the evaluation of three native grass species and a tree
TRANSCRIPT
1
The Evaluation of Three Native Grass Species
and a Tree Species as a Vegetation Option for
Coal Mine Rehabilitation on the
Mpumalanga Highveld of South Africa
By
Martin Platt
Submitted to COALTECH Research Association
Native Species Trial
2
ABSTARCT
Three field trials were established in early March 2004 on topsoil prepared for
seeding at Kleinkopje Colliery, Optimum Colliery and Syferfontein Colliery, all
situated on the Mpumalanga Highveld of South Africa. Cynodon dactylon, Themeda
triandra, and Hyparrhenia hirta plugs were established in plots and were treated
with and without fertilizer. Field measurement of survivorship, cover, and biomass
production, were taken until July 2007. Acacia sieberana was also established and
was evaluated for survivability, height and basal diameter. The results indicate that
Cynodon dactylon out-performed the Themeda triandra and Hyparrhenia hirta,
achieving 100% survivability and cover at all sites by 2007, regardless of fertilizer
addition. Trees were able to establish at Kleinkopje Colliery attaining 97%
survivability by the end of the trial, but performed poorly at Optimum Colliery and
Syferfontein Colliery. Establishing plugs as a vegetative option on mined land could
be used when slopes for a planter machine is too steep, and in establishing buffers
against pasture grass intrusion into ecologically sensitive areas.
3
TABLE OF CONTENTS
ABSTARCT.......................................................................................................................i
TABLE OF CONTENTS.....................................................................................................ii
CHAPTER 1
LITERATUREREVIEW…………………………………………………………………………………………………1
1.1 INTRODUCTION……………………………………………………………………………………………..1
1.2 OPENCAST MINING AND REHABILITATION METHOD…………………………………….2
1.3 SOIL COMPACTION………………………………………………………………………………………..3
1.4 SOIL AMELIORANTS………………………………….……………………………………………………4
CHAPTER 2
MATERILAS AND METHOD..……………………………………………………………………………………..5
2.1 EXPERIMENTAL LAYOUT………………………………………………………………………………..5
2.1.1 SITE DESCRIPTION………………………………………………………………………………5
2.1.1.1 KLEINKOPJE COLLIERY…………………………………………………………….5
2.1.1.2 OPTIMUM COLLIERY………………………………………………………………5
2.1.1.3 SYFERFONTEIN COLLIERY……………………………………………………….6
2.2 EXPERIMENTAL DESIGN…………………………………………………………………………………6
2.2.1 TRIAL ESTABLISHMENT………………………………………………………………………6
2.2.2 SPECIES………………………………………………………………………………………………8
2.3 TRIAL SETUP………………………………………………………………………………………………….8
2.3.1 PLANTING………………………………………………………………………………………….8
2.3.2 FERTILIZER APPLICATION…………………………………………………………………..8
MAINTENANCE……………………………………………………………………………………………..9
2.4 FIELD MEASUREMENTS……………………………………………………………………………….10
2.4.1 SURVIVORSHIP…………………………………………………………………………………10
2.4.2 COVER……………………………………………………………………………………………..10
2.4.3 BIOMASS……………………………………………...............................................11
2.4.4 TREE SURVIVORSHIP………………………………………………………………………..12
2.4.5 TREE HEIGHT……………………………………………………………………………………12
2.4.6 TREE BASAL COVER………………………………………………………………………….13
CHAPTER 3
RESULTS………………………………………………………………………………………………………………….14
3.1 KLEINKOPJE COLLIERY………………………………………………………………………………….14
3.1.1 SURVIVORSHIP…………………………………………………………………………………14
3.1.2 COVER……………………………………………………………………………………………..15
3.1.3 BIOMASS…………………………………….…………………………………………………..16
3.1.4 TREE SURVIVORSHIP…………………………………………..……………………………17
3.1.5 TREE HEIGHT……………………………………………………………..…………………….17
3.1.6 TREE BASAL DIAMETER…………………………………………………….………………17
3.2 OPTIMUM COLLIERY……………………………………………………………………………………20
4
3.2.1 SURVIVORSHIP…………………………………………………………………………………20
3.2.2 COVER……………………………………………………………………………………………..21
3.2.3 BIOMASS………………………………………………………………………………………….22
3.2.4 TREE SURVIVORSHIP………………………………………………………………………..23
3.2.5 TREE HEIGHT DIAMETER………………………………………………………………….23
3.3 SYFERFONTEIN COLLIERY…………………………………………………………………….………24
3.3.1 SURVIVORSHIP…………………………………………………………………………………24
3.3.2 COVER……………………………………………………………………………………………..25
3.3.3 BIOMASS………………………………………………………………………………………….26
3.3.4 TREE SURVIVORSHIP…………………………………………………………................26
3.3.5 TREE HEIGHT……………………………………………………………………………………27
3.3.6 TREE BASAL DIAMETER…………………………………………………………………….27
CHAPTER 4
DISCUSSION AND CONCLUSIONS……………………………………………………………………………28
4.1 SURVIVORSHIP…………………………………………………………………………………………….28
4.2 COVER…………………………………………………………………………………………………………30
4.3 BIOMASS……………………………………………………………………………………………….......31
4.4 TREE DATA…………………………………………………………………………………………………..31
4.5 RECOMMENDATIONS………………………………………………………………………………….33
CHAPTER 5
REFERNCES………………………………………………………………………………………………………...……3
4
5
CHAPTER 1
LITERATURE REVIEW
1.1 Introduction
Coal is the world’s most abundant and widely distributed fossil fuel and it remains
the primary energy source for several countries world-wide. In South Africa, coal
mining makes a significant contribution to economic activity, development of
sustainable job opportunities and foreign exchange earnings. The coal mining sector
contributes 1.8% the South Africa’s GDP.
