Perennial grass vegetation dynamics of heavy grazing, moderate grazing and ungrazed treatments were analyzed during two extreme drought events: the drought of 1951 to 1956 and the drought events centered on the year 2000. Analysis of each drought event from weather records and Palmer Drought Severity Index values showed that the intensity, duration and pattern of each drought event were structurally unique. Grazing intensity was the primary driver of perennial grass species composition and community structure both during and between each drought event. Total basal area for each drought event was driven primarily by variation in precipitation pattern. Basal area per plant dynamics were significantly influenced by grazing intensity while plant density was driven by both precipitation and grazing intensity. Topo-edaphic variation significantly influenced the persistence and distribution of perennial grass species during an extreme drought event centered on the year 2000. The presence of large or abundant surface rock features facilitated the survival of perennial grasses during this drought event by creating a positive soil microenvironment. Sites with large surface rock features acted as drought refugia for perennial grass populations. Sites with abundant surface rock features had 10 times greater perennial grass basal area and 5 times greater plant density than sites with few surface rock features. Grazing intensity was the primary driver of species composition and community structure within both refugia and non-refugia sites. Grazing intensity had no effect on perennial grass basal area. However, grazed treatments had two times greater perennial grass density than non-grazed treatments. Species response to grazing intensity and surface rock cover was individualistic. Grazing response groups (intolerant, intermediate, and tolerant) separated along a gradient of surface rock cover and grazing intensity. Abundant surface rock features act as refugia for perennial grasses by facilitating their persistence during extreme drought events on the Edwards Plateau.

The mesic forests distributed within the Rocky Mountains of northern Idaho are unique because many species contained within the forest are separated from their main distribution along the Pacific Northwest coast. It remains unclear whether most species within the inland disjunction survived the glacial periods of the Pleistocene, or whether they were more recently dispersed from coastal populations. To see if the dominant tree taxa of the mesic forests today could have persisted in a refugium south of the large ice sheets, four sediment cores were used to reconstruct the vegetation and climate history of the region. A nearly continuous record of pollen and sediment composition (biogenic silica and inorganic and organic matter) over the last ca. 120,000 years provides evidence of a dynamic ecosystem. Over a long timescale, the slow shifts in vegetation are attributed to the changes in climate. During the last interglacial period, the region was warmer and drier with a Pinus dominated mixed conifer forest. Approximately 71,000 years ago, a Pseudotsuga/Larix forest became established in the area as a response to the increased available moisture. As climate cooled and glaciers expanded the Pinus and Picea forest was the dominant vegetation type until ca. 40,000 years ago. The environment during the Last Glacial Maximum (LGM) was so harsh that no vegetation record was recorded. After the LGM, climate warmed, enabling a Pinus and Picea forest to establish and persist until the Holocene. The mesic taxa that dominate the modern forests did not arrive in northern Idaho until the mid- to late-Holocene. The recent arrival of the dominant tree species, Thuja plicata and Tsuga mertensiana, suggests that they likely did not persist in a refugium during the last glaciation. Instead, these species recently dispersed from coastal populations, but expansion into their interior distributions was likely limited by both climate and species competition in already established forests. During the late-Quaternary, the deposition of thick tephra layers (>20 cm) from the eruptions of Glacier Peak (ca. 13,400 years ago) and Mt. Mazama (ca. 7,600 years ago) also facilitated an abrupt and persistent change in vegetation in northern Idaho.

