African
Journals Online
Southern African Forestry Journal
Issue 196, November 2002
ABSTRACTS
The
impact of the addition of Eucalyptus grandis wood chips on
nitrogen availability in plantation soils: scientific paper
Bird,
Theresa L.; Scholes, Mary C.
Abstract:
The impact of plantation residues, as a result of clearfelling, on
nutrient availability in plantation systems, as well as the
difficulties during subsequent planting and harvesting, should be
considered in the development of plantation management strategies. The
aim of this experiment was to determine if the addition of stump wood
chips would result in the immobilisation of nitrogen. Soil from two
plantations, one of the Kranskop soil form (0,57% nitrogen) and one of
the Hutton soil form (0,23% nitrogen), were analysed in a laboratory
experiment for changes in nitrogen availability. Soils were amended
with wood chips and varying amounts of nitrogen fertilizer. Inorganic
nitrogen was measured after 14,60 and 90 days of aerobic incubation.
Net mineralisation rates, regardless of treatment or soil, ranged
between -24,98 and +2,53 mg nitrogen / g soil / day, over the 3-month incubation
period. Immobilisation of nitrogen was found to occur in those
treatments that received the highest nitrogen additions. Addition of
wood chips on their own did not alter the nitrogen availability
patterns. However, it was observed that wood chips, together with high
levels of additional nitrogen, resulted in an extended period of
release of nitrogen in these plantation soils.
Weed composition in relation to
site in re-established pine compartments on the Mpumalanga Escarpment,
South Africa: scientific paper
Jarvel, Leander; Pallett, Robert
Abstract:
A survey of weed species distribution patterns and abundance in
clearfelled pine compartments in the Mpumalanga escarpment region was
undertaken to determine the relationship between weed species and
cover abundance in relation to environmental and compartmental
factors. In total 359 transects were sampled each with 5 X 25 m2
quadrats (1 795 square quadrats in total).
Phytolacca
octandra
and Solanum mauritianum were found to be the most widespread
species in the study area and dominated most transects. Less common
were Pteridium spp., Bidens pillosa, Oplismenis hirtillus
and Senecio tamoides, but these species had high cover
abundance ratings where they did occur and therefore may be considered
as having a high potential to compete with the tree crop for
resources.
The
most important factor affecting vegetation cover abundance and species
composition was altitude. Other factors which were important in
determining weed distribution patterns were the length of time since
clearfelling, aspect, the proximity of the stand to indigenous woody
vegetation in ravines, local moisture conditions as affected by slope
shape and type and position in the landscape with respect to river
valley systems.
Eight
weed groups were identified in the survey area using discriminant
function analysis to link environmental variables to weed communities.
Each weed group is characterised by differences in cover abundance and
relative proportions of different weed types. The weed groups and
their association with environmental variables are used as a
predictive tool for developing weed control strategies and control
measures in forest operations.
The
effect of bottom heat on rooting Pinus patula and Pinus
elliotti x Pinus caribaea stem cuttings in South Africa:
scientific paper
Mitchell,
R.G.
Abstract:
Five trials, testing the effect of bottom heat on rooting, were set
between January 1995 and December 1996 on P. patula and P.
elliottii x P. caribaea cuttings as a method of improving root
strike. In four out of five trials rooting percentages improved with
the addition of bottom heat at optimal temperatures and in all trials,
where root dry mass was assessed, bottom heat had a positive influence
on root dry mass irrespective of season. The increase in root dry mass
ranged between 97 % and 166 %. In one trial, where cuttings were set
in the warmest months of the year, rooting remained unchanged. Rooting
declined for those treatments where average media temperatures were
raised to extreme levels (>300 oC). Optimum media
temperatures, during the period of root initiation, were found to
range between 250 oC and 280 oC. Rooting media
temperature was also found to influence the amount of stem decay and
basal callusing. Future research should concentrate on the
relationship between moisture and heat requirements during rooting.
