The overall aim of the study was to investigate re-vegetation of disturbed sites, using nursery grown
plugs (from seedling trays) of Themeda triandra, Heteropogon contortus and Hyparrhenia dregeana in
order to reach practical management guidelines for re-vegetation using indigenous grass plugs. A
number of field trials were set up at Kamberg Nature Reserve (29°24'S, 29°40'E) on a site that was
clear felled of A. mearnsii in October 1997. The trials were established in January 1998 and January
1999. A total of approximately 52 ,000 nursery raised plugs of T. triandra, H. contortus and
H. dregeana were planted into an area of approximately 7,000 m2
.
In the planting density trial , plugs of H. dregeana only and a combination of T. triandra/H. contortus
were planted at 15 cm and 30 cm spacings. The T. triandra/H. contortus combination at 30 spacing
showed the greatest survival and lateral plant growth (tiller number and basal area) and this
combination is thus recommended.
In the over-sowing trials, the H. dregeana and T. triandra/H. contortus combination at both 15 cm and
30 cm spacing were over-sown with E. curvula. The survival and lateral growth of the T. triandra/
H. contortus combination at 30 cm was again greater than the other treatments. Over-sowing with
E. curvula suppressed the survival and lateral growth of the planted plugs across all treatments
compared to not over-sowing. The over-sown conditions showed a significant decrease in the
diversity of the plots, both in the number of species present and the Shannon diversity index.
An area that had been cleared of A. mearnsii and sown to E. curvula 25 years previously was shown
to have a lower number of species than the neighbouring veld. Nursery raised plugs of T. triandra
were planted into the mature E. curvula in an attempt to improve the biodiversity of these areas. To
re-introduce T. triandra into these E. curvula swards the plugs must be planted into the centre of a
gap rather than around the base of an E. curvula plant. For improved survival of the plugs the
E. curvula tufts must be clipped, while for best lateral growth the E. curvula tufts must be sprayed with
a glyphosate herbicide three months prior to planting and clipping. However, the added expense of
spraying and clipping is not warranted as the clipped treatments also showed good growth.
Transplant shock is common when planting nursery raised plugs out into the field, as there is a
relatively small root volume in the plug compared to the above ground leaf biomass. Alleviation of
moisture stress at planting using a starch based polymer with high water holding capacity
(Terrasorb®) and a white, needle punched geo-fabric (Agrilen®) to provide a seven day period of
artificial shade after planting did not show significant improvements over the control with regards to
survival or plant growth. Thus these methods of moisture amelioration are not recommended in revegetation
through planting of plugs at this study site.
A trial was established to investigate the biomass production of six different treatments to determine
their potential to support a fire. The total biomass for the plots which were over-sown by E. tef and
planted to only H. dregeana were on average sufficient for a fire, but there was a discontinuous fuel
load across these plots, especially in the replications that had very low survival rates and thus these
plots could not be burnt. The control and herbicide sprayed plots also showed sufficient fuel load for
a fire, but this fuel load was made up of A. mearnsii saplings and bramble with very little grass cover
and thus a fire would not have burnt through these plots either. The T. triandra/H. contortus
combination did not produce sufficient fuel load, due to poor survival. Thus only the plots over-sown
with E. curvula were able to burn in this trial and as a burning trial per se the trial was abandoned.
Seed bearing hay (thatch) was collected in early summer (December 1997) and late summer (April
1998). Both times of year of harvesting proved to be successful in terms of grass cover, although the
early harvested thatch had a greater number of species per plot. The Shannon diversity indexes of
the two treatments were not significantly different. The multi-response permutation procedure
technique confirmed that there was a compositional difference between the treatments. By the end of
the trial Harpochloa falx and T. triandra and H. dregeana were indicators for the early and the late
harvested thatch respectively. Comparing the thatching trial and the planting density trial indicated
that the T. triandra/H. contortus combination at 30 cm spacing would be recommended to maximize
biodiversity.
The summer months have been shown to be the best time to plant the plugs, although the actual
success will be dependant on the conditions within a particular year. The plugs should not be kept in
the nursery for longer than three months and larger plugs (96 seedlings per tray) should be used.
Nursery raised plugs of T. triandra and H. contortus were planted in an equal mix in an area that was
cleared of A. mearnsii in 1996. By June 1998 661 H. contortus seedlings and 14 T. triandra seedlings
had germinated naturally. The November 1998 population consisted of 418 H. contortus seedlings
and 18 T. triandra seedlings. By May 2000 the June 1998 population showed a survival of 78.4% and
the November 1998 population showed a survival of 91 .1 %.
In the various trials, the ability of the nursery raised plugs used for re-vegetation to suppress the regrowth
of A. mearnsii was investigated by determining the number of A. mearnsii seedlings per metre
squared. The plant spacing and species of plugs used did not have a significant effect on the number
of A. mearnsii seedlings per metre squared. Over-sowing with E. curvula did, however, significantly
suppress the wattle re-growth. In the thatching trial the early harvested plots showed lower numbers
of A. mearnsii per metre squared than the late harvest plots, as they were covered with a thick layer
of thatch soon after the A. mearnsii was cleared which suppressed the A. mearnsii re-growth.
Although E. curvula is able to produce a high biomass and suppress the A. meansii seedlings, it has
a detrimental effect on the biodiversity of the area. Therefore, in conservation areas, where
biodiversity is of great importance the planted plugs (at 30 cm spacing) or seed bearing hay must be
used in preference to sowing E. curvula , although it must be remembered that greater follow up
control is likely to be needed with planted plugs or seed bearing hay. The area must be planted or
thatched as soon as possible after clear felling to provide competition for the A. mearnsii seedlings. / Thesis (M.Sc.Agric.)-University of KwaZulu-Natal, Pietermaritzburg, 2005.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:ukzn/oai:http://researchspace.ukzn.ac.za:10413/5516 |
| Date | January 2005 |
| Creators | Glaum, Melanie Jane. |
| Contributors | Zacharias, Peter J. K., Granger, J. Ed., Everson, Terry M., Smith, M. |
| Source Sets | South African National ETD Portal |
| Language | en_ZA |
| Detected Language | English |
| Type | Thesis |
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