One of the most challenging questions surrounding the Clovis colonization of North America is the character and structure of terminal Pleistocene environments, including floral and faunal communities. A series of cores in the mouth of an arroyo revealed late Pleistocene - early Holocene wetland sediments buried 12 meters below surface, at the approximate elevation of the entrenched modern San Pedro River channel. A suite of ¹⁴C dates show that wetlands of the ancestral San Pedro River occupied portions of the inner valley coincident with the Younger Dryas (13,000 - 11,500 cal yr BP) and the early Holocene (10,000 - 9,500 cal yr BP). A lack of Sporormiella fungal spores indicates that mammoths were rare or absent when Clovis populations appeared in the valley around 12,800 cal yr BP. Palynological and stable carbon isotope analyses show that C₄ grasses increased at 9,940 cal yr BP, just prior to frequent burning after 9,510 cal yr BP and rapid erosion at 9,470 cal yr BP. δ ¹⁸O values from soil carbonates vary but do not record a systematic shift in precipitation source or temperature during the late Pleistocene - early Holocene transition. The establishment of C₄ grasslands in the inner valley correlates with widespread changes in the Chihuahuan Desert flora around 10,000 cal yr BP. A relatively dense accumulation of Clovis-mammoth associations in San Pedro Basin contrasts the lack of megaherbivores indicated at Palominas Arroyo. The upper San Pedro Basin of southeastern Arizona contains a minimum of four Clovis-mammoth associations, making it possibly one of the densest concentrations of human-proboscidean sites on earth in terms of time and space. I use the Younger Dryas-age stratum known as the "black mat" to compare the Clovis-age archaeofaunal record of the basin to its paleontological background in order to measure the level of human predation that created this remarkable record. This analysis indicates that Clovis people were affecting the last mammoth populations to a significant degree, a situation expected only in the presence of abundant mammoths. I argue that this condition was met in the San Pedro Basin, possibly in the form of a terminal Pleistocene refugium. If the refuge hypothesis indeed explains mammoth predation, then Clovis-mammoth associations should occur as clusters as they do in the San Pedro Basin rather than as isolates as they are known to occur elsewhere. The use of radiocarbon frequency distributions to reconstruct prehistoric human and animal populations must account for taphonomic loss and other factors that affect the archaeological and paleontological records. Surovell et al. (Journal of Archaeological Sciences, 36, 1715–1724) have recently proposed a volcanic-based correction factor for removing "taphonomic bias" from temporal frequency distributions. Analysis of 718 radiocarbon dates sampled from the alluvium of the San Pedro and Santa Cruz Rivers and their tributaries in southeastern Arizona shows that discovery and scientific biases play an equally important role in the creation of radiocarbon frequency distributions, and that "taphonomic bias" has not been systematic through time. The latter principle is further demonstrated using a sample of 123 Pliocene to Clovis-age proboscideans from the San Pedro Valley. We propose an alternative model that is based on the nature of the stratigraphic record, with discovery bias, scientific bias, taphonomic loss, and the shape of the calibration curve all operating to influence the temporal frequency distribution of prehistoric phenomena.

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Many paradoxes exist about postglacial tree migration and they dont solve for many European trees. One example is wetland trees subgenus Alnus, which spread across Europe during the last glacial very quickly according to fossil records. The aim of this thesis is detection their migration potential, with the help of empirical evaluation of interpolated pollen data (interpolation method IDW) and a simulation model based on environmental characteristics of the species. The results of interpolated maps are similar to the rate previously estimated speed and the results of simulation model achieve these speeds only by A. incana but with specific extreme environmental conditions. The mason of this may be adapting its seeds to anemochorii because the simulation model confirmed their good potential to spread by the wind. Results of model for A. glutinosa don´t confirm the ability to rapidly spread by the wind and the observed rate must have another explanation. Maybe rivers can explain the empirical spread rate. This suggests visualization of migration lines and river networks. The model has also been disclosure of environmental properties that are related to migration potential. Within the parameterization of the model is demonstrated, that R0 of A. glutinosa is significantly better than A. incana. But main parameters of anemochory model are terminal velocity and generation time, which is shorter by the A. incana, and therefore is probably able to spread faster than A. glutinosa.