A new approach to modelling
streamflow reductions resulting from commercial afforestation in South
Africa: scientific paper
Gush,
M.B.; Scott, D.F.; Jewitt, G.P.W.; Schulze, R.E.; Hallowes, L.A.;
Gorgens, A.H.M.
Abstract:
The Department of Water Affairs and Forestry has, for some time,
needed a comprehensive tool to incorporate the impacts of commercial
afforestation on water resources into water use authorisation and
allocation processes. Simulation modelling on a national scale, using
the ACRU model, was identified as one possible solution.
However, in order to establish confidence in the national simulation
results, it was necessary to first verify model output against
reliable observed data from process studies and long-term catchment
afforestation experiments. In the verification phase, long term
reductions in streamflow resulting from afforestation were
satisfactorily simulated for five research catchments. Some problems
were experienced with catchments in the Western Cape, with
verifications on shorter duration experiments and the simulation of
specific evaporative processes. Modelling of low flows was less
successful than for total flows. In the second phase (the generation
of the national database), simulations were first performed for the
dominant Acocks (1988) veld type (i.e. 0% afforestation) within 843
Quaternary Catchments exhibiting afforestation potential (to determine
baseline streamflow), followed by simulations of streamflow after 100%
afforestation with eucalyptus, pine and wattle respectively. The
difference between the unafforested and afforested simulations equated
to streamflow reduction caused by afforestation.
This
culminated in the generation of maps and tables expressing reductions
in streamflow per Quaternary Catchment, which represents a working
solution for immediate application but may be improved upon with
further work.
Stand stability in pines: an
important silvicultural criterion for the evaluation of thinnings and
the development of thinning regimes: management paper
Hinze,
W.H.F.; Wessels, N.O.
Abstract:
This article deals with the role played by the stability factor (SF)
in the evaluation of thinnings in fastgrowing, even-aged pine stands.
It also illustrates how the stability factor is influenced by
thinnings and site over time. The SF is expressed as the ratio between
breast height diameter in centimeters and tree height in meters. The
minimum cut-off values used by SAFCOL are 0,85 for P. radiata and 1,15
for the other major commercial pines. Most of the data was collected
in the late 70's and was lost during the many changes in the
Department of Forestry and SAFCOL. (See Editorial Comment on page
40)
A framework for analyzing
workforce dynamics in forest harvesting in South Africa: management
paper
Manyuchi,
Killian Tendai; Pulkki, Reino E.
Abstract:
People are the industry's most valuable asset. However, due to its
dynamic nature, labour cannot be owned but only rented. A framework
for measuring, monitoring and managing labour dynamics is used and
tested in forest harvesting operations in South Africa and the results
presented. Overall, the workforce in forest harvesting is unstable:
the median labour turnover (monthly basis) and absenteeism (daily
basis) are 4 % and 6 %, respectively. Of further concern are: high
instability in some individual contractor businesses (employees were
much more stable with private grower companies than presently with
contractors) ; and contractors not measuring and monitoring labour
turnover. Labour turnover rates depend primarily on the conditions of
employment offered by the contractor. The framework and results
presented in this article are prerequisites for sustainable
development. Efforts should be made to put appropriate short, medium
and long term measures in place to reduce labour turnover and
absenteeism, and to manage it.
Guidelines for the design and
management of artificial raptor perches and nest-tree stands on
forestry estates in South Africa: management paper
Malan,
G.; Marais, A.vN.
