The effects of increased soil moisture on the timing of senescence of three plants grazed by Svalbard reindeer

Climate change is affecting the Arctic faster than anywhere else on the planet, with increases in temperature and precipitation predicted to have significant effects on Arctic ecosystems. Water availability is of key importance to plant growth in the Arctic, and the availability of grazing in the autumn is of particular importance to the winter survival of Arctic herbivores. Despite this, the effects of water availability on the senescence of plants in the Arctic is largely understudied. I experimentally tested how different levels of soil moisture impacted the senescence of a grass, an herb, and a shrub all commonly found on Svalbard, that are also important to the grazing of Svalbard reindeer. Increased soil moisture had a strong positive effect by delaying the timing of senescence of the grass in particular. Meanwhile, senescence was delayed for the herb and forb only under moderate increases in soil moisture, while high increases in soil moisture led to earlier senescence. Flooding events caused by heavy rainfall may have a strong negative impact on some species, such as the herb and forb, while species like the grass may be more resilient. These results indicate that a moderate increase in precipitation in the future may have a positive effect on the length of time with high quality forage available during the autumn, which may ameliorate the negative effects expected from increased icing events during the winter on Arctic herbivores such as the Svalbard reindeer

Experimentally testing the effect of increased temperature on senescence rate of three plant species utilized by the Svalbard reindeer

The Arctic is experiencing the most rapid climate warming on earth. While the climate induced changes in spring have received a lot of attention, similar studies for the effects in autumn have been neglected. In this thesis I experimentally investigate the effects that elevated temperatures and moisture levels in summer may have on the senescence rate of three of the most common foraging plants of the Svalbard reindeer. Open top chambers and heating ovens were used to manipulate the temperature and additional water was given to manipulate the soil moisture. I found that increased temperatures had a positive effect on all three species, while moisture only influenced Salix polaris. Onset of senescence was delayed for Alopecurus ovatus and Bistorta vivipara, and the rate of senescence was slowed for S. polaris and B. vivipara. The prolonged autumn with a greater amount of plant biomass could counteract the negative effects of harsh winters on the body mass of the Svalbard reindeer, and result in population growth. Thus, the future of the Svalbard reindeer and its foraging plants may be brighter than previously expected

Short-Term Impacts of the Air Temperature on Greening and Senescence in Alaskan Arctic Plant Tundra Habitats

Climate change is warming the temperatures and lengthening the Arctic growing season with potentially important effects on plant phenology. The ability of plant species to acclimate to changing climatic conditions will dictate the level to which their spatial coverage and habitat-type dominance is different in the future. While the effect of changes in temperature on phenology and species composition have been observed at the plot and at the regional scale, a systematic assessment at medium spatial scales using new noninvasive sensor techniques has not been performed yet. At four sites across the North Slope of Alaska, changes in the Normalized Difference Vegetation Index (NDVI) signal were observed by Mobile Instrumented Sensor Platforms (MISP) that are suspended over 50 m transects spanning local moisture gradients. The rates of greening (measured in June) and senescence (measured in August) in response to the air temperature was estimated by changes in NDVI measured as the difference between the NDVI