Fire refugia, defined as unburned, functionally intact patches of habitat within a fire footprint, play an important role in post-fire recovery and landscape resilience to fires. Increased fire activity in the Canadian boreal forest due to climate change highlights the need to properly identify and manage wildfire refugia to protect the natural resilience of boreal ecosystems. While previous fire refugia research has focused on western Canada, we present the first characterization of fire refugia, with a focus on peatland fire refugia, in Ontario. We use remotely sensed multispectral imagery and stereo-derived DEM data from the 2018 Parry Sound 33 wildfire in the Ontario Boreal Shield to determine the primary drivers of fire refugia formation on this landscape, and to develop a model to predict the occurrence of potential fire refugia based on these drivers. We found that the Normalized Difference Moisture Index (NDMI) and the Topographic Position Index (TPI, 200m radius neighbourhood) had the strongest control on wildfire refugia probability in the model, with a combined relative influence of 63.8%. Additionally, wildfire refugia tended to form in peat-filled depressions, valleys, and forested areas within the study area, whereas drier, open rock barrens were most susceptible to fire. Overall, the model had a high predictive accuracy, with a cross-validated AUC of 0.88, and a sensitivity of 81.2%. We conclude that local scale topography and simple flow accumulation models can act as a powerful tool in predicting fire refugia occurrence in this landscape. In the second part of this study, we examined the in-situ indicators of peatland fire refugia occurrence. We conducted vegetation surveys at eight peatland fire refugia and eight reference sites representative of the range of wetland types found on this landscape. We found that the peatland fire refugia had a significantly different understorey vegetation composition when compared to the reference sites. Environmental factors within the peatland fire refugia which significantly influenced this separation included median peat depth, pH, and specific conductance (SpC); where peatland fire refugia were deeper and had a lower pH and SpC when compared to the reference sites. While no vascular indicator species were identified within the peatland fire refugia, there were two bryophyte indicator species: Sphagnum rubellum and Sphagnum magellanicum which were significantly associated with the peatland fire refugia. We conclude that understorey vegetation composition, indicator species presence, peat depth, pH and SpC could be useful when distinguishing peatlands with a high refugia probability, however, further research is needed to understand how this may vary geographically and in response to top-down controls, such as fire weather. Overall, the preliminary characterization of fire refugia in the Ontario Boreal Shield will provide a basis for the identification and mapping of fire refugia within this ecozone for applications in conservation, restoration, and fire and land management. / Thesis / Master of Science (MSc) / Areas which remain unburned, or burn at a low severity during a wildfire, are referred to as fire refugia by scientists and conservationists for their role in providing habitat to plants and animals following a fire and promoting the regeneration of the burned landscape. Here, we use modelling and field survey methods to examine the biological and physical controls of fire refugia occurrence in an Ontario Boreal Shield landscape. We find that large, deep peatlands and wetlands in bedrock depressions on this landscape are more likely to act as fire refugia, and that confirmed peatland fire refugia have distinct vegetation communities and more stable water tables when compared to other peatlands and wetlands on this landscape. These insights into fire refugia occurrence in the Ontario Boreal Shield will assist in the detection of potential refugia for the targeting of conservation and management strategies to help protect these ecologically important areas.

