Arctic ecosystems are experiencing rapid changes as a result of climate warming and more frequent natural and human-caused disturbances. Disturbances can have particularly large effects on high-latitude ecosystems because ecosystem structure and function is controlled by strong feedbacks between soil conditions, vegetation, and ground thermal regime. My MSc. research used fieldwork and broad-scale GIS data to investigate post-disturbance ecosystem recovery along roads in two permafrost zones (discontinuous and continuous). In the first of two case studies, I focussed on tall shrub proliferation along the Dempster Highway at the Peel Plateau, NT. To explore the drivers of tall shrub proliferation and to quantify shrub expansion in this region of continuous permafrost, greyscale air photos (1975) and Quickbird satellite imagery (2008) were used to map landcover change within a 1.2 km buffer next to the road and inside a buffer 500 m away from the road. Extensive tall shrub proliferation in the study area indicates that warming air temperatures and disturbance both facilitate vegetation change in tundra environments. My findings also indicate that accelerated shrub expansion adjacent to the road was caused by increased soil moisture. Tall shrub proliferation adjacent to the road occurred at lower elevation sites characterized by wetter soils with thicker organic layers. Areas that resisted tall shrub encroachment were located at higher elevations and had drier soils with thin organic layers. These observations also support previous work that illustrates that tall shrub expansion next to the highway promotes strong positive feedbacks to ongoing shrub growth and proliferation. In a second case study I examined ecosystem recovery in an area of discontinuous permafrost 30 years after construction and abandonment of a winter access road in Nahanni National Park Reserve. Ecosystem recovery was studied by comparing disturbed (road) and undisturbed (adjacent to the road) sites in spruce muskeg, black spruce parkland, deciduous forest, and alpine treeline terrain. Field data showed that disturbances to discontinuous permafrost terrain can lead to large and persistent changes to ecosystem composition and structure. In spruce muskeg, permafrost thaw triggered by road construction dramatically increased soil moisture and facilitated a transition from spruce muskeg to sedge wetland. At alpine treeline the removal of stabilizing vegetation and organic soil during construction slowed subsequent ecosystem recovery. These findings are consistent with resilience theory that predicts that changes to key environmental factors will increase the likelihood of regime shifts. In terrain types where disturbance fundamentally alters ecosystem processes, the management of disturbance impacts in NNPR will be extremely difficult. Overall, this thesis contributes to our understanding of effects of disturbance on vegetation and abiotic conditions, and provides insight into the future of high-latitude ecosystems in a warmer climate with increased disturbance. / Graduate

3 pp. / A description of the popular bird of paradise shrubberies available for use in the desert southwest.

Reproductive studies in invasive plants are necessary for an understanding of their potential to establish and spread in foreign environments. Elaeagnus umbellata Thunb. (autumn olive) is an invasive woody shrub that flowers early in the spring and is often noted for its abundant fruit set. This study examined the reproductive biology of E. umbellata in Illinois, where it is highly invasive. Hand-pollination experiments were performed to determine the breeding system of E. umbellata, and floral visitors were collected to determine its pollinators. Experiments showed that E. umbellata is a predominantly outcrossing species with a self-incompatible breeding system. However, individual variation was detected in several reproductive characteristics. Pollen tube analyses revealed that a small percentage of individuals allow successful self-pollen tube growth, and self-fruit set resulting from automatic self-pollination (autogamy) was relatively high in a few plants. Automatic self-pollination is possible because the male and female parts of flowers mature sychronously, but the likelihood of autogamy may vary among individuals due to variability in the spatial separation of male and female parts (herkogamy). Variability in the incompatibility system and the level of herkogamy may impact the outcrossing rates and reproductive success of individuals. The majority of floral visitors to E. umbellata were generalist pollinators. Frequently visiting bees included small and large species such as native Andrena spp., Augochlorella aurata, Bombus spp., Ceratina calcarata, Xylocopa virginica, and the introduced Apis mellifera. Bombylius major (large bee fly) and the moth Mythimna unipuncta (armyworm) were also frequent visitors. Most of the above insect taxa are pollinators of E. umbellata based on analysis of pollen on insect bodies. E. umbellata is likely to achieve its abundant fruit set where these common pollinators and other E. umbellata are present. However, in my study sites, many individuals experienced low fruit set on branches that were open to pollinator visitation, suggesting pollen limitation may be common in some years and at certain sites. The discovery of autogamous individuals demonstrates that some E. umbellata individuals may be able to establish and spread even when mates or pollinators are limiting.

