Arceuthobium americanum is a vascular plant which is parasitic upon Pinus contorta var murrayana. Its documented effects include reductions in host growth, vigor and wood quality. The specific physiological changes that occur in the host are, for the most part, unknown.

Nurse plant and object facilitation is an important factor mitigating abiotic stress, improving seedling recruitment, and shaping the fine-scale spatial patterns of many plant communities. I investigate the role of facilitation on lodgepole pine regeneration following blowdown in central Oregon. My objective is to examine the importance of nurse objects on seedling recruitment under varying stand conditions. I base my analysis on 1) the mapped locations and attributes of seedlings, saplings, trees, shrubs, snags, stumps, and sound and decomposed logs in each of five, 500 m2 circular plots, 2) water holding capacity estimates of woody and leafy litter and pumice soil, and 3) growing-season air temperatures. My analysis identifies seedling patterns at multiple spatial scales (~0-8 m) using nearest neighbor and Ripley’s K statistics and identifies differences in canopy structure, seedling development, and temperature using non-parametric rank-sum tests. My results show blowdown severity varies with pre-disturbance stand structure, resulting in a multi-modal stand structure with a wide range of canopy and seedling microhabitat conditions. Stand-wide, post-blowdown regeneration patterns reveal >80% of seedlings grow near nurse shrubs, logs, and woody litter, suggesting preferential germination and survival in these microhabitats. High seedling densities correspond with median shrub diameters, and up to 38% of seedlings grow near recently downed logs, indicating both shrubs and logs serve as important nurse objects. The role of nurse objects in mitigating moisture stress is implicated by the potentially high evaporative stress under extreme growing season temperatures in areas of severe blowdown and by the high moisture-holding capacity of woody litter relative to the pumice soil. Stand-wide, 91% of all seedlings and 87% of all shrubs grow on woody litter, and seedlings growing on woody litter show the greatest development. The positive spatial correlation of seedlings and shrubs with nurse plants and woody litter supports the assertion that both are important facilitators for seedling regeneration and emerging spatial patterns of stand recovery. These results have important management implications, suggesting that the removal of nurse plants and objects through salvage logging or prescribed burning may have negative long-term impacts on local and regional forest regeneration.

The biweekly diets of tame elk (Cervus canadensis nelsoni) were established on a species dry-weight basis for different habitat segments of the lodgepole pine (Pinus contorta) type, Principal species in the diets (5% or more) on each habitat segment were generally composed of preferred species. However, some highly abundant but non-preferred species took on principal dietary status, whereas some preferred species, scarce in the vegetation, contributed less than 5 percent to diets. Forbs contributed most to total consumption; grasses and sedges were the second largest contributors. Browse appeared to be of limited importance, but mushrooms had special significance in forested habitat segments. Preference changes were evident as forb species matured. Consumption rates were significantly higher in habitat segments having greater species diversity and forage density. The time tame elk spent grazing, ruminating, lying, grooming, traveling, standing, drinking, and playing was referenced to specific habitat segments in which each activity occurred. One thousand and eight hours of individual elk activity were observed over a series of six 24-hour periods. Wet meadows, dry meadows, clearcuts. and revegetated roads were preferred as grazing sites, while mature and stagnated forests were clearly non-preferred. Wet meadows, revegetated roads, and mature forest were preferred for resting and non-grazing activities. The distribution of pellet groups deposited by tame elk was determined with reference to habitat segment and form of activity at the time of deposition. Pellet group distributions thus obtained, were strongly unrepresentative of relative time spent in various habitat segments.

Ninety-four unmanaged lodgepole pine stands were examined to evaluate the relationship between stand density and susceptibility to mountain pine beetle attack. Sample included stands from a broad geographical range in the western United States. Beetle population trends were not significantly related to variation in stand density as measured by stand density index (SDI). The percentage of trees killed per acre by the mountain pine beetle in stands with greater than eighty percent lodgepole pine did vary significantly with changes in SDI. From these data three SDI zones were identified: 1) stands with SDI's of less than 125 showed low potential for attack, 2) stands between 125 and 250 SDI showed much greater levels of tree mortality, gradually decreasing toward the 250 SDI, 3) tree mortality decreased in stands as density increased beyond the 250 SDI value.

