Recent growth declines and mortality of trembling aspen throughout western Canada and the United States have been linked to drought, often interacting with outbreaks of insects and fungal pathogens, resulting in a “sudden aspen decline” throughout much of aspen’s range. In 2015, we noticed an aggressive fungal canker causing widespread mortality of aspen throughout interior Alaska and began a study to quantify potential drivers for the incidence, virulence, and distribution of the disease. Stand-level infection rates among 88 study sites distributed across 6 Alaska ecoregions ranged from <1 to 69%, with the proportion of trees with canker that were dead averaging 70% across all sites. The disease is most prevalent north of the Alaska Range within the Tanana-Kuskokwim ecoregion. Modeling canker probability as a function of ecoregion, stand structure, landscape position, and climate revealed that smaller-diameter trees in older stands with greater aspen basal area have the highest canker incidence and mortality, while younger trees in younger stands appear virtually immune to the disease. Sites with higher summer vapor pressure deficits had significantly higher levels of canker infection and mortality. We suspect the combined effects of this novel fungal canker pathogen, drought, and the persistent aspen leaf-miner outbreak are triggering feedbacks between carbon starvation and hydraulic failure that are ultimately driving widespread mortality. Warmer early-season temperatures and prolonged late summer drought are leading to larger and more severe wildfires throughout interior Alaska that are favoring a shift from black spruce to forests dominated by Alaska paper birch and aspen. Widespread aspen mortality fostered by this rapidly spreading pathogen has significant implications for successional dynamics, ecosystem function, and feedbacks to disturbance regimes, particularly on sites too dry for Alaska paper birch.

Bark beetle epidemics are one of the main causes of natural disturbances in temperate and boreal forests causing increasing economic losses. Our study aimed to unravel the drivers of the European spruce bark beetle (Ips typographus, L.) infestation patterns in the High Tatra Mts. in Central Europe over time. Such epidemics affect resilience of forest ecosystems. Our study area was a non-intervention part of a National park. We used habitat suitability modelling (HSM) to identify environmental variables predicting the occurrence of the “bark beetle infestation spots”, i.e. group of trees identified by remote sensing as tree death caused by bark beetle infestations. We used a 10-years long dataset on bark beetle induced Norway spruce (Picea abies, Karst.) tree mortality derived from Landsat satellite images as response variable. Three variables related to climate characteristics of the area were tested yet; these being mean air temperature, maximum air temperature and potential solar radiation.

We applied several modeling methods, such as surface range envelop (SRE), classification tree (CT), random forests (RF), multiple adaptive regression splines (MARS) and flexible discriminant analysis (FDA). We used ROC-value (receiver operating characteristic) to assess model performances. ROC ranges from 0 and 1, where ROC value of 0.5 indicates no discriminative value. Our ROCs values reached 0.54 (SRE), 0.7 (CT), 0.69 (RF), 0.72 (MARS) and 0.71 (FDA) indicating ecological significance of the air temperature and solar radiation on bark beetle infestation pattern over time. We conclude that CT, MARS and FDA model should be applied in future studies to predict the patterns of bark beetle infestations and improving accuracy of the bark beetle infestation risks. For the future, we plan to include more explanatory variables related to local geography, forest stand characteristics and create ensemble models for supporting decision making regarding natural disturbances in forestry and nature conservation.

The experiment aims to quantify the influence of environmental factors on the spread of spruce bark beetles in Šumava National Park (South Bohemian regions of the Czech Republic). The main question to be solved is that the factors threatening the role in the spreading of bark beetles? The partial question does it affect individual factors related to different gradations? The selection of the host tree and the propagation of the outbreaks of the attack will be evaluated back based on the tree map entries. To do so, we used available aerial photographs of terrestrial measurements. Part of the project also is the determination of the population density of the bark beetles in the redeveloped stands. Evaluation of the spruce bark beetles population will take place upon the unexpected takeover of passive traps by monitoring of infested trees. In selected areas with the wind fallen trees, the rate of occupation of tree trunks by spruce bark beetles and the calculation of successfully developed individuals will be evaluated. We found out that with the speed of the wind 2m/s is hard for the bark beetles to fly against it.

Plants with persistent fleshy fruits provide a crucial source of high quality food for frugivores in fall and winter. Earlier springs, warmer summers, and extended fall seasons may lead to earlier fruit ripening and increasing fruit loss to frugivores and decomposers in early fall, resulting in reduced availability to late fall, winter, and spring frugivores. Participants in the Winterberry citizen science network tracked fruit retention for Rosa acicularis, Viburnum edule, Vaccinium vitis-idaea and Empetrum nigrum. We used data collected at 45 sites across Alaska in 2016 – 2020 to determine the potential for rapid changes in cold season fruit availability. Observers tracked at least 100 fruits on 20 plants on a weekly basis starting in August or September until the ground was covered in snow and again following snow melt. The data show three potential sources of vulnerability for frugivores that depend on persistent fruits. First, absolute fruit loss rates (# per day) declined throughout the fall while relative loss rates (% per day) were constant for most species; individual fruits represent a constant value to plants but supply rates to frugivores decline throughout fall. A 3-week advance in fruit ripening is predicted to reduce % fruits remaining at the time of season-long snow fall by approx. 50% in the intermontane boreal ecoregion for all four species. Second, there was high interannual and spatial variation in the % fruits that were rotten or dehydrated ("unhealthy"); for example, for Rosa in interior Alaska this ranged from <50% to 100% by early October. Third, although V. vitis-idaea and E. nigrum had low % unhealthy fruits, this was because unhealthy fruits dropped from the plants more quickly than in the other two species. These results suggest that decomposers will play a major in controlling this food source under continuing climate change.

