Thesis (M.S. - Renewable Natural Resources)--University of Arizona, 1988. / Includes bibliographical references (leaves 23-24).

Thesis (Ph. D.)--University of Washington, 2000. / Vita. Includes bibliographical references (leaves 154-161).

Thesis (M.S.)--Oregon State University, 2006. / Printout. Includes bibliographical references. Also available on the World Wide Web.

The accurate simulation of snowpack deposition and ablation beneath forested areas is confounded by the fact that the vegetation canopy strongly affects the snow surface energy balance. The canopy alters the radiation balance of the snowcover, and reduces the wind speed at the snow surface. Data collected as part of the BOREAS experiment are used to analyze the effects of a variety of forest canopies on the climate at the snow surface. Simple algorithms are developed and used to adjust climate data collected above forest canopies to the snow surface. A 2-layer coupled energy- and mass-balance snowmelt model is used to simulate the deposition and ablation of the snowpack at five forested sites within the Canadian boreal forest for the 1994-1995 snow season. Results of the snowcover simulations indicate that the net snowcover energy balance remains close to zero for the winter months, but exhibits a sharp increase in the spring months. The rapid energy gain in the spring is strongly controlled by canopy cover, and is dominated by net radiation fluxes, with minor contributions from sensible, latent, soil, and advected energy fluxes. Net snowcover irradiance dominates during the spring months due to increased solar intensity and longer day lengths, coupled with increased radiation transmission through canopies at high sun angles, and reduced snowcover albedo resulting from the deposition of fine organic debris. Turbulent (sensible and latent) energy fluxes comprise a relatively minor portion of the net snowcover energy exchange, indicating that the sub-canopy snowcover is relatively insensitive to the meteorological parameters controlling these fluxes. The low thermal conductivity of organic-rich boreal soils must be considered for studies focusing on snowcover development when soil heat flux comprises a large portion of the snowcover energy balance. Model outputs at all sites generally show good agreement with measured snow depths, indicating that the techniques used in these investigations accurately simulate both the deposition and ablation of seasonal snowcovers. Results indicate that snowcovers in the boreal environment may be more sensitive to land-use transitions, rather than climate shifts, due to the strong control exerted by vegetation canopies on radiation transfer processes. The results also suggest that simple canopy adjustment algorithms may be effectively applied to spatially distributed snowcover simulations. More data is required to evaluate the accuracy of these methods for computing energy transfer within canopies having significantly different structures than the sites used in this study. / Graduation date: 1999

This study is an interdisciplinary ecological study addressing the fine-scale relationships between plants, invertebrates and the environment in an alpine ecosystem. Alpine environments are marked by steep environmental gradients and complex habitat mosaics at various spatial scales. Regular forming periglacial patterned ground landforms on the Old Man Range, Central Otago, South Island, New Zealand present an ideal medium for studying plant-invertebrate-environment relationships due to their partitioning of the landscape into discrete units of contrasting environmental conditions, and the existence of some baseline knowledge of the soil, microclimate, vegetation and flora. The study was conducted in three types of patterned ground (hummocks, stripes and solifluction terraces) on the Old Man Range. Each component of the study was sampled at the same spatial scale for comparison. Temperature was recorded in the soil and ground surface from April 2001 to March 2004 in microtopographic subunits (microsites) of each patterned ground landform. Plant species cover was sampled within each microsite; invertebrates were sampled from soil cores taken from the same locations as plant samples in April 2001 and September 2001. The two sampling occasions coincided with autumn before the soil freezes, and winter when maximum freezing was expected. Fine-scale changes in the topographic relief of the patterned ground led to notable differences in the timing and duration of snow. The steepest environmental gradients existed during periods of uneven snow distribution. The soil in exposed or south-facing microsites froze first, beginning in May, and typically froze to more than 40cm depth. Least exposed microsites rarely froze. Within the microtopography, patterns of freezing at specific locations were consistent between years with only minor differences in the timing or depths of freezing; however, notable variation in freezing existed between similar microsites. Within the microtopography, different assemblages of organisms were associated with different microsites. In total, 84 plant and lichen species were recorded, grouping into six community types. Species composition was best explained by growing degree-days, freeze-thaw cycles, time frozen and snow-free days; species diversity and richness increased with increasing environmental stress as indicated by freeze-thaw cycles, time frozen and exposure. In total 20,494 invertebrates, representing four Phyla, 12 Classes, 23 Orders and 295 morpho-taxa were collected from 0.17m� of soil. Acari, Collembola and Pseudococcidae were the most abundant invertebrates. Over 95% of the invertebrates were found in the plant material and first 10cm depth of soil. Few significant relationships were found between diversity, richness or abundance of invertebrate taxa and the microsites; however, multivariate analyses identified distinct invertebrate assemblages based on abundance. Invertebrate composition was best explained by recent low temperature and moisture, particularly in winter; however, plant composition also explained invertebrate composition, but more so in autumn. This research has shown that organisms in the alpine environment of the Old Man Range are sensitive to fine-scale changes in their environment. These results have implications as to how historical changes to the ecosystem may have had long-lasting influences on the biota, as well as how a currently changing climate may have further impacts on the composition and distribution of organisms.

