Doctoral Degrees (Forest and Wood Science)

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Biological control potential of the spotted stem borer Chilo partellus (Swinhoe) (Lepidoptera: Crambidae) with the entomopathogenic fungi Beauveria bassiana and Metarhizium anisopliae
(Stellenbosch : University of Stellenbosch, 2011-08-11) Mekonnen, Tadele Tefera; Tadele Tefera; Pringle, K. L.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Biological control studies were conducted with isolates of entomopathogenic fungi Beauveria bassiana and Metarrhizium anisopliae from Ethiopia and South Africa against the spotted stem borer Chilo partellus. The study was conducted from April 2002 to April 2003, at the department of Entomology and Nematology, University of Stellenbosch, South Africa. The objectives were to screen these isolates for pathogenicity and to determine the susceptibility of different larval instars; to study the effect of temperature on fungal development and virulence; to investigate food consumption of fungus treated larvae; to determine compatibility of fungal isolates with insecticides; to study the effect of exposure methods and diets on larval mortality; and to evaluate promising isolates under greenhouse conditions using artificially infested maize plants. Four isolates of B. bassiana and six isolates of M. anisopliae were tested against second instar larvae. Of these isolates, B. bassiana (BB-01) and M. anisopliae (PPRC-4, PPRC-19, PPRC-61 and EE-01) were found to be highly pathogenic inducing 90 to 100 % mortality seven days after treatment. In subsequent assays, the fungal isolates were tested against third, fourth, fifth and sixth instar larvae. Second and sixth instar larvae were more susceptible to these isolates than third, fourth and fifth instar larvae. Conidial germination, radial growth and sporulation of the isolates PPRC-4, PPRC-19, PPRC-61, EE-01 and BB-01 were retarded at 15 and 35 0C. A suitable temperature range for the isolates was from 20 - 30 0C. At 25 and 30 0C the isolates induced 100 % mortality to second instar larvae within four to six days. Second and third instar C. partellus larvae were treated with the isolates PPRC-4 and BB-01, and daily consumption of maize leaf was measured. Treatment with the fungi was associated with a reduction in mean daily food consumption. In in-vitro studies, five concentrations (0.1 ppm, 1 ppm, 5 ppm, 10 ppm, and 100 ppm active ingredients) of the insecticides benfuracarb and endosulfan were tested with the isolates PPRC-4, PPRC-19, PPRC-16, EE-01 and BB-01. Increasing the concentration of the insecticides adversely affected germination, radial growth and sporulation of the isolates. In in-vivo studies combining the fungi, PPRC-4 and BB-01,with low concentrations (1 and 5 ppm a.i.), of the insecticides increased the mortality of third instar larvae from 65 to 100 %. Larvae sprayed directly with conidia, exposed to conidia treated leaves and dipped into conidial suspensions suffered high mortality of 98 to 100 %. Larvae exposed to treated leaves and larvae sprayed directly with conidia produced high numbers mycoses in cadavers. Exposure of larvae to treated leaves yielded high sporulation. At a low conidial concentration (1.25x107 conidia/ml), mycosis and sporulation were high. The optimum temperature was 20 0C for mycosis and 15 0C for sporulation. In greenhouse trails, a conidial suspension of 2 x 108 conidia/ml of the pathogenic isolates was sprayed on 3 to 4 week-old maize plants infested with 20 second instar larvae per plant. This resulted in suppression of foliar damage. Treatment with the fungi also reduced stem tunneling and deadheart. In addition, fungal treatment increased mean plant fresh and dry biomass compared to untreated control plants. In general, results from laboratory and greenhouse studies indicated that there was good potential for the use of these fungal isolates for controlling C. partellus larvae.
Development of a method to forecast future systems in the forest engineering value chain
(Stellenbosch : Stellenbosch University, 2001-12) Brink, Michal; Kellogg, L. D.; Uys, H. J. E.; Buys, A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: The objective of this study is to develop a new method which can be used to forecast the Forest Engineering value chain. The method is then applied in the South African context in order to validate the use thereof. Finally, the South African results are used to propose strategies, which the industry should pursue in the future. To forecast the future an understanding of the past is required. To this end, the historical development of Forest Engineering is discussed, both globally and in South Africa. The current status quo in Forest Engineering in South Africa was determined through a national survey of plantations larger than 200 ha. The results are reflected in Chapter 2. Because of the importance of globalisation and technology, Chapter 3 gives a literature review of relevance of technology in today's business world, including various forecasting techniques that are relevant to the study. These techniques are a combination of traditional forecasting methods, technology forecasting methods and strategic planning methods. Various approaches to financial analysis have also been discussed, in order to determine the soundest method of comparing various forest engineering systems with each other. This includes an overview of traditional machine cost calculations. The core of the study lies in the combination of these methodologies into a useful method, which is particularly suited to forecasting the Forest Engineering value chain. Such a method is developed in Chapter 4, based on the literature review of forecasting methodologies. The method is then validated in Chapter 5, through the application thereof in the South African forestry industry. Global trends are established with the use of a Delphi study. This technique uses a panel of experts who give their views on future developments on a multiple round basis. The study then evaluates 14 Forest Engineering systems for pine sawtimber, pine pulpwood and Eucalyptus pulpwood, based on various scenarios of the future. The scenario matrix is based on the future cost of labour vs. the future cost of machinery. Finally, a strategy is proposed on how the South African forestry industry should prepare itself for the future.
Development of geopolymer bonded wood composites
(Stellenbosch : Stellenbosch University, 2021-03) Olayiwola, Hamed Olafiku; Tyhoda, Luvuyo; Meincken, Martina; Stellenbosch University. Faculty of AgriScience. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: In the wake of finding alternative sustainable and environmentally friendly products to conventional construction materials, geopolymers offer large potential as a low carbon footprint material. Their excellent properties and the ability to be synthesized from industrial waste make them promising alternative binder sin wood-based composites where durability, environmental sustainability, structural integrity,and low cost of final products are of utmost importance. This study investigated the application of unary and binary precursor based geopolymer sin the development of composite products for use in outdoor conditions. The unary geopolymer is based on 100% ground granulated blast slag,while the binary precursor is composed of 75% class F fly ash and 25% metakaolin. The precursors were activated with a combination of sodium hydroxide and sodium silicate solutions formulated at a weight ratio of 1:2.5. The lignocellulosic materials used include sugarcane bagasse(Saccharum officinarum) and forest biomass waste from the clearing of locally occurring invasive alien species including Long-leaved wattle (A. longifolia), Black wattle (A. mearnsii) and Port Jackson (A. saligna). The production process involved using a mixed factorial experimental design. The variables considered included precursor-activator ratio (PA), curing pattern (CP), amount of lignocellulosic material (LM) and alkali concentration (MCon). For the unary system, the variables were CP, LM and MCon. PA and CP were considered at 2 levels, while LM and MCon were considered at 3 levels. The effects of the main factors and their interactions on the observed composite properties were evaluated using analysis of variance (ANOVA). The boards have comparable physical properties to cement-bonded particleboard according to the EN 632-2: 2007 standard. However, for the unary system only A. saligna boards produced with 6M NaOH and cured at 40°C for 24 h met the mechanical strength requirements, while in the binary system, only A. longifolia boards produced with 12M NaOH, PA ratio of 2:1 and cured at 100°C for 6h met the mechanical strength requirements. The boards were also thermally stable as the residues retained at the end of thermal analysis was above 70%. setting, the degree of geopolymeric reaction was impeded.The lignocellulosic materials were subjected to alkalization, acetylation, and hot water extraction to remove the lower molecular components,which could impede geopolymerization kinetics and enhance their surface characteristics. This was aimed at improving the durability of LM in the matrix and the overallproperties of the boards. The influence of each treatment on the lignocellulosic materials was evaluated using HPLC, SEM and FTIR, while the resulting boards were tested to specification and characterized using SEM and FTIR. The treatments improved the surface characteristics of the fibres and the fibre yield was not impacted significantly. FTIRindicated formation of more geopolymer products after fibre treatment, which was confirmed by SEM micrographs. The treated samples exhibited a compact and densely populated gel-like amorphous microstructure with fewer unreacted precursor particles.In the unary system, the mean modulus of rupture (MOR) increased by 3.25% for hot water extracted,23.61% for acetylated and23.94 % for alkalized AM boards. In the binary system, the mean MOR increased by 18.31% for hot water extracted, 6.03% for acetylated and 18.22% for alkalized AM boards. The study concluded that South African woody invasive plants (IPs)and sugarcane bagasse are suitableto produce both unary-and binary precursor-based geopolymer wood composites of comparable properties to cement-bonded particle boards.
