Habitat structure is an important driver of many ecological patterns and processes, but few studies investigate whether habitat structure interacts with other environmental variables to affect community dynamics. The main objective of this study was to disentangle the relative importance of prey availability and shrub architecture on the distribution, abundance, and biodiversity of spiders of northern Utah, USA. We conducted field experiments which focused on: (1) describing the importance of these factors on spider community organization, (2) specifically evaluating whether prey availability mediates the relationship between shrub architecture and spider abundance and biodiversity, and (3) investigating spider and prey responses to manipulations of surrounding vegetation structures. For the first two experiments, big sagebrush shrubs were randomly assigned to six experimental treatments: two levels of prey attractant (shrubs were either baited or not baited) and three levels of foliage density (low, natural/control, or high). The purpose of manipulating both prey availability and shrub architecture was to delineate their significance to spiders. For the last experiment, changes in these factors were investigated at two different levels of spatial context (a single manipulated shrub surrounded by untreated shrubs vs. a manipulated shrub surrounded by a patch of similarly treated shrubs). We found both prey availability and shrub architecture directly influenced patterns of spider abundance and species richness and that spider species diversity and community composition varied in response to shrub architecture alone. Preferences of some spiders for certain shrub types likely reflect differences in foraging strategies or the substrate required to support different types of webs. We also demonstrate that spider response to shrub architecture is the result of multiple processes (i.e., a combination of direct and indirect effects via prey availability) and that surrounding vegetation structures affect spider abundances on shrubs. In addition, prey composition varied among different shrub foliage density treatments, but only when surrounding vegetation structures were also manipulated. More generally, this study suggests that ecological responses to habitat structure are in part mediated by associated variables and the significance of shrub architecture varies depending on the organisms examined and the spatial scale to which they respond most strongly.

Astragalus filipes Torrey ex. A. Gray (Fabaceae) is being studied and propagated for use in rangeland restoration projects throughout the Great Basin. Restoration forbs often require sufficient pollination services for seed production and persistence in restoration sites. Knowledge of a plant's breeding biology is important in providing pollination for maximal seed set. Reproductive output from four manual pollination treatments (autogamy, geitonogamy, xenogamy, and distant xenogamy) was examined in a common garden. Pod set, seed set, and seed germination were quantified for each of the treatments. Seed set from four wild populations was compared to that of an openly visited common garden array. A. filipes was found to be self-compatible, but to benefit greatly from outcrossing. Less seed germinated from distantly outcrossed treatments than for any other treatment, indicating possible outbreeding depression. Common garden plants set less seed per pod than any wild population, possibly due to a depauperate pollinator guild in the common garden. Bees were surveyed at wild A. filipes populations to identify common pollinators. Solitary and social bee species were observed visiting A. filipes to estimate aspects of their pollination efficacies, particularly foraging tempo and frequency of stigmatic contact. The nesting biologies of bees that visit A. filipes were considered as a component of bee manageability. Bees in the genus Osmia (Megachilidae) dominated this pollinator guild. Bombus nevadensis queens were the fastest foragers; honey bees and native solitary bees did not differ in foraging tempo. Megachilid bees consistently contacted the stigma during foraging, but honey bees exhibited sideworking behavior, contacting stigmas far less frequently than any other bee species observed. Two solitary bee species (Osmia bruneri and Hoplitis hypocrita) are recommended as prospective pollinators for management in association with Great Basin rehabilitation efforts.

The projected increase of shrubs across the Arctic is expected to alter patterns of snow cover, which may affect the phenology and survival of arthropods such as spiders. In this study, we simulated shrub encroachment on a series of tundra plots and examined the effects on the spider assemblages during the following growing season. Our simulated shrub treatment did not affect the abundance or composition of spider communities over the season; however, adults from the dominant genus Pardosa (Lycosidae) had significantly higher body mass on treatment plots. This difference in mass was observed following snow melt and persisted until halfway through the growing season. Given the importance of spiders as arthropod predators and as food sources for breeding birds, such a change in summer body mass could represent a shift in spiders’ functional contributions to Arctic ecosystems.

The projected increase of shrubs across the Arctic is expected to alter patterns of snow cover, which may affect the phenology and survival of arthropods such as spiders. In this study, we simulated shrub encroachment on a series of tundra plots and examined the effects on the spider assemblages during the following growing season. Our simulated shrub treatment did not affect the abundance or composition of spider communities over the season; however, adults from the dominant genus Pardosa (Lycosidae) had significantly higher body mass on treatment plots. This difference in mass was observed following snow melt and persisted until halfway through the growing season. Given the importance of spiders as arthropod predators and as food sources for breeding birds, such a change in summer body mass could represent a shift in spiders’ functional contributions to Arctic ecosystems.