Coal extraction is essentially mined by two methods, namely underground and
opencast method. Unfortunately, these are very destructive processes, and the
environmental implications associated with this very serious. Unfortunately, highly
potential agricultural lands, ecologically sensitive environments and surrounds are
compromised for development, often resulting in loss of ecosystem value.
A large portion of coal reserves and operation on the Eastern Highveld is situated in
the heart of the South African grassland biome. On a global scale, this biome is
considered to be one of the most devastated, and the South African grassland biome
has been identified as critically endangered (Olsen and Dinerstein, 1998). In South
Africa, the grassland biome covers an area of approximately 349 174 km 2
(Neke and
Du Plessis, 2004). Approximately 100 000 ha has already been transformed or
destroyed by opencast and underground mining on the Eastern Highveld of South
Africa (Neke and Du Plessis, 2004). According to Neke and Du Plessis (2004), this
could increase to 325 081 ha with the amount economically mineable coal available
in the area.
By law (Minerals and Petroleum Resources Act of 2002; National Environmental
Management Act) opencast mines have to be rehabilitated and the post mining
landscape returned to a sustainable land use. Although the objective of most
6
rehabilitation programs aim to restore land to its pre-mining agricultural land
capability (Mentis, 2006) by establishing a pasture with fertilizer-responsive grass
species on topsoil replaced topsoil. These pastures are made productive through
defoliation management and fertilizer additions. After a few years, reversion to
native grassland is opted for by withdrawing fertilizer application and applying
defoliation management. However, this is a very slow process of secondary
succession and often pre-mining ecological status is not achieved (Mentis, 2006).
1.2 Opencast Mining and Rehabilitation Method
The Vryheid Formation (Ecca Group) of the Karoo Sequence, which is present on the
Eastern Highveld of South Africa, attains some 140 m at the thickest point and
contains a number coal seam, of which four are considered to have economic
potential. Mining this coal is dependent on the economic limit of the depth of over
burden above the coal seam, which could reach up to 30 m, and the thickness of the
underlying coal seam.
In order to access the coal, the material above the coal seam (known as burden
material), is excavated and removed. Once the overburden is exposed, it is drilled,
blasted and then removed. This material is placed such that it can be profiled,
typically by dozer. The slope and depth of topsoil placed on the profiled burden
material, ultimately determines the post mining land class capability for that area.
Before the overburden is removed, topsoil is stripped and is either stockpiled or is
placed on profiled overburden material. The placed topsoil is then levelled, thus
creating a surface for seeding, and later vegetation establishment.
The seed mix used for seeding typically comprises an annual species such as
Eragrostis teff in combination with perennial species. Such species might include
Chloris gayana, Cenchrus ciliaris, Cynodon dactylon, Digiteria eriantha, Eragrostis
curvula, Eragrostis teff, and Medicago sativa (Mentis, 1999). The ratio of the seed
7
mix used for re-vegetation is usually specified in the mine’s Environmental
Management Programme (EMP).
1.3 Soil Compaction
The process by which topsoil is stripped, stockpiled and placed on regarded burden
material often results in severe compaction. This is detrimental to the physical,
chemical and biological properties of the soil. Consequently, these soils have lower
soil aggregate stability, lower infiltration rates, reduced water holding capacity, and
a greater capacity to resist root extension (Chapman et al, 1994), all of which inhibit
the potential for plant growth and establishment on the rehabilitated soil.
The major cause of soil compaction is trafficking of machinery on re-placed soil. This
is further exacerbated by settling under gravity and (Haigh, 2000). As a consequence
of this the particle-to-particle contact within the soil increases and the percentage of
macro pores decreases (Haigh, 2000). This affects nutrient availability with de-
nitrification a result of anaerobic conditions (Davies et al, 1995). Because of these
changes, the soil becomes a less favourable environment for soil organisms reducing
growth of surface vegetation (Haigh, 2000).
The soil chemical properties of the soil also deteriorate when topsoil is stockpiled. In
these stockpiles, oxygen becomes limiting and anaerobic environment is created. As
a result, large quantities of nitrogen are lost to the atmosphere as gaseous N2 or N2O,
through the process of de-nitrification. Loss of nitrogen and other nutrients by
leaching also occurs, reducing the capacity for vegetation establishment. Davies et
al (1995) reported a 2600kgha-1
loss of nitrogen from reinstated topsoil from a
stockpile.