Ecology of the bushpig Potamochoerus porcus Linn. 1758 in the Cape Province, South Africa
(Stellenbosch : Stellenbosch University, 1990-12) Seydack, Armin H. W.; Bigalke, R. C.; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science; Jacobs, Ivan
ENGLISH ABSTRACT:Bushpig sociology, energetics, reproduction and population dynamics were studied over an 8-year period in the Cape Province, South Africa. The social organization was found to be strikingly different from that known from other suid species. The basic social unit is a unimaternal family group, occupying a resource-based territority, with a monogamous mating system. This form of social organisation is related to the dispersed nature of food resources, to which it provides exclusive access. It is reminiscent of canid social systems. Agonistic behaviour, communication and maternal behaviour were studied as the opportunity arose. The average home range size was 7,2 kmª, ranging from 3,8 to 10.1 kmª. Home ranges were often traversed within 1-4 days, as part of territory patrolling. The average diel ranging distance was 3 km. Bushpig were active during both night and day and exhibited a basic bimodal rhythm. The main phase of intensive foraging occurred from before dusk to midnight, with a secondary activity peak after dawn. Activity schedules were geared to avoid extreme ambient temperatures. Temperature regulation and water use were investigated, with particular reference to thermoregulatory behaviour (nest building). pelage characteristics, body core temperature dynamics, thermoneutral zones and resting metabolic rates. The thermoneutral zone for 10 kg bushpig juveniles was estimated to lie between 13° and 30°C and that for adults between 8° and 25°C. Foraging behaviour, diet and its nutritient content were investigated. Regional differences in the nutritional quality of bushpig diets in the Eastern and Southern Cape were associated with the predominance of nutrient-rich and nutrient-poor substrates respectively. These in turn were reflected by divergent life history features in the populations from the two regions. Patterns of growth and energy storage were described and the value of various parameters (e.g. mass to size ratio, fat depositions, blood composition) to evaluate condition was investigated. In studying reproductive biology, sexual maturation, female reproductive cycles, prenatal litter statistics, foetal development, 1actation, breeding seasonality and reproductive turnover were the main aspects addressed. The role of food quality, body condition and social status in determining reproductive success was discussed. Bushpig population density estimates in the Southern Cape ranged between 0,3 and 0,5 animals/kmª• The dynamics of Southern and Eastern Cape populations were found to differ. The differences are consistent with the hypothesis that social organisation is determined by the distribution and availability of food while diet quality shapes life history tactics. A life history model was developed which links edaphoclimatic environmental conditions with diet quality, metabolic turnover rate and, ultimately, life history features. In the concluding chapter some of the managerial implications of the research findings are discussed.
The effect of fire damage on the growth and survival mechanisms of selected native and commercial trees in South Africa
(Stellenbosch : Stellenbosch University, 2015-04) Odhiambo, Benedict Oithe; Seifert, Thomas; Meincken, Martina; Stellenbosch University. Faculty of Agrisciences. Dept of Forest and Wood Science.
ENGLISH ABSTRACT: Surface fires are known to affect trees of different species differently, depending on the capacity of the bark to shield the cambium from heat. Tree bark characteristics differ among species and thus potentially influence the protective ability against cambium damage. The objectives of this study were to compare the protective role of bark against fire for selected indigenous and exotic species in the Western Cape, South Africa, and to investigate post-fire growth impacts following surface fire damage on Pinus radiata. In the first part of the study, trees were felled and billets of 25 cm height harvested from different heights along the trunk. Bark thickness, compass direction, stem diameter at breast height, bark moisture content and relative height of the sample in the stem were tested for their effect on heat insulation capacity of bark. Heating experiments were conducted at 400°C on the fresh billets with intact bark. Time to heat the cambium to lethal 60°C was determined. The second part of the study investigated the role of bark surface topology, bark density and bark chemical composition for its fire resistance. The same size billets were harvested from the lower trunk section of selected species. Surface topology was characterised by means of x-ray based computer tomography, density by moisture saturation method and bark chemical composition by thermo-gravimetrical analyses (TGA). The third part of the study investigated the impact of high intensity surface fires on growth of an 18 year old Pinus radiata plantation which was exposed to a ground fire 5 years prior to the analysis. Tree ring measurements were done on cores obtained by non-destructing coring method and various growth indices, based on yearly basal area increment (iBA) used to quantify growth response to the fire damage. Statistical analysis based on correlation, multi-model inference and multiple regression revealed no significant influence of compass direction and diameter at breast height. Heat resistance was mainly determined by bark thickness and to a lesser degree by moisture content. In several species relative height at the stem modulated the bark thickness effect. Higher up the stem bark of the same bark thickness offered less protection against heat. The results also suggest that in particular bark topology plays a role, while the correlations with bark density and chemical composition could not be secured statistically. A main finding was that fissures in the bark play a significant role. A regression model showed a significant influence of fissure width, fissure frequency and the minimum bark thickness to the cambium, which is a function of fissure depth. The results show that structural bark parameters are a necessary addition to explain heat resistance of bark. Statistical analysis employing one-way Anova and incorporating Tamhane’s T2 Post Hoc test revealed significant growth reductions following high intensity surface fire damage on Pinus radiata in the fire year with the impact being passed on to the following year. The recovery phase extended a two year period. During this time the trees showed increased diameter growth probably due to increased water availability.
Effect of population size on viable seed output, seed rand and natural regeneration pattern of a tropical conifer Widdringtonia whytei-Rendle in Malawi
(Stellenbosch : Stellenbosch University, 2013-12) Chanyenga, Tembo Faera; Geldenhuys, Coert Johannes; Sacande, Moctar; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Widdringtonia whytei is a tropical endemic, fire-adapted pioneer coniferous tree species within natural fire-fragmented Afromontane forest patches in a confined area on Mulanje Mountain in Malawi. Natural and anthropogenic fires within the surrounding fire-prone landscape, insect attacks, and uncontrolled harvesting of mature trees for timber threaten the survival of W. whytei. This study investigated the effects of population fragmentation on the reproductive biology of W. whytei, through four specific studies: effects of population size, tree size and crown position on viable seed output; seed rain variation among population sizes; effects of temperature and light on viability and germination of W. whytei seeds; and the influence of population size on natural regeneration patterns. The study was conducted during 2008 and 2009 on three sites using three W. whytei population sizes: small (≤10 reproductively mature cone-bearing W. whytei trees), medium (11-20 cone-bearing trees) and large (>20 cone-bearing trees). Data were collected using field and laboratory experiments and a review of secondary information. The effect of fragment size and crown position on viable seed output and seed rain pattern was tested with a nested linear mixed model. The influence of stem diameter (dbh) on viable seed output was tested using a separate data set. The variation in seed rain was explored with a generalised linear model (GLM) with a negative binomial link function. Variations in seed germination was analysed with a Weibull regression model. The influence of fragment size on seedling regeneration was tested with a GLM (binary logistic regression). Viable seed output from W. whytei cones was very low (23%) and was not affected by population size, tree diameter or crown position. W. whytei population size influenced seed rain with large fragments having higher seed rain densities. Number of dispersed seeds was generally very low and poorly dispersed. W. whytei cones are semiserotinous and depends on moderate to severe fires for heavy seedfall and wider dispersal. Such fires did not occur during the study period. Temperature is a critical factor for seed germination. Seeds germinate between 15 and 25°C with the optimum at ~ 20°C either under light or dark conditions. Regeneration density followed the seed rain pattern indicating that seed availability is a critical factor for regeneration. Regular cool fires outside the forest patches and along the edges during the hot dry season, and the thick litter layer and shady conditions inside forest patches, caused most of the seedling mortality. This study highlighted the difficulties W. whytei experiences with low output of viable seed, limited seed dispersal and low seedling regeneration in and around forest patches, i.e. factors important for conservation management of this species. It is recommended that gaps with diameter equal to canopy height and occasional spot fires would promote seed dispersal onto exposed mineral soil for rapid seedling establishment and subsequent population growth. Such natural fire disturbance events may show the true seed rain and seedling establishment patterns in this species.