This study investigated the use of high resolution satellite imagery in research involving habitat selection, and movement patterns of white-tailed deer and cattle in a semi-arid landscape. Vegetation classification was developed based on Ikonos satellite imagery that was then used to define habitat selection and characterize movement paths of deer and cattle to allow a better understanding of these 2 species. Pasture attributes were also measured to determine animal distribution throughout the study area in relation to roads, fences, water location, and supplemental feeders. Three cattle and 3 free ranging white-tailed deer were used during 3 trials to test seasonal differences in habitat selection and spatial distribution across the pasture. Ikonos satellite imagery was classified to a final classification accuracy of 83.6%. Seven vegetation classes were defined in the classification with 1 class of bare ground/ herbaceous that represents interspaces between shrub vegetation. Classification accuracy was obtained using a ?? meter buffer to all ground control points increasing the accuracy from 71.29%. All physical pasture attributes were significant to animal distributions in the study area when compared to the random distribution. Roads and water location were most important to cattle during the spring and summer. White tailed deer use of the pasture was more dependent on vegetation characteristics than physical attributes. Both cattle and deer selected habitat patches with a proportionately large percentage of bare-ground/interspaces (>40%). Deer were predominately found in areas containing higher percentages of shrub species, while cattle were found in areas containing a mixture of larger tree species in addition to shrub complexes. Travel velocity and path tortuosity were measured to determine effects of vegetation attributes on animal movements. Both cattle and deer followed fairly linear paths (Fractal Dimension<1.2). Factors contributing to path tortuosity included mean patch size, number patches, and patch fractal dimension. Travel velocity was also measured and compared to vegetation association attributes. Travel velocity was significantly different between seasons for white-tailed deer however cattle and deer comparisons were not significant across the 3 trials. Number of patches, patch fractal dimension, mean patch size, and patch area were significant in the travel velocity model.

Historic land uses impose discernable legacy effects that may influence ecosystem function, a concern of particular importance in actively managed landscapes. In recent history (ca. 150 years) tree and shrub abundance has increased at the expense of native grasses in savannas and grasslands. The magnitude and patterns of change are spatially heterogeneous, highlighting the need for analytical approaches spanning multiple spatial scales, from individual plants to patches to landscapes. The overarching goal of this dissertation was to explore long-term dynamics associated with woody plant encroachment with aerial photography and field studies to examine cover, density, soils and land use history at the Santa Rita Experimental Range.The first study characterized patterns in woody cover change on contrasting soils over 60 years using aerial photography. Woody patch dynamics revealed encroachment and stabilization phases in woody plant proliferation. Soil properties reflected the rate at which uplands reached a dynamic equilibrium, but not the endpoint (ca. 35% cover). Fluctuations around dynamic equilibrium reflected net change in patch growth and acquiescence combined with colonization and mortality. Efforts to characterize changes in land cover will require patch-based assessments beyond coarse estimates of percent cover.The second study capitalized on historic field measurements of shrub canopies to validate estimates of shrub cover derived from the earliest aerial photography, quantified detection limitations of 1936 aerial photographs for mapping shrub cover, assessed species-specific contributions to percent cover, and translated detection limitations to proportions of velvet mesquite (Prosopis velutina var Woot.) biomass missed with 1930s aerial photography.The third study was a field-based approach investigating how livestock grazing influenced mesquite cover, density, biomass, and stand structure over 74 years. The study supplemented traditional statistical analysis of grazing effects with methods quantifying spatial autocorrelation structure of mesquite density by grazing treatment. The outcome re-affirmed the supposition that mesquite cover may be dynamically stable at ca 30%, and revealed that livestock grazing slowed the shrub encroachment process from 1932 to 2006, counter to expectation. Results indicate that shrub growth trajectories persist long-term. Overall, this work affirms the importance of land use legacies and long-term perspectives in rangeland shrub dynamics.

Decadal changes in the surface area of small ponds in the Kluane region, Yukon were quantified from remote sensing and dendrochronological techniques. Both dead and live shrubs from the genus Salix were sampled and cross-dated from a total of 28 pond ecotones in two different study areas. The rate of ecotone shrub colonization was calculated for each pond by determining the minimum age of Salix spp. in ten zones extending from forest edge to shoreline. Changes in the surface area of 20 ponds in each study area, for a total of 40 ponds, since 1948 were measured using multi-temporal remote sensing analysis. Measured changes were then validated using colonization rates derived from the dendrochronological analysis. Results were compared with meteorological records to elucidate the connection between climate change and shoreline dynamics. Ponds experiencing similar rates of ecotone colonization exhibited similar changes in shoreline position over the last 60 years. Ponds measured with remote sensing showed an overall decline in surface area since 1948; however, direction and extent of change varied within and between the two study areas. Colonization rates also varied within and between study areas. This corresponded to differences in pond ecotone population structure as well as relative extent and direction of changes in surface area, and supported the changes observed in the low-resolution remote sensing time series data. Changes in ponds tended to correspond to increases in annual temperatures which, when combined with a longer growing season and stable precipitation, may have accelerated evaporation potential causing ponds to decrease. The negative consequences of surface area decline are exacerbated by the potential increases in evapotranspiration and the much less extensive wetland system in southwest Yukon relative to other regions in the North. The successful implementation of remote sensing and dendrochronological techniques has value for remote areas that are sensitive to climate change, yet lack direct measurement of changing environmental conditions. / Thesis (Master, Geography) -- Queen's University, 2012-09-28 13:03:05.43