The unique species, ecosystems and landscapes of the Western United States are experiencing unprecedented pressures from climate change, creating new challenges for conservation. As temperatures rise and patterns of precipitation shift, plant and wildlife species have been shifting their ranges to new areas in search of more suitable climates, building groupings of species that are historically unfamiliar. These climate -driven migrations place an additional burden on species that are already threatened from habitat loss and other human-related activities. The impacts of climate change are of particular concern in landscapes that have long been conserved and managed based on the ecological features that define them, including national parks, wildlife refuges, and wilderness areas. With many of these existing protected areas experiencing ecological shifts due to climate change, there is a growing need to identify the places within wider regions that will help species cope with impacts of changing climatic conditions. In some cases, those places are those where the pressures of climate change are least pronounced, what are referred to as “climate refugia.” At other times, helping plants and wildlife cope involves aiding their movement across the landscape in response to climate shifts, by preserving the connectivity between critical habitats and other highly important areas. While many efforts have been made to assess the potential of different areas as climate refugia and corridors, these practices have usually been carried out looking at individual species or ecosystems at a relatively local scale. Unfortunately, many of the decisions to conserve new parts of the landscape occur across much broader regions that span a multitude of species and ecosystems, ranging from individual states to entire continents. As a consequence, assessing climate refugia and corridors on a case-by-case basis for every ecological feature is neither feasible nor an efficient use of the limited resources available for conservation. Additionally, when deciding which areas are best suited for protecting native species and ecosystems from the impacts of climate change, one cannot ignore the existence of the other prevalent threats to conservation, such as habitat loss or invasive species. In this thesis, I have explored methods for widely incorporating climate change into the complex process of identifying high priority areas for conservation across broad regions. As a case study for this work, I chose the Southern Rockies Landscape Conservation Cooperative, a collaborative public and private effort for conserving and managing the ecological characteristics of a distinct region spanning seven states in the US Intermountain West. After broadly measuring climate change impact and connectivity in a manner that was not tied to any particular species, I simulated climate refugia and corridors that simultaneously represented the ranges of 31 separate wildlife species. Though further research is needed to better understand the full suite of threats to species persistence, the means already exist for conservation decision makers to account for climate change in their actions. I believe that my work supports that decision making process, providing a framework for identifying areas that are most critical for aiding diverse species and ecosystems in their responses to the pressures of climate change.

Recent studies applying innovative technologies, such as genetic analysis and carbon dating, contradict the palynological based assumption that Scots pine (Pinus sylvestris) and Norway spruce (Picea abies) vanished from Fennoscandia during the Last Glacial Maximum (c. 20.000 yrs BP) and re-colonized after the cold Younger Dryas (c. 12.000 yrs BP). Instead, those studies indicate glacial survival of boreal trees in ‘cryptic’ refugia within Scandinavia, which is still heavily debated. In this report, I try to get a better grip on the discussion if Norway spruce and Scots pine survived Weichselian glacial periods in isolated ‘cryptic’ refugia within Scandinavia, or either re-colonized Fennoscandia by post-glacial migration from eastern areas such as Russia. To this aim, climatic settings are described and an overview is given on what is already known on the distribution of boreal trees during the Weichselian glaciations and the post-glacial landscape. Several records are important to detect ancient boreal trees: pollen, macrofossils and currently DNA. Macrofossils indicate early post-glacial tree growth in the central Scandes just after the Younger Dryas, aDNA indicates the existence of a ‘cryptic’ refugium on Andøya during the Last Glacial Maximum and modern DNA analysis possibly indicates isolation of spruce in western Norway, which are all contradicted by the current interpretation of low pollen percentages. Altogether, alternative hypotheses supporting glacial survival of plants might have been overlooked and pollen interpretations need revision, which could turn the exclusion from the past into supporting evidence for the glacial survival of P. abies and P. sylvestris in Scandinavia.

