Arceuthobium americanum is a flowering plant which parasitizes Pinus contorta (Lodgepole pine). This study examined branch performance of P. contorta infected to varying degrees with A. americanum.

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A study has been conducted with the objectives of (1) identifying weevils and their parasitoids emerging from infested lodgepole pine leaders, (2) determining emergence patterns of hosts and their parasitoids, and (3) obtaining further information on the biologies of the terminal weevils and their natural enemies in British Columbia. The major experiments and biological observations were carried out in young spaced lodgepole pine, (Pinus contorta Dougl. var. latifolia Engelm.), stands at Ellis creek, near Penticton, B.C. A total of 1046 infested leaders were collected. One-third of the terminals were dissected and the numbers of weevils and parasitoids at developmental stages were recorded. The remainder of the leaders were set up for individual rearing. Observations were also made on the feeding and ovipositional behavior of the weevils. Feeding habits of the parasitoids were also studied. Dissections showed that a few adult weevils emerge in the fall of the year of attack. The majority of adults overwinter as larvae but pupation also may occur prior to winter. In addition, dissections indicated that parasitism plays an important role in larval mortality of weevils. Weevils which emerged in the laboratory were identified as being of the following species: Pissodes terminalis Hopping, Magdalis gentilis LeC. and Cylindrocopturus sp. (COLEOPTERA: Curculionidae). M. gentilis is the first weevil species to emerge, in late May. This emergence is followed by that of P. terminalis from early June through mid-July, while Cylindrocopturus sp. emerges from early June through mid-July. P. terminalis attacks the current year's leaders, whereas adult M. gentilis and Cylindrocopturus sp. feed on foliage. All three weevil species utilize lodgepole pine terminal shoots for breeding. Larval feeding under the bark almost always results in the death of the terminal. The terminal weevils have a complex of natural enemies in British Columbia. Parasitoids belong to six families of the order Hymenoptera. The pteromalid Rhopalichus pulchripennis Crawford is the most widely distributed parasitoid species in the province. Two species of Eurytoma (Eurytomidae) ranked second in abundance. Emergence patterns of adult parasitoids are closely synchronized with that of their hosts. Parasitoids were observed feeding on pollen of flowering weeds in the field. This observation suggests that natural parasitoid populations could be enhanced by cultivating lupin, Lupinus sp., in lodgepole pine stands. It was concluded that every effort should be made to minimize weevil numbers in order to prevent formation of crooks, forks and stag-heads. Early emergence of M. gentilis suggests that leader clipping projects should be carried out by early spring. Further research is recommended to ensure correct association between parasitoids and host weevil species and to develop or establish methods for preservation of parasitoids for clipped leaders for release in the forest. / Forestry, Faculty of / Graduate

The pine engraver beetles (~ spp.:Coleoptera:Scolytidae) may be serious pests depending on certain prerequisite conditions. In their secondary or "normal" role they breed in slash and damaged, dying, and dead trees. The broods emerging from these sources normally attack similar material. When such material is scarce due to cessation of cutting operations in mid-season or when conditions are especially favorable for brood development, an excess of beetles is often produced which, due to the lack of more suitable material, attack healthy trees. Repeated attacks cause these trees to succumb and die. When normally healthy trees are weakened by fire, flood, defoliation, drought, stagnation, etc., then they become more acceptable host material for successful engraver attacks. When the production of a very large number of beetles in "normal" breeding material coincides with physiological stress in "healthy" trees, then population explosions can occur. When large numbers of beetles and low host vigor do not coincide, spot kills cornnon1y occur. According to Thatcher (32), spot kills, although not conspicuous, add up to large volumes of timber loss each year. / Ph. D.

To prevent the buildup of epidemic level mountain pine beetle populations, conditions of the stand environment they inhabit must be altered. Silvicultural treatment is the most effective means for doing this. Preventative treatments work best when applied while mountain pine beetle populations are still at the endemic population level. Therefore, information necessary for making decisions concerning mountain pine beetle populations in lodgepole pine stands needs to be included in the initial silvicultural prescription planning process, at a time before beetle populations reach outbreak numbers. In this dissertation, several quantitative descriptions of the mountain pine beetle/lodgepole pine relationship were investigated. Models were developed to 1) describe the temperature-dependent development of six mountain pine beetle life stages and 2) describe the amount of loss a stand could sustain if an epidemic level population were to occur in the stand. Concepts of mountain pine beetle risk rating were also discussed. These models and additional information pertaining to the mountain pine beetle/lodgepole pine relationship were incorporated into a knowledge-based system, the MPB Advisory System. This system was designed to help U.S. Forest Service silviculturists include decisions concerning mountain pine beetle populations in the stand management process. / Ph. D.

