Student Number : 0115350V - MSc dissertation - School of Plant, Animal and Environmental Science - Faculty of Science / The effect of between-tree competition in separate even aged stands of a Eucalyptus grandis seedling and a single Eucalyptus grandis x Eucalyptus urophylla hybrid clone was assessed. This was done by comparing treatments within an experiment, that was designed to test the effect planting density and genotype had on timber production and stand dynamics through time. This experiment is located on an escarpment in the Summer rainfall region of South Africa, approximately 7 km North West of Albert Falls dam in the Kwa-Zulu Natal Midlands. The terrain is flat with deep apedal soils, and the site has an estimated mean annual precipitation of 1143 mm. The simplest method of evaluating competition effects in plantation stands is through the use of spacing trials. Spacing trials create stands/plots in which all silvicultural and climatic variables are constant. Differences between treatments can then be attributed to competition alone. The planting densities tested were 6667 stems.ha-1, 3333 stems.ha-1, 2222 stems.ha-1, 1587 stems.ha-1 and 1111 stems.ha-1 respectively. Competition was measured at three levels, namely; (i)individual tree, (ii)size-class and (iii)stand level. Vigour and its distribution within the population were used to explain competition processes. Basal area was chosen as the size variable for which vigour would be analysed. Relative Growth Rate (RGR) and Relative Production Rate (RPR) were chosen as the measures of vigour for analysis. Morphological changes in the trees as a result of competition were also used to understand the competitive mechanisms. It was found that resources are not shared amongst individuals in proportion to their size, but rather the larger individuals use disproportionately more of the resources than the smaller individuals, and therefore competition is asymmetrical. The dominant form of competition was found to be resource pre-emption where larger individuals passively prevent solar resources from reaching smaller competitors. Using RPR as the measure of vigour, competition was found to be one-sided, meaning that smaller individuals do not reduce the vigour of larger ones. If RGR is accepted as the measure of vigour then competition is two-sided meaning that the smaller individuals do reduce the vigour of the larger ones to a certain extent. There was no difference in the degree to which the smaller competitors in the clonal and seedling treatments reduced the growth of the larger individuals. The self-thinning rate in the seedling treatments was significantly higher than in the clonal treatments. Increases in mean tree size and production per hectare were accompanied by increases in mortality in the seedling treatments. In the clonal treatments it was found that even once the mean tree size approached the self thinning line, very few or no trees died, however there was also very little or no increase in mean tree size. When the relationship between number of live trees and production per hectare was analysed it was found that the clone could increase production per hectare without any change in survivorship, which is contrary to popular theory. As time progressed the skewness of the population progressed from negative to positive. This increase was the most pronounced in the higher planting density treatments, and the clonal treatments. The size variability in the population first decreased, then steadily increased. This increase was more pronounced in the high planting density treatments, and the clonal treatments. Clones and seedlings react in very different ways to competition. The large differences in population dynamics observed, indicate that we cannot just apply knowledge built up over the years regarding the management of Eucalyptus grandis and other plantation species to Eucalyptus hybrid clones.

An algorithm is presented which partitions space among mapped plants according to their relative sizes and positions using one of eight rules for locating boundaries between individuals. The performance of those rules is examined using several natural and artificial data sets with diverse measures of individual size. The relative performance of the rules was the same for all natural data sets examined. The best rule, as measured by a high correlation between individual size and assigned space, placed the boundary at a distance between neighbors proportional to the relative sizes of neighbors as long as a maximum distance (also a function of size) was not exceeded. It is inferred that the algorithm identifies contact neighbors and quantifies the extent of their contact. Afield experiment is proposed to test this inference.

Graduation date: 1991

One way people enhance their learning is through a desirable difficulty that makes the learning phase more difficult. The present research was devised to further explore these results and test the hypothesis that desirable difficulties benefits inductive learning by helping people engage in deeper processing strategies. In this experiment, participants were instructed to process perceptual disfluency and study different butterfly species that were presented in a clear or blurry manner. All participants were exposed to the interleaved and blocked conditions (within subjects), there was also a between subjects condition of fluent vs. disfluent. I hypothesized that subjects would perform better when presented with disfluency (blurry picture) because people would be able to engage in deeper processing strategies. This supported my hypothesis that desirable difficulties benefits inductive learning by engaging the subject in deeper processing.

Interference for adjacent wells may be beneficial to Coalbed-Methane production. The effect is the acceleration of de-watering which should lead to earlier and higher gas rate peaks. It is inherent that permeability anisotropy exists in the coalbed methane formation. It means that the placement of wells (wells configuration) has an effect on the development of coalbed methane field. The effect of Palmer-Mansoori Theory is increasing effective permeability at lower pressures due to matrix shrinkage during desorption. This effect should increase the gas recovery of coalbed methane production. Palmer and Mansoori model should be considered and included to coalbed methane reservoir simulation. These effects and phenomena can be modeled with the CMG simulator. A systematic sensitivity study of various reservoir and operating parameters will result in generalized guidelines for operating these reservoirs more effectively.

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Glass Fibre-Reinforced Polymer (GFRP) bars offer a feasible alternative in locations where steel is not the suitable reinforcement; namely locations that are sensitive to corrosion. In this study 60 specimens, 52 GFRP reinforced and 8 steel reinforced, were constructed and tested under direct tension in order to investigate the tension stiffening and cracking behaviour. The effects of different variables such as the bar type, the bar diameter, the reinforcement ratio and the concrete strength on tension stiffening and crack spacing were studied. The current code provisions for tension stiffening, namely ACI-440 and CEB-FIP were evaluated against the obtained test data. It was determined that the current code provisions significantly overestimate tension stiffening in GFRP reinforced specimens. A new tension stiffening model was, therefore, developed that provides better simulation of the test data. The CEB-FIP 1978 model for crack spacing was also modified for GFRP reinforced members.

Glass Fibre-Reinforced Polymer (GFRP) bars offer a feasible alternative in locations where steel is not the suitable reinforcement; namely locations that are sensitive to corrosion. In this study 60 specimens, 52 GFRP reinforced and 8 steel reinforced, were constructed and tested under direct tension in order to investigate the tension stiffening and cracking behaviour. The effects of different variables such as the bar type, the bar diameter, the reinforcement ratio and the concrete strength on tension stiffening and crack spacing were studied. The current code provisions for tension stiffening, namely ACI-440 and CEB-FIP were evaluated against the obtained test data. It was determined that the current code provisions significantly overestimate tension stiffening in GFRP reinforced specimens. A new tension stiffening model was, therefore, developed that provides better simulation of the test data. The CEB-FIP 1978 model for crack spacing was also modified for GFRP reinforced members.