Effects of clear felling and residue management on nutrient pools, productivity and sustainability in a clonal eucalypt stand in South Africa
(Stellenbosch : Stellenbosch University, 2012-12) Dovey, Steven Bryan; Du Toit, Ben; De Clercq, W. P.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
The subtropical ecosystem of the Zululand coastal plain is prized by the South African commercial plantation forestry industry for its rapid clonal Eucalyptus growth, short rotations (6 to 7 years) and high yields. This region is typified by sandy soils that are low in clay and organic matter, have small nutrient reserves and are poorly buffered against nutrient loss. The subtropical climate induces rapid decomposition of residues and tree litter resulting in small litter nutrient pools and rapid nutrient release into the soil, particularly after clearfelling. A combination of large nutrient demands through rapid growth, rapid nutrient turnover and small soil nutrient reserves implies that sites in this region are sensitive and may be at risk of nutrient decline under intensive management. The work in this study set out to determine the risk of nutrient depletion through harvesting and residue management on a site within the Zululand region, to assess nutritional sustainability and the risk of yield decline in successive rotations. Some bulk biogeochemical cycling processes of macro-nutrients nitrogen (N), phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg) were assessed, and assessments also included sodium (Na). An existing Eucalyptus stand was clearfelled and treatments were imposed on the residues after broadcasting to simulate various levels of nutrient loss through levels of harvesting intensity and residue management. These included residue burning (Burn), residue retention (No-Burn), fertilisation (stem wood nutrient replacement), whole tree harvesting and residue doubling. Outer blocks of the stand were not felled, but included as replicates of an undisturbed standing crop treatment. Biogeochemical nutrient cycling processes were assessed primarily in the standing crop, Burn and No-Burn treatments, in the assumption that these represented the furthest extremes of nutrient loss. Data collection commenced a year prior to clearfelling and continued to two years and six months after planting with key data collection over a 20.1 month period from clearfelling to canopy closure (one year after planting). Water related nutrient pools and fluxes were assessed as atmospheric deposition (bulk rainfall, throughfall and stemflow) and gravitational leaching to 1m soil depth. Drainage fluxes were predicted using the Hydrus model and real-time soil moisture data. Zero tension lysimeters collected soil solution for chemical analysis. Sequential coring in the 0 to 30cm soil layer was used to determine in situ soil N mineralisation. Soil chemical and physical properties were assessed over the first meter of soil at clearfelling and new crop canopy closure to determine soil nutrient pools sizes. Biomass nutrient fluxes were assessed from litterfall, residue and litter decomposition, and above ground accretion into the tree biomass. Leaching and N mineralisation were monitored in the No-Burn, Burn and standing crop treatments only. Atmospheric deposition, while variable, was shown to be responsible for large quantities of nutrients added to the Eucalyptus stand. Nitrogen and K additions were relatively high, but within ranges reported in previous studies. Rapid tree canopy expansion and subsequent soil water utilisation in the standing crop permitted little water to drain beyond 1m resulting in small leaching losses despite a sandy well drained soil. Further leaching beyond this depth was unlikely under the conditions during the study period. Mineralisation and immobilisation of N also remained low with net immobilisation occurring. The standing crop was shown to be a relatively stable system that, outside of extreme climatic events, had a relatively balanced or positive nutrient budget (i.e. nutrient inputs minus outputs). Large quantities of nutrients were removed with stem-wood-only harvesting in the No-Burn treatment leaving substantial amounts on the soil surface in the harvest residues. Whole tree removal increased losses of all nutrients resulting in the largest losses of P and base cations compared to all other treatments. This was mostly due to high nutrient concentrations in the removed bark. Loss of N in the Burn treatment exceeded whole tree N losses through combustion of N held in the harvest residues and litter layer. The majority of K leached from the residues prior to burning and a relatively small fraction of the base cations were lost from the partially decomposed residues during burning. Ash containing substantial amounts of Ca and relatively large amounts of N and Mg remained after burning. Surface soil Ca and Mg was significantly increased by the ash which moved into the soil with rainfall directly after burning. Rapid soil moisture recharge occurred within a few months after clearfelling, increasing leaching from the upper 50cm of soil. Clearfelling increased net N mineralisation rates, increasing mobile NO3-N ions in the soil surface layers. Nitrate concentration peaked and K concentration dipped in the upper soil layers of the Burn treatment directly after burning. Deep drainage and leaching (beyond 1m depth) over the 20.1 month period was, however, not significantly different between the Burn and No-Burn treatments. Rapid soil moisture depletion and nutrient uptake with new crop growth reduced leaching fluxes to levels similar to the standing crop by six months after planting. Taking the full rotation into account, clearfelling induced a short-lived spike in N and cation leaching compared with the low leaching losses in the undisturbed standing crop. Soil N mineralisation over the 20.1 month period in the burnt treatment was half that of the No-Burn treatment. Growth and nutrient accumulation was significantly higher in the fertilised treatment than in other treatments up to 2.5 years of age. Growth in the Burn treatment was greatest compared to other treatments during the first few months, but slowed thereafter. No significant growth differences were found between all other treatments from a year to 2.5 years after planting. Early growth was therefore apparently not limited by N supply despite large differences in N mineralisation between Burn and No-Burn. Foliar vector analysis indicated that fertilisation improved growth initially through increased foliar N and P at six months after planting followed by Mg and Ca at one year. The Burn treatment was not nutrient limited. These growth results contrasted with similar international research on sandy tropical sites where growth was reduced after residue removal and increased after residue doubling. The combined nutrients released from pools in the litter layer or ash and soil in addition to atmospheric inputs were sufficient to provide most nutrients required to maintain similar growth rates across all treatments. This demonstrated the importance of residue derived nutrients to early growth nutrient supply. Reduced N mineralisation through a lack of substrate may limit N supply later in the rotation where residue had been removed. Construction of a nutrient budget for the system revealed that high levels of atmospheric inputs have the potential to partially replenish a large proportion N, K, and Ca lost during clearfelling, provided losses are constrained to stemwood removal only. However, loss of Mg that occurred primarily through leaching may not be replaced under the low Mg inputs recorded in this study. Larger nutrient removals (i.e. stemwood plus other plant parts) placed a heavier reliance on the small soil nutrient pools at this site which can limit future productivity. More intense harvesting and residue management practices dramatically increased the risk of nutrient depletion. Losses of specific nutrients depended on a combination of clearfelling biomass removal, residue burning and subsequent leaching. Nitrogen losses due to harvesting and burning were more substantial than those due to leaching. Mg and K losses depended most strongly on the time after clearfelling before re-establishment of the new crop and rainfall patterns, while Ca and P losses depended directly on the amount of biomass removed. Depletion risk was the greatest for Mg and K through rapid leaching, even after stem wood only removal. Deep root uptake and deep drainage with associated cation loss needs to be investigated further to quantify ecosystem losses and recovery of cations displaced beyond 1m. Atmospheric deposition is one of major factors countering nutrient losses. However, atmospheric inputs may not be reliable as these may lessen in future through pollution control legislation and climate change. Changes in growth rate under poor nutrient management practices are small and difficult to detect relative to the large impacts of changing weather patterns (drought), wildfire and pest and disease. This makes it difficult to prove nutrient related growth decline. It may be possible that improvements in genetics, silvicultural technologies and atmospheric inputs may also be masking site decline (in general) and in part explain the lack of evidence of a growth reduction in the region. As the poorly buffered sandy soils on the Zululand Coast are at risk of nutrient depletion under the short rotation, high productivity stands, it may be necessary to stipulate more conservative harvesting and residue management practices. A more conservative stem-wood only harvesting regime is recommended, retaining all residues on site. Residue burning should be avoided if N losses become a concern. The length of the inter-rotation period must be kept short to reduce cation leaching losses. Site nutrient pools need to be monitored and cations may eventually need to be replenished through application of fertilisers or ash residues from pulp mills. Management practices therefore need to be chosen based on the specific high risk nutrients in order to maintain a sustainable nutrient supply to current and future plantation grown Eucalyptus.