Compaction is accelerated in the presence of percolating water especially following
intensive rains (Haigh, 2000). This is often the case in stockpiled soil, which may be
stockpiled for tens of years (Lipiec et al, 2003). When water percolates through the
soil, the aggregates disperse and trapped air within the soil is displaced. As a result,
the soil loses structure and after drainage, tight packing of the soil particles occurs
8
(Haigh, 2000). In addition to this, the soil may become waterlogged resulting in an
anaerobic environment. This leads to increased anaerobic bacteria activity, which
attack the organic materials that bind the aggregates together, thus lowering the
stability of the soil, and increasing its potential for compaction (Haigh, 2000).
1.4 Soil Ameliorants
Substrates can be added soil to alleviate the severity of soil compaction. These
might include sewage sludge, pine bark, earthworms, and microbes. Many studies
have illustrated the use of these additives as ameliorants of soil compaction.
Earthworms improve soil physical structure. Their burrowing activity results in the
production of increased macro pores. This improves hydraulic processes in the soil,
improves aeration (Tian et al, 2000) and can decrease the bulk density of a soil
(Jascho et al, 1989; Whalley et al, 1995). Additions of pine bark have been reported
to decrease then bulk density of a soil. Brown et al (1975). They showed that
increased additions of pine bark to sand decreased the bulk density of the media.
Illera et al (1999) showed a decrease in soil bulk density from 1.22cm-3
– 1.06gcm-3
with addition of municipal sewage sludge compared to a control soil.
9
CHAPTER 2
MATERIALS AND METHODS
2.1 Experimental Layout
2.1.1 Site Description
2.1.1.1 Kleinkopje Colliery
Kleinkopje Colliery is situated approximately 20km south of Witbank and is owned by
Anglo American. The trial site (26o00’S; 29
o12’E) was established on 21 March 2004
on topsoil prepared for seeding operations.
According to the mine’s EMPR, the average yearly rainfall is 696 mm. Summer
temperature ranges between 12oC to 29
oC, while winter temperatures range from -
3oC to 20
oC.
The dominant soils in the area are Avalon, Hutton, Glencoe, Mispah, Clovelly, and
Wasbank.
2.1.1.2 Optimum Colliery
Optimum Colliery, now owned by Optimum Coal Holdings (PTY) LTD, is a coal mine
situated 30 km south east of the town Middelburg. The trial site (25o59’S; 29
o37’E)
was established on 20 February 2004 on topsoil prepared as part of the
rehabilitation program.
The area receives an annual rainfall of 682 mm with a mean maximum temperature
of 22.5oC and mean minimum temperature of 7.7
oC.
The dominant soils in the area are Hutton, Clovelly, Glencoe, Avalon, Fernwood,
Kroonstad and Glenrosa (Lachenicht, 2005).
10
2.1.1.3 Syferfontein Colliery
Syferfontein Colliery is a Sasol owned coal mine operating an opencast and
underground section. It is situated 20 km south east of Secunda in the Mpumalanga
Province (Republic of South Africa). The trial site (26o27’S; 29
o16’E) was established
on 20 March 2004 on topsoil placed on profiled spoil that formed part of the
rehabilitation program.
The area receives 689 mm rainfall per annum with an average summer temperature
ranging between 10oC and 30
oC, with an average temperature of 20
oC. Average
winter temperature varies between -3oC and 21
oC.
The soil in the area is generally a heavy clay soil (55%) with an average bulk density
of 1.4 Mg m-3
(Beletse, 2004).
2.2 Experimental Design
2.2.1 Trial Establishment
The trial was established at Optimum colliery on 20 February 2004. Planting at
Syferfontein Colliery and Kleinkopje Colliery was postponed until 20 March following
intensive rains and subsequent waterlogged soil at the trial sites.
The trial was setup as a random bock design, with plugs grown in 5 m x 5 m plots. In
each plot, 272 plugs were planted at 18 cm intervals. The trial layout at the various
sites is given in Figure 1.
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H T Ct
Tt Tt C
Ht T H
Ht Tt Ct
T Ht Ct
C C H
A A A
Kleinkopje Colliery
Ct T Ht
C H C
Ht H C
T Tt Ht
Ct T Ct
H Tt Tt
A A A
Optimum Colliery
C Tt C
H Ct Ct
H T H
Ht Tt Ht
Ht T C
T Tt Ct
A A A
Syferfontein Colliery
Figure 1: A diagram of the trial set up at Kleinkopje Colliery, Optimum Colliery, and
Syferfontein Colliery. Refer to Table 1 for abbreviations.
Table 1: A key of abbreviations for the different species and treatments used in
Figure 1.
T Themeda triandra No fertilizer
Tt Themeda triandra With fertilizer
H Hyparhennia hirta No fertilizer
Ht Hyparhennia hirta With fertilizer
C Cynodon dactylon No fertilizer
Ct Cynodon dactylon With fertilizer
A Acacia sieberana With fertilizer
Key
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2.2.2 Species
Three native species were used in the trial namely Themeda triandra, Hyparrhenia
hirta and Cynodon dactylon. Two treatments were applied, one with fertilizer and
the other without. Each treatment and species was replicated three times (refer to
Figure 1).