The circulation of the atmo -, hydro-and lithosphere on Earth leads to the formation of a single space in which all components are interconnected through different connections. Underground space is not an exception, since, natural objects and artifacts that have been evolving for a long time, isolated, can be buried in them. When a dungeon is destroyed, these components can enter terrestrial ecosystems and have a negative / positive impact. The underground space is also constantly affected by terrestrial ecosystems. Forest ecosystems are no exception. Soil, as part of forest ecosystems, can be a source of various chemical elements, microorganisms. Microorganisms and micro-and macronutrients with soil particles on the shoes of tourists are transferred to the cave. The need to monitor the properties of the underground space and assess their changes against the background of anthropogenic impact makes the research relevant. The work was done in the Northern part of the Ladoga region of Karelia (61056`45, 30034`49). The work was carried out within the framework of the EU Project "Baltic Sea Underground Innovation Network" (BSUIN). One of the objectives of the study was to establish the chemical composition of the soils adjacent to the underground space and the soils in the cave. Micro-and macroelements were determined in the selected soil and soil samples. The research was carried out using the equipment of the Core Facility of the Karelian Research Centre of the Russian Academy of Sciences. The results showed a higher content of micro-and macronutrients in the soils located near the cave, compared to the soils of Karelia. The cave soils have a low content of C, N, P, and K compared to the soils of terrestrial ecosystems. The distribution of elements in the cave shows a gradient of change from the entrance to the central part.

Individuals living at the edge of a species' range are approaching the limit of conditions that allow species to persist. Both biotic and abiotic factors can limit a species' success at the range boundary. By experiencing strong limiting factors, populations inhabiting boundary edges may experience greater variability in survival and reproduction. Highly adaptable, North American red squirrels (Tamiasciurus hudsonicus) exploit a variety of food sources and shelters across their habitat. Due to their nature of caching food in underground middens and being the only squirrel species inhabiting the northern treeline, red squirrels fill an essential niche as seed predators and dispersal agents at the edge of the boreal forest. The treeline, separating the boreal forest from the tundra, defines the northern range boundary for red squirrels. The area is heavily fragmented, with low fragmentation areas in the continuous forest extending to high fragmentation regions at the treeline. Additionally, at high latitudes, the treeline is exposed to extremely low winter temperatures. However, increased winter temperatures and lengthened growing seasons resulting from climate change are altering the vegetation at the treeline and on the tundra. My research will focus on the red squirrel population inhabiting the treeline near Churchill, MB, and will explore the population dynamics and limitations that squirrels face living at the subarctic edge of their habitat. I will assess food availability and squirrel diet through seed density and cone production estimates, and stable isotope analysis. Additionally, I will examine the importance of squirrels as a prey species at the treeline, by placing camera traps at middens, and through stable isotope analysis of diets of known squirrel predators. As the growing season in the subarctic increases, understanding the limiting factors for squirrel populations at the treeline will predict future shifts in range sizes and population dynamics.

Wildfires act as extreme disturbance events that create landscape-level changes. As a result of climate change, the frequency and severity of wildfires are increasing across the boreal forest, leading to conversions of coniferous forest to deciduous. Shifts in forest type and associated below-ground microbial processes have important implications at the ecosystem and global scales. Boreal forest soils house an estimated 25% of forest vegetation carbon and 60% of forest below-ground carbon stocks. Therefore changes in forest type have the potential to affect global carbon balances. Post-fire plant recruitment and productivity play key roles in successional trajectories, yet the mechanisms underlying plant succession, particularly microbial processes, are not well understood. Captured within the Bonanza Creek LTER regional site network is a widely distributed and well-characterized series of sites that facilitate long-term studies of successional dynamics following fires of differing severity. Changes in below-ground microbial community structure post-fire have not been determined. For this study, we sampled soil microbial communities spanning three successional stages (11-14 yr, 40-60 yr, and >80 yr) post fire. We collected a total of 250 soil cores from 25 sites capturing both within-site variation and variation between successional stage.We tested if microbial community composition changed significantly across successional stages post fire using 16S rRNA gene amplicons. Furthermore we identified how changes associated with soil moisture and forest stand types post-fire. Soil moisture affected microbial community composition across the sampled sites. Increased time post fire was linked to increased heterogeneity of microbial community composition. Using co-occurrence networks, we are identifying particular microbial taxa that are more commonly associated with early or late successional sites, plant species, and soil moisture content. This study provides a better understanding of how increased fire frequency may affect the dynamic relationship between below-ground microbial and plant communities.