The effects of forestry policy on the sustainability of forest resources in Southern Africa
(Stellenbosch : Stellenbosch University, 2002-03) Watts, White Scotney; Milton, Sue J.; Ward, David; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: This study aims to evaluate the effects of forestry policy on the sustainability of forest resources in Southern Africa. However, the study has confirmed that forestry policy does not operate independently of other policies. Its scope is defined by overarching framework legislation and policy, while it functions within a complex mesh of crosscutting and sectoral policies. Therefore, the implications of these external policies for forest conservation have also been assessed. The method used employs predominantly qualitative assessment of documentary data, which constitute the main contents of the three case studies: South Africa, Tanzania and Zambia. This qualitative information has been transformed into quantitative data, using a scoring scale of one to five for certain indicators of sustainable forest management (SFM). The average score for each country makes up a forest conservation index (FCI), which provides a comprehensive insight into the performance of a country's forestry and other resource conservation policies. South Africa's FCI is estimated at 3, while Tanzania and Zambia's indices have been rounded to 2 each. As South Africa's forestry policy and other biological resource conservation policies came into existence as recent as the mid- and late 1990s, this index suggests that these policies will lead to SFM subject to satisfactory implementation. Indeed, South Africa has a congruous forestry legislation whose regulatory mechanisms are appropriately blended with financial and framework incentives. Its overarching framework legislation and policy define forestry policy, while the crosscutting policies reinforce it. However, the country's performance on intergovernmental and intersectoral policy co-ordination is poor, as well as on the economic valuation of its natural forest resources. Furthermore, the formulation of South Africa's forestry policy was not founded on up-to-date forest resource data. Contrary to the South African case, Tanzania and Zambia's indices indicate the likelihood of unsustainable forest use and management. These countries' existing forestry and other resource conservation policy-making processes are narrow-based and gender-insensitive, rendering them unpopular among policyaffected and policy-connected stakeholders. These inappropriate policies and their blunt instruments distort markets for forest resources, i.e., create situations in which benefits are dissociated from costs, prices from scarcities, rights from responsibilities and actions from consequences. Both forestry policies and their governing tools were not founded on contemporary forest resource data, i.e., they are not issue centred. The countries' framework laws have also failed to institutionalise environmental impact assessment, monitoring and evaluation, intersectoral policy co-ordination, participatory approaches to natural resource management and ownership of environmental assets such as land and forest resources by local communities. The administration of forestry policy requires competent professional and technical staff. South Africa has adequate human resources in the forestry sector, although the personnel appear to lack the necessary skills for participatory forest management for poverty reduction. Tanzania has adequate but ineffective forestry personnel, resutting in lack of law enforcement and corruption while Zambia lacks professional staff to interpret and implement the existing forestry policy. The ineffectiveness and the lack of professional and technical staff, inter alia, is reflected in the high rates of deforestation, which have been estimated at 91,000 halannum for Tanzania and 851,000 halannum for Zambia. Unlike South Africa, both Tanzania and Zambia's sectoral policies fail to cultivate concerns for forest conservation. This situation is aggravated further by the pervasive lack of intra- and intersectoral policy coordination among biological resource conservation divisions and departments. The coherence of South Africa's forestry and other resource conservation policies is attributable to the scarcity of natural forests in the country. Approximately, 7.0% of South Africa's landscape is under forest cover, while Tanzania and Zambia have 37% and 42%, respectively. Decreasing supplies of forest coupled with the increasing demands for forest resources causes the value of forest resources to appreciate. Naturally, there is a stronger need for the forest-scarce South Africa to pursue prudent conservation policies to protect its limited forest than Tanzania and Zambia whose governments treat their respective vast land and forest resources as a safety valve for economic hardship without adequate investment in SFM. In summary, forest resource use and management in Tanzania and Zambia are littered by market and policy failures. It is envisaged that the opportunities and constraints identified in each market and policy failure will inform future forestry and related policy-making process, not only in the concerned countries but also in other African countries experiencing similar forest conservation problems.
’n Ekonomiese ondersoek na die produksie van timmerhout uit uitheemse naaldhoutplantasies in die unie van Suid-Afrika
(Stellenbosch : University of Stellenbosch, 1954-06) De Villiers, P. C.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.; Jacobs, Ivan
No abstract
Estimation of tree biomass, measurement uncertainties, and morphological topology of Androstachys Johnsonii prain
(Stellenbosch : Stellenbosch University, 2016-03) Magalhaes, Tarquinio Mateus; Seifert, Thomas; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: This research was aimed at estimating biomass stocks separated in above- and belowground tree components, and studying the topology of the shoot and root systems of Androstachys johnsonnii Prain in woodlands in Mozambique. A two-phase sampling design was used to determine above- and belowground biomass. In the first phase 3574 trees were measured in 23 randomly located circular plots (20-m radius). In the second phase, 93 trees were randomly selected as a subsample from the first phase sample for destructive measurement of biomass and stem volume, along with the variables of the first phase and for topological analysis of the shoot and root systems. Estimates of biomass stocks and quantification of the errors associated with those estimates were obtained using Phase-1 data and regression models. Additionally, biomass expansion factors (BEFs) were fitted based on the 93 trees harvested in the second phase. The estimated total tree forest biomass was 167.05 Mg ha–1 using biomass models and 150.74 Mg ha–1 using BEFs. The percent error resulting from plot selection and biomass regression equations for whole tree biomass stock was 4.55% and 1.53%, respectively, yielding a total error of 4.80%. Among individual variables in the first sampling phase, diameter at breast height (DBH) measurement was the largest source of error. Tree-height estimates contributed substantially to the error as well. For the second sampling phase, DBH measurements were the largest source of error, followed by height measurements and stem-wood density estimates. Of the total error (total variance) of the sampling process, 90% was attributed to plot selection and 10% to the biomass model. The BEF values of tree components were unrelated or weakly related to tree size, and root-to-shoot ratio (R/S) was independent of tree size; therefore, for A. johnsonii, constant component BEF and R/S values can be applied within the interval of sampled tree sizes. Visual analysis indicated herringbone-like branching pattern for both the root and shoot systems. However, the topological index (TI) and topological trend (TT) suggested otherwise. This discrepancy was attributed to the fact that A. johnsonii has multiple laterals per stem/taproot node, suggesting that the topological indexes (TI and TT) might yield biased conclusions regarding the branching pattern when the main axis has multiple laterals per node. Hence, a modified topological index (TIM) was developed that could be applied in the cases of multiple laterals per node while conserving the values of TI for cases with one lateral per node; the modified index was more efficient and realistic than TI. The area preserving branching was confirmed for each stem node confirming the self-similar branching. For the root system, the area-preserving branching was only confirmed for the first node; therefore, self-similarity was not confirmed.
Fertilisation of semi-mature Pinus elliottii and Pinus elliottii x caribaea stands on a climatic gradient in the Tsitsikamma and its effect on system nutrition and stand productivity
(Stellenbosch : Stellenbosch University, 2018-12) Gerhardus Petrus, Scheepers; Drew, David M.; Du Toit, Ben; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Eight field trials were established in October 2015 to test the effect of different nitrogen and phosphorous combinations on Pinus elliottii and P. elliottii x caribaea growth. Fertiliser is costly, and the financial return is governed by the degree of the response, application costs and product worth. Commercial pine plantations are commonly fertilised at two stages – at establishment, and at mid-rotation following a final stem reduction. National and international studies are uncertain regarding the economic feasibility and response of semi-mature pine plantations to fertilisation. These uncertainties can be attributed to the substantial edaphic, topographic and climatic variations under which commercial plantations and forests are grown. The formulation of site-specific fertilisation rates could allow commercial and private forest companies to increase the profitability of fertilisation and achieve optimal growth responses. The field studies were established in the Tsitsikamma in the Eastern Cape, across a water-availability gradient and on sandy loam soils with soil pH (KCl) values ranging from 2.9 to 4.0. The field trials were designed to test the interaction of six fertiliser treatment combinations (all in kg ha-1) and consisted of a control treatment of 0 N and 0 P (T0), and then treatments of 0 N and 50 P (T1), 0 N and 100 P (T2), 100 N and 50 P (T3) and 100 N and 100 P (T4), and a maximum application rate of 200 N and 100 P (T5). These application rates were based on the findings of previous softwood fertilisation projects in the Southern Cape, as well as in the Boland region of the Western Cape. Data collection was done at 0, 6, 12, 18 and 24 months after fertilisation. The primary objective of this study was to formulate site-specific fertilisation rates for the semi-mature pine plantations of the Cape forest region. To achieve this, the study was divided into four sub-studies. The first sub-study focused on the effect of water availability on stand growth. It investigated whether the water deficit estimate by Thornthwaite (1948) and Thornthwaite and Mather (1955) could be used as a reliable estimate of soil water availability, relative to other widely accepted (lesser and increasingly complex) estimates of water availability generally used in forestry and other agricultural practices. The second sub-study made use of the Soil Nitrogen Availability Predictor (SNAP) model to predict the N mineralisation rates of all field trials. The predicted N mineralisation rates were then used to determine whether the N