Abstract:
The aim of this paper is to provide timber growers with silvicultural
guidelines for the establishment of raptor perches and nest stands on
forestry estates. Rodents do extensive damage to young saplings and as
an ecologically friendly alternative to rodenticides, we provide
guidelines on perch height and densities that can be implemented to
facilitate rodent-eating, perch-hunting raptors. For example, if
eight, 2-m high, even spaced poles are erected per hectare, the
raptors will be able to hunt the entire area. The aim of creating nest
stands on forestry estates is to establish 3-6 small (625 m2)
designated areas where raptors can breed separately from commercial
forestry activities. Guidelines for small, tree-nesting raptors
include dense stands (1000 trees / ha) to hide nests from predators,
whereas stands for intermediate size raptors must be thinned to 163
trees / ha to allow an increase in trunk diameter that, in turn,
allows the trees to support bigger nests. Cultivating large trees for
large raptors is problematic as these birds require trees with open
branch structures and easy access, features not associated with
single-stem, commercial trees. If timber growers adhere to the above
recommendations they will be able to combine wildlife and timber
management objectives on forestry estates.
Management
options for Australian Blackwood (Acacia melanoxylon) in
Southern Cape Forests, South Africa: management paper
Seydack,
A.H.W.
Abstract:
Australian Blackwood (Acacia melanoxylon) was actively
introduced into the indigenous forests of the southern Cape until
about 1930. On the perception that this exotic species constituted a
threat to the indigenous forest, a policy of eradication was followed.
This perception that Blackwood is capable of progressively replacing
the native biota was questioned periodically. Recent investigations
support the contention that the species is subject to constraints to
its effective self-replacement within the indigenous forests. In the
context of a policy re-evaluation, it is recommended that in the
medium-term and until monitoring has provided clarity on outstanding
issues, the control programme be restricted to areas where exotics are
inherently unacceptable, as is the case for nature reserves. Two
harvesting options for the remaining old-growth Blackwood timber in
the forest are presented. According to the short-term depletion
harvesting option, ca 2000 m3 of timber can be
harvested annually until the year 2003. The medium-term optimisation
option makes provision for annual harvest of 1500 m3 until
2010. Particularly in the case of the second option care must be taken
to harvest the more senile trees early in the sequence if an
acceptable degree of mortality pre-emption is to be achieved.
Knowledge
on Sclerocarya birrea subsp. caffra with emphasis on its
importance as a non-timber forest product in South and southern
Africa: a summary: part 2: commercial use, tenure and policy,
domestication, intellectual property rights and benefit-sharing:
review paper
Wynberg, Rachel; Cribbins, Jill; Leakey,
Roger; Lombard, Cyril; Mander, Myles; Shackleton, Sheona; Sullivan,
Caroline
Abstract:
Sclerocarya birrea (marula) forms an integral part of the diet,
tradition and culture of rural communities in southern Africa and also
is central to various commercial initiatives. This second part of a
review on the species provides an overview of current commercial
activities, the policy framework within which commercialisation
occurs, and future prospects with regard to domestication. Much work
has been conducted over the years on the properties of S. birrea
fruit, juice, nuts and oil. Despite this research there has been
little commercialisation. Two main commercial enterprises trade marula
products in South Africa: one, a large corporation, and the other, a
rural development project. In Namibia, marula commercialisation is
undertaken through a collaborative project between primary producers,
a cooperative, contract processors and a local NGO. Commercialisation
is influenced by a wide set of customary and government laws which
regulate marula use in southern Africa, comprising different tenure
systems, access rights, and levels of protection. Strong customary
rules can be linked to the long history of marula use in the region,
with clear evidence of early domestication and the selection of
desirable traits by local people. Such knowledge has been applied in
the development of marula domestication strategies, both by private
plant breeders in Israel and southern Africa, and by the International
Centre for Research in Agroforestry (ICRAF), which works with
small-scale farmers to develop agroforestry options. A number of
issues are raised by the domestication of marula which relate to
intellectual property and benefitsharing. They include the
compensation of small-scale farmers and original holders of local
knowledge for the commercial use of such knowledge ; the impact of
Plant Breeder's Rights on communities using marula; and the
possibility of domestication shifting benefits from poorer groups of
farmers to richer ones. Current and future commercialisation
strategies clearly need to take these factors into account, and to
balance associated costs and benefits.
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