Climate change impacts are particularly prevalent in the Arctic where warming is occurring at an accelerated rate. Shifts in air temperature and precipitation patterns have altered hydrology that directly impact fish species with life history strategies synchronized with long-term timing of seasonal flow events. Juvenile and adult Arctic Grayling (Thymallus arcticus) rely on environmental cues to access seasonal rearing habitats (e.g., headwaters) necessary to complete their life histories. Headwater streams are strongly linked to the surrounding landscape, thus susceptible to climatic variability (e.g., snowmelt timing, precipitation) and disturbance (e.g., fire, flood, drought), and comprise 70-80% of the total stream length within a river network. With the imminent threat of climate change, the goal of our study is to better understand the extent tributary watersheds contribute to fish population viability and structure in boreal riverscapes via long-term population monitoring. During the summer 2020 pilot season, we determined the longitudinal distribution, quantified size and age structure, and evaluated movement and migratory patterns of Arctic Grayling in the Caribou-Poker Creek Watershed (CPCW), a small tributary to the Chatanika River. A temporary PIT antenna was installed near the tributary-mainstem confluence, and we sampled throughout the study watershed (~10 km) using hook and line sampling. We PIT tagged, measured, weighed, and conducted bioelectrical impedance analysis (a measure of body condition) on all fish, and otoliths were collected from a subset of size classes to quantify age and growth. We caught 175 grayling that ranged from 69-380 mm FL, and recaptured 16 individuals. Fish were observed passing over the PIT antenna as late as October 2020. We will build upon these preliminary data via continued monitoring to evaluate relationships among movement patterns, demographics, and hydrology within the CPCW. Our study will advance the current understanding of Arctic Grayling life history and habitat use, allowing managers to adapt and prioritize habitat conservation needs.

Wildfire is the primary natural disturbance in boreal forest stream ecosystems and fires are expected to continue to increase in duration and frequency owing to climate change. Wildfire has been shown to have positive (e.g., increased nutrients) and negative (e.g., increased sedimentation) impacts on stream ecosystems. Increased productivity as a result of recent fire may lead to more complex aquatic communities owing to higher food resource availability. As a result, fire may play a key role in determining macroinvertebrate and fish assemblages in boreal streams, but complex interactions make it challenging to quantify these effects. During summer 2019, we investigated community responses to wildfire at 26 spatially-balanced sites on wadeable streams in interior Alaska with varying time since fire disturbance (recent: 0-10 years, historic: 10-30, control: 40+). At each site, we measured physical habitat (e.g., fine sediment, riparian canopy cover, bank stability) and water chemistry, quantified macroinvertebrate and fish assemblage structure, determined fish mass-abundance relationships, and assessed aquatic food webs via stable isotope analysis. Fish community assemblages were relatively simple, with no more than five species detected per site. Mean species diversity, overall fish density, and mean fish biomass were higher at recently burned sites relative to control or historic sites. Analysis of habitat characteristics revealed that recently burned sites had more woody debris, less percent fines, lower mean percent canopy cover, and warmer water temperatures than control and historic sites. Preliminary stable isotope data reveal that streams that recently experienced wildfire have a wider carbon breadth and longer food chain length than control streams. Knowledge of how aquatic community and food web structure relate to variables associated with fire disturbance may promote a better understanding of how climate change and fire interact to impact boreal stream ecosystems and provide insight into community-wide responses to wildfire.

Yukon's Northern Boreal valley bottoms are under growing pressures from resource development and climate change. Mineral extraction of previously intact forested areas has expanded across central Yukon in recent decades, resulting in an increasing footprint caused by placer and hard rock mining, and roads. In addition, northern Canada is particularly vulnerable to the effects of climate change due to changing wildfire regimes, permafrost thaw, warming temperatures, and increased precipitation, which are projected to alter terrestrial and aquatic ecosystems. These stressors are often studied individually and at local scales, but the cumulative effects of these co-occurring disturbances on wildlife populations, community structure, and habitat quality are not well understood, particularly in northern contexts. We therefore investigated cumulative effects of resource development and climate stressors on water quality in salmon spawning habitat and other fish-bearing rivers in central Yukon, Canada. Specifically, we investigated additive and interactive effects between climate associated disturbances such as changing wildfire activity, temperature, precipitation patterns and permafrost thaw, and human associated land disturbances such as mining and linear features on water quality. Water quality characteristics including turbidity, suspended solids, dissolved oxygen, and organic carbon content, can impact egg, larvae, and juvenile salmon survival and fish recruitment. Understanding effects of individual and multiple stressors, and how they combine to influence wildlife and habitat is an important, yet understudied topic in the natural environment due to challenges in collecting broad-scale spatial and temporal monitoring data, particularly in northern regions. We provide some of the first results to date of cumulative effects assessment whilst considering climate change drivers in Yukon. Such results can be used to construct patterns of disturbance thresholds for compliance monitoring and land use planning and can provide important insight for sustaining the development of other northern boreal systems and the protection of aquatic ecosystems under climate change.