Frost damage to sapling size plantation Douglas-fir [Pseudotsuga menziesii (Mirb.) Franco.] in the central interior of B.C. was identified as the major cause of dieback and canker through tree dissections. Prominent frost rings in the wood and frost damage to buds and shoots corresponded to the dates of dieback initiation and canker events throughout the history of the plantations. Frost rings and frost cankers were reproducible using an artificial freezing technique. Symptomatic frost-damaged buds and elongating shoots were described for Douglas-fir, white spruce [Picea glauca (Moench) Voss] and subalpine fir [Abies lasiocarpa (Hook.) Nutt.]. The effect of growing season frost was most noticeable on early flushing trees. Frost and dieback damage was most severe on concave and flat landforms, which are conducive to cold air pooling on nights with strong radiative cooling. Several pathogens isolated from recently killed stems were identified from fruiting bodies and culture. Leucocytospora kunzei (Sacc.) Urban was the pathogen most commonly isolated from the edge of expanding cankers and progressive dieback margins. Sclerophoma semenospora Funk was commonly found fruiting on dead stems and leaders killed by frost or by mechanical means. Cinara pseudotaxifoliae Wilson feeding caused latent cankers on one year old leaders of Douglas-fir, which are thought to be activated by frost. Boron levels of both healthy and severely affected trees were in the intermediate range, and were not considered to play an important role in frost or pathogen susceptibility for Douglas-fir in the interior. / Forestry, Faculty of / Graduate

An interlocking group of studies was carried out to address the concept of the free-to-grow seedling. This term is an attempt to define plantation establishment in a manner cognizant of early hazards from brush competition and other stresses. The studies were carried out on one- to five-year old Douglas-fir plantations on moist, rich sites in coastal British Columbia. Data were generated from field measurements and harvest sampling of the planted trees and their associated competing vegetation. On these productive sites, tree growth appears sensitive to interference from neighbouring brush species. An index implying competitive shading was derived and proved a useful measure of stress on the planted trees, particularly when measured as a relative production rate. Growth losses varied with the light environment at specific crown positions. Therefore, height growth was not affected by competition until the terminal leader was shaded. This allows height growth to remain independent of competition level until the tree is overtopped on these sites. The trees studied showed great ability to acclimate and survive relatively heavy shading by competing vegetation. After competition release treatment, trees were generally able to re-acclimate the current seasons growth to the increased light intensity. Growth following competition release was significantly improved by a chemical brush control treatment, while mechanical brushing resulted in little net change in competition levels after one year. The growth on these trees in the year following release from competition was also best measured as a relative production rate. The vegetation on untreated areas followed a strong successional trend during the period studied. The trend was a function of differences in height growth patterns between species modified by leaf area index. In general, woody species tend to succeed geophytes and microphanerophytes on these sites. A proposed free-to-grow definition in biological terms states that a tree must be free from competitive shading on the terminal leader and increasing in height relative to the competing vegetation. The free-to-grow status can be assessed by on a threshold value of the competition index and a predictive model for the comparative height increment of the tree and its competitors. / Forestry, Faculty of / Graduate

The transition from old-growth to second-growth British Columbia coastal Douglas-fir has resulted in reduction of log size and increased proportion of juvenile (core or crown-formed) wood. Determination of the zone of transition from juvenile to mature wood is critical to the definition of wood quality and timber value. Thirteen unpruned, two pruned second-growth, and two unpruned plantation-grown coastal Douglas-fir trees were sampled to analyze the hypothesis that the transition in relative density from juvenile to mature wood occurs at the base of the live crown. X-ray densftometric techniques were utilized to determine yearly pith to bark relative density data of five cross-sectional discs from each tree. Segmented linear regression techniques were utilized to estimate the juvenile - mature wood transition age from the data. The average number of growth increments from the pith at which juvenile - mature wood transition occurred on sections sampled at breast height, 20 percent and 40 percent of total height was 22.18. When the hypothesis was tested on unpruned trees, before and after harvest, the juvenile - mature wood transition occurred below the base of the live crown. When the hypothesis was tested on pruned trees, the transition occurred at the base of the live crown, which represented the upper limit of pruning height. This information may provide a greater insight into juvenile - mature wood transition. It will likely assist in the determination of wood quality and economic value of forest products manufactured from second-growth coastal Douglas-fir. / Forestry, Faculty of / Graduate

Concern about potential losses of biological diversity and productivity following clear-cut logging of old-growth forests in British Columbia led me to compare ectomycorrhizas in old-growth and mature stands of Douglas-fir. Two sites were selected, each with an old-growth (288-, 441-yr-old) and a mature stand (87-, 89-yr-old) well-matched in tree species, soil and topography. A total of 120 soil cores ≤15 cm deep by 5 cm diameter were taken at random from four 60 m square plots (one per stand). Samples were taken in spring and fall at each site. All morphological types of ectomycorrhizas in one half of each core were counted and characterized in detail. Ectomycorrhizal abundance and frequency was compared in logs, stumps, the forest floor over bedrock or gravel, the forest floor near the base of trees, the forest floor elsewhere, and mineral soil. Old-growth and mature stands were very similar in richness, diversity and types of ectomycorrhizas. Sixty-nine types of ectomycorrhizas were described. Nineteen types each accounted for more than one percent of the 17,500 ectomycorrhizal root tips examined, and eighteen types were found in five or more of the 120 soil cores. Extrapolation indicates a total richness of roughly 100 types in the four plots. Co-dominant fungi were Cenococcum geophilum Fr. (24% of all ectomycorrhizal root tips), a Rhizopogon Fr. of the section villosuli (10%), Hysterangium vitt. (9%), Lactarius deliciosus (Fr.) S.F.G. (6%), and Piloderma fallax (Libert) Stalpers (4%). Cenococcum geophilum, Rhizopogon Fr. and L. deliciosus were abundant in both mineral soil and organic substrates, Piloderma fallax was associated with decayed wood, and Hysterangium and type 27 were in organic substrates only. A bright greenish-yellow felty type was found in 5 cores in mineral soil only. The similarity of the ectomycorrhizal communities of old-growth and mature stands was probably due to their proximity ($<$200 m apart) and the similarity of their vegetation and soil. Differences may occur at some sites if ectomycorrhizal succession has been delayed or redirected as a result of frequent or severe disturbance, lack of old-growth legacies (logs and stumps), or lack of old-growth stands from which fungi can disperse. / Graduate

Potential uses of dry weight information for simulation, and sources of data, for simulation of forest fuels were discussed. Tree and crown component dry weights of 23 Douglas fir, 18 western hemlock, and 23 western red cedar trees expanded to 314 "model" trees were investigated. Data were collected on the University Research Forest near Haney, British Columbia. Multiple regression techniques were used for the analysis. The best four independent variables are listed and the possibility of retaining a single independent variable, with its implications, are discussed. All predicting equations were conditioned to zero intercept and statistically tested for significance by the F-test. Of the independent variables tested, the combined variable of breast height diameter squared times total tree height was most closely related to tree component dry weights. The product of diameter and crown width squared was found to be the best single variable to describe crown component dry weights for Douglas fir. The dry weights of western hemlock and western red cedar crown components were most closely associated with breast height diameter times crown length. Reliable estimates of tree component dry weights were obtained. Crown components were highly variable and widely dispersed about the mean which resulted in less accurate estimates. / Forestry, Faculty of / Graduate