Ecology of the microbiotic crust of the antelope-brush (Purshia tridentata) shrub steppe of the South Okanagan, British Columbia

This thesis examines two aspects of the microbiotic crust in the antelope-brush (Purshia tridentata (Pursh) D.C.) shrub steppe of the South Okanagan, British Columbia: (1) relationships between the extent, distribution, and composition of the microbiotic crust, soil texture, and primary grazer (wildlife versus livestock), and; (2) effect of the microbiotic crust on soil moisture content and loss. The floral characteristics of the microbiotic crust of five antelope-brush sites are summarised in Chapter I. Differences in species richness and extent, lifeform composition, and quality of the microbiotic crust are described. Preliminary studies identified differences in the floral characteristics of the antelope-brush sites and discussed these differences in relation to soil texture and type of primary grazer. No conclusive relationships between microbiotic crust species numbers, lifeform composition, crust extent, or moss thickness were identified. It was concluded that microbiotic crust colonisation was influenced by soil surface stability and stability may be affected by physical disturbance, such as livestock grazing, or by the mechanical composition and degree of aggregation of the soil. Two of the sites examined were the focus of the soil moisture study presented in Chapter II. The study addressed three questions: 1. Does the microbiotic crust influence soil water content and loss on the antelope-brush sites? 2. Does the soil moisture effect differ with microbiotic crust species? 3. Is the role of the microbiotic crust on soil water more important than influences from other ecosystem components? Soil moisture content was uniformly sampled after two rain events and two factors (shrub and microbiotic crust) were tested in a 2 x 2 factorial design. Shrub cover was included in the experimental design to account for the possible effects of shading and hydraulic lift. Data were analysed with the general linear model and both analysis of variance (ANOVA) and repeated measures multivariate analysis of variance (repeated measures MANOVA) were used. The study determined plots with microbiotic crust at the sample point (crusted plots) reduced infiltration initially, but soils beneath a crust retained the moisture for longer periods than areas sampled in bare soil (non-crusted plots). Shrub cover had little relevance to surface soil moisture conditions other than its effect on microbiotic crust characteristics. Soils beneath lichen crusts received more precipitation and soils beneath moss had better retention of soil water. The water retention ability of soils beneath moss increased with moss thickness. The effect of surrounding plot conditions varied, but generally the conditions at the sample point were paramount. If the sample point was covered by a microbiotic crust (crusted plots), the positive effect on soil moisture was enhanced by surrounding crust characteristics. However, if the sample point was bare (non-crusted plots) the ability of the surrounding microbiotic crust to moderate soil moisture varied. Vascular plant and litter cover moderated moisture conditions in bare soil, but were not as effective as the microbiotic crust.Forestry, Faculty ofGraduat