• Refine Query
  • Source
  • Publication year
  • to
  • Language
  • 597
  • 168
  • 80
  • 31
  • 26
  • 23
  • 13
  • 7
  • 7
  • 7
  • 6
  • 6
  • 6
  • 6
  • 6
  • Tagged with
  • 1268
  • 248
  • 180
  • 126
  • 116
  • 110
  • 93
  • 90
  • 88
  • 85
  • 84
  • 84
  • 83
  • 81
  • 77
  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
181

A study of epidemics of lodgepole pine dwarf mistletoe in Alberta

Muir, John Alexander January 1966 (has links)
The increase of discrete populations of dwarf mistletoe (Arceuthobium americanum Nutt.) plants or infections was studied in 20 year old stands of lodgepole pine (Pinus contorta Dougl.). Mistletoe infections were selected from infected trees in three areas 100 to 200 ft. in diameter. The age of each infection was determined by dissecting the infected host wood. It was found that the number of infections established annually had increased logarithmically during the preceding 8 to 10 years. Therefore the logarithmic rates of increase in the number of infections could be calculated to describe the past epidemic growth of each mistletoe population. The logarithmic rates (equivalent to "compound" increase of 66 to 96 per cent per year) demonstrated rapid population increase. Although the three mistletoe populations had developed in apparently different environments, the population rates of increase were not statistically different. However, for the study of ecological aspects of dwarf mistletoe epidemics this approach appears quite promising. / Forestry, Faculty of / Graduate
182

Effects of Trifolium-Rhizobium symbiosis on Pinus contorta regeneration, forest soil, and selected native plant species

Trowbridge, R. L January 1990 (has links)
This study reports on the early effects of the Trifolium hybridum-Rhizobium symbiosis on Pinus contorta Doug, ex Loud (lodgepole pine), soil, and selected native plant species. Four rates of seeding (0, 10, 20, and 30 kg/ha) using inoculated Trifolium hybridum (alsike clover) seed were applied to three different site preparation treatments (broadcast burn, windrow burn, and mechanical scraping) using a split-plot design. Alsike clover and the Rhizobium inoculant were found to have excellent establishment and infectivity, and the symbiosis was assessed to be fixing nitrogen effectively. No effect of site preparation treatments was observed on establishment of the symbiosis, and clover-seeded plots averaged 76% cover by the end of the third growing season. The symbiosis had no significant (p < 0.05) effects on lodgepole pine total or incremental height or survival during the first three growing seasons, nor was there any observed effect on lodgepole pine foliar total nitrogen (N) concentration and ઠ¹⁵N values at the end of the second growing season. Small, but significant (p < 0.05) decreases were observed for lodgepole pine total and incremental diameter in the second and third growing seasons, as well as needle mass in the second growing season. The growth decreases were probably attributable to the effect of shading by the clover cover. However, lodgepole pine seedlings overtopped the clover by the end of the third growing season and shade effects are likely to decrease as tree seedlings continue to grow. After one growing season, the symbiosis significantly (p < 0.05) increased mineralizable N in the forest floor and mineral (0-15 cm) soil layers. However, no significant changes in total N were detectable. The changes in mineralizable N were likely a measure of increased microbial biomass attributable to greater amounts of rhizosphere soil in clover-seeded plots compared to controls. Available phosphorus (P) in the forest floor significantly (p < 0.05) decreased as rate of seeding increased after one growing season. The decrease of forest floor available P may be attributed to greater assimilation of P in clover-seeded plots for plant and microbial growth, as well as the additional requirements for P in the supply of biological energy needed for active N₂ fixation. All native plant species had low cover values which made interpretation of results difficult. However, percent cover of Calamagrostis canadensis, Rosa acicularis, and Spiraea betulifolia were significantly less in clover-seeded plots compared to controls at the end of the second growing season. Replacement of some herb and low-growing shrub species by legume-Rhizobium symbiosis may be desirable if the net result is an increase in site N without detrimental effects to tree crop species. It is recommended that the legume-Rhizobium symbiosis be established in the early regeneration of lodgepole pine plantations on similar sites that are inherently N deficient and have experienced further site N depletion through forestry practices such as slashburning. / Forestry, Faculty of / Graduate
183

Regional, provenance and family variation in cold hardiness of western white pine (Pinus monticola Dougl. ex. D. Don)