In New Zealand, native shrubs are considered an important potential carbon-sink in disturbed or abandoned land (e.g., pastoral land that is unsustainable for long-term pastoral agriculture). However, the impact of varying environmental drivers on carbon uptake from photosynthesis and carbon loss from respiration of a developing shrubland remains uncertain. In this study, the effects of both temperature and soil water content (θ) on photosynthesis and respiration were examined under controlled growth cabinet and field conditions in a pasture grass and the native shrub, kānuka (Kunzea ericoides var. ericoides). The purpose of the investigation was to assess the combined impacts of varying temperature and θ on canopy processes and to disentangle the effects of θ on photosynthesis and respiration for the two different plant types. A controlled growth cabinet study (Chapter 2) showed that θ had a greater effect on the short-term temperature response of photosynthesis than the temperature response of respiration. The optimum value of θ for net photosynthesis was around 30 % for both kānuka and the grass. Statistical analysis showed that the temperature sensitivity of photosynthetic parameters was similar for both plant types, but the sensitivity of respiratory parameters was different. Reduction in θ induced an inhibition of photosynthetic capacity in both plant types. The response of respiratory parameters to θ was not related to substrate limitations, however available evidence suggests that it is likely to be a species dependent plant mechanism in regulating the cost of maintenance due to reduced photosynthate assimilation and decreasing energy supply to support the activity of respiratory enzymes. Results obtained from a field study (Chapter 3) showed that photosynthesis and respiration in the grass and kānuka were sensitive to seasonal changes in temperature and θ. Photosynthetic parameters showed little acclimation following changes in seasonal growth conditions. In contrast, respiratory parameters tended to acclimate more strongly. Respiratory acclimation to multiple environmental conditions was characterised by changes in temperature sensitivity and a shift in the response of respiration to temperature, demonstrating the involvement of both ‘Type I’ and ‘Type II’ acclimation in both plant types. The results from controlled growth cabinet and field studies were used to drive a leaf level model that integrates the responses of photosynthesis and respiration to changes in temperature and θ and incorporates acclimation using variable photosynthetic and respiratory parameters (Chapter 4). This model was used to estimate the annual canopy carbon exchange of the grass and kānuka in response to seasonal changes and to predict changes in canopy carbon exchange under varying future climate change scenarios. The model highlighted the importance of considering seasonally-acclimated parameters in estimating canopy carbon exchange of both plant types to concurrent changes in multiple environmental variables. The overall results support the conclusion that understanding the combined effects of environmental variables on canopy processes is essential for predicting canopy net carbon exchange of a pasture-shrub system in a changing global environment. It has been shown here that the rate of increase in photosynthesis with increasing θ is greater than that of respiration which results in a progressively greater apparent carbon gain at moderate values of θ. Moreover, the impact of lower values of θ, which reduced the apparent sensitivity of respiration to temperature, may effectively decrease the rate of respiration during warmer summer months and enhance thermal acclimation via downregulation of respiration. Therefore, considering the influence of soil water conditions on the temperature sensitivity of photosynthetic and respiratory model parameters has important implications for precisely predicting the net carbon exchange of a pasture-shrub system.

Shrub fuels are capable of extreme fire behaviour under conditions that are often moderate in other fuels. There is also a narrow range of conditions that determine fire success in these fuels, below which fires may ignite but hardly spread and above which they ignite and develop into fast moving and high intensity fires. This is due to the elevated dead fine fuels that dry rapidly and carry fire. Fire danger rating systems designed for forest and grassland fuels do not predict fire potential in shrub fuels very well. Fire management requires fire danger rating systems to provide accurate and timely information on fire potential for all important fuel types. Studies of fuel moisture, ignition and fire spread were carried out in the field in gorse (Ulex europaeus L.) shrub fuels to predict the moisture content of the elevated dead fuels and to define the conditions that govern fire development. The accuracy of the Fine Fuel Moisture Code (FFMC) of the Canadian Forest Fire Weather Index (FWI) System to predict moisture content of this layer was assessed. A bookkeeping method to predict moisture content was developed based on semi-physical models of equilibrium moisture content, fuel response time and the FFMC. The FFMC predicted moisture content poorly, because the FWI System is based on the litter layer of a mature conifer forest. The gorse elevated dead fuel layer is more aerated and dries faster than this conifer forest litter layer. The bookkeeping method was reliable and allowed adjustment of fuel response time based on weather conditions. Difficulties in modelling meteorological conditions under the gorse canopy limited its accuracy. Separate thresholds determined ignition and fire spread success, with both based on the elevated dead fuel moisture content. Options to improve the shrub fire danger rating system were presented based on these findings. The results are significant because they are based on data collected in the field under real conditions. Validation of these results and extension to other shrub fuels is required before the findings are used to change current models. However, the study has significantly advanced the knowledge of fire behaviour in shrub fuels and will contribute to safe and effective fire management in these fuels.