High-latitude ecosystems have experienced substantial warming over the past 40 years, which is expected to continue into the foreseeable future. Consequently, an increase in vegetation growth has occurred throughout the circumpolar North as documented through remote sensing and plot-level studies. A major component of this change is shrub expansion (shrubbing) in arctic and subarctic ecotones. However, these changes are highly variable depending on plant species, topographic position, hydrology, soils and other ecosystem properties. Changes in shrub and other vegetation properties are critical to document due to their first-order control on water, energy and carbon balances. This study uses a combination of multi-temporal LiDAR (Light Detection and Ranging) and field surveys to measure temporal changes in shrub vegetation cover over the Wolf Creek Research Basin (WCRB), a 180 km2 long-term watershed research facility located ~15 km south of Whitehorse, Yukon Territory. This work focuses on the smaller Granger Basin, a 7.6 km2 subarctic headwater catchment that straddles WCRB’s subalpine and alpine tundra ecozones with a wide range of elevation, landscape topography, and vegetation. Airborne LiDAR surveys of WCRB were conducted in August 2007 and 2018, providing an ideal opportunity to explore vegetation changes between survey years. Vegetation surveys were conducted throughout Granger Basin in summer 2019 to evaluate shrub properties for comparisons to the LiDAR. Machine learning classification algorithms were used to predict shrub presence/absence in 2018 based on rasterized LiDAR metrics with up to 97% overall independent accuracy compared to field validation points, with the best-performing model applied to the 2007 LiDAR to create binary shrub cover layers to compare between survey years. Results show a 63.3% total increase in detectable shrub cover > 0.45 m in height throughout Granger Basin between 2007 and 2018, with an average yearly expansion of 5.8%. These changes in detectable shrub cover were compared across terrain derivatives created using the LiDAR to quantify the influence of topography on shrub expansion. The terrain comparison results show that shrubs in the study area are located in and are preferentially expanding into lower and flatter areas near stream networks, at lower slope positions and with a higher potential for topographic wetness. The greatest differences in terrain derivative value distributions across the shrub and non-shrub change categories were found in terms of stream distance, elevation, and relative slope position. This expansion of shrubs into higher-resource areas is consistent with previous studies and is supported by established physical processes. As vegetation responses to warming have far-reaching influences on surface energy exchange, nutrient cycling, and the overall water balance, this increase in detectable shrub cover has a wide range of impacts on the future of northern watersheds. Overall, the findings from this research reinforce the documented increase in pan-Arctic shrub vegetation in recent years, quantify the variation in shrub expansion over terrain derivatives at the landscape scale, and demonstrate the feasibility of using LiDAR to compare changes in shrub properties over time. / Thesis / Master of Science (MSc)

Climate change has coincided with expansion of deciduous shrub species in the Arctic. Increased deciduous vegetation in the tundra could have profound implications on regional climate, carbon balance, and biogeochemical cycling of nutrients. Winter biological processes may be a mechanism explaining shrub expansion in the Arctic. Tall shrubs accumulate relatively deep snowcover, raising winter soil temperature minima, enhancing microbial activity and promoting nitrogen mobilization that may then be taken up by shrubs. However, it has yet to be determined if shrubs can acquire winter-mobilized nitrogen, and if so, whether they acquire it early in the spring, or over the growing season. The purpose of this study was to test if increased snow alone or the combination of vegetation-type and snow depth affect nitrogen cycling and plant uptake. To test this, inorganic 15nitrogen tracer was added to control and experimentally deepened snow plots (using snowfences) in low birch hummock tundra, and to tall birch-dominated plots near Daring Lake, N.W.T. in the Canadian low Arctic. The first study (Chapter 2) characterizes soil 15nitrogen cycling over a single winter to investigate if experimentally deepened snow in low birch hummock ecosystems enhances nutrient availability to plants in the early spring. In addition, 15nitrogen cycling in low birch hummock and tall birch ecosystems were compared to characterize the combined impacts of vegetation-type and snow depth on nutrient availability to plants by early spring. The second study (Chapter 3) investigated the longer term fate of added 15nitrogen to determine if 15nitrogen acquisition and allocation differs among plant species over a two year period. Together, the results indicate that nitrogen cycling in the low birch hummock tundra was not significantly affected by deeper snow over short (after one winter) or longer terms (two years). By contrast, nitrogen availability in early spring, and birch shrub 15nitrogen uptake after two years were enhanced in the tall birch as compared to the low birch hummock ecosystem. These results suggest that the combination of vegetation-type and snow depth effects in the tall birch ecosystem could be a mechanism contributing to tundra to shrubland transitions across the Arctic. / Thesis (Master, Biology) -- Queen's University, 2009-09-18 13:36:29.401