25 Acacia sieberana trees were planted in three tree 6m x 6m plots at 1.5m spacing.
Each plot was treated with a fertilizer application.
The plugs and trees were raised at Topcrop Nursery, which is situated 30 km East of
Pietermaritzburg. These plugs were transported to the three collieries and planted.
2.3 Trial Setup
2.3.1 Planting
Holes were dug at 18 cm interval, in which a plug was inserted. Prior to placement,
the hole was filled with hydrated tera-sorp, a powder that forms a thick gel when
hydrated, and which enhances establishment of plugs and seedlings by supply of
water during the first two weeks of establishment. The roots of the plug were also
dipped in the tera-sorp solution prior to planting.
2.3.2 Fertilizer Application
Soil samples from each site were taken in November 2003. These samples were sent
to Cedara Soil Research Laboratories and a fertilizer recommendation given. Prior to
planting, each treated plot received an application of fertilizer which was
broadcasted by hand. Using a rake, this fertilizer was then worked into the soil to a
depth of 3 cm – 5 cm. The amount of fertilizer applied at each site is given in Table 2
and Table 3.
13
Table 2: Fertilizer application for Kleinkopje Colliery and Optimum Colliery.
Fertilizer kg/ha kg/plot
Lime Ammonium Nitrate 1200 3
Diammonium Phosphate 90 0.225
Potassium 210 0.525
Table 3: Fertilizer application for Syferfontein Colliery.
Fertilizer kg/ha kg/plot
Lime Ammonium Nitrate 1200 3
Diammonium Phosphate 280 0.700
Potassium 125 0.313
2.3.3 Maintenance
Once the trial was established, the trial was left to its own devices. Irrigation was
supplied by rainfall. Weed control at the three sites was conducted in March 2005,
where weeds were physically removed by hand. Kleinkopje Colliery received
additional weed removal in March 2006. The other sites did not receive this
additional activity.
2.4 Field Measurements
Measuring and sampling at did not necessarily occur at the same time owing to
constraints by the mine and by the research team. Constraints included decline in
access to the mine. The various sampling dates are given in Table 4.
14
Table 4: A schedule indicating the dates that the various trials were sampled.
Kleinkopje Optimum Syferfontein
March 2004
November 2004
April 2005
April 2006
June 2007
CollieryDate
Key
Sampled
Not
Sampled
2.4.1 Survivorship
Survivorship was measured by counting the number of plugs in each plot, dividing by
272 and expressing as a percentage. During sampling, wilted plugs were not counted
as ‘survived’.
2.4.2 Cover
Basal cover was assessed using two different methods depending on the growth
morphology (i.e. tufted and stoloniferous growth forms) of the grass being assessed.
Basal cover of the tufted growth forms (i.e. Themeda triandra and Hyparrhenia hirta)
was measured once the plugs had been harvested. Using a measuring rule, the
diameter of the exposed tuft was measured. Two measurements were taken, one
along the head axis, and another along the body axis of the plot. Plots were divided
into four quadrants and measurements were taken from 10 random samples within
each quadrant. This was then expressed as a percentage cover over the entire plot.
A photo illustrating measuring the diameter of a Themeda triandra tuft is depicted in
Figure 2.
For the stoloniferous growth form (i.e. Cynodon dactylon), a 30 cm x 30 cm quadrat
with nylon string strung from corner to corner to form a ‘cross hair’ was placed at
the centre of the plug. The percentage area in each sub quadrant of the quadrant
was then estimated and recorded. Forty random samples were taken from each plot.
This was then expressed as percentage cover of the plot.
15
Figure 2: A photo of basal diameter measurement of a Themeda triandra tuft.
2.4.3 Biomass
At the end of each growing season, each plot was harvested. Using a pair of shears,
each plug within the plot was cut approximately 10 cm from above the ground
surface. All above ground matter was collected and placed into 9 litre potato bags.
These bags were then transported from the mine and placed in a drying oven for a
period of 48 hours at 70oC at the Anglo Coal Environmental Services laboratories.
Once the bags had been oven dried, they were allowed to equilibrate to room
temperature over a period of 24 hours. Thereafter, each bag containing oven dried
material was weighed. Next, the material was removed from the bag and the bag
weighed separately. The difference between the bag holding the dry material and
the empty bag represented the biomass produced. All biomass figures in each plot
were summed and expressed in g ha-1
. A photo of a cropped trial at Optimum
Colliery is given in Figure 3.
16
Figure 3: A photo illustrating a trial harvest at Optimum Colliery.
2.4.4 Tree Survivorship
Each tree that survived was counted. These were totalled and divided by 75, and
expressed as a percentage.
2.4.5 Tree Height
Using a steal taped tape measure, each tree was measured from the ground surface
to the highest point on the tree. After each winter, and once the trees had re-
coppiced, the same measuring principle was applied. A picture illustrating
measuring is shown in Figure 4.
17
Figure 4: Photos showing tree height measuring at Optimum Colliery.
2.4.6 Tree Basal Diameter
Using a pair of vernier callipers, the diameter of each tree was measured
approximately 5 cm from the ground surface.