mineralisation potential of a soil significantly affects the fertilisation response after 24 months. The third sub-study was a development of the second: the mineralisable N and P, from simple to increasingly complex, was determined in controlled laboratory conditions by means of aerobically and anaerobically incubating soil samples acquired from each field study. The relationships between (a) calculated mineralisation rates, together with the basal daily N mineralisation rate predicted by the SNAP model and (b) the growth response at 24 months after fertilisation were evaluated. The final sub-study investigated whether canopy N and P contents were significantly affected by fertilisation and whether the application of different N and P fertiliser combinations can address the potential nutrient deficiencies of semi-mature slash plantations in the Tsitsikamma. Findings: This study shows that Thornthwaite’s soil water deficit methodology is an improved and increasingly accurate estimate of plant-available water relative to mean annual precipitation, and (FAO) estimates of aridity index a moisture growing season. The methodology has fewer and more easily obtainable data requirements and paints an accurate picture of soil water availabilities at times of seasonal fluctuations and inconsistent climatic conditions. The water deficit estimate has the potential to identify sites where growth is limited by soil water availability to larger and/or smaller degrees. Soils from slash pine plantations in the Tsitsikamma region have superior water-retention capabilities relative to sites from the Knysna and Boland regions of the Western Cape. No significant correlations were observed between the predicted annual N mineralisation rate of the SNAP model and the growth responses at 24 months after fertilisation; however, the model predicted the highest annual rates for the least responsive field trial: a N mineralisation rate in the range of 149 (after subtracting the 𝑁𝐻4+ before incubation from the final 𝑁𝐻4+ pool) to 238 kg N ha-1 yr.-1 (final pool only) was predicted for field trial A, and this field trial exhibited the poorest growth response to added fertiliser over the experimental period. In addition, field trial A had a higher soil pH, and a significant interaction was observed between the N mineralisation potentials of each site and the soil pH (p = 0.040). Significant Pearson correlations were observed between the total N, anaerobic N and aerobic P estimates and the growth response at 24 months after fertilisation. Field trials with higher total N contents were less responsive to increased N applications in the presence of P. The opposite was observed for increased P applications: sites with higher total N contents were increasingly responsive to higher applications of P. Sites with inherently higher anaerobic N mineralisation rates exhibited weaker growth responses to increased N application in the presence of P. Sites with higher P mineralisation rates were less responsive to P fertilisation. The anaerobically incubated N mineralisation rates were superior to the aerobic rates in this study, although the predicted basal N mineralisation rate of the SNAP model (which relies on an estimate of aerobic N) correlated with the volume responses at 24 months after fertilisation. Canopy N and P contents differed significantly between sites (p < 0.001). The N contents were significantly affected by fertilisation, at a confidence level of 90% (p = 0.059), and the N contents increased according to the highest fertilisation rates (T0 to T5). Significant treatment differences were observed for the canopy P content (p = 0.014) after 24 months, with the highest P content observed for the highest application of phosphorus (T2), in the absence of a N source. Plant nutrient availability appeared to be primarily driven by site-specific edaphic and topographic conditions and, to some extent, by the higher N and P fertiliser combinations. The field trials were established on highly acidic soils. This finding, together with the documented volume responses, suggests that stand growth in the Tsitsikamma can be improved with moderate N and P fertiliser application rates. It also calls for further testing of micronutrient and lime additions, as low pH conditions and sub-optimal foliar micronutrient levels were associated with lower stand growth responses.
A fibre optimisation index developed from a material investigation of Eucalyptus grandis for the Kraft pulping process.
(Stellenbosch : Stellenbosch University, 2012-03) Du Plessis, Marius; Rypstra, T.; Zbonak, A.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: A primary reason for the existence of the forest industry is to provide a renewable and natural resource for much needed timber and fibre products. Substantial improvements in management practices are required to increase forest volume and pulp yields for increased demand. Eucalyptus grandis clonal trees of age 6.75 years, grown in a Nelder 1a spacing experiment, were sampled and analysed to describe the effect of planting density on i) growth and yield, ii) wood properties and iii) pulp and paper quality. The main objective was to populate a fibre productivity index (FPI) which would be suitable from technical and economical perspectives. A material study was conducted on the wood and in addition, two methods were developed to further describe the variability of the forest resource to i) separate growth rings by means of wood density peaks from gamma-ray densitometry and ii) calibrate near infrared (NIR) prediction models. The results indicated that planting density did not influence the variability of wood density but mechanisms affecting available soil water are important. NIR prediction models were developed to rapidly and reliably assess wood properties on a non-destructive basis. The validation models for wood density, total pulp yield, kappa number and insoluble lignin returned high predictive ability. When applied to predict chemical properties from an independent data set, the outcomes were accurate in comparison with measured data. Growth and yield functions were developed for tree survival, dominant height and basal area. They accurately predicted outcomes as demonstrated by the goodness of fit and their logical behaviour tested over the range of planting densities. When the most extreme stand density treatments, 6809 and 275 trees per hectare (TPH) were evaluated for wood and fibre properties, the larger trees grown at 275 TPH, produced wood of better quality for pulp processing; basic wood density at 0.520 g cm–3 (21 % higher), fibre cell wall thickness at 2.10 μm (18.6 % thicker) and fibre lumen diameter at 8.16 μm (9.9 % lower) than for 6809 TPH. Intra-specific tree variability of wood and product properties increased from diameter at breast height (DBH) to 35 % and then decreased to 65 % of tree height. The effect of planting density was carried throughout the product value chain up to the paper manufacturing phase. Paper with higher bulk mass and thickness and more porous sheets is most likely to be made from lower planting densities (801 and 275 TPH), and stronger, smoother and denser paper is most likely to be made with trees at high planting densities (6809 or 2336 TPH). From the growth and yield and materials investigation, technical indicators identified to populate a fibre productivity index were: i) mean annual increment (MAI) as a forestry growth indicator, ii) wood density, summarising the composition of wood and, iii) pulp yield, the indicator of the amount of fibre processed through a chemical cooking process. Delivered cost of timber to the mill, was identified as the most suitable economic indicator which included fixed costs elements, variable costs and aspects of mill efficiency. The product of the technical and economic indicators concluded in a profit/loss scenario of producing 1 ton of pulp was deemed the best index to describe the entire and integrated value chain. This index, termed the Fibre Productivity Index (FPI) at the Mill, denoted as FPMill, is an integrated index that is easy to interpret in the realms of a forestry - pulp manufacturing, and can be used for differential pricing of timber for wood quality.
Growth and physiological parameters related to shoot dieback in Pterocarpus angolensis DC seedlings
(Stellenbosch : Stellenbosch University, 2004-04) Mwitwa, Jacob Pacific; Van Wyk, G.; Stellenbosch University. Faculty of Agrisciences. Dept. of Forest and Wood Science.; Jacobs, Ivan
ENGLISH ABSTRACT:Six experiments, five in the glasshouse and one in the field near Nelspruit, were carried out to ascertain the effect of factors related to shoot die-back, and of water treatments on the growth and physiological responses of Pterocarpus angolensis seedlings. The study was undertaken to broaden the knowledge and understanding of the phenomenon of shoot die-back in order to enhance our ability to regenerate the species. The following experiments were carried out (a) Assessment of biomass accumulation; anatomical characteristics of the shoot apical meristem; foliar, stem and root concentration of micro- and macronutrients associated with each phenophase, (b) Effect of seedling age and seed source on the occurrence of shoot die-back under field conditions; (c) Water treatment effects on ChI. afluorescence traits of£'. angolensis seedlings obtained by assessing the fluorescence yield of photosynthetic samples subjected to dark- and light-adaptation; (d) Genetic variation in shoot die-back and other traits of sixteen halfsib families of £.. angolensis from Malawi, Namibia and Zambia grown over two die-back seasons. Experiments conducted revealed the following 1. Patterns of growth observed in phenophases are indicators of seasonal changes in annual biomass allocation to the shoot and root. Phenophases such as leaf loss and stem senescence, whether shoot die-back occurs completely or not, are directly related to the decline in above-ground biomass and declined rate of increase in root biomass respectively. Leaf flush, expansion and maturation result in increased biomass accumulation whilst shoot die-back has a minimal downregulatory effect on root biomass accumulation compared to the shoot. Shoot dieback is not sudden, therefore from the first day of germination, seedlings synchronise growth and development with the occurrence of shoot die-back. 2. Phenophasic concentration of foliar N, Ca and Mg, stem Fe and Cu and root concentrations of P, K, Mg, Fe and B are associated with shoot die-back. Patterns of mineral nutrient concentration obtained in foliage and roots but to a lesser extent in the stem, may be related to nutrient remobilisation during shoot dieback. Higher relative mineral nutrient changes during leaf yellowing and shoot die-back may be an indication of the removal of significant volumes of mobile nutrients from senescing tissues. 3. The volume of the shoot apex of E. angolensis remains constant during different phenophases which points to seasonal uniformity in the size of the apical dome. Changes in phenology associated with declined growth, or shoot die-back, is revealed through declined cell number in the tunica which is a reflection of declined mitotic activity. 4. Shoot die-back occurs in all seedlings from nursery stock planted under field conditions and all seedlings of up to two years experience complete shoot dieback. Shoot die-back takes place irrespective of seed source or the age of nursery stock that is planted. Survival after the first shoot die-back is normally low. Water treatments had no significant effect on the function of PSIJ reaction centres of P. angolensis nursery seedlings. In the case of both dark- and light-adapted leaves, water treatment had no significant effect on the measured Chi. a fluorescence parameters or the calculated parameters (specific activities, phenomenological fluxes, structure-function and performance indexes and drivingforces). 5. Water treatments affect the shape of ChI. a fluorescence transients of lightadapted compared to that of dark-adapted photosynthetic samples of E. angolensis. No significant water treatment effect was obtained for extracted and technical Chi. afluorescence parameters, specific fluxes, quantum efficiencies and phenomenological fluxes. Quantum yield, relative electron transport and quantum yield limitation, de-excitation rate constants, structure-function, performance indexes and driving forces were also not significantly different across water treatments.6. Genetic variation was observed to exist among 16 halfsib families from Malawi, Namibia and Zambia. High heritabilities were obtained for shoot die-back and other traits, indicating that shoot die-back is genetically controlled. The trait is passed from parents to offspring and it is highly probable that it occurs, throughout its natural range, in all seedlings. Since shoot die-back is genetically programmed, it remains crucial to the ability of a seedling to regenerate in the following rainy season