Annosus root rot caused by the fungus Heterobasidion annosum (fr.) Bref., causes a destructive root and butt rot of many important tree species throughout the world. Presently, methods for determining disease incidence and severity and destructive. In this study, the most effective, non-destructive, disease severity prediction parameters were determined for thinned Pinus taeda plantations growing on high hazard sites. Above-ground tree parameters and 0.03m³ soil-root (SR) samples were used as predictions variables. Base-line data for predictions was obtained by excavations of 190 tree root system from plantations located in Eastern Virginia and Central Alabama. Multiple regression analysis indicated that stem diameter (DBH), radical growth (GR5) live crown ration (LCR), and SR samples were the most effective parameters in explaining the variation in the root sustem colonizatio levels of the plot trees studied. / M.S.

Mycorrhizal synthesis studies revealed that allopatric populations of Suillus granulatus differ in host specificity. Tissue cultures of Suillus granulatus used were from Nepal, (associated with Pinus wallichiana), Korea (Pinus densiflora) and the U.S. (Pinus strobus). Mycorrhizal effectiveness was used to measure host specificity. Useful characters for measuring mycorrhizal effectiveness were determined by ANOVAs between the uninoculated controls and mycorrhizal treatments. In addition, those characters which were stable within one population were determined via ANOVA. Useful characters, as defined by these two tests were: shoot wet weight, total wet weight, percentage mycorrhizal short roots, shoot dry weight, total dry weight and Hartig net penetration. These characters were subsequently used to measure variation in mycorrhizal effectiveness among the allopatric populations of Suillus granulatus. Isolates associated with Pinus strobus were most effective with Pinus strobus and least effective with the other trees, whereas isolates from Pinus wallichiana and Pinus densiflora showed variable effectiveness with all three trees. Phenetic analyses used to determine how similarly the isolates responded with the hosts confirmed these results. We conclude that isolates associated with Pinus strobus are most specific for this host, whereas isolates from the other two trees are not host specific. These results are discussed and hypotheses put forward to explain them. / Master of Science

A decline of eastern white pine, Pinus strobus L., has been observed for over 80 years in the eastern United States. The syndrome has not always been discussed as a decline but reported under a variety of names. Symptoms vary with time required for trees to die, but generally include chlorotic foliage, in many cases needle loss producing a tufted appearance, premature annual loss of needles, drooping of needles in some cases, shriveling of bark after a period of time, and eventual death after a period of months to years. An investigation into the causes of decline on landscape sites in Virginia included an indexing technique to compile and analyze, systematically, pertinent data from good and poor quality sites. Over 300 variables were studied from over 100 observations to narrow down the apparent causal factors for future investigation in a controlled environment. Observations were organized into two groups for analysis, one called the “decline habitat” and the other the “natural habitat”. Natural habitat observations consisted of trees from a site in the Jefferson National Forest (VA) and decline habitat observations consisted of trees from mostly western Virginia landscapes. After thorough study for a period of two years, a group of growth indicators were weighed against a group of site quality indicators. Growth quality indicators included: a height vs. age index, a 10-year compilation of tree ring increments and inter-branch whorl measurements converted to percent growth per year, and seasonal foliar color changes using a Munsell rating index. Site quality indicators centered around the soils with soil pH, clay content, amounts of compaction and soil disturbance as the most prominent factors derived from the study. Soil pH averaged 6.95 with a range of 5.9-8.1 for decline habitats; while the pH averaged 5.50 with a range of 5.0-6.0 for the natural habitat. Clay content averaged 37.05% for decline sites vs. 17.76% for the natural site for soils above and in the root zones of white pines. Clay content averaged 43.99% for decline sites vs. 17.95% for the natural site for soils beneath the root zones of white pines. Soils under decline habitat trees were highly compacted with measurements as high as 1806.1 psi to penetrate some decline habitat soils, while the natural habitat soils had little if any compaction, with readings of between 138 and 273 psi. Soil disturbance was not present in the natural site while present in most decline sites. The major cause of disturbance was construction and earth-moving activities around landscape sites. Important abiotic factors which worked in concert with soil factors included poor planting practices, competition with tree feeder roots from turfgrass, chemical pollutants, and mechanical damage by weather and man. Biotic factors were viewed as secondary agents attracted to already weakened trees after initiation of decline by the previously discussed factors. Separate studies of seasonal foliar color changes and the initial finding of the pinewood nematode in Virginia aided in identifying additional indicators of and contributors to decline. / Ph. D.