Thesis (Ph. D.)--University of Hong Kong, 2006. / Title proper from title frame. Also available in printed format.

Table Mountain pine is an Appalachian endemic that occurs in a patchy distribution from Georgia to Pennsylvania and is prolific at sites with a history of fire disturbance. The purpose of this dissertation was to reconstruct the fire regimes of Table Mountain pine stands in the Jefferson National Forest, Virginia. Sections from firescarred Table Mountain pines were collected at four sites to analyze fire history, while increment cores and stand composition information were collected from macroplots within each fire history site to investigate the possible influence of fires that were more ecologically severe. Results show that fire was frequent before the fire suppression era, with a Weibull median fire return interval between 2–3 years. The majority of fires occurred during the dormant season and beginning of the early growing season. Two of the four sites had a more even distribution of fire seasons, and these sites also had significant Table Mountain pine regeneration. Cohorts of tree establishment were visible in the fire charts of three of these sites, indicating fires that were likely moderate in severity. The canopy at three of the four sites is currently dominated by Table Mountain pine, but the understory at all sites has large numbers of fire-intolerant hardwoods and shrubs. These Table Mountain pine stands will likely succeed to xeric oak and fireintolerant hardwoods, such as red maple and black gum, in the future. Fire statistics indicate that all four sites currently exist outside their range of historical variation in fire occurrence.

Diss. : Philosophische Fakultät : Zürich : 1979. - Bibliogr. p. 449-461. -

Texte remanié de: Th. doct.--Lettres--Paris 3, 1995. / Bibliogr. p. 269-285. Index.

Texte remanié de: Diss.--Kulturwissenschaftliche Fakultät--Bayreuth, 1987. / Bibliogr. p. 387-406. Index.

Chlorosis of the foliage of higher plants has constituted a severe fertility problem in many areas of the world. It has been reported in no less than 30 countries. It has manifested itself in the western states and has usually been associated with a high CaCO3 content in the soil. The problem considered here will be limited to the effects of age, and of calcium and bicarbonate ions on the uptake of iron by plants, and on chlorophyll formation. It is the hope of the author to determine which of the ions in the soil are conducive to "lime-induced chlorosis." Great Northern beans were selected as experimental material in view of their susceptiblity to typical "lime-induced chlorosis." These beans were grown in solution.

Zinc deficiency in Utah is found in about 7 per cent of the orchards. The severity varies from minor cases to sever instances in which many of the trees have died. The areas where zinc deficiency is found are becoming more extensive as land cultivation continues. The treatment of the disorder is expensive and must be repeated often, for it cannot be overcome by the addition of zinc to the soils. The soils in Utah seem to have ample zince, but in areas where zince deficiency occurs it apparently is in a form which is not available for plant growth. Preliminary evidence indicates high soluble phosphate in the siol may reduce the availability of zinc to higher plants. It is the purpose of this study to test the validity of this hypothesis. This report is not an attempt to determine the mechanism of zinc fixation or its reduction in availability; its purpose is to determine if there is a reduction in zinc availability as measured by uptake by plants in the presence of high soluble phosphate.

Agriculture first developed in the Middle East where, probably about 15,000-10,000 B.c., the earliest wheat crop was reaped from cultivated wild grasses. In Biblical times the Middle East acted as a granary of the western world and led the world in cereal production. Now, however, the situation is different. The Middle East is one of the lowest yielding areas in the world. This failure of the agriculture of the Middle East may be due to both climatic and cultural reasons. Many students of the Middle East report tha tthe climate has changed and that there has been a gradual decline in the amount of rainfall, especially of the autumn rainfall on which the grower of winter wheat depends for the sowing and germination of his crop. Cultural practices have not change appreciably in that region even though the while area may have changed from sub-humid to semi-arid. farmers still follow the same routine thousands of years ago. Another eason for agricultural failure is the lack of knowledge about climate and crop relationships and the attempts of growing wheat in areas where the climatic pattern is not suited to wheat production. The present problem is to investigate weather in relation to winter wheat production and to determine the extenet to which yields are influenced by climatic factors at different periods of the growth cycle of the wheat plant. Knowledge of such relationships makes it possible to determine, to a certain degree of accuracy, the suitability of a region to winter wheat production.

In the summer of 1944 a disease of apricots in Utah County, Utah, was brought to the attention of the staff of the Utah Agricultural Experiment Station. This disease was characterized by a scorched appearance of the edges of the leaves and therefore was called "apricot scorch." They typical sympotms of apricot scorch are a scorching and curling of the margins of the leaves. The "schorched" area usually turns a characteristic reddish-brown color, but sometimes is quite light brown or gray. The injury starts at the margins of the leaves and works inward in "waves" first scorching the marginal portion of the leaves, then, after a period during which no injury takes place, scorching the out edges of the formerly uninjured part of the leaves. At the edge of each "wave" of iinjury a darker brown line is usually left in the scorched portion of the leaf. Aparently health leaves from an apricot tree which shows some scorching will often develop a marginal necrosis if they are picked and are stored for 48 hours in a closed Mason jar. Apricot leaves form orchards in areas where scorch is not common do not exhibit this marginal necrosis when they are given the same treatment. A tree which has been slightly scorched may later appear to a casual inspection to have never been scorched. This is because the dead areas at the margins of leaves may eventually drop off, leaving the tree with a completely green appearance but with the leaf margins gone. The Chinses type of aptricot is apparently more susceptible to apricot scorch than is the Moorpark type. In the work reported in this paper, however, no attempt was made to classify samples or results on a varietal basis.

<p>Geochronological study of the Grenville Province has been an ongoing project at McMaster for the past 20 years. Over 1,500 orthogenesis samples have been collected from a 700,000 square kilometer region, and geochemically analyzed for Neodymium model ages. This vast area has been subjected to multiple accretion and ductile deformation episodes, creating great geological complexity.</p> <p>The two mam belts of the Grenville Province are the Allochthonous Belt, consisting of terranes which were laterally transported by the Grenville orogeny, and the underlying Parautochthonous Belt. The boundary separating these two major belts is termed the Allochthon Boundary Thrust (ABT) and represents the northwesterly limit of major crustal movement during the Grenville orogeny. Due to the high degree of exhumation of mid to lower crustal levels, identification of the ABT is difficult within Southwestern Ontario. As a result, lithological maps, such as the Geological Survey of Canada (GSC) map of the Grenville Province created by Davidson (1998), do not correctly identify sections of the ABT. In addition, impOliant geological features such as structural outliers (klippen) of the Allochthonous belt are not correctly identified. Along much of its length the ABT defines the boundary between Archean- Paleoproterozoic (> 1.8 Ga) and the Paleo- Mesoproterozoic «1.8 Ga) crust. Therefore, by measuring the isotopic composition of either side of the ABT the boundary can be clearly defined.</p> <p>Previously collected Nd isotope data were plotted on ESRI's Geographical Information System (GIS) and digitally represented. Interpolation based on sample age distribution was conducted to assess completeness of the data set. Interpolation techniques included triangulated irregular networks, inverse distance weighting, and kriging, which were used to obtain global and localized trends. This approach highlighted discrepancies between geological and geospatial interpretation, therefore highlighting areas which needed additional sampling.</p> <p>Nd-model analysis of olihogneiss from four areas collected within Northeastern Ontario and Southwestern Quebec have provided additional information to this interpolation process. Through the addition of these samples the boundaries of the ABT and klippen have become much more precise. Digital mapping of the terranes of the Grenville Province through integration of the aforementioned techniques has provided an improved understanding to the geological history of the Grenville Orogeny.</p> / Master of Science (MS)