Thomas, Barbara R. January 1990 (has links)
Thirty-seven seedlots of western white pine (Pi nus mont i col a Doug. ex. D. Don) were tested for frost hardiness to determine how transferable seed would be from different seed sources within white pine's coast and interior ranges in British Columbia. Twenty-nine seedlots represented the coast and interior of British Columbia (BC), two were from coastal United States (US), three were from interior US and three were hybrids between interior US and interior BC parents. Detached needles were exposed to a series of freezing temperatures in a programable freezer and relative hardiness was calculated as the length of injured needle expressed as a percentage of total needle length 10 days after freezing. Seasonal progress in hardening was tested using five dates in the autumn of 1989. Seedlings were maintained at the University of British Columbia nursery. Testing also was carried out from samples collected on separate dates from Nakusp in the BC interior and from Ladysmith, a coastal BC site. There was a statistically significant (p<0.0l) regional difference between the BC coast and BC interior sources in all test runs, excluding the first UBC run and the Ladysmith run. In the runs where regions differed significantly, the difference in percent damage response of needles to freezing was approximately 20%. Measurements of shoot growth phenology were planned as an additional component of growth rhythm. Injury from uncontrolled freezing forced a change of objective to evaluation of genetic differences in recovery from freezing. Those evaluations did not reveal genetic differences in recovery. / Forestry, Faculty of / Graduate
184

Studies related to: bark extractives of western white pine; and synthesis of indole alkaloids

Eigendorf, Günter Klaus January 1974 (has links)
Part I of this thesis describes the structural elucidation of eleven triterpenes isolated from the benzene extract of Western white pine (Pinus monticbla Dougl.) bark. Chemical and detailed spectroscopic investigations revealed the presence of a common tetracyclic A9(ll)-lanostene skeleton in all of the investigated materials. Structural variations were found at the C3 position and in the side chain at C17. The following assignments have been made: compound I, 33~methoxy-5a-lanost-9(ll)-en-24S,25-diol (43); compound II, the corresponding 33-hydroxy derivative (51); compound III, 33-methoxy-5a-lanost-9(11)-en-24-one (59); compound IV, 33-methoxy-5a-lanost-9(11),25-dien-24S-ol (65); compound V, 3a-hydroxy-5a-lanost-9(ll),25-dien-24-ol (66); compound VI, 33-methoxy-5a-lanost-9(ll)-en-22,25-diol (70); compound VII, 33-methoxy-26,27-bis nor-5a-lanost-9(ll)-en-24-one (71). Compound VIII was shown to be the ethylidene derivative of 33-methoxy-5a-lanost-9(ll)-en-24S,25-diol (76) and compounds IX and X were assigned to structures (78) and (80), respectively. A novel dimeric steroidal structure (83) has been proposed for compound XI. Part II describes synthetic investigations which lead to the development of a sequence providing a synthon [(193) and (194)] for the synthesis of vobasine (78)- and sarpagine (77)-type alkaloids. 2-Amino-3-indolyl(3a)-propanol (121), obtained by lithium aluminum hydride reduction of L-tryptophan (106), was converted to its ditosylate (150). Treatment of the latter with cyanide ion provided 3-(N~tosylamino)-4-indolyl(3a)-butanonitrile (151) which was transformed to 3-(N-tosylamino)-4-indolyl(3a)-butanoic acid (152) by means of 30% sodium hydroxide solution. 3-Amino-4-indolyl(3a)-butanoi.c acid methyl ester (155) was obtained through reductive cleavage of (152), followed by Fischer esterification. Compound (155) could then be converted to 3-CN-.formylami.no)-4- (N-benzyl-indolyl)(3a)-butanoic acid methyl ester (163) by treatment with a mixture of formic acid and acetic anhydride followed by sodium hydride and benzyl bromide. Reaction with trifluoroacetic acid converted compound (163) to the tricyclic 3-carbomethoxymethyl-N -benzyl-3,4-dihydrocarboline (173) which upon condensation with 3-methylene-pentan-2-one (126) afforded the tetracyclic 2-oxo-3-ethyl-6-carbomethoxymethyl-l,2,3,4,6,7,12,12b-octahydro-(N-benzylindolo)(2,3-a)-quinolizine (175). The ethylene ketal (177) of the latter material was treated with diisopropyllithium amide and methyl chloroformate to provide 2-oxo-3-ethyl-6-dicarbomethoxymethyl-l,2,3,4,6,7, 12,12b-octahydro-(N-benzylindolo)(2,3-a)-quinolizine ethylene ketal (178), which possesses a highly activated acidic proton (C6a) in the side chain. A suitable leaving group at the C2 position, necessary for subsequent transannular cyclisation, was available through conversion of the tetracyclic ketone (175) to the corresponding C2cx-alcohol (181) and further transformation of the latter into various derivatives such as the acetate (182), the mesylate (183) and the p-nitrobenzoate (185). In order to allow generation of an exocyclic olefin at C3, the C2-olefin, 3-ethyl-6-carbomethoxymethyl-l,4,6,7,12,12b-hexahydro-(N-benzylindolo)(2,3-a)quinolizine (184), obtained via dehydration of the alcohol (181), was converted to 2,3-a-dihydroxy-3-ethyl-6-carbomethoxymethyl-l,2,3,4,6,7,12,12b-octahydro-(N-benzylindolo) (2,3-a)-quinolizine (186) by osmium tetroxide oxidation. Treatment of (186) with acetic anhydride or p-nitrobenzoyl chloride provided the diacetate (187) or the C2 mono p-nitrobenzoate (188), respectively. The 10-membered ring system, present in the vobasine skeleton, became availahle through reductive cleavage of the C/D ring junction in the tetracyclic alcohol (181), thus, affording 2a-hydroxy-3a-ethyl-N^-methyl-6-carhomethoxymethyl-l,2,3,4,6,7,12,12b,12b-nonahydro-(N-benzyl-indolo)(2,3-a)-12b,N^-seco-quinolizine (190). Acetic anhydride treatment of the ethylene ketal (177) provided two isomeric components, 2-oxo-3-ethyl-Nb-acetyl-6-carbomethoxymethyl-1,2,3,4,6,7,12,12b-octahydro-12b-acetoxy-(N-benzylindolo)(2,3-a)-12b,Nb-seco-quinolizine ethylene ketal (191a and b), also possessing the 10-membered ring skeleton. Furthermore, the latter materials enable an entry into the family of 2-acylindole alkaloids as well as members of the dimeric alkaloids such as voacamine (75). / Science, Faculty of / Chemistry, Department of / Graduate
185

