African
Journals Online
Southern African Forestry Journal
Issue 199, November 2003
ABSTRACTS
Killing Eucalyptus
grandis cut stumps after multiple coppice rotations in the KwaZulu-Natal
midlands, South Africa: scientific paper
Little,
Keith M.
Abstract: The repeated regeneration of Eucalyptus
grandis through the management of coppice shoots results in large
multi-stemmed stumps that are difficult to kill. To test the most effective
manner in which these stumps could be killed, a trial was initiated at felling
on a fourth rotation stand of E. grandis stumps in the KwaZulu-Natal
Midlands. Triclopyr (amine salt, 360 g l-1), triclopyr (butoxy ethyl
ester, 480 g l-1), imazypyr (100 g l-1),
metsulfuron-methyl (600 g kg-1) and a combination of triclopyr
(butoxy ethyl ester, 480 g l-1) + glyphosate (isopropylamine salt,
192 g l-1) were applied to a basal frill, the cut surface, or the
foliage of coppice regrowth of E. grandis stumps. These treatments were
compared to an untreated control where the coppice regrowth was manually cut
with an axe. Irrespective of the active ingredient, the use of herbicides
proved to be more effective in preventing coppice regrowth than by manual
control with an axe. The application of herbicides to a basal frill killed 90 %
of the stumps and required the least follow-up control.
Keywords: Coppice regrowth,
Sprouts, Stool, Cut surface, Foliar, Basal frill, Herbicides
Effects of site management operations on the nutrient
capital of a eucalypt plantation system in South Africa: scientific paper
Du Toit, Ben
Abstract: The Karkloof Project is a case
study of the effects of intensive site management operations during the
interrotational period, on (a) the nutrient capital of the system, and (b) the
availability of growth resources (nutrients and water) in a commercial Eucalyptus
grandis stand in South Africa. This paper specifically focuses on the
nutrient contents in various pools of the system, namely the soil, the forest
floor, and the above- and below-ground biomass. The effects of nutrient removal
through harvesting operations, slash management or slash burning were examined
in relation to estimates of readily plant-available nutrient pools in the
system. The removal of individual nutrient elements through harvesting plus
slash burning was calculated for a regime of one planted crop followed by two
coppice crops. In this regime, slash burning (if used) and fertilization are
normally only implemented immediately before replanting. The combined losses of
harvesting and burning (averaged per crop cycle) amounted to 13, 25, 11, 5 and
3% of the readily available pools for N, P, K, Ca and Mg, respectively. The
system is thus well buffered against the depletion of most macronutrients over
the short term. Despite this fact, the cumulative effect of nutrient removal
through successive rotations could add up to substantial amounts over long
periods of time. Nutrients removed from the system need to be replenished to
ensure sustained productivity in perpetuity. The comparatively large percentage
loss of P is small in actual quantity (ca. 20 kg ha-1 per
crop cycle) and is commonly mitigated to some degree by recommended
fertilization practices. Losses of Mg are very small relative to available Mg
pools. However, N, K and Ca losses are not replenished under current management
regimes and management will need to deal with this to ensure long-term
ecological sustainability. Strategies to ensure sustainable supplies of these
nutrients are discussed.
Keywords: Intensive
silviculture, Eucalyptus grandis, Harvesting, Slash burning, Fertilization
Site and
stand age effects on fertiliser responses in Pinus patula pulpwood
plantations in Swaziland: scientific paper
Morris,
Andrew R.
Abstract: Six fertiliser trials were
established in separate stands in their 4th, 7th or 12th
year on both granite and gabbro derived soils in the Usutu Forest, Swaziland.
All trials compared the same factorial combination of N, P and K fertilisers.
Tree growth response to fertiliser was measured five years after application.
The trials demonstrate that meaningful responses to fertiliser can be obtained
when applied to established pulpwood stands without thinning. Both stand age at
application and soil parent material were found to influence response to
fertiliser. With K, positive responses were obtained in the 3 and 6 year old
stands but negative responses were evident applied to 11-year-old stands.
Positive responses to K were also more pronounced on gabbro derived soils. Tree
growth was improved by P applied in 6- and 11-year-old stands and by N applied
in 11-year-old stands. Results are discussed in relation to nutrient cycling,
stand development, soil fertility and records of long-term productivity at
Usutu. It is proposed that observed declines in second rotation productivity in
block A of the forest are associated with gabbro-derived soils and that this
decline can be corrected by fertiliser application.
Keywords: Fertiliser
response, 2R decline, Pinus patula, Stand age, Soil nutrition
Does soil compaction on harvesting extraction roads affect
long-term productivity of Eucalyptus plantations in Zululand, South
Africa?: scientific paper
Smith,
Colin W.
Abstract: The effect of soil compaction on
the growth of Eucalyptus grandis and two clonal hybrids (Eucalyptus
grandisx urophylla (E. gxu) and Eucalyptus grandis x camaldulensis (E.
gxc)) was evaluated on harvesting extraction roads at three sites in the
Zululand region of KwaZulu-Natal. Significantly lower initial survival was
observed in the extraction road compared to the uncompacted area for E. gxu
and E. grandis, the effect being site dependent whereas no significant
differences were observed for E. gxc at any site. Soil compaction
resulted in significantly lower tree growth on the extraction road at 8 years
on a Constantia soil (4 to11% clay content) for all species/clonal hybrids (8
to 26% decrease) but there was no significant effect on tree growth at either
of the other sites (8 and 5 year old stands) where the soils had a coarser
texture. Even when a significant growth effect was observed in the extraction
road the net effect on the compartment was reduced with increasing width
between the extraction roads. Thus a 26% growth loss on an extraction road
corresponded to a 3, 7% decrease in volume in the compartment in a 7th row
extraction system. The paper emphasises the difficulty in quantifying growth
losses since growth varies in a cyclical manner with distance from the
extraction road. The lack of substantial growth losses on old extraction roads
is attributed to relatively low levels of soil strength even when compacted,
increasing available water capacity with increasing bulk density on very sandy
soils, non-critical aeration levels when compacted and the effects of old tree
roots providing access through compacted zones. This work has shown that,
provided controlled traffic is practised rotation after rotation, the effects
of harvesting extraction roads on the productivity of Eucalyptus
plantations on sandy soils in Zululand are not pronounced.
