African
Journals Online
Southern African Forestry Journal
Issue 193, March 2002
ABSTRACTS
Measuring total economic benefits from water in
plantation forestry: application of quasi I-O framework to the
Crocodile catchment in South Africa: scientific paper
Hassan, Rashid M.; Olbrich, B.; Crafford, J.
Abstract: A quasi input-output framework was applied to
measuring direct and indirect economic benefits from water use in
plantation forestry in the Crocodile river catchment of South Africa.
The study accounted for indirect economic benefits generated in
downstream timber processing activities and input supply sectors
linked with timber plantations as part of the total economic benefits
from water use in forestry. The derived measure of total economic
benefits from water use was 9 to 16 fold higher than the estimate of
direct benefits (in terms of value added and employment) generated at
the primary gum and pine production activities (plantation gate),
respectively. The study results showed the importance of considering
indirect economic benefits realised in forward and backward sectors
linked with the primary production activity in evaluating water
allocation strategies and policy regimes.
Acacia mearnsii sensitivity to the
application of pre-emergent herbicides applied at planting: scientific
paper
Little, Keith M.
Abstract: Five pre-emergent herbicides were applied either
on their own or in various combinations to commercially planted Acacia
mearnsii De Wild. seedlings in the KwaZulu-Natal Midlands. Acacia
mearnsii growth responses to the protected or unprotected
application of these herbicides were compared to a weedfree and weedy
control. Compared to the weedfree control, suppression from weed
competition only caused a significant reduction in tree growth from 92
days after planting, by which stage most of the residual capabilities
of the herbicides tested had been reduced. The herbicides which did
give good control of both grasses and volunteer wattle regeneration
relative to the weedy treatment were oxyfluorfen alone, or when
combined with thiazopyr or thiazopyr + metazachlor. When applied as an
unprotected spray, only the herbicide combinations of simazine /
terbuthylazine and metazachlor did not cause a significant reduction
in tree growth. Although only significant at p < 0,1 the
herbicides of oxyfluorfen and glyphosate / simazine / terbuthylazine,
when applied as an unprotected spray, caused a reduction in tree
survival (arcsine transformed) when compared to the weedfree control.
Tree variability was found to be a function of the presence or absence
of weed growth and the method of herbicide application. Lower tree
variability was exhibited in those treatments for which no
pre-emergent herbicides were applied or where the seedlings were
protected during spraying.
Identification of pine hybrids using SSR loci.:
scientific paper
Doyle, Jacqueline H.; Botha, Anna-Maria; Wingfield, Brenda D.
Abstract: We have screened 11 microsatellite markers
developed in other Pinus species for their ability to produce
fingerprints in the Pinus elliottii x Pinus caribaea hybrid as
well as their ability to determine gene flow and parental contribution
in this hybrid. We found that cross-species amplification was possible
with two thirds of the microsatellite markers screened and that by
pooling information from several microsatellite loci it was possible
to determine gene flow and parental contribution in the hybrid.
Coppicing potential of Eucalyptus nitens:
results from a field survey: scientific paper
Little, K.M.; Van den Berg, G.; Fuller, G.
Abstract: In order to determine factors which could have a
positive influence on the coppicing potential of Eucalyptus nitens
, a field survey was carried out at Draycott, near Estcourt in the
KwaZulu-Natal Midlands. Five measures of the ability to coppice (stump
survival, height of coppice, number of dominant shoots, coppicing
potential and coppice vigour) were assessed in seven recently felled
compartments. Within these compartments 50 sample and 200 sub-sample
sites were selected to provide a range of explanatory variables
against which the ability to coppice could be assessed. The
explanatory variables included factors related to the previous stand
of trees as well as various physiographic factors. The data were
analysed using correlation and multiple linear regression techniques.
Of the explanatory variables, bark damage, stump volume and landscape
aspect were able to account for 73 % of the total variation associated
with the response variate of coppicing potential. Despite the amount
of variance accounted for, aspect and stump volume may prove to be
surrogates for factors not assessed, for example soil moisture or tree
size when felled respectively. This field survey provides a basis for
future studies in this area of research.
Evaluation of methods for estimating the metabolic
rate according to ISO 8996 in forestry work in Zimbabwe: scientific
paper
Wasterlund, Dianne Staal
Abstract: Forestry activities in Southern Africa may expose
forest workers to uncompensable heat stress risk when the climate
conditions are such that the body experiences difficulties to
dissipate its excess heat to the environment. A study was made in
North Eastern Zimbabwe during the hot season to evaluate ISO standard
methods for heat stress risk determination in manual forestry work.
The differences between the metabolic rate assessments by three
methods of ISO 8996 were evaluated, as well as the effects of these
variations in the assessments on the heat stress risk determination by
ISO 7243 and 7933. The results showed significant differences between
the metabolic rate assessment methods, with variations of up to 36%
for the same observation period. It was also found that the methods
responded inconsistently for different activities. ISO 7243 and 7933
gave contradictory assessments of the heat stress risk in the
prevailing climate conditions and the differences in the recommended
allowable exposure times by ISO 7933 were up to 265 minutes. It is
therefore questionable whether the ISO heat stress standard methods in
their present versions are applicable to all work situations in
forestry.