The biology and impact of the lodgepole terminal weevil in the Cariboo Forest Region

Maher, T. F. January 1981 (has links)
The objectives of this study were to define the life history of the lodgepole terminal weevil (Pissodes terminalis Hopping) in the Cariboo Forest Region, to quantify the magnitude of damage resulting from weevil attacks, and to determine if P. terminalis activity was associated with measurable tree and stand parameters such as leader dimensions and density. Four study plots in juvenile lodgepole pine (Pinus contorta Dougl. var. latifolia Engelm.) stands near Riske Creek, B. C. were selected to provide data on the biology of the lodgepole terminal weevil. In each plot, weekly collections of 10 weevil-attacked terminal shoots were made from June 3 to August 29, 1980, and monthly collections were taken during September through November. All leaders were dissected and the numbers of each P. terminalis life stage and associated predators/parasitiods were recorded. Seventy-one survey plots in lodgepole pine stands between 8 and 29 years of age throughout the Cariboo Forest Region were assessed for weevil activity. Each survey plot contained 25 trees over 2 metres in height, and each tree was measured for height, diameter at breast height, leader length, and basal leader diameter. Stand age, elevation, density, and all weevil attacks (including year of attack and type of resultant stem deformity) were also recorded. Weevil development appeared to be fairly uniform regardless of stand density and/or elevation; therefore, the data from all four biology study plots were combined to construct a life history diagram. In 46% of the survey plots one or both of the leader dimensions was significantly greater for attacked trees as compared to unattacked trees. In 28% of the plots attacked trees were either significantly taller or larger in diameter. Over 50% of the trees in stands of less than 4,000 stems per hectare had been attacked by P. terminalis at least once. Severe stem deformities such as forks and "stag-heads" comprised a larger proportion of damaged trees in the lower stand density classes. Weevil activity appeared to be higher in 1980 than in 1979. It was concluded that the lodgepole terminal weevil is currently a widely distributed and serious pest of young lodgepole pine stands in the Cariboo Forest Region. Given the present levels of weevil-caused damage as well as the possibility of future attacks, it was recommended that the activity of P. terminalis be considered when silvicultural practices such as juvenile spacing are undertaken in these stands. / Forestry, Faculty of / Graduate
186

Ecology and appraisal of pine vole damage in Ohio apple orchards

Collins, Roger Lee January 1975 (has links)
No description available.
187

Physiological and biochemical response of sensitive and tolerant Pinus strobus L. clones to fumigation with low concentrations of sulfur dioxide /

Eckert, Robert Theodore January 1978 (has links)
No description available.
188

Stem sapwood water transport and storage strategies in three conifers from contrasting climates /

Barnard, David M. January 1900 (has links)
Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 93-100). Also available on the World Wide Web.
189

Greenhouse growth of Pinus x rigitaeda seedlings in response to water stress and correlations with 7 year plantation performance

Hodge, Gary R. January 1983 (has links)
M.S.
190

Nitrogen fertilization of Pinus sylvestris seedlings

Aldridge, E. Gray. January 1986 (has links)
Call number: LD2668 .T4 1986 A42 / Master of Science

Page generated in 0.0983 seconds