The Bogong High Plains are a series of alpine and subalpine plateaux in NE Victoria. The vegetation of the High Plains consists of woodland, heathland, grassland herbfield and wetland communities. On the better drained sites, the transition from heath dominated communities to grass dominated communities is correlated with gradients of decreasing accumulation and persistence of snow, increasing exposure to wind and low minimum air temperatures, and decreasing steepness and rockiness of terrain. In many areas, shrubs have increased in cover and abundance, especially over the last 50 years. In particular, shrubs have invaded many areas of grassland, which has resulted in an expansion of both open heath and closed heath. The High Plains have been grazed by free ranging cattle each summer since the 1850's, and a primary aim of this thesis is to investigate the dynamics of heathland and grassland, and the impact that cattle grazing has upon these two vegetation types.

Herb- or shrub-chronology, a technique adapted from dendrochronology, is the study of the annual growth rings in roots of certain perennial dicotyledonous plants. The presence of annual growth increments in high-elevation plants is significant as it highlights the applicability of herbchronology for climatic, ecological and geomorphologic applications in alpine and other extra-arboreal regions. For alpine sites along the eastern crest of the Sierra Nevada range I present the first shrub-ring chronologies of the species Linanthus pungens (Torr.) J.M. Porter & L.A. Johnson. L. pungens individuals were collected at, and are especially ubiquitous at rock glacier sites in north-east trending glacial-cirque valleys. Rock glaciers are an increasingly recognized and studied feature on the alpine landscape, supporting floristically diverse plant populations, distinct thermal regimes decoupled from the external air and perennial water sources fed by interstitial ice. These landforms are expected to be refugia for alpine flora and fauna in some regions for projected warmer and drier climates. To evaluate plant growth on rock glaciers as compared to adjacent talus slopes in the central Sierra Nevada range of California, USA, a series of five cirque basins were selected as sites for paired rock glacier- talus slope vegetation comparisons. Vegetation cover, species richness, diversity measures and plant functional traits were recorded at ten sites (five rock glaciers, five talus slopes) along a 100-kilometer latitudinal span of the eastern slope of the Sierra Nevada range. Canonical correspondence analysis was used to evaluate general patterns in cover, diversity and functional traits for the 10 sites and inform subsequent statistical analyses. Both vegetation cover and species richness were significantly greater on rock glacier sites than on adjacent talus slopes even though mean slope values for the rock glacier sites were higher. Significantly, for the present study, rock glaciers support a higher number of the species Linanthus pungens, a climatically sensitive, long-lived alpine sub-shrub, showing that these periglacial landforms are not only floristically distinct but are also habitats containing natural climate archives useful to the field of herbchronology. L. pungens shrub-ring chronologies are determined to be distinct from Pinus albicaulis chronologies growing at the same five sets of sites in the Sierra Nevada study location. P. albicaulis (PIAL) tree-ring chronologies and L. pungens (LIPU) shrub-ring chronologies were constructed for four cirque basin sites. Comparisons were made between chronologies based on growth form (shrub or tree) and site, and on chronology response to average monthly temperature, total monthly precipitation and April 1 snowpack values. Chronologies are significantly more similar to other chronologies of the same growth form (PIAL-PIAL or LIPU-LIPU) than are same-site chronologies of different growth form (i.e. PIAL-LIPU chronologies) (p < 0.05). This holds true for comparisons based on Pearson’s correlation coefficients or Gleichläufigkeit (GLK) values. Growth response to monthly temperature and precipitation values is highly variable for same-site chronologies and also for same growth form chronologies. Topographical position and proximity to treeline was held constant at all sites so differences in climate-growth response within sites and within species may be attributed to factors that are unrealized in the sampling design. Based on composite climate anomaly maps, wide ring widths in PIAL chronologies occur after average winter and spring precipitation and with warm growing seasons while narrow PIAL rings fall after wet springs and with average summer temperatures. Years in which all LIPU rings are wide are found to occur during warm dry springs and growing seasons while years in which all LIPU rings are narrow occur in conjunction with wet winters and springs. Investigation into the longest and most replicated chronology at the Barney Lake (BL) site allowed a climate-growth comparison over a longer period of time (the BL chronology is 112 years in length with sufficient sample replication (EPS > 0.85) to capture a robust common signal from 1952 through 2007). Marker years in the BL chronology correspond to drought (wide rings) and persistent snowpack (narrow rings). Response function analysis indicates significant correlations with July minimum temperatures and the previous year's November precipitation. Increase in the radial growth of the taproot of L. pungens at BL has not decreased over the past century and is more highly correlated to temperature (positively) and snowpack and precipitation (negatively) during the latter half of the chronology period. Predictions of decreasing snowpack and warming temperatures for the alpine Sierra Nevada could indicate increased shrub growth over the next century and possible shrub range expansion if unprecedented drought does not prove to limit growth in the future. Work at BL and the other four alpine L. pungens chronology locations demonstrate a potential for additional research on climate-shrub growth interactions and in particular for investigations into climate controls on upper shrubline growth and movement in the Sierra Nevada range in California.

