Mpumalanga Escarpment Research Articles

Hydrostratigraphy of the Malmani Subgroup dolomites within the northeastern escarpment (Limpopo and Mpumalanga, South Africa)

Abstract The Late Archaean to Early Proterozoic Malmani Subgroup comprises of dolomites and limestones forming part of the Chuniespoort Group within the Transvaal Supergroup, outcropping as an arc structure east of the Pretoria Group along the Limpopo and Mpumalanga escarpment. These rocks form a fractured karst aquifer in the area and have a high degree of heterogeneity and anisotropy. The aquifers are unconfined to semi-confined, with compartmentalisation by dolerite dykes being a possible effect (if the dykes are large and extensive enough) due to the dykes acting as aquitards or barriers to groundwater flow. The contact zones between the dolomite formations and dolerite dykes are usually fractured however, and along with any other faults and fractures result in preferential dolomite dissolution and the development of groundwater flow paths in the area. Borehole yields ranges between 2 to 5 l/s and potentially >10 l/s per borehole in the vicinity of large regional fractures or dolerite intrusions. Groundwater from the Malmani Subgroup generally meets the drinking water quality standards for major constituents and it is of Mg-Ca-HCO3 nature. Groundwater development within this particular hydrostratigraphy is linked to potential well field target zones that take cognisance of various surface water-groundwater interaction affecting surface water discharge rates as well as groundwater over-abstraction concerns. Preliminary results have indicated that given a groundwater potential of 44 hm3/a, the aquifer will be able to support abstractions of up to 29 hm3/a if systematically developed adaptively and could be used and managed conjunctively with surface water to alleviate the pressure on the already stressed Olifants Water Management Area.

Two new species of Acontias (Acontinae, Scincidae) from the Mpumalanga Highveld escarpment of South Africa.

The African genus of fossorial legless lizards (Acontias Cuvier) currently comprises 26 species and subspecies. In a recent study on the two disjunct populations of Acontias breviceps Essex, the presence of cryptic species was discovered. Here, we increase the sampling size and describe these disjunct populations from the Mpumalanga Escarpment of South Africa as new species. The new species differ from congeners based on a combination of factors, including the number of midbody, ventral, and subcaudal scale counts, ventral pigmentation, allopatric distributions, and genetic divergences. The new species are genetically distant from nominal A. breviceps, with which it shares overall pigmentation and scalation. The new description adds to the growing number of Mpumalanga escarpment endemic reptiles, and highlights the area as a biodiversity hotspot. The use of vertebral counts as a distinguishing character between species is briefly discussed.

The sclerophyllous wetlands on quartzite substrates in South Africa: Floristic description, classification and explanatory environmental factors

A description of wetland habitats on nutrient-poor sandstone and quartzite substrates across South Africa is given. Most of these are situated in the Fynbos Biome and are dominated by sclerophyllous shrubs but there are some sedge-dominated vegetation types as well as geographical outliers found in Pondoland, the Kamiesberg, the Mpumalanga escarpment, the Soutpansberg and the Waterberg. A subset from a national survey of wetland vegetation was selected for analysis in terms of classification and ordination. This resulted in a classification of 27 communities which are summarized in eight community groups. The variation in the dataset can be largely differentiated by means of altitude and cations and the associated ordination separates a small number of plots belonging to communities that are also distributed outside of the Fynbos Biome from the rest of the dataset. Within the Fynbos Biome, there are different wetland vegetation types found on steep slopes, with shallow soils and a high sand content versus the valley bottoms with deeper soils and a higher silt and clay content. There are also small differences in the nutrient status of different communities. This research showed that wetland plant communities in nutrient-poor communities have a distinct species composition. Species originate from a diverse range of functional types and phylogenetic groups compared to the typical wetland vegetation found in nutrient-rich grassy habitats in the rest of the continent.

A method for three-dimensional stem analysis and its application in a study on the occurrence of resin pockets in Pinus patula

Information on the external shape, internal properties and defects of a tree is important for the forest and wood-processing industries. Resin pockets are internal defects, associated with some softwood species, and are especially undesirable in furniture, joinery and veneer products. In this study, we propose a new lower-cost method for measuring tree shape and macroscopic internal characteristics. The objectives of this study were to: (1) design, construct and test a mobile system that can be used in field to obtain a three-dimensional model of a log or tree stem indicating selected macroscopic internal characteristics and (2) to use the system to investigate the occurrence and causes of resin pockets in Pinus patula from the Mpumalanga escarpment in South Africa. In order to establish the cause of resin pocket formation in Pinus patula, four 3-m logs from 24 trees from three compartments were dissected and digitally reconstructed into three-dimensional models. The results from the study suggest that the formation of Type 1 resin pockets in Pinus patula was due to bending stresses caused by wind sway. It was not possible to establish with certainty the cause of Type 2 resin pocket formation. However, there was evidence that damage events, and specifically thinning damage, have been the cause of some of the Type 2 resin pockets observed.