Keywords: Harvesting impacts,
Soil compaction, Soil damage, Zululand, Long-term site productivity
A
breeding strategy for Acacia mearnsii (black wattle) in South Africa:
management paper
Dunlop,
R.W.; Barnes, R.D.; Nixon, K.M.; Hagedorn, S.F.
Abstract: The black wattle breeding programme
that has served the wattle bark industry of South Africa for the past five
decades put little emphasis on improving the yield and quality of the timber,
as timber was not the product of importance. Today the timber is as important,
if not more so, than the bark. A decision was taken, by the industry to
re-design the breeding and production strategy for the species in South Africa,
to improve timber yield and quality while maintaining an acceptable bark
quality. Using the available seed at the ICFR at present, a Multiple Population
Breeding Strategy has been chosen. The sub-populations have been established
using the origin of the seed as the determining factor. Five sub-populations
were established in KwaZulu-Natal during November 2002. The sub-populations were
designed as progeny tests and as seedling seed orchards planted adjacent to one
another. The performance of the families in the progeny tests will determine
the management of the seed orchards. Generation turnover will be via open
pollination in the initial years. Once a nucleus population is established,
controlled pollinations may be used. The benefits from this strategy will be
passed on to the industry in the form of improved seed.
Keywords: Acacia mearnsii, Black wattle, Bark, Timber,
Multiple population breeding strategy, Subpopulation
Potential for genetic improvement of yield of exotic
softwood tree species in Rwandan plantation forestry: research note
Mugunga,
C.P.; Van Wyk, G.
Abstract: Exotic softwood tree species play a
major role in Rwandan plantation forestry. They are used to produce sawn timber
used for various purposes. Pinus patula is the major commercial species.
Growth and yield of this species were compared in terms of seed source
variation based on two trials, one established in Muhanga- Ndiza, Mushubati
District, Gitarama Province at 16 years and another in Cyeru District,
Ruhengeri Province at 15 years. Yield comparison was also made between P.
patula and other new species being tested namely P. caribaea, P. kesiya,
P. maximinoi and P. tecunumanii.
Although
results are variable, it seems that genetic gains are possible in P. patula
through the use of appropriate geographic sources. Land races from other
African countries may play a major role in establishing a simple breeding strategy
based on more seed introductions. Very significant improvements in volume
production can be achieved through the use of other promising species such as P.
maximinoi and P. tecunumanii. Further testing and improvement may
confirm the potential of the two species since the current conclusions were
drawn from results from small trials. Further improvements may possibly be
achieved by introducing other tropical pine species such as P. oocarpa
and also through crossing of related species. Unlike the other pine species, P.
kesiya proved to be poorly adapted to local conditions and should not be
considered in Rwanda as a plantation tree species. It is recommended that
improved germplasm from external sources be included to accelerate the tree
improvement programme for the most promising species in Rwanda.
Keywords: Pinus patula, P.
caribaea, P. kesiya, P. maximinoi, P. tecunumanii
African
sandalwood (Osyris lanceolata): resource assessment and quality
variation among populations in Tanzania: research note
Mwang'ingo,
P.L.; Teklehaimanot, Z.; Hall, J.B.; Lulandala, L.L.L.
Abstract: African sandalwood (Osyris
lanceolata) populations occurring in Tanzania were assessed to determine
the current resource status and ascertain variation in quality existing among them.
This will provide a guide in the selection of populations where conservation
efforts and improvement programmes can be concentrated. The resource status was
assessed through estimation of the species' density per unit area and
measurements of tree dimensions. Quality variation was assessed by determining
the amount of oil extracted from a given amount of wood and the proportion
composition of santalol, a prime determinant of sandalwood oil quality. The
study revealed that populations supporting O. lanceolata in Tanzania
occur mostly in arid to semiarid areas with the majority being on stony and
rocky soils. However, big sized trees are supported in humid climates, being
favoured by relatively low soil pH and reasonable amounts of soil nitrogen.
Tree density ranged from 38 individuals to 76 per hectare. The mean tree height
was 3, 8 m (2, 1 to 6, 5 m) while the mean diameter was 5, 7 cm (3, 6 cm to 8,
6 cm). The best quality and quantity of oil came from populations of relatively
arid climates compared to those of humid climates. Populations differed
significantly in both yield and quality. The highest yield obtained was 8, 45 ±
0, 54% from Gubali population while the highest santalol content (32, 2 ± 1,
2%) was from Bereko populations. Within trees, quantity and quality of oil was
higher in wood portions close to the ground in both the root and shoot system.
The amount decreased toward the root and shoot tip. The root and the shoot
system were similar in quality and quantity of oil. The observed harvesting
selectivity is thus primarily influenced by quality differences among
populations while the large dimension and density differences among populations
seem to be secondary. Inclusion of the root systems during harvesting is also a
matter of maximizing the raw material to be collected rather than differences
between the two portions. The exact factors controlling wood quality in the
species have however remained uncertain. Probably, genetic factors alone or in
combination with the environmental factors play a significant role.
Keywords: African sandalwood,
Osyris lanceolata, Oil yield, Santalol content, Resource status
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