Observational and modelling studies show that the warming of the Arctic is leading to shrub expansion. This shift in vegetation cover is expected to significantly alter the distribution of snow across the landscape and the interactions between the land surface and the atmosphere. Shrubs capture wind-blown snow, increasing snow depth and decreasing winter water loss through sublimation, and bend beneath the weight of snow, affecting albedo. Snow is highly insulative and affects the soil hydrological and thermal properties. Therefore, as the snow-vegetation-soil interactions is expected to be at the core of feedback loops leading to further shrub expansion, there is a need for models to be able to simulate these processes accurately. Initially using the community land surface model JULES (Joint UK Land Environment Simulator) this study investigates the effects of shrub-tundra on snow and runoff. Alternative formulations of soil processes are proposed, which are better adapted to the representation of subgrid heterogeneity in cold regions than the current model formulation, and evaluated over the Abisko and Torne-Kalix river basins. In addition, a high resolution shrub bending model, which calculates the exposed winter shrub fraction, is developed and parameterised for use alongside the snow cover parameterisation in JULES in order to provide a better representation of shrub-specific processes. This revised JULES more than doubles the efficiency coefficient and halfs the negative bias between modelled and observed runoff in the shrub-tundra Abisko basin. However, the current structure of the model is found to be inadequate for use in investigating the effect of shrub-tundra expansion because it calculates a single energy balance for the snow-free and the snow-covered areas. To address this issue, a distributed three-source (snow-shrub-ground) model (D3SM) is developed. D3SM is evaluated against snow and energy ux measurements from a shrub-tundra basin in the Yukon, Canada, and is found to reproduce snowmelt energetics well. The effects of shrub expansion on the energy balance of the basin during snowmelt are then investigated by increasing the vegetation fraction and canopy height of the current shrub distribution, which is found to be positively correlated with topography. D3SM shows that the most significant effects of shrub expansion in the basin are to reduce the spatial variability of snow depth and to increase the sensible heat flux from the surface to the atmosphere.

Understanding the impacts of explosive contamination on vegetation is key to understanding explosives behavior in the environment. I quantified shrub growth responses to 1,3,5-trinitroperhydro-1,35-triazine (RDX) soil contamination across three life stages and I hypothesized that RDX would have the greatest impact on seed germination. Morella cerifera seeds were germinated on soils amended with RDX up to 1500 mg RDX kg-1 dry soil. Juvenile and adult individuals were exposed for 6 weeks to soil amended with RDX up to 750 and 1500 mg RDX kg-1 dry soil, respectively. Morphological responses were quantified for juveniles while physiological measurements were quantified for adults. RDX induced a significant response in all age groups and, in accordance with the hypothesis, germination was the most impacted of the three stages. Impacts varied by concentration in addition to life stage, showing that many variables influence plant response to RDX.

Species composition, temperature, soil nutrients, and leaf area index (LAI) were recorded across three encroaching Morella cerifera thicket edges and three free- standing shrubs on Hog Island, Virginia to characterize the effect of shrub thickets on the plant community and microclimate. Electron transport rate (ETR) was taken on shrub leaves to determine if microclimate benefits M. cerifera physiology. Species richness was lowest inside shrub thickets. Soil water content and LAI were higher in shrub thickets compared to grassland. Soil organic matter, N, and C were higher inside shrub thickets. Summer and fall maximum temperatures were more moderate in shrub thickets and at free-standing shrubs. Fall and winter minimum temperatures were higher inside shrub thickets. ETR was higher at the free-standing shrubs compared to the thicket edge. Morella cerifera impacts microclimate characteristics and species composition immediately upon encroachment. Improved shrub physiology was neither supported nor rejected by the research presented here.