Variation in selected solid wood properties of young Pinus patula from diverse sites in the Mpumalanga escarpment area in South Africa

Regression analyses identified ‘Growth Days’ (an index expressing site moisture availability) as the only site variable contributing significantly to the prediction to wood density (R2 = 0.57), whereas the model predicting grain angle included only ‘Altitude’ (R2 = 0.60). These results surfaced during an investigative study to quantify various sources of variation in wood properties and to quantify the effect of a number of site factors on wood properties of Pinus patula grown in the Mpumalanga escarpment area of South Africa. For this purpose, 10 trees were sampled from each of 17 diverse sites for wood property analyses. The effects of site, distance from the pith and differences between trees within site on wood density, transverse shrinkage, grain angle and dynamic modulus of elasticity were investigated. The site factors considered included a wide variety of soil and climatic factors. The effect of radial distance from the pith and differences between individual trees within sites were highly significant, accounting for most of the variation in wood properties. Although the effects of a number of site factors were statistically significant, they generally explained relatively small but important variation in wood properties among sites. The study not only quantified the effects of important sources of variation on a few key wood properties, but it also revealed that the extent of differences between sites can be explained in terms of some specific site factors. It is envisaged that the results will contribute significantly towards the refinement of current forest site classification systems for improved decision-making with respect to wood quality in intensively managed plantation systems.

A method for determining knotty core sizes of standing Pinus patula trees based on tree ring sampling

The objectives of this study were to develop and assess a method of using tree ring measurements in standing pruned Pinus patula trees for modelling the knotty core of the pruned section of a tree and to assess variability in knotty core diameters in the tree stem. A total of 170 trees from 17 compartments on a wide variety of growth sites from the Mpumalanga escarpment in South Africa were selected and destructively sampled. We show that ring width measurements at breast height can be used to predict growth in the upper pruned section which in turn can be used to reconstruct the internal knotty core through the full pruned section of the log.Analysis of variation for the entire data set from ring width measurements showed that there was far greater variation in knotty core percentages (the percentage of diameter occupied by knotty core) between different compartments than within compartments. Within a tree, the knotty core percentages between three stem sections, 0.0–2.4m, 2.4–4.8m, and 4.8–7m, differed significantly. As expected the knotty core percentages were found to increase from the bottom section (49.1%) to the top section (65.4%).A comparison of the actual measured knotty core size and the modeled knotty core size of a sub-sample of trees showed only a modest relationship (R2=0.62). Reasons for this might be variability in pruning quality, inaccurate pruning records, nodal swellings, and the methodology used to measure the actual knotty core sizes.Knowledge of knotty core sizes can be used as a decision aid in the forest and forest products industry.

The variation of microfibril angle in South African grown Pinus patula and its influence on the stiffness of structural lumber

Reduction in the rotation ages of softwood saw-log plantations in South Africa is causing increased proportions of low stiffness sawn lumber at final harvest. It has been shown for some species that the microfibril angle (MFA) of the S2 layer of tracheids is strongly related to the modulus of elasticity (MOE) of wood, even more so than wood density, especially in wood formed during juvenile growth. The objectives of this study were to describe the variation in MFA in young Pinus patula trees and to determine the relationship between MFA and the dynamic MOE of sawn P. patula lumber. Thirty 16- to 20-year-old trees from six compartments from the Mpumalanga escarpment were processed into discs and lumber. The MFA, density and ring width were measured at two height levels using Silviscan 3. The average annual ring MFA varied between 7° and 29°; the pattern of variation depended mainly on height level and the ring number from the pith. The MFA in P. patula followed the same within-tree variation trends as in New Zealand-grown Pinus radiata but the average MFA was lower in absolute terms and differences between height levels were less pronounced. The MFA and density exhibited highly significant Pearson correlations of 0.73 and 0.70, respectively, with board dynamic MOE. A multiple regression model, which included MFA, density and ring width, explained 71% of the variation in the dynamic MOE of boards. A sensitivity analysis on the model showed that MFA and density had approximately similar influences on predicting the dynamic MOE of Pinus patula boards.

