| Summary: | The net photosynthetic and dark respiration response to moisture, light level and temperature is discussed with reference to the unique Cladonia rangiferina (L.) Wigg.-Shrub association in Cladonia stellaris (Opiz.) Pouz. Spruce Woodland at Hawley Lake, Ontario. Field measurements provide a description of the summer and winter environmental complex. Winter data shows an exceptional thermal insulation afforded by snow cover, protecting lichen thalli from extreme air temperatures. Summer environmental data highlights the need to dissociate periods of thallus hydration (metabolic activity), and thallus dehydration in order that meaningful comparisons may be made with experimentally derived levels of metabolic activity. Experimentally derived physiology of the hydrated thallus showed a broad amplitude of tolerance to light level and temperature correlating with the wide range of temperature and light level experienced during a single thallus drying cycle in the field. Heat stress experiments illustrate this is indeed, a sensitive species restricted to the more ameliorated temperature regime of mature Spruce-Lichen Woodland. Heat sensitivity may also act to restrict C. rangiferina to the cooler micro-site afforded by the elevated shrub-hummocks. A spring to summer series of collections of a Muskoka population of C. rangiferina were coursed through heat stress experiments. Significant heat tolerance acclimation emerged as an essential response to withstand the high summer temperature regime. Thesis Master of Science (MSc)
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