The influence of site factors on nitrogen
mineralization in forest soils of the Mpumalanga escarpment area:
South Africa: scientific paper
Louw, J.H.; Scholes, M.
Abstract: The complex biophysical environmental conditions
that occur in South African forestry plantations prompt appropriate
guidelines for nutrient management applications. Nutrient budget
studies in plantation ecosystems indicated a negative nitrogen (N)
balance on many sites. Empirical fertilizer trails have shown that,
although responses are highly variable, the application of inorganic
fertilizers remain an efficient means of improving tree growth. This
study was carried out to investigate the influence of variable site
conditions on N mineralization, as well as the effect of N
mineralization on forest productivity. Data were collected from 31
sample plots, covering a wide range of site conditions in the study
area. N mineralization was monitored using multi-week in situ
incubations, and compared to a wide spectrum of site factors recorded
at each sample plot. The phase of plantation canopy closure (age 6-10
years) was used as the reference age.
A significant positive correlation was found between NH 4
+ mineralization during summer and the growth of Pinus
patula (r = 0,77, p < 0,001). This process of the N cycle can
therefore be considered as the rate limiting step influencing tree
growth. N mineralization is controlled by a complex interaction of
various site factors, and numerous correlations and interactions
between NH4 + mineralization (summer) and site
factors are discussed. Statistical models were developed through
multiple regression techniques, to predict N mineralization from
independent site variables. The in situ rates of N
mineralization could be predicted with an acceptable degree of
accuracy by making use of the natural log of mean annual temperature,
geological substrate and total N levels in the topsoil (r2
= 0,71). These models are suitable for incorporation into existing
plantation decision support systems. The significance of the response
in tree growth, following fertilization with N in existing
mid-rotation forest nutrition trials, was evaluated against the
predictions of N mineralization using the proposed models. An inverse
linear model ( r2= 0,89, p < 0,0001) was found to best
describe this relationship. Additional research on the process of N
mineralization in South African plantations is required to provide
accurate recommendations on nutrient management for the various forest
management practices currently in use.
The effect of a soil-amended hydrogel on the
establishment of a Eucalyptus grandis clone on a sandy clay
loam soil in Zululand during winter: scientific paper
Viero, P.W.M.; Chiswell, K.E.A.; Theron, J.M.
Abstract: To ensure acceptable survival and growth of Eucalyptus
grandis clonal material planted in the sandy clay loam soils of
the Zululand interior of South Africa, the current planting season is
limited to the summer rainfall period. A field trial was initiated
with the primary objective of being able to successfully extend the
planting period (May to September) within which Eucalyptus grandis
clones could be planted. This was done by testing tree growth and
survival by the addition of a soil-amended hydrogel (Stockosorb 400K)
and comparing it to traditional water planting methods. Five levels of
water (0 ml, 500 ml, 1000 ml, 2000 ml and 4000 ml) were combined with
five levels of hydrogel (0 g, 3 g, 6 g, 9 g, and 12 g) and applied to
the pit at planting in a 5x5 factorial design. The tree variates of
mortality, height, groundline diameter, crown diameter, corrected leaf
surface index (LSIC) and corrected biomass index (BIC)
were assessed at 7, 47, 86 and 118 days after planting.
There was a highly significant (p<0,01) interaction
between hydrogel and water which had a positive impact on both
transplant survival and growth. There were significant differences
between water only treatments when compared with all levels of
hydrogel, with the hydrogel treatments performing significantly
better. Optimum survival for water only treatments was achieved at the
4000 ml application level (50 %) while optimum survival for hydrogel
and water was achieved for 6 g / 1000 ml and 12 g / 2000 ml of
hydrogel and water (100 %). There were no significant differences for
survival within all but one of the hydrogel treatments over all
applications of water. Both the variates LSIC and BIC
indicated that tree growth was significantly enhanced by the addition
of hydrogel over all applications of water. Optimum tree performance
was found to occur at 2000 ml water and 12 g hydrogel.
The results from this trial indicate the possibility of using a
soil-amended hydrogel (Stockosorb 400K) to:
i successfully establish a Eucalyptus grandis clone in the
Ntonjaneni area during winter, thereby successfully extending the
planting season (between May and September) ;
ii significantly reduce water volumes used at planting without
negatively affecting current silvicultural standards.
Post-establishment vegetation control in a Eucalyptus
grandis x E. camaldulensis stand: research note
Little, Keith M.; Rolando, Carol A.
Abstract: In eucalypt plantations, the effect of shading
following canopy closure reduces the growth of competing vegetation.
In some eucalypt stands full canopy closure is not achieved and the
important characteristic of complete shading is lost. This results in
stands with the potential to support competitive levels of
postestablishment vegetation. A trial was established on a two year
old Eucalyptus grandis x E. camaldulensis stand to determine
the competitive effect of post-establishment vegetation on tree
growth. A weedfree treatment was implemented annually over a period of
five years and compared to a weedy control to determine the time
period for the post-establishment vegetation to reach competitive
levels. There was no significant tree growth or survival response to
competition from post-establishment vegetation for the duration of the
trial.
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