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CHAPTER 3
RESULTS
3.1 Kleinkopje Colliery
3.1.1 Survivorship
Figure 5: Plug survivorship at Kleinkopje Colliery. Refer to Table 1 for abbreviations.
Cynodon dactylon achieved 100% survivorship throughout the duration of the trial
for both treated and untreated plots.
Treated Hyparrhenia hirta decreased from 100% to 44% over the four seasons.
However, survivability remained constant around 60% for three season (2004 -2006)
but this decreased by 20% in 2007.
Both treated and untreated Themeda triandra behaved similarly in that survivability
decreased from 100% to about 65% from the first to the second season. However,
both treatments were able to recover to 80% and 87% respectively by the end of the
trial period.
19
3.1.2 Cover
Figure 6: Cover percentage at Kleinkopje Colliery. Refer to Table 1 for abbreviations.
Overtime, both untreated and treated Cynodon dactylon attained 100% cover. In
the second season, untreated Cynodon dactylon attained 86% cover, and by the third
season cover had levelled off at 100%. Treated Cynodon dactylon had a 98.75%
cover in the second season and reached 100% in the following season.
Hyparrhenia hirta within the untreated plots covered 1.73% in the second season of
the trial and increased to 2.75% in the following season. 2.65% was recorded in the
final season of the trial period. Treated Hyparrhenia hirta achieved a maximum
cover of 7.51% in the third season from a first season measurement of6.19%. Cover
subsequently decreased to 4.09% in the fourth season.
Themeda triandra cover within the untreated plots increased stepwise year on year,
from 1.61% in the second season, to 3.41% in the final season (2007). Maximum
cover of 4.36% for treated Themeda triandra was achieved in the third season of the
20
trial period from an initial cover of 3.64%. Cover decreased to 3.86% in the final
season (2007).
3.1.3 Biomass
Figure 7: Biomass production at Kleinkopje Colliery. Refer to Table 1 for
abbreviations.
Treated Cynodon dactylon produced more above ground year on year compared to
untreated plots. The biomass produced from the untreated Cynodon dactylon plots
reached a maximum of 74.66 g m-2
in the 2007 season, from an initial 49.13 g m-2
in
2005. Treated plots decreased overtime from 443.73 g m-2
produced in 2004 to
174.47 g m-2
in 2007.
Biomass more than doubled in year 2 from 393.59 g m-2
to 961.40 g m-2
, but reduced
to 419 g m-2
in the third season. Untreated Hyparrhenia hirta in 2005 measured
176.71 g m-2
. This increased to 508.58 g m-2
in 2006. However, this decreased to
444.85 g m-2
in 2007.
21
Treated Themeda triandra increased year on year, with the second harvest
producing three times more material than the first (64.77 g m-2
to 248.32 g m-2
).
Aboveground biomass produced in the third harvest increased slightly from the
second, with 248.32 g m-2
being produced. Untreated plots increased from 42.27 g
m-2
to 206.71 g m-2
to 199.10 g m-2
during the trial duration.
3.1.4 Tree Survivorship
Tree survivorship at Kleinkopje Colliery remained fairly consistent throughout the
trial period. In the last season, tree survivorship measured 97.33%. Survivorship
dipped to 97.33% in September 2005, and it this it remained for the next two years.
3.1.5 Tree Height
The average tree height increased from 42.79 cm to 172 cm at the end of July 2007.
In the two seasons after this there was no significant increase in height, however, in
the fourth and fifth seasons, there was a substantial increase in tree height with
trees averaging 172 cm.
3.1.6 Tree Basal Diameter
The same relationship exhibited for height over time is shown for tree diameter. In
the first two seasons, the diameter of the trees hovered between 0.48 cm and 0.65
cm. However, over the next three seasons the tree diameter increased significantly
from 0.65 cm (March 2005) to 2.17 cm (September 2005) to 4.67 cm (August 2006)
to 3.67 cm (July 2007).
22
Figure 8: Tree survivorship at the Kleinkopje Colliery, Optimum Colliery, and
Syferfontein Colliery.
Figure 9: Tree height at the Kleinkopje Colliery, Optimum Colliery, and Syferfontein
Colliery.
23
Figure 10: Tree diameter at the Kleinkopje Colliery, Optimum Colliery, and
Syferfontein Colliery.
24
3.2 Optimum Colliery
3.2.1 Survivorship
Figure 11: Plug survivorship at Optimum Colliery. Refer to Table 1 for abbreviations.
Cynodon dactylon was able to record 100% survivability by the end of the trial period
for both treatments. At the end of the first season, survivability decreased to 77%
and 85% for untreated and treated plots, however, both treatments increased to
100% the following season, and it remained that way for the duration of the trial.
Hyparrhenia hirta decreased overtime from 100% in the first season to 28% and 22%
for untreated and treated plots. A drastic drop of 40% and 60% for untreated and
treated plots occurred after the first winter. Thereafter, species died off at a much
slower rate, with a 28% and 22% survivorship being recorded at the end of the trial
period.