The prediction of the flexural lumber properties from standing South African-grown Pinus patula trees

Pinus patula is the most intensively planted conifer in the tropics and subtropics. The increased proportion of corewood that results when rotation ages of pine plantations are shortened has become a wood quality factor of growing concern worldwide. The purpose of this study was to develop empirically based models for predicting the flexural properties of the wood produced from relatively young P. patula trees. Models were based on the properties of standing trees, and their effectiveness was evaluated at board, tree, and compartment levels. Sample material was obtained from 170 P. patula trees, 16–20 years old, established in 17 compartments on the Mpumalanga escarpment of South Africa. Multiple regression models were developed, which managed to explain 68, 60, and 95 % of the variation in the dynamic modulus of elasticity (MOE) on individual boards, trees, and compartments levels, respectively. At compartment level, 80 % of the variation in the 5th percentile MOR value could be explained by the model. Sensitivity analyses showed that site index at base age of 10 years, acoustic time of flight, wood density, and ring width were influential variables in the MOE models. The models indicated that tree slenderness during early growth seems to play a major role in determining the dynamic MOE and MOR of lumber. This is in agreement with Euler’s buckling theory and the bending stress theory. The results from this study indicated that the MOEdyn and MOR of lumber can be accurately predicted on especially a compartment level. The predictive models developed can be used as management tools to improve operational decisions around tree breeding, silvicultural practices, and rotation ages.

The structural grading of young South African grown Pinus patula sawn timber

In this study sawn timber from 16- to 20-year-old Pinus patula trees were obtained from a wide variety of sites along the Mpumalanga escarpment in South Africa. The objectives of this study were to assess the efficiency of the current visual and mechanical grading rules on this timber and to evaluate the potential of some indicator properties to be used as structural grading parameters on this resource. A large number of non-destructive measurements were performed on all samples (i.e. X-ray density scanning, acoustic frequency measurement, year-ring measurements and stiffness measurement) before it was destructively tested in bending and tension. The young P. patula timber tested in this study had good bending strength (MOR) properties with higher characteristic grade values than required. The timber, however, had low stiffness and did not comply with the SANS 10163-1 requirements for mean modulus of elasticity on edge (MOEedge) for any of the structural grades. Dynamic MOE (MOEdyn), calculated from acoustic frequency tests on the timber, was found to be the best single predictor of MOEedge, MOR and tension strength. Multiple regression analysis showed that a combination of MOEdyn, density and knot parameters can be used to improve the predictability of some of the strength and stiffness characteristics of the timber.

The use of near-infrared scanning for the prediction of pulp yield and chemical properties of Pinus patula in the Mpumalanga escarpment area of South Africa

Near-infrared (NIR) scanning technology is regarded as a potential tool for rapid determination of wood properties, which can substitute time-consuming and costly traditional methods. Pinus patula is the most important softwood species in South Africa, and this study is aimed at developing NIR calibration models for quick prediction of its pulp yield and chemical composition. A total of 85 trees from 17 plots, covering the range of site conditions in the Mpumalanga escarpment area, were sampled. Two samples were taken from each tree: a 1 m billet above breast height and a 20 mm disc at breast height. The billet was pulped using the kraft pulping process to determine pulp yield. The disc was ground into sawdust and the chemical composition was determined using conventional wet chemistry. Sawdust was scanned on a NIR spectrophotometer to produce NIR spectra. Calibration models to predict pulp yield, cellulose and lignin content were developed by applying chemometrics and partial least squares regression. Validation and determination of prediction accuracy of the models were performed using independent data. The prediction of cellulose and lignin were acceptable with correlations of determinations (r 2) of 0.71 and 0.70 respectively. Standard errors of prediction were generally low (less that 0.86) for all the models. The prediction r 2 for both total and screened pulp yield were only 0.62. Although the cellulose and lignin models can be used with confidence, the expansion of the sample size for follow-up research must be considered in order to increase the variability of tested wood properties and improve the prediction strength of the models. The NIR calibration provided in this study can contribute to the efficient examination of forest site-to-wood quality relationships that would enhance precision forest management and wood processing efficiency.

Results from four Pinus patula water planting trials in the summer rainfall region of South Africa

Planting with water is used by some forestry companies in South Africa to reduce post-planting water stress. Four trials were implemented to test the response in survival of Pinus patula to water applied at planting. Two trials each were situated in the KwaZulu-Natal Midlands and Mpumalanga escarpment. The first trial at each site was planted in spring (October) and the second in summer (February). Watering treatments consisted of different quantities of water used in the planting operation and included 0.5l, 2l, 4l and no water. At all sites the planting treatment affected the depth at which the seedlings were planted. Only at the spring-planted trial in the KwaZulu-Natal Midlands was survival of the dry-planted seedlings significantly lower than that of the seedlings planted with water from 90d after planting. This may have been due to low rainfall during the week before and two weeks after planting, or the small size of the seedlings. Application of 0.5l of water to the planting pit at this trial was s...

A new species of Disa (Orchidaceae) from Mpumalanga, South Africa

A new species, Disa vigilans D. McMurtry and T.J. Edwards, is described from the Mpumalanga Escarpment. The species is a member of the Disa Section Stenocarpa Lindl. Its alliances are discussed in terms of its morphology and its phylogenetic placement is elucidated using molecular data. D. vigilans has previously been considered as an anomalous form of Disa montana Sond. but is more closely allied to Disa amoena H.P. Linder.

Site index functions using site descriptors for Pinus patula plantations in South Africa

The quantification of the complex interaction of water and nutrients on forest productivity has long been a challenge to forest scientists worldwide. South Africa is no exception, and an industry that is experiencing increased management intensity, requires reliable decision support systems to remain competitive. Empirical growth models as well as site quality prediction models have played a significant role in forest management to date. However, there is a definite need for models incorporating process-based information to permit better assessment of management options as well as to capture dynamics caused by climate changes. The Mpumalanga escarpment area, one of the major timber growing areas in South Africa, was used as a study area, with data on Pinus patula growth. Two site quality prediction models were developed, using multiple regression techniques. Both models use a range of site factors that express the moisture and nutrient balance of the specific site. These models were found to predict site index values with a high degree of accuracy to be used as management tools. A third model was produced by combining a site quality prediction model with a Chapman–Richards type model in order to provide a site-specific growth curve. The performance of these models was compared with a process-based model called 3-PG, using independent site and growth data from the study area. Although some encouraging results were found with the 3-PG model for the prediction of growth curves, significant deviations existed between observed and predicted values of MAI 20 values. Possible reasons for the difference in accuracy between the models are discussed. Future research is required to enable the proper parameterisation of the 3-PG model for South African conditions. The 3-PG model can potentially contribute substantially to a wide spectrum of applications to, and interpretations of, existing high resolution site classification systems in South Africa, especially in the fields of growth and yield prediction and economic analysis of forest site potential.

Foliar nutrient levels as indicators of site quality forPinus patulain the Mpumalanga escarpment area

Synopsis The South African forest industry is based on intensively managed monoculture systems, and requires diagnostic tools for the development of site-related nutrient management policies. Worldwide, the evaluation of foliar nutrient concentrations is one of the most widely used techniques in forest nutrition research, with many different applications. This paper forms part of a comprehensive study of the differential nutrient supply offorest sites in the study area, as well as the effect thereof on the growth of Pinus patula. The aim of this paperis to investigate the complex interactions between site factors, absolute foliar nutrient levels and tree growth. The levels recorded in this study indicate that most elements are in adequate supply, with possible exceptions being nitrogen and calcium. A range of site factors was found to correlate significantly with foliar nutrient levels, including climatic parameters, topsoil cation levels, N mineralization rate and soil texture. The season of sampling was...

Weed composition in relation to site in re-established pine compartments on the Mpumalanga Escarpment, South Africa

Synopsis 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 total359 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 influence of site factors on nitrogen mineralization in forest soils of the Mpumalanga escarpment area: South africa

Synopsis The complex biophysical environmental conditions that occur in South Mrican 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...

Streamflow responses to afforestation with Eucalyptus grandis and Pinus patula and to felling in the Mokobulaan experimental catchments, South Africa

The reductions in streamflow following the afforestation of grassland with Eucalyptus grandis and Pinus patula in the Mokobulaan research catchments on the Mpumalanga escarpment, and the subsequent response in streamflow to clearfelling of the eucalypts are presented. Afforestation with eucalypts of an entire catchment with a virgin annual runoff of 236 mm, caused a statistically significant decrease in streamflow in the third year after planting and the stream dried up completely in the ninth year after planting. The eucalypts were clearfelled when 16 years old but full perennial streamflow did not return until five years later. Afforestation with pines of an entire catchment with a virgin annual runoff of 217 mm, produced a significant decrease in streamflow in the fourth year after planting and caused the stream to dry up completely in the twelfth year after planting. The drying up of the streams was not altogether surprising as the annual runoff was lower than the expected reductions owing to complete afforestation. The delayed return of streamflow in the clearfelled catchment is surprising though, and is attributed to the desiccation of deep, soil-water stores by the eucalypts. These stores had to be replenished before the streams could return to normal behaviour.

A Site-growth Study ofEucalyptus grandisin the Mpumalanga Escarpment Area

SYNOPSIS A site-growth study was conducted on Eucalyptus grandis on the granitic soils of the Mpumalanga escarpment area. The objectives were twofold, namely to identify those site factors that can be related to the growth of the species, as well as the development of a statistical site-growth model for the quantitative evaluation of sites for tree growth performance. An integrated approach was followed using multiple regression analysis, incorporating attributes on topography, climate and physical and chemical soil characteristics, with Site Index at 20 years (SI20) as the dependent variable. The study revealed that the growth of E. grandis is mainly influenced by factors controlling available soil moisture, together with the organic carbon content of the topsoil. A statistically significant site-growth model was developed, although the model showed bias by overpredicting at low potential sites and underpredicting at high potential sites. This could be ascribed to the use of a growth model (for standardising on growth data to SI20) that was developed in a geographically different area. Suitable site-specific growth models are not yet available for the study area.