No description available.

No description available.

No description available.

Tensile and compression strength properties of six coniferous woods were studied at the tissue level. Relationships of these properties to specific gravity variations in three adjacent growth increments of each species were explored. Pacific yew was excluded from tensile strength analyses, since the material available did not lend itself to micro-tensile testing. The main purpose of the investigation was to examine, at the tissue level, in what manner specific gravity influences tension parallel and compression perpendicular to grain strengths. Wood strength—specific gravity relationships for gross wood based on earlier studied, were compared to tissue relationships. Distributions of specific gravity and stresses within growth increments of woods having gradual transition from earlywood to latewood, as represented by western white pine, and of woods having abrupt transition, as Douglas fir, were also compared. Feasibility of radial micro-compression test methods established previously for Douglas fir were re-examined and extended to all six species. Experimental material, from freshly felled trees was never dried before physical testing, except western red cedar. Specimens for tensile and compression tests were cut from each increment studied. Micro-specific gravity determinations, based on green volume and oven-dry weight, were performed on broken tensile test specimens after extraction with standard solvents. Physical tests were carried out by established techniques. Regression analysis was employed to establish equations and curves best describing relationships of maximum micro-tensile and micro-compression stresses to specific gravity. Test results revealed highly significant relationship between maximum micro-tensile stress and specific gravity, and between maximum micro-compression stress and specific gravity. The latter relationship is curvilinear, expressed by an exponential curve fitting five of the six species studied. Pacific yew, also significantly correlated to specific gravity at 95 per cent probability, was described by the same basic equation applied to the grouping of the other five woods, but with different constants. This suggests that specific gravity influences maximum micro-compression stress variations in species of greatly different physical and anatomical, characteristics in varying degrees. Comparing tensile and compression stress—specific gravity variations of gross wood with those of wood tissue, it was found that in both properties specific gravity caused greater stress increase of gross wood than of tissue, as illustrated by respective regression lines. No definite trend of specific micro-compression stress within growth increments was found. Specific micro-tensile stress distributions showed a peak-value close to or at the initiation of latewood. Specific gravity, maximum micro-tensile stress and maximum micro-compression stress in woods having gradual transition from earlywood to latewood vary gradually across the increment, suggesting trends of a second degree parabola. In woods where transition is abrupt, the increase of these properties is abrupt at or close to the initiation of latewood. If in such woods the latewood zone is wide the distribution curve is sigmoid. Methods for testing wood tissue in radial compression, as well as theories related to the analysis of stress-deformation curves, have been verified. Ultimate load is recorded at the inflection point on the curve, beyond the proportional limit. At this phase of compression ultimate compressibility of the tracheids is achieved. / Forestry, Faculty of / Graduate

LD2668 .T4 1962 M25

No description available.

The distribution of the above-ground biomass and macronutrient content of the trees were studied on two sample plots in south coastal British Columbia, near Vancouver. The plots differed in elevation (4,600 and 2,200 feet; 1,500 and 700 m), in soil type and depth. Tree age was similar in both plots, ranging from 150 to 530 years. The tree cover on the high elevation plot consisted of Tsuga mertensiana (Bong.) Carr. (mountain hemlock) and Abies amabilis (Dougl.) Forbes (Pacific silver fir) while the lower elevation plot was occupied by Tsuga heterophylla (Raf.) Sarg. (western hemlock), Thuja plicata D. Don (western red cedar) and Chamaecy- paris nootkatensis (D. Don) Spach (yellow cedar). Twenty-four trees were sampled to determine the biomass and nutrient content of wood, bark, branches, twigs, foliage and cones. Another nine trees were sampled for the biomass and nutrient content of wood and bark only. Multiple regression analysis was used to establish the relationship between d.b.h., tree length, crown length and biomass of the various tree components. The regression equations obtained were used to estimate the total biomass of wood, bark, branches, twigs and foliage contained in the trees on each of the sample plots. The data thus obtained were combined with data on chemical concentration and used to estimate the distribution of macronutrient elements in different above-ground biomass components of the stands. / Forestry, Faculty of / Graduate

Climate change, induced by increases in the concentration of greenhouse gases in the atmosphere, can affect the growth and community structure of ecosystems in two ways. Firstly directly through changes in atmospheric concentration of CO2, and secondly indirectly through changes in temperature and rainfall. The aim of the present investigation was to test the effect of elevated CO2 and altitude-related temperature differences on the growth of two species of Acacia that form important components of the vegetation of KwaZulu-Natal. Plants of Acacia sieberana and Acacia nilotica were grown in chambers at elevated (700 pll-1) and ambient (350 IJW1) CO2 with and without rhizobial inoculation. Both treatments (elevated CO2 and the presence of rhizobial inoculation) stimulated growth and branching. A. nilotica was the most responsive to both elevated CO2 level and inoculation. Inoculated plants showed greater increases in mass and height than uninoculated plants. While elevated CO2 had a significant effect on plant mass, height and leaf area accumulation, other factors, such as species type and rhizobial inoculation had a somewhat greater influence on the short term mass accumulation under elevated CO2 , Significant differences existed between the average percentage leaf nitrogen for the two species (P < 0.001), and for inoculated and uninoculated plants (P < 0.005). There were no significant differences in photosynthetic rates (A) at any internal CO2 concentration (Cj) between plants grown in elevated CO2 compared to those grown under ambient conditions. When photosynthesis was plotted against C, (A/CJ, the initial slopes of the graphs for both A. sieberana and A. nilotica were shallower for plants grown in elevated CO2 , compared to plants grown in ambient conditions , indicating a decreased Rubisco concentration at low C, and greater nitrogen use efficiency. At higher C; A. sieberana continued to have lower A in plants grown at elevated CO2 levels suggesting an inability to regenerate RuBP or the possible accumulation of soluble carbohydrates. A. nilotica grown in elevated CO2 had a slightly increased Pj regeneration capacity at higher CO2 concentrations. While the A/Cj results demonstrate that CO2 ·has a minor effect on photosynthesis, growth responses indicated otherwise. This is a result often reported and indicates the importance of measuring as many parameters as is possible to determine actual plant responses to elevated CO2 levels. In the field experiment, the effect of temperature was studied by transplanting twenty plants of each species at three different elevations in the Drakensberg at Cathedral Peak. Plant height, mass, condition and finally survivorship were measured . All of these attributes decreased as elevation increased. Plants growing at the highest elevation all died back prior to winter while those growing at lower elevations grew throughout the experimental period. Results suggest that elevation and hence temperature are important factors controlling Acacia distribution. If the greenhouse gas induced increases in temperature occur as predicted, and the estimated latitudinal migration rates of 30-100km per decade are required for species to remain within their current climatic envelopes, it is expected that the structure and appearance of vegetation in the Drakensberg will change markedly with global warming . The presence or absence of Rhizobia in the soil will further complicate this. Those plants that have access to the elevated nitrogen levels as a result of these root nodule bacteria will have a distinct advantage over competitors growing without them. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.