Resultant survivorship was much higher in untreated Themeda triandra (51%) than
was for treated Themeda triandra (32%). A severe decrease was exhibited after the
first winter. Untreated species decreased to 65% and treated Themeda triandra
25
decreased to 48%. Another severe drop in numbers was experienced in the second
season where untreated Themeda triandra decreased to 43% and treated Themeda
triandra 25%. Numbers remained consistent for two seasons, after which an
increase in numbers occurred in the last season for both treatments (untreated 50%,
treated 30%).
3.2.2 Basal Cover
Figure 12: Cover percentage at Optimum Colliery. Refer to Table 1 for abbreviations.
Both untreated and treated Cynodon dactylon plots achieved 100% cover throughout
the duration of the trial.
Untreated Hyparrhenia hirta plots achieved maximum cover of 3.29% in the third
season of the trial, up from 1.98% in the second season of the trial. Cover measured
in the final season of the trial was 2.18%.
Cover in the untreated Themeda triandra plots increased stepwise from 1.98% in
2005 to 2.51% in 2006 to 3.04%. Treated Themeda triandra increased year on year
from 1.03% in 2005 to 1.80% in 2007.
26
3.2.3 Biomass
Figure 13: Biomass production at Optimum Colliery. Refer to Table 1 for
abbreviations.
Treated Cynodon dactylon plots achieved a higher aboveground biomass year on
year compared to the untreated plots. Production produced in the untreated plots
decreased overtime from 199.71 g m-2
in 2005 to 126.70 g m-2
in 2007. Production in
the treated plots peaked after the second harvest at 358 g m-2
up from 296.13gm-2
in
2006. Biomass reduced to 288.14 g m-2
in the third season.
Untreated and treated Hyparrhenia hirta plots showed similar biomass production
trends. Production for both treatments peaked after the second harvest with 145.81
g m-2
and 358.71 g m-2
produced for untreated and treat plots respectively, up from
237.99 g m-2
and 235.072 g m-2
after the first harvest. Biomass production
decreased after the final harvest to 187.29 g m-2
and 228.86 g m-2
.
Untreated Themeda triandra increased from 60.31 g m-2
in 2005 to 302.77 g m-2
in
2006, but decreased in 2007 to 204.19 g m-2
. Biomass produced under treated plots
increased year on year from 50.71 g m-2
in 2005 to 135 g m-2
in 2007.
27
3.2.4 Tree Survivorship
Tree survivability at Optimum decreased form 96% in the first season to 78.66% in
the fifth and final season. An annual 10% loss of trees was experienced from 2004
and 2005, with a 77.33% being recorded at the end of 2005. This remained
consistent into the next season with a final 78.66% survivorship being.
3.2.5 Tree Height
Over the first three seasons tree height remained fairly consistent, decreasing only
slightly from 47.28 cm to 43.44 cm. However, in the season of 2006, tree height
increased significantly to 108.08 cm and a final height of 119.59 cm was recorded in
the final season (2007).
3.2.6 Tree Basal Diameter
Basal diameter remained relatively low during the first three seasons, ranging from
0.61 cm to 0.91 cm. In the fourth season, basal diameter increase considerably to
2.12 cm. However, in the final season the basal diameter decreased to 1.58 cm.
28
3.3 Syferfontein Colliery
3.3.1 Survivorship
Figure 14: Plug survivorship at Syferfontein Colliery. Refer to Table 1 for
abbreviations.
Both untreated and treated Cynodon dactylon attained 100% survivability by the end
of the trial period. However, both treatments experienced a decrease in
survivorship after the first winter, but increased to 100% by 2005.
Hyparrhenia hirta achieved 44% and 45% survivability by the end of the trial period.
Numbers did not decrease radically after the first winter period with only a 4% and
2% decrease recorded for untreated and treated treatments. Untreated
Hyparrhenia hirta decreased substantially over the next three seasons with 75%
recorded at the end of 2005, and 45% by the end of 2006. Treated plots decreased
significantly from 2004 to 2005, with a 50% decrease recorded. Survivorship
remained consistent thereafter, with a similar survivability was measured in the final
season.
29
Untreated and treated Themeda triandra decreased to 38% and 25% respectively by
the end of the trial. After the first winter Themeda triandra had decreased by 12%.
By the third season, survivability decreased to 55% and 71% for untreated and
treated plots respectively, after which a further decrease to 35% and 25% occurred
in the final season.
3.3.2 Cover
Figure 15: Cover percentage at Syferfontein Colliery. Refer to Table 1 for
abbreviations.
Cover in the both untreated and treated Cynodon dactylon plots maintained 100%
for the two seasons it was measured.
Untreated Hyparrhenia hirta increased from 6.84% to 7.01% from 2004 to 2005.
Treated Hyparrhenia hirta plots increased from 4.87% to 4.17%.
Themeda triandra decreased in cover over the two seasons for both treatments.
Untreated Themeda triandra decreased from 3.98% to 2.38% from 2005 to 2006.
30
Treated Themeda triandra plots decreased from 4.31% to 1.70% during the same
period.
3.3.3 Biomass
Figure 16: Biomass production at Optimum Colliery. Refer to Table 1 for
abbreviations.