Growth Response of Brachystegia longifolia to Copper Mining Pollution-Induced Heavy Metal Toxicity
(Stellenbosch : Stellenbosch University, 2022-10) Mulenga, Charles; Meincken, Martina; Clarke, Catherine E.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Mining-induced heavy metal dispersion often contaminates the soil in forests surrounding copper mines. Heavy metals are highly toxic to plant health at elevated levels depending on many factors, including species. However, the impact of copper mining-induced metal toxicities on the productivity of miombo forests is not well known. This study investigated the degree of forest soil contamination, bioavailable proportions of heavy metals, uptake and their subsequent effect on the growth and wood quality of Brachystegia longifolia, one of the commercially important miombo woodland species growing in a mining environment. The effect of copper mining activities on B. longifolia was studied as a function of distance and wind direction around an active copper mine in Mufulira, Zambia. Four sampling plots were demarcated along each transect, stretching 19 km upwind and 12 km downwind from the mine and trees were sampled from 50 m radius sample plots. Wood discs and crown leaves free of visible growth abnormalities were collected to form the biomass samples, as well as topsoil. Portable X-ray fluorescence was used to analyze the total concentration of Mn Fe, Cu and Zn in sieved soil and ashed leaves. The degree of soil contamination was analyzed using the geoaccumulation and enrichment factors, while the bioaccumulation potential of the studied elements in B. longifolia was assessed by the bioaccumulation factor. Furthermore, the bioavailable proportions of trace elements were analyzed by ICP-AES. The annual ring widths were measured and the relative tree growth was determined using the mean annual increment (MAI) across the sampling plots. The growth-limiting trace elements and stress conditions were then identified using the growth-response curve with the relative tree growth as a dependent variable. Furthermore, wood cell dimensions, wood density and elemental composition were analyzed from selected annual rings that included dry and wet years based on the mean annual temperature and mean annual precipitation, respectively. The degree of soil contamination illustrated that the forest soils around Mufulira are strongly polluted by heavy metals dispersed from the copper mine. Soil contamination extended up to 7 km upwind and the entire sampled 12 km stretch downwind. The sample plot at 2 km downwind was the most polluted site accounting for 296 mg/kg, 2337 mg/kg, 1101 mg/kg and 109 mg/kg accumulation of Mn, Zn, Fe and Cu in B. longifolia leaves, respectively. In contrast, only 3196 mg/kg, 154 mg/kg, 516 mg/kg and 55 mg/kg of Mn, Zn, Fe and Cu, respectively, were reported on the furthest unpolluted site upwind 19 km from the mine. Significant decreases in the concentration of Fe and Cu were observed with increasing distance from the mine, whereas the Zn and Mn content increased significantly. Furthermore, it was also observed that B. longifolia leaves accumulated Zn (x15) and Mn (x38) more than the soil throughout all sample plots. The radial growth of B. longifolia on all contaminated sites was significantly reduced compared to the control site. A multivariate analysis attributed the reduction in tree growth to Fe and Cu toxicities and it confirmed that B. longifolia trees accumulate and tolerate Zn and Mn. The decrease in radial expansion results from a significant reduction in wood cell dimensions and proportions on polluted sites. It was further observed that Cu and Fe toxicity increases the basic wood density of B. longifolia and compromises the capacity of wood tracheary elements to transport water and nutrients. This study demonstrates that copper mining-induced heavy metal forest soil pollution and the subsequent metal stress affects the growth and productivity of B. longifolia. It shows that Cu and Fe are highly toxic to this tree species, although it can accumulate and tolerate elevated levels of Zn and Mn. Fe and Cu toxicities alter the anatomical characteristics of B. longifolia wood, affecting the sustainable utilization of this tree species and possibly other miombo species naturally growing in heavy metal polluted environments.
The growth response of selected Zambian hardwood species to changing climatic conditions
(Stellenbosch : Stellenbosch University, 2019-03) Munalula, Francis; Meincken, Martina; Seifert, Thomas; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Factors such as precipitation and temperature are key to the growth of trees. The expected change in growing conditions, i.e. rise in temperature and reduction in precipitation will influence tree growth, wood structure and on wood quality. Due to lack of instrumental data, little is known about how Miombo trees growing in Zambian Miombo woodlands have responded to climate change. The objective of this study was to examine the extent to which climate variables related to water availability and temperature during cambial periods shape wood anatomical properties of three hardwood species growing in Miombo woodlands in Zambia, namely Brachystegia spiciformis, Burkea africana, and Isoberlinia angolensis. The species were selected based on value, distribution across the climate zones, dendrochronological potential, and relative ease of coring. To understand how Miombo trees growing in Zambia have responded to climate change, the ring structure and wood anatomical properties were related to known extreme climatic events. Sample materials, in the form of increment cores, were collected from areas differing in water availability. From the three climate zones, sites with climate data were selected and their aridity determined based on mean annual precipitation and mean annual temperature using De Martonne’s Index. At each site, 15-20 living trees were selected for sampling. For each tree, diameter at breast height (1.3 m), total height, bole height, and crown diameter were measured, after which two increment cores were then obtained from breast height at 90° and 180° to the wind direction. After collection, the cores were labelled to indicate site name, species, tree number, and core number for ease of identification in the lab and then placed in a core holder. In the lab, the cores were prepared for ring measurement and analysis using standard dendrochronological procedures after drying. The cores were then placed on a wooden mount and their ring structure studied under a microscope attached to a computer with ring measurement and analysis software. For wood anatomical studies, a Nano-CT scanner was used to obtain images from prepared cross sections representing wood formed during dry and very wet years. To compare the growth response of each species to different sites, ring structure was studied. Ring analysis revealed that mean sensitivity negatively correlated very well with mean annual precipitation. For all the species, sensitivity was significantly different between dry and wet sites. Sensitivity was high on the drier sites while complacent growth occurred on the wetter sites. In all the species, about 20% of the ring width variance could be explained by precipitation, but growth was unresponsive to temperature. The second part of the study looked at how the trees responded to extreme climate events. Each of the species was looked at separately. In all the species, data analysis revealed statistically significant (p<0.05) differences in fibre and vessel characteristics between those formed during wet and dry years, and those from dry and wet sites. Studies on effect of ring width on density revealed that, typical of diffuse-porous woods, density was independent of ring width. Fit functions developed from models based on projected values of precipitation under climate change scenario RCP8.5 revealed that cell wall thickness, which will increase by an average of +10.6 µm in all the species, will have the biggest influence on wood density. Wood quality will therefore change because of climate change. The study proved that in the absence of long-term data measured across the climate zones on the same trees, tree-ring studies can provide answers to questions on how particular trees react to adverse effects of climate change.
Growth, yield and economics of Pinus patula in the Natal Midlands
(Stellenbosch : Stellenbosch University, 1965) Crowe, N. D; Wicht, C. L.; Becking, J. H.; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: This thesis deals with the mensurational and economic studies in plantations of Popatula in the Natal Midlands o In Chapter I the climate of P.patula areas in Natal I is classified with the Thornthwaite method. The present silvicultural practice in the Natal Midlands is surmnarised o In Chapter II the construction of Volume Yield tables is discussed. These tables are based on the measurement of stand characteristics of temporary sample plots which have been measured once. The past diameter and the basal area i ncrement is determined from increment cores o A multiply regression analysis is used to determine the relationship between basal increment as dependent variable, stand density» age, sit e index and their interactions as independent variableso Site index is deleted l::lltage and stand density are retained as explaining variables . Site index curves, based on temporary sample plots are constructed, but the yield tables are based on the mean site index of 81 . 9 feet at 20 years. The volume increment is estimated from separately determined height and basal area increment equations., Four thinning models are introduced and for each of them a yield table is constructed., For these thinning regimes the diameter- = , volume--, and log class volume distributions are investigated . In Chapter IV the results of the economic analysis are presented.,Production costs have been investigated through questionnaires. Various types of rotations are calculated for each of the four thinning regimes. The profitability of different rotations and thinning regimes are compared. The implications of these calculations on the practice of silviculture and management are discussed.