This study is an interdisciplinary ecological study addressing the fine-scale relationships between plants, invertebrates and the environment in an alpine ecosystem. Alpine environments are marked by steep environmental gradients and complex habitat mosaics at various spatial scales. Regular forming periglacial patterned ground landforms on the Old Man Range, Central Otago, South Island, New Zealand present an ideal medium for studying plant-invertebrate-environment relationships due to their partitioning of the landscape into discrete units of contrasting environmental conditions, and the existence of some baseline knowledge of the soil, microclimate, vegetation and flora. The study was conducted in three types of patterned ground (hummocks, stripes and solifluction terraces) on the Old Man Range. Each component of the study was sampled at the same spatial scale for comparison. Temperature was recorded in the soil and ground surface from April 2001 to March 2004 in microtopographic subunits (microsites) of each patterned ground landform. Plant species cover was sampled within each microsite; invertebrates were sampled from soil cores taken from the same locations as plant samples in April 2001 and September 2001. The two sampling occasions coincided with autumn before the soil freezes, and winter when maximum freezing was expected. Fine-scale changes in the topographic relief of the patterned ground led to notable differences in the timing and duration of snow. The steepest environmental gradients existed during periods of uneven snow distribution. The soil in exposed or south-facing microsites froze first, beginning in May, and typically froze to more than 40cm depth. Least exposed microsites rarely froze. Within the microtopography, patterns of freezing at specific locations were consistent between years with only minor differences in the timing or depths of freezing; however, notable variation in freezing existed between similar microsites. Within the microtopography, different assemblages of organisms were associated with different microsites. In total, 84 plant and lichen species were recorded, grouping into six community types. Species composition was best explained by growing degree-days, freeze-thaw cycles, time frozen and snow-free days; species diversity and richness increased with increasing environmental stress as indicated by freeze-thaw cycles, time frozen and exposure. In total 20,494 invertebrates, representing four Phyla, 12 Classes, 23 Orders and 295 morpho-taxa were collected from 0.17m� of soil. Acari, Collembola and Pseudococcidae were the most abundant invertebrates. Over 95% of the invertebrates were found in the plant material and first 10cm depth of soil. Few significant relationships were found between diversity, richness or abundance of invertebrate taxa and the microsites; however, multivariate analyses identified distinct invertebrate assemblages based on abundance. Invertebrate composition was best explained by recent low temperature and moisture, particularly in winter; however, plant composition also explained invertebrate composition, but more so in autumn. This research has shown that organisms in the alpine environment of the Old Man Range are sensitive to fine-scale changes in their environment. These results have implications as to how historical changes to the ecosystem may have had long-lasting influences on the biota, as well as how a currently changing climate may have further impacts on the composition and distribution of organisms.