Treated plots showed a higher biomass production compared to untreated plots for
all species. Treated Cynodon dactylon produced 505.17 g m-2
compared to 216.17 g
m-2
in the untreated plots. Treated Hyparrhenia hirta produced 902.19gm-2
, while
untreated plots produced 654.81 g m-2
. Treated Themeda triandra produced 171.06
g m-2
with 163.58 g m-2
produced from the untreated plots.
3.3.4 Tree Survivorship
Survivorship decreased to almost half, from the first to the final season (100% to
56%). The trees suffered a 4% loss after the first winter spell, after which there was
a major drop of 17% in the second season. Another substantial decrease of 25%
occurred in the final season, reducing survivability to 56%.
31
3.3.5 Tree Height
In the first three season of growth, tree height did not increase much. Initially, a tree
height of 38cm was recorded. This decreased to 20 cm in the second season, and
then attained a height of 37cm in 2005. However, in the fourth season, the trees
grew by 100 cm to attain a height of 137cm.
3.3.6 Tree Basal Diameter
Over the four seasons, tree diameter increased from 0.58 cm to 0.95 cm.
32
CHAPTER 4
DISCUSSION AND CONCLUIONS
4.1 Survivorship
The main objective for establishing vegetation on restored soils of mined areas is to
create a cover against soil erosion by wind and rain (Tanner, 2007). A major factor in
achieving this is to firstly get vegetation to establish, and thereafter ensure that the
cover remains sustainable over time.
In this study, Cynodon dactylon exhibited the highest survivability with 100%
achieved throughout the trial period regardless of fertilizer additions. Themeda
triandra performed well at Kleinkopje Colliery under both treatments attaining 87%
and 80% survivorship for untreated and amended treatments. However, Themeda
triandra did not perform well at Optimum and Syferfontein collieries for both
treatments, attaining only 28% and 22% respectively at Optimum Colliery and 35%
and 25% at the Syferfontein site (refer to Figure 5, 11 and 14).
The stoloniferous growth form of Cynodon dactylon may have favoured the success
over the tufted growth forms of Hyparrhenia hirta and Themeda triandra, as the
network radiating from the central planting point may have been able to attain more
nutrients available in the soil and from the fertilizer applied.
Interestingly, Themeda triandra performed better in the untreated plots than in the
fertilizer amended plots, and indicates that this species favours lower fertility
environments on reclaimed soil. This is consistent with Le Roux and Mentis (1986)
work conducted at the University of Kwa-Zulu Natal’s Agricultural research farm,
uKulinga, where they showed that Themeda triandra responded poorly to nitrogen
fertilizer application.
33
In a study conducted Baer, Blair, Collins and Knapp (2004), the affect of three fertility
three levels of nitrogen availability (ambient, enriched, and reduced fertilization) on
species diversity and richness response was measured. The study revealed that total
diversity and richness declined over time in the ambient nitrogen and enriched
nitrogen, but increased in the reduced nitrogen soil in the second and third year of
the study.
Hyparrhenia hirta performed the poorest at all the sites except at Syferfontein. An
interesting point to note is the increase in survivability in the last season in the
untreated plots at Kleinkopje and Optimum sites, as well as the treated site at
Syferfontein. This was attributed to the ability of this species in the said plots to
‘self-seed’. Masses of seed are produced after it flowers from September to March
(van Oudshoorn, 1999), were able to germinate and establish, and in so doing,
increased the ‘survivability’ (Figure 17).
Figure 17: A photo illustrating the ‘self-seeding’ effect of Hyparrhenia hirta at
Kleinkopje Colliery.
The poor survivability of the Hyparrhenia hirta and Themeda triandra may also be
attributed to weed infestation, especially at the Optimum and Syferfontein sites
where only once weed control was undertaken as compared to two at Kleinkopje
Colliery.
34
The low survivability of plugs at the three trial sites is not unique to survivability on
restored soils. In a study carried out by Harwood, Hacker and Mott (1999) at Saraji
mine in Queensland Australia, almost half of the seedlings that had emerged from
seeded topsoil, died after two weeks. Seven weeks after seedling emergence, the
highest survivability achieved in the study was only 44%.
4.2 Cover
Generally, treated plots showed a higher basal diameter than untreated plots at the
various sites. However, at the Optimum site Themeda triandra showed better basal
cover in 2006 and 2007 than its treated counterpart at Optimum Colliery.
Hyparrhenia hirta achieved better basal cover for treated plots at Kleinkopje Colliery
and Optimum Colliery throughout the trial period. An isolated case of better greater
basal cover of Hyparrhenia hirta occurred in 2006 at Syferfontein.
Basal cover as a measure of determining the effectiveness of a cover against soil
protection can be used in isolation. Basal cover of the individual species expressed
as a cover of the entire plot is more valuable in determining the effectiveness of a
cover. This was achieved by multiplying the average basal cover recorded by the
number of plugs survived in each plot, and expressed a percentage.