Résumé : Cette recherche présente l'analyse spatio-temporelle de l'évolution conjointe de l'augmentation de la présence arbustive et de la dynamique de la fonte de la neige au Nunavik, Québec, Canada. Cette zone est caractérisée par la complexité de l'interaction de multiples changements simultanés de la température, de la couverture de la neige ainsi que de la pousse végétative. La première partie de ce travail consiste à faire l'analyse de l’évolution temporelle de ces multiples changements. Cette analyse a nécessité la mise en place d’une importante base de données climatiques, satellitaires et de couverture de sol à plusieurs échelles, sur une période allant jusqu'à 60 ans, soit de 1950-2012. La deuxième partie du travail consiste à faire l'analyse spatiale à haute résolution de l’influence de la fraction du couvert arbustif sur la fonte de la neige. L'analyse et l'interprétation des résultats obtenus dans la première partie montrent clairement un changement climatique significatif sur la région étudiée, découpée en 3 bandes de latitude correspondant à la toundra, la taïga ouverte et à la taïga forestière, respectivement du Nord au Sud. Ce changement de climat correspond à un réchauffement marqué, entre 0.75°C et 1.57°C par décade entre les zones 1 (toundra) et 3 (taïga forestière) respectivement. On peut noter que la hauteur de neige maximale annuelle a diminué dans les trois zones alors que les précipitations hivernales ont augmenté en zone 1 et 3 sur les 45 dernières années. Les résultats montrent une nette augmentation de la végétation arbustive dans les zones 2 et 3 (LAI plus élevé de 100% dans la zone 3 par rapport à la zone 1). L'impact de la végétation a été analysé à partir de la durée de fonte relative entre le début de la fonte et la disparition de la neige. Il apparait clairement que la végétation active la fonte précocement, allongeant ainsi significativement la durée de fonte (+600%). Cependant, l'impact de la végétation ne retarde pas la date de fin du couvert nival qui est de plus en plus précoce pour les zones 2 et 3. L'analyse spatiale à haute résolution montre que la présence arbustive entraine une date de fin de neige plus précoce par rapport au sol nu. Cette étude démontre clairement que la croissance de la végétation qui résulte du réchauffement climatique impacte la dynamique du couvert nival, aussi affectée par ce réchauffement. Une étude approfondie des processus en causes avec des mesures in situ appuyées par leur modélisation permettrait de mieux comprendre ces phénomènes. // Abstract : This study presents a spatial-temporal analysis of the joint evolution of the increase of shrubiness and the dynamics of snowmelt in Nunavik, Quebec, Canada. This zone is characterized by the complexity of the interaction of multiple changes of temperature, snow cover and vegetation growth. The first part of this study analyzes the temporal evolution of these changes. The analysis required the use of a large database on climate, satellite data and ground cover at multiple scales over a period of up to 60 years, from 1950 to 2012. The second part of the study consists of a spatial high-resolution analysis of the influence of the fraction of shrub cover on snowmelt. The analysis and interpretation of the results clearly show a significant climate change over the study area, divided into three latitudinal transects corresponding to tundra, open taiga and forested taiga. A significant warming of 0.75 ° C and 1.57 ° C per decade was experienced between zones 1 (tundra) and 3 (forested taiga) respectively. The maximum annual snow depth on the ground decreased over the 3 zones studied while winter precipitations increased in zones 1 and 3 over the last 45 years. The results show a significant increase in shrub vegetation in zones 2 and 3. The impact of the vegetation on snow was analyzed with melt duration (from melt onset to complete melt). It appears clearly that the vegetation triggers the melting process earlier and significantly extends the melt duration (+600%). However, the impact of vegetation does not delay the date of the snow cover disappearance. The high-resolution spatial analysis showed that shrubs cause an earlier snow cover disappearance date than bare soil. This study clearly demonstrates that vegetation growth resulting from global warming impacts the snow cover dynamics, which are also affected by global warming. A thorough study of the processes with in-situ measurements supported by models would help gaining a better comprehension of these phenomena.