<p> The thaw rates of the active layer above the permafrost zone from a series of sites along the Hudson Bay coastline at lat. 56° have been examined with respect to temperature and moisture gradients, the characteristics of the surface layer and the bulk thermal properties for each profile. The thermal properties have been examined using firstly a Fourier approach with the parameter of degree days and using secondly a graphical approach employing thermal relationships obtained in the laboratory analyses by Kersten (1949).</p> <p> It was found that thaw rates are controlled by the interaction of a number of environmental factors of which vegetation appears to be the most important.</p> <p> The two approaches to the derivation of thermal properties give quite different results, such that the graphical approach is deemed to be unsuitable to field application.</p> / Thesis / Bachelor of Science (BSc)

<p> 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.</p> <p> 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.</p> / Thesis / Master of Science (MSc)

<p> This thesis examines the field performance of the water balance and equilibrium evapotranspiration models, and defines the environmental conditions for which they provided accurate estimates of water loss from a corn crop in Southern Ontario.</p> <p> It is shown that the water balance model should be used only when surface runoff is measured and drainage is negligible. An error analysis indicated that soil moisture change could be estimated within 10 percent when measurements were conducted at six sites every eight days.</p> <p> The equilibrium model predicted daily evapotranspiration within 6 percent when the latent heat exchange utilized between 65 and 80 percent of the available energy, indicating that the model can be applied within temperature limits of 17° and 32°C.</p> / Thesis / Doctor of Philosophy (PhD)

Due largely to fire exclusion and land use changes, upland oak ecosystems in the central and eastern U.S. are shifting dominance from fire-tolerant oaks (Quercus spp.) to shade-tolerant, fire-sensitive species (mesophytes). This shift has been hypothesized to occur via a positive feedback loop termed mesophication, where mesophytes create shaded understory that limits oak growth and wetter fuels and soils, decreasing forest flammability. To determine how canopy water partitioning varies between oaks and mesophytes, I measured stemflow, throughfall, and surface soil moisture monthly over a 14-month period for overstory and midstory trees of oaks (Q. alba, Q. falcata) and hypothesized mesophytes (Carya tomentosa, Acer rubrum, Ulmus alata) in northern Mississippi. Overstory oaks partitioned 5.1% of rainwater into stemflow, while mesophytic species partitioned 7.2%, leading to 3.5% wetter soils under mesophytes. The hydrology of mesophyte canopies may reduce forest flammability and promote conditions favorable for mesophyte regeneration, ultimately compromising long-term oak regeneration.

In historically fire-dependent upland oak forests of the eastern U.S., anthropogenic fire exclusion is likely causing a hypothesized feedback loop between an increase in fire-sensitive species and self-promoting, fireree conditions at the detriment of oak regeneration. This study determined how shifts from oaks (Quercus stellata and Q. falcata) to fire-sensitive non-oaks (Carya spp., Liquidambar styraciflua, and Ulmus alata) affected flammability and related processes that consequently determine species composition. Using treatments of increasing non-oak leaf litter, experimental burns were conducted and flammability measured under field conditions, and a laboratory litter moisture desorption experiment was conducted. As litter composition shifted from oak-dominated to non-oak-dominated, flammability decreased (R2 = 0.59, P < 0.001) and moisture-holding capacity increased (R2=0.88, P<0.001). To prevent further shifts toward fireree conditions and loss of economically and ecologically valuable oaks, prescribed fire should be reintroduced soon while oak maintains overstory dominance and controls forest flammability.

Moisture susceptibility of hot mix asphalt (HMA) pavements continues to be a major pavement distress. Past research has primarily focused on HMA stripping prevention through material component evaluation/testing and addition of preventative additives. Stripping is caused by traffic, water, and high in-place service temperatures. Today, agencies use various methods to evaluate HMA moisture susceptibility with varying degrees of success. The study objective was to evaluate a prototype stripping simulator?s ability to predict HMA moisture susceptibility. The simulator evaluates moisture susceptibility by measuring conditioning water turbidity. Boil test and indirect tensile strength testing were also conducted for comparison purposes. Stripping simulator results indicate further refinement is required before it can be used for moisture susceptibility prediction.

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