timber harvesting and mechanical
seed-bed preparation about 87% of the coupe
i
i
L
i
General logging
1
•
Snig track
Operational categories
i
I
J
Log landing
Fig. 1. Distribution of disturbed area by operational categories and level of soil profile disturbance.
220
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
Table 1
Texture of 0-100 m m soil depth (mean _+standard error) for undisturbed and disturbed sites in two logging coupes
Sampling site
Soil component (g per 100 g)
Soil texture
description
Sand
Silt
Clay
48 ± 7
20 ± 6
32 ± 3
Clay loam
48 2 5
53 _+3
49 ± 5
13 ± 2
18 + 5
18 ± 4
39 ± 3
29 _+3
33 ± 3
Clay
Clay loam
Clay loam
51 +
49 ±
53 ±
46 ±
5
3
3
1
25 ± 3
21 ± 6
14 ± 2
22 ± 1
24 + 7
30+2
33 ± 2
32 ± 1
Clay
Clay
Clay
Clay
55 ± 3
26 ± 1
19 ± 4
Silty loam
46 ± 1
49 ± 3
50 _+4
31 ± 2
31 ± 1
31 ± 4
23 ± 3
20 ± 3
19 ± 2
Silty loam
Silty loam
Silty loam
Old Mill
Undisturbed area
General logging area
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Snig tracks
Primary
Secondary,
Tertiary
Log landing
loam
loam
loam
loam
Deception Spur
Undisturbed area
General logging area
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Table 2
Effect of soil profile disturbance on organic carbon, organic matter and bulk density of 0- 100 mm soil depth (mean + standard
error)
Soil profile
disturbance
Organic carbon
content (%)
Organic matter
content (%)
Bulk density
10.7 ± 0.9
8.7 ± 1.4
6.8 ± 1.3
3.2 ± 0.2
24.6 ± 3.0
17.9 ± 0.5
15.5 ± 1.3
I0.0 ± 1.7
0.69 ± 0.08
0.73 ± 0.11
0.90 ± 0.04
1.15 ± 0.12
9.1 ± 0.1
8.4 + 2.2
6.4 ± 0.4
3.5 + 0.4
23.5 ± 0.9
22.9 + 4.0
19.2 ± 0.8
13.6 + 0.5
0.63
0.71
0.85
1.03
(Mg m -3)
Old Mill
Undisturbed
Litter disturbed
Topsoil disturbed
Subsoil disturbed
Deception Spur
Undisturbed
Litter disturbed
Topsoil disturbed
Subsoil disturbed
± 0.05
± 0.09
± 0.04
± 0.07
Table 3
Organic carbon, organic matter and bulk density of 0-100 mm soil depth (mean ± standard error) in snig tracks and log
landing
Sampling site
Organic carbon
content (%)
Organic matter
content (%)
Bulk density
(Mg m -3)
Undisturbed area
Primary snig tracks
Secondary snig tracks
Tertiary snig tracks
Log landing
10.7 + 0.9
5.0 + 0.5
5.2 + 1.3
7.8 + 0.8
6.2 +_0.7
24.6 + 3.0
14.2 + 1.1
14.3 + 1.5
18.0 _+2.7
16.4 ± 1.5
0.69 + 0.08
1.12 ± 0.02
1.13 ± 0.05
0.96 ± 0.05
0.98 ± 0.01
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
10!
i
I
I
-=
•
,
O0
~
o •
"~'"
" 00
•
2~
I
I
221
turbed areas decreased by about 33% and 66%
respectively compared with undisturbed areas.
Organic carbon and organic matter content in
the snig tracks and the log landing was also significantly lower than that of undisturbed areas
(Table 3 ). Organic carbon content decreased by
about 53%, 27% and 42% respectively in the primary and tertiary sing tracks and the log landing
respectively compared to undisturbed areas. Organic matter content decreased by about 42%,
27% and 33% respectively in the primary and
tertiary snig tracks and the log landing respectively compared to undisturbed areas.
oI
0.4
0.6
0.8
1.0
1.2
1.4
1.6
3.4. Bulk density
1.2
1.0
0.8
0.6
b
0 ¸ •
•
e.
00
•
0.4
0.2 ~
e~
0.0
0.4
.
•
gO
O ~ "
0.6
0.8
1.0
1.2
]
1.4
1.6
Bulk density (Mg m "3)
Fig. 2. Relationship between bulk density and eucalypt height
a n d d i a m e t e r growth.
graphic position and the interaction between
topographic position and level of soil profile disturbance were not significant but the effect of soil
profile disturbance was significant at the 1%
level. The LSD test showed that organic carbon
and organic matter content in the litter disturbed
areas was not significantly different from that of
undisturbed areas. In contrast, organic carbon
and organic matter content in the topsoil and
subsoil disturbed areas was significantly lower
than that of the undisturbed areas. Mean organic
carbon content in the topsoil and subsoil dis-
Analysis of variance of bulk density data (see
Table 2 ) indicated that the effect of topographic
position and the interaction between topographic position and level of soil profile disturbance were not significant but the effect of soil
profile disturbance was significant at the 1%
level. The LSD test showed that bulk density in
the litter disturbed areas was not significantly
different from that of undisturbed areas. In contrast, bulk densities in the topsoil and subsoil
disturbed areas were significantly greater than
that of the undisturbed areas. Mean bulk density
in the topsoil and subsoil disturbed areas increased by about 33% and 65% respectively
compared to undisturbed areas.
Soil compaction significantly increased bulk
densities in the snig tracks and the log landing
(see Table 3). Bulk density increased by 64%,
64%, 39% and 42% in the primary, secondary and
tertiary snig tracks and the log landing respectively compared with undisturbed areas.
The height and diameter growth of 1-year-old
E. regnans was related to bulk density (Fig. 2).
The height and diameter growth reduced with
increase in bulk density. The regression of height
growth was negative and linear within the range
of data. The diameter growth followed a similar
pattern. However, the bulk density had a larger
effect on the height growth than diameter growth.
M.A. Rab / Forest Ecology and Management 70 (1994) 215-229
222
Table 4
Effect of soil profile disturbance on total porosity, macroporosity, microporosity and saturated hydraulic conductivity (Ks) of
0-100 mm soil depth mean +_standard error)
Soil profile
disturbance
Total porosity
(%)
Macroporosity
(%)
Microporosity
(pore diameter