Spatiotemporal heterogeneity in predator activity can generate and influence the availability of refugia to prey. In eastern forests, white-footed mice (Peromyscus leucopus) and eastern chipmunks (Tamias striatus) are abundant generalist rodents, and large-scale removal experiments have confirmed they are important predators of gypsy moth (Lymantria dispar) pupae and songbird nests and eggs. Models predict the extinction of gypsy moth populations when confronted with abundant mouse populations, but small-scale (10s of m) heterogeneity in rodent activity may allow for the persistence of moth populations. I quantified the magnitude, variability, temporal persistence, and spatial structure of white-footed mouse and eastern chipmunk activity, and evaluated the effects of small-scale (30 x 30 m "spots") rodent removal, on 3 pairs of oak-dominated plots for 3, 2-week periods in summers 2008 and 2009 at the Cary Institute of Ecosystem Studies, Millbrook, NY, USA. Small-mammal track activity (1/check) was best fit by a beta-binomial distribution, and the mean and CV ranges of mouse and chipmunk track activity were similar between years. Disattenuated correlations of mouse and chipmunk activity were similar between sampling periods, as well as between years. I found little evidence of spatial structure in rodent activity at the scales sampled (15-250 m). Mean local track activity counterintuitively increased in removal spots compared to control spots for mice in 2008 and chipmunks in 2009. Local, between-year track activity was more strongly correlated and of greater magnitude in persistent removal spots than in non-persistent removal spots for both mice and chipmunks Environmental factors like abundant alternative food sources can influence predator foraging behavior by concentrating predator space use and altering predation rates on incidental prey items. However, the spatial scale of this aggregative effect, and impact on consumption rates on incidental prey items, are not well understood. In spring 2010, I conducted live-trapping, measured local rodent track activity, and quantified consumption rates on two incidental prey items (almonds [Prunus dulcis] and maple [Acer saccharum] seeds) on 6 plots provided with 3 supplemental food treatments (control, corn, and sunflower seeds) at Touch of Nature Environmental Center, Carbondale, IL, USA. A half-normal, cosine detectability function best fit our live-trapping data in both pre- and post-experiment trapping sessions, but considerable support remained for other models. Overall mean track activity was greater in control treatments than in sunflower and corn treatments. I found a significant interaction effect of treatment and distance, and significantly increased activity in control treatments at distances of 0, 10, and 40 m. Overall mean almond and maple seed consumption was greater in control treatments than in sunflower and corn treatments, but was greater in corn than sunflower treatments and increased from period 1 to period 3 at all distances. Mean almond consumption by mouse only and mouse + unknown predator groups was greater in control treatments than in sunflower and corn treatments. Mean maple seed consumption by mouse only and mouse + unknown predator groups was greater in control treatments than in sunflower and corn treatments.

Current species distribution in Europe was mainly influenced by massive climatic and environmental changes during the Quaternary period. Different theories concerning survival of tree species during the last ice age in Europe were proposed and up to date the position of glacial refugia and directions of migration routes are under active debate. My dissertation thesis aimed to combine information from fossil records and genetic analysis to improve knowledge on postglacial history of Alnus glutinosa and Alnus incana. The synthesis of palaeoecological data supports the idea that not only southern but also northern populations were important sources of postglacial Alnus expansion. The delayed Alnus expansion apparent in some regions was likely a result of environmental limitations. Our findings from molecular study showed differences in postglacial histories between temperate A. glutinosa and boreal A. incana. In the case of A. incana, we found an effective refugium in Central Europe located outside classical southern refugia confirming the existence of northern refugia for boreal trees in Europe. Fennoscandian populations are derived from Central-European ones that originated from populations in the Alps. For A. glutinosa, multiple southern refugia were revealed and three main directions of postglacial expansion were proposed: 1) from the northern part of the Iberian Peninsula to Western and Central Europe and subsequently to the British Isles, 2) from the Apennine Peninsula to the Alps, and 3) from the eastern part of the Balkan Peninsula to the Carpathians followed by expansion towards the Northern European plains. It has been shown that colonizing lineages have met several times and formed secondary contact zones with unexpectedly high population genetic diversity in Central Europe and Scandinavia. For the first time, we discovered tetraploid populations of A. glutinosa situated in the putative main glacial refugia on the Iberian and Balkan Peninsulas. Neither of them was probably involved in the colonization of Central and Northern Europe after glacial withdrawal. In conclusion, thanks to extensive population sampling, testing of hypothesis postulated based on fossil data by molecular data and using two molecular markers, i.e. chloroplast DNA and microsatellites, with different mode of inheritance and polymorphisms, this project revealed not only the position of glacial refugia of European tree species and discriminate between effective and non-effective ones, but also help infer the main migration routes. This approach enabled us to change some long-lasting paradigms and brought new pieces of knowledge about postglacial colonization of European tree species.