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A comparison of between-tree competition effects in separate stands of a Eucalyptus grandis seedling and a single Eucalyptus grandis x urophylla hybrid cloneSale, Giovanni 15 November 2006 (has links)
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.
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Plant Spacing: A Size Sensitive Model With Implications for CompetitionBayn, Robert L, Jr. 01 May 1982 (has links)
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.
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Influence of planting density on spike size and grain yield in five winter wheat cultivarsWang, Shi Ping, 1956- 09 November 1990 (has links)
Graduation date: 1991
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The Process of Inductive Learning in Spaced, Massed, Interleaved, and Desirable Difficulty ConditionsPark, Sae Bin 01 January 2012 (has links)
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.
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Simulation study of the effect of well spacing, effect of permeability anisotropy, and effect of Palmer and Mansoori model on coalbed methane productionZulkarnain, Ismail 12 April 2006 (has links)
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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Effect of plant population on agronomic characteristics and yield of cotton and grain sorghumPitombeira, João Bosco January 1972 (has links)
No description available.
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Effects of plant spacing and soil moisture on growth and yield of grain sorghumMiyata, Satoru January 1978 (has links)
No description available.
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Spacial patterns of the genders in Dioecius plant speciesIglesias, Maria Claudia. January 1986 (has links)
No description available.
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Tension Stiffening and Cracking Behaviour of GFRP Reinforced ConcreteKharal, Zahra 26 June 2014 (has links)
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.
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Tension Stiffening and Cracking Behaviour of GFRP Reinforced ConcreteKharal, Zahra 26 June 2014 (has links)
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.
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