The impact of subsistence use of forest products and the dynamics of harvested woody species populations in a protected forest reserve in Western Zimbabwe
(2007-03) Mudekwe, John; Geldenhuys, Coert J.; Grundy, I. M.; University of Stellenbosch. Faculty of Agrisciences. Dept. of Forest and Wood Science.
Developing sustainable mechanisms for use-management of forest products by user communities has been suggested as a possible solution to the often-observed conflict between forest use and the conservation of protected forests. In Zimbabwe, the use of forest products in protected forests by local communities has a long history, but few studies have explored both the socio-economic and ecological aspects of this use. This study was conducted in the Baikiaea plurijuga forests and woodlands in and around Fuller Forest in western Zimbabwe, protected since 1943. It explored the characteristics and dynamics of forest products use by communities surrounding this protected forest. Further, the demography and dynamics of commonly harvested woody species was examined in order to establish the present status of populations of these species. This examination, focusing on diameter class distributions, was aimed at informing whether species populations were expanding, stable or declining in view of their capacity to continue providing required goods and services. Results indicated that all households, rich and poor, were harvesting at least some forest resources from the protected forest, with the most frequently harvested resources being firewood, wood for curios, thatch grass, wild fruits, timber for construction and fencing and those who owned livestock used the forest for livestock grazing. The extraction and use of 23 different products was recorded across the villages. The top five harvested forest products in terms of the mean proportion of households using them were fuelwood, building poles, thatch grass, wild fruits and broom grass. Forest products were harvested both for own consumption and for sale. At present Baikiaea plurijuga, Colophospermum mopane, Brachystegia spiciformis, Diplorhynchus condylocarpon, Commiphora mocambicensis and Bauhinia petersiana out of 14 commonly harvested species appear to have relatively stable populations as indicated by their inverse J-shaped diameter class distribution profiles. Preliminary indications from this baseline information point towards the successful integration of local use of forest products and conservation objectives noting that there is need for caution until further studies as recommended in this study are taken.
The Interaction between site, harvest residue management and plant stock quality on eucalyptus transplant survival, growth and uniformity in Kwazulu-Natal, South Africa
(Stellenbosch : Stellenbosch University, 2021-03) Da Costa Alpoim, G. D.; Du Toit, Ben; Little, Keith; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Most eucalypt plantations are managed forshort rotations (6 to 8 years) and established across regions with varying water and nutritional stresses. The design and implementation of silvicultural management techniques should be adapted to the specific production and protection objectives, which are strongly governed local edapho-climatic conditions, water resources management, and protection against soil erosion, diseases, pests, bushfires, strong winds and alien species (Goncalves et al., 2017). Although a number of studies have reviewed factors such as planting stock quality and harvest residue management, and their interactive responses, few have quantified the interaction over different sites and the effect on early survival, growth and uniformity through to full rotation. Documented work, specifically in South Africa, focusing on the interaction of mulch residue and differing planting stock of different plug cavity volumes is scarce. Costa et al. (2004); Guarnaschelli et al. (2003)and Guarnaschelli et al. (2006) all confirm that eucalypt seedlings exposed to water stress preconditioning, do experience morphological adjustments whereby total biomass, leaf area and shoot:root biomass ratio, as well as certain physiological dynamics, can be associated with drought hardening. A combination of substandard nursery plant quality and inconsistent planting practices have been associated with poor survival and sub-optimal growth in eucalypt pulpwood plantations of South Africa and attributed to morphological differences found within plant stock. Plantation forestry is entirely sustainable under conditions of good husbandry, but only where wasteful and damaging practices are avoided. Our understanding of the mechanisms underpinning growth response to harvest residue mulching in hardwood eucalypt plantations remain limited. Forest residue retention is well understood to be an important tool in the sustainability of production forestry; however, it is but one component of a number that are just as critically important.Gonçalves et al. (2008)and Stape et al. (2002) report that under water and nutritional stress, residues retained on certain sites canincrease nutrient availability. This is strongly associated with reduced nutrient and organic matter losses, and the maintenance of important soil physical properties such as porosity, permeability, infiltration and aeration. Du Toit (2003) reports that plantation management operations carried out during the inter-rotational period (harvesting, residue management and certain silviculture operations) have a major impact on the productivity and long-term sustainability of forest stands, especially where short rotations are applied. Retaining residues following harvesting is thusan important strategy for sustaining the productivity of subsequent rotations; however the threat of fire on sites where residues have are retained can be catastrophic with financial losses running into millions of Rands. Four field trials were planted in the Midlands of KwaZulu-Natal Province, South Africa, to understand the interaction of residue treatments, plant stock size, nursery conditioning protocols and the application of insecticides on survival, growth and uniformity of E.dunnii (seedling) and E.gxn (clone),up to clear fell age. It was hypothesised that a combination of mulching, combined with the planting of larger,more robust plants,would ultimately result in better stocked and more vigorously growing out-plantings, with the goal of maximising utilisable timber availability at the end of the rotation. Although burning is a valuable and viable residue management tool, efforts to augment with alternative residue management techniques that are just as productive and beneficial in terms of long-term site sustainability are essential. There is a management aversion to harvest residue mulching due to the high cost; however, experience has shown that there are benefits to be garnered, with fire protection being a potentially strong additional point. The environmental benefits of this technology are promising and the potential gains measurable in the long term.With ever shrinking plantable areas, the environmental and legal pressures placed on obtaining water permits and the growing impacts of climate change, understanding the driver so fearly survival, growth and uniformity at the commercial scale are the cornerstone to our business survival. Trial results from this research endorsed the importance of plant quality but this factor can never be viewed in isolation when examining long-term field performance, as nursey plant size, residue management and insecticide applications are all equally important silvicultural inputs, specifically in their early interactions up to canopy closure. Main effects of the treatments tested that were strongly significant at final rotation, included site, in terms of explaining differences in mean annual increment (MAI), stocking (Spha) and height. Furthermore, stocking was significantly different among residue management treatments. The application of insecticide (main effect) explained significant differences in stocking but mean annual increment did not differ significantly among the insecticide treatments. The best performing treatments across all sites included a combination of a large transplant root plug volume (105 cm3), planted on slash spread treatment(MAI = 24.8 m3ha-1), whilst the worst performing was a standard plug (60 cm3) planted on a burn treatment (MAI = 22.6 m3ha-1). Relative differences in mean basal area (BA) between burning and mulch, showed initial gains up to 3 years, but this dissipated to zero by full rotation. Transplant root plug volume revealed early gains up to at 3 months but this declined to zero by full rotation. Increases in BA were more specific at the individual trial level,with early plug volume response (1 to 3 years) driven by genotype, but disappeared at full rotation. Small relative gains accrued by not applying nursery hardening up to 1 year, but thereafter were negligible for the duration of the trial.In summary, relative differences between treatments all showed promising early gains in basal area growth from 3 months, but these all declined to around zero by 4 years and thereafter remained constant through to full rotation. The results from this study showed that silviculture factors such as transplant plug volume, residue management, nursery hardening and insecticide application, all applied simultaneously at planting,were most responsive (statistically significant differences in basal area growth) from planting to approximately 3.5 years. Thereafter, their individual and combined effects became increasingly difficult to explain or isolate as either main effects or interactions with the additive response of three to four interacting silviculture treatments only able to explain less than 15% of variability after canopy closure, even where significant difference exist. This result was in agreement with several of the key references cited in this study. Nursery plants raised in large volume cavities (105 cm3) did not require hardening in the nursery where as the standard plug volume (60 cm3)benefited from a gradual reduction in irrigation. Positive gains from 1 to 3 years for root plug volume, residue management, insecticide application and hardening lost significance with time to form only part of an interaction as site effects and intraspecific competition became more dominant. 5of the trial.In summary, relative differences between treatments all showed promising early gains in basal area growth from 3 months, but these all declined to around zero by 4 years and thereafter remained constant through to full rotation. The results from this study showed that silviculture factors such as transplant plug volume, residue management, nursery hardening and insecticide application, all applied simultaneously at planting,were most responsive (statistically significant differences in basal area growth) from planting to approximately 3.5 years. Thereafter, their individual and combined effects became increasingly difficult to explain or isolate as either main effects or interactions with the additive response of three to four interacting silviculture treatments only able to explain less than 15% of variability after canopy closure, even where significant difference exist. This result was in agreement with several of the key references cited in this study.Nursery plants raised in large volume cavities (105 cm3) did not require hardening in the nursery where as the standard plug volume (60 cm3)benefited from a gradual reduction in irrigation. Positive gains from 1 to 3 years for root plug volume, residue management, insecticide application and hardening lost significance with time to form only part of an interaction as site effects and intraspecific competition became more dominant. Stocking and MAI showed very different responses to silvicultural treatments,but for explainable reasons. Stocking proved highly responsive to early silvicultural treatments, and less so to site.A plausible reason for this observation is that mean water deficits were moderate (<100 mm y-1on average)across all site types tested and stocking differences were more affected by silvicultural inputs, either main or interactive effects, over the full rotation. However,basal area growth and MAI, although initially highly influenced by both silviculture inputs and edapho-climatic factors, became increasingly more responsive to the effects of water deficits and nutrient capital driven by intraspecific competition with age.