Cynodon dactylon demonstrated the 100% cover by the end of the trial at all the
sites. Cynodon dactylon success as a cover compared to Themeda triandra and
hyparrhenia hirta may be attributed to its growth form. Cynodon dactylon has a
stoloniferous growth form, whereby lateral shoots grow along the soil surface. The
main apex of the lateral stem elongates indefinitely as nodes, with roots and shoots
developing at these nodes (Tainton, 1999). As growth is continuous, a resultant
network of stolons and shoots radiating from the central planting point and this
creeping effect allows for a greater area of the soil surface to be covered. However,
in the tufted species, roots grow to depth in the soil, and even though tillering did
occur after the first harvest (increase in basal diameter), the extent of this did not
result in the cover achieved by Cynodon dactylon.
35
Ultimately, survivability has the greatest influence on cover when comparing the
tufted species. Generally, better survivability results in better cover. At Kleinkopje
Colliery, treated Hyparrhenia hirta showed best cover by the end of the trial period
of 4.09% compared to 2.66% of untreated Hyparrhenia owing to greater survivorship
of 43.75% (treated) compared 31% (untreated).
Themeda triandra showed better cover in the untreated plots at Optimum
throughout the trial period, owing to approximately 40% higher survivability year on
year of the untreated plots compared to treated plots. This trend occurred at both
the Syferfontein and Kleinkopje sites (refer to Figure 6, 12, and 15).
4.3 Biomass
Biomass production was generally greater in treated plots compared to untreated
plots. This is especially so for Cynodon dactylon plots across all the sites, where the
yield year on year was greater in treated plots compared with untreated plots. This
is consistent with research conducted by Longhurst and O’Connor (1999) in the
Waikato coal fields, where they showed that relative yields increased with increased
fertilizer additions. Relative yields of 72%, 100%, 126% and 147% were produced
from 250, 500, 1000, and 2000 kg ha-1
fertilizer additions.
In an experiment conducted by Ebelhar, Barnhisel, Akin and Powell (1982) at a site in
Western Kentucky, the effects of lime, N, P, and K fertilizer amendments on
bermudagrass growth and development was tested. Results showed that dry matter
yields increased significantly with each additional increment of nitrogen applied. 0
kg Nha-1 produced 371 kg ha-1
; 50 kg Nha-1
produced 537 kg ha-1
; and 100 kg Nha-1
produced 834 kg ha-1
.
4.4 Tree Data
36
Tree survivability only proved successful at Kleinkopje Colliery with 97% survivability
by the end of the trial period. Survivability at Optimum Colliery and Syferfontein
Colliery did not prove very successful with 79% and 56% recorded at the end of the
study. Poor survivorship at the Optimum and Syferfontein sites could be attributed
to the high incidence of frost that occurs at these sites. Not chemically treating the
area for weeds may also have contributed to the lowered survivability of the trees.
Other studies have also demonstrated the difficulty in establishing trees on
reclaimed mine soils. In a 12 year study conducted by Chaney et al (1995), it was
demonstrated that the most rapid decline in seedling survival occurs during the first
four years after planting. It also showed that survival continues to decline gradually
thereafter.
Treatment of weeds in tree rows is vitally important to the success of trees. Chaney
et al (1995) reported that chemical control of ground cover in the first two years of
seedling establishment was the most important factor that influences seeding
survival. Their study indicated that after 12 growing seasons on a mined site, black
walnut and northern red oak survival was 61% and 39% respectively with chemical
plant-control. Without chemical plant control, these two trees showed a
survivability of 2% and 0.2% after 12 growing seasons.
This could be attributed to the high incidence of frost experienced at the various
sites as well as and cold winter temperatures. Over the first three growing seasons,
although tree height was low, the roots might have stabled well which allowed for
eventual growth in the fourth season.
Soil condition resulting from soil bed preparation also has a major influence on tree
survival and performance. In a study conducted by Conrad et al (2002), soil
compaction as a result of topsoil placement for seedbed preparation, was shown to
be most detrimental for establishment and survivability of trees. The study indicated
that with an increase in bulk density, tree-survival rate decreases. Data from the
study showed that when dry bulk density in the top 50mm of the soil was greater
37
than 1723 kg m-3
, tree survivability averaged less than 50%. This report does not
indicate any soil data from the sites, but it can be assumed that high compaction as a
result of current topsoil placement practice would have influenced the survivorship
of the trees.
4.5 Recommendations
Planting plugs as a vegetative option on mined out land is too expensive and
impractical if applied to the vast areas that area mined out throughout the life of a
coal mine. However, there might be application for re-vegetation technique,
especially in areas inaccessible to planters, and in ecologically sensitive areas.
In areas that are inaccessible to tractor and planters, such as on steep coal dumps
and protection berms, plugs can be planted by hand. Cynodon dactylon appears to
be the species of choice for this owing to its effective creeping ability and
survivability. This species is able to establish cover very quickly and would reduce the
potential of erosion in steep areas.
Themeda triandra and Hyparrhenia hirta could be used in establishing buffers
between ecologically sensitive areas and rehabilitated areas. Because these species
don’t spread aggressively compared to species used in rehabilitation seed mixes,
these buffers would prevent or reduce current pasture grasses from intruding into
such areas. This practice could form part of a biodiversity management plan.
38
CHAPTER 5
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