Natural disturbance events influence the patterns and processes in many forest ecosystems. Ecosystem management of coniferous forests in western North America requires the recognition of the importance that natural disturbance regimes have in achieving sustainable resource production and maintaining biological diversity . Mountain pine beetle epidemics have played an historic role in the succession and structure of lodgepole pine forests in this region. Their effects on wildlife habitat and communities are undocumented, but are presumed to be substantial. I sought to quantify these effects in forty 1-ha stands of monotypic, even-aged, mature lodgepole pine forest in northern Utah approximately 3-8 years following an extensive epidemic. I selected 5 stands that were unaffected by the epidemic and 35 that had tree mortalities ranging from 14 to 95 %. Mean understory biomass in 50 1-m2 plots demonstrated an exponential increase from 4g m-2 in unaffected stands, 40 g m-2 in stands with moderate (51-75% dead) tree mortalities, and up to 110 g m-2 in severely (76-100 % dead) affected stands. Plant species diversity and heterogeneity were highest in stands with moderate tree mortality. Horizontal visual obscurity (from 0- 2.5 m high) was highest in stands with> 40% tree mortality. Canopy cover and volume decreased linearly and curvilinearly, respectively, with increasing tree mortality. Foliage height diversity was higher in stands with moderate tree mortality than in stands with high, low, or no mortality. Abundance and diversity of avian species were highest in stands with moderate tree mortality. Small and medium-sized mammal species were more abundant and diverse in stands with moderate and severe tree mortality than in stands with no or low (26-50 % dead) tree mortality, but the pattern is less clear than for avian species. Fecal pellet groups of large ungulates increased linearly with increasing tree mortality, but the pattern of occurrence of snowshoe hare fecal pellets to increasing tree mortality was less clear. Insect abundance and species diversity increased linearly with tree mortality. Canonical correspondence analysis of insect, avian, and mammalian communities revealed that understory vegetation biomass, diversity, and heterogeneity, as well as foliage height diversity, were the habitat factors that consistently explained the distribution of these species in stands affected by beetle-caused tree mortality.

The main goal of this thesis was to improve our understanding of the long-term effects of establishment treatments and climate change on lodgepole pine and white spruce growth in the western boreal forests. My dissertation also investigated the combined effects of climate and competition on white spruce and trembling aspen growth in boreal mixtures. In the first part of the thesis I evaluated the effects of site preparation treatments on growth of lodgepole pine and white spruce in north-eastern British Columbia. Results indicate that mechanical site preparation can provide yield gains of up-to 10 percent for pine and spruce at 60 and 80 years, respectively. These stands are showing a Type 1 growth response which implies that the treatment effect will eventually cease 90-100 years after planting. In the second part of the thesis I explored pine and spruce growth in relation to past climate and site preparation. Results indicate that up-to 45% and 37% of the respective variation in spruce and pine growth can be explained by selected climatic variables. Future projections indicated that height growth of young pine plantations in the sub-boreal zone could benefit (in the short term) from longer growing seasons by up-to 12% on untreated stands. Untreated young spruce plantations in the boreal zone may suffer height growth decreases of up-to 10% due to increased drought-stress. Vegetation control and mechanical site preparation treatments appear to mitigate effects of climate change to some extent. In the third part of the thesis I explored the combined effects of climate and trembling aspen competition on spruce and aspen growth using data from a long-term study in the boreal zone. Results indicate that climate variables and initial size of the tree can account for significant portions of the annual growth of spruce. Including an estimate of aspen competition in the equations improved the predictive ability of these models. Evidence of the inter-annual variability in aspen competitiveness on spruce and aspen growth indicates that the stress-gradient hypothesis can be applied in boreal mixedwood forests. / Forest Biology and Management

Thesis (M.S.)--Oregon State University, 1978. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Thesis (M.S.)--Oregon State University, 2003. / Typescript (photocopy). Includes bibliographical references. Also available on the World Wide Web.

Knowledge of the potential productivity of a tree species becomes especially important when timber production is the primary management objective. However, direct determination of potential productivity is often not possible. For example, in situations where the site is unstocked, stocked with trees unsuitable for productivity measurement, or stocked with species other than the one of interest. In these cases, an indirect estimate using known characteristics of the site itself is required. Such estimates were made using regression to model site index with indirect measures of site quality for lodgepole pine (Pinus contorta) and interior spruce (Picea engelmannii × P. glauca) in the Sub-Boreal Spruce (SBS) zone of central BC. We tested the utility of these productivity relationship models for predicting the site index of lodgepole pine and interior spruce (Kayahara et al. accepted for publication).

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