Investigating pollination success between Pinus radiata and selected pine species
(Stellenbosch : Stellenbosch University, 2018-03) Ham, Hannel; Du Toit, Ben; Kanzler, Arnulf; Botha-Oberholster, Anna-Maria; Stellenbosch University. Faculty of AgriSciences. Dept. of Forest and Wood Science.
ENGLISH ABSTRACT: Pinus radiata is not only an important commercial plantation species in the Southern Hemisphere, but it is highly susceptible to Fusarium circinatum. Interspecific hybridisation attempts between P. radiata and some pine species is an ongoing process to improve F. circinatum tolerance. To date, limited pollination success between P. radiata and some pine species (P. tecunumanii, P. oocarpa, P. pringlei and P. patula) might be a result of biological or reproductive barriers that limit gene flow between species. Seven Pinus species (P. tecunumanii, P. oocarpa, P. pringlei, P. maximinoi, P. elliottii, P. taeda and P. patula) and one interspecific hybrid (P. patula×tecunumanii) with F. circinatum tolerance were selected as possible hybridisation partners for P. radiata. Previous studies indicated that the eight pure pine species are grouped in three distinctly different subsections with no difference in the karyotype. A generic Pinus cross-pollination protocol was developed and tested. Pollination success was evaluated with pathology diagnostic tests and DNA fingerprinting. Not only did the pathology tests indicate that all the screened seedlings were indeed infected and susceptible to F. circinatum (as would be expected from P. radiata pure species seedlings), but DNA fingerprinting assigned seedlings to the P. radiata population. Low pollen germination and pollen contamination from external sources might have contributed to the limited pollination success. However, Computed Tomography (CT) scans were successfully conducted to determine seed set of intact cones at 104 weeks after pollination. The generic protocol was adapted (green woven cloth bags to be replaced regularly, seal openings created by bulb applicators daily, sterilise breeding equipment, needles and female strobili before bagging and pollination events) and tested to determine whether pollination success could be improved. Studies on the climatic conditions inside (micro) and outside (macro) the pollination bags indicated that placement of the bags in the top northern side of P. radiata trees at the Karatara seed orchard, might increase temperatures closer to Sabie temperatures where the eight pine taxa (eight pure species and one hybrid) yield viable seed. Temperature fluctuations between day and night time are more severe at Karatara than Sabie and might be a constraint to pollination success. Three circadian models were developed to simulate climatic conditions at Karatara (micro and macro) and Sabie (average between Tweefontein, Witklip and Spitskop seed orchards). Biplots (discriminant analysis and principal component analysis), resembling the natural provenance climate data, grouped P. elliottii, P. taeda and P. radiata with Karatara, indicating good site species matching. When altitude was ignored as a vector, P. patula was grouped with the trio as well. In vivo pollination success between P. radiata, P. tecunumanii, P. oocarpa and P. maximinoi were determined by counting the number of visible ovules, pollen grains inside the ovules, pollen grains outside the ovules and pollen tubes. Data was collected with a standard fixation-dehydration-embedding histology sequence over the seven-week period, indicating that P. radiata×oocarpa, P. radiata×tecunumanii and P. radiata×maximinoi, differed significantly from P. radiata×radiata for all four factors investigated. The paraffin wax method was not suitable to study conelets older than eight weeks. MicroCT scans were used to confirm if fertilisation occurred between 15 to 16 months after pollination. Seed were visible from week 68 after pollination and viability of seed could be determined with quantitative porosity and defect analyses. Pearson correlation with biplots between natural provenance data (altitude, precipitation and temperature), PTGR (length and width) and hydrated pollen grain size (length and width) at micro- and macrotemperature regimes for the eight pure species, identified three distinct climatic response groups. These are (1) P. oocarpa and P. tecunumanii; (2) P. maximinoi and P. patula; and (3) P. elliottii and P. taeda. Although P. pringlei and P. radiata were not included in the three distinct climatic response groups, P. pringlei grouped with P. patula because of altitude, while P. radiata grouped with P. elliottii and P. taeda due to precipitation and minimum temperature. Data collected at Karatara during this study, correlated with previous studies indicating that P. radiata is better adapted to drier summers and wetter winters than the more tropical species. Therefore, pollination success at Karatara is not likely to be constrained by site factors, but if the pollen partner is not comparable with the temperature regimes at Karatara, it might result in limited pollination success. Therefore, data collected indicated that P. elliottii and P. taeda might be potential hybridisation partners for P. radiata. During this study valuable information was collected in terms of pollen grain size, PTGR, climatic data, three circadian models, in vivo pollination success and microCT scans. As this study focused on climate and pollen aspects, future studies need to concentrate on the female strobili, such as the hormonal and/or chemical interaction and whether ovule abortions are affecting pollination success.
Investigating the photosynthetic and hydraulic trade-off during drought recovery in eucalypts
(Stellenbosch : Stellenbosch University, 2022-04) Saunders, Alta; Drew, David M.
ENGLISH ABSTRACT: Stomatal regulation plays a vital role in maintaining the water status of a plant by minimising water loss, however, decreases in stomatal conductance can lead to reductions in carbon uptake. The stomata balance a trade-off between water loss and carbon gain. The hydraulic system and stomatal conductance are closely linked but play opposing roles within a plant. The hydraulic system ensures that there is a sufficient water supply to leaves, while stomatal conductance regulates the loss of water from the leaves. During periods of drought, reductions in hydraulic conductance due to embolism formation can be seen, however stomatal regulation can help reduce embolism formation or prevent runaway cavitation during drought. Understanding how plant hydraulics and stomatal regulation influence production rates is becoming more important to model stomatal responses in a changing climate, especially for Eucalyptus species which is often grown in drought prone environments. Plants use a wide range of strategies to reduce or mitigate the negative impact of embolism formation, with this study focusing on the strategies utilised by commercially significant Eucalyptus hybrids. Two Eucalyptus hybrids, E. grandis X camaldulensis (GC) and E. urophylla X grandis (UG), where subjected to a drought-recovery treatment where they were periodically droughted. During the experimental period the stomatal responses, together with transpiration rates, photosynthetic capacity and biomass allocation was measured. Hydraulic measurements together with CT-scan imaging was also utilised to determine whether these plants can recover lost hydraulic pathways post-drought, and what the underlying mechanism for this might be. During the study two distinct hydraulic strategies were observed. GC was more resistant to embolism formation compared to UG, however GC showed lower levels of hydraulic recovery after rewatering. The drought responses could also be split into a resilient v. a resistant response, with the more resilient hybrid, UG, maintaining stomatal conductance throughout drought periods running the risk of hydraulic failure, however with the ability to recover lost hydraulic pathways through refilling post- drought. This is in comparison with the resistant strategy seen in GC, where water loss during drought was minimised, however this also reduced carbon uptake and production. From this study the stomatal responses could also be accurately modelled using a gain-risk model that assumes stomata optimise the trade-off between water loss and carbon gain. It was however clear, that the strategy used by plants need to be considered when using a gain-risk model, with the gain-risk model performing better for the Eucalyptus hybrid that utilised a resistant strategy, since plants that uses a resilient strategy will maintain stomatal conductance during drought, regardless of the hydraulic risk. The use of alternative models was also investigated during this study, with Machine Learning models being able to accurately predict stomatal responses on a global scale. Major increases in tree mortality are predicted due to changes in climate. To properly predict these changes, accurate models of plant responses to water limitations and other environmental changes are therefore becoming increasingly important for effective forest management. Understanding how hydraulic traits and stomatal regulation covary, can help model drought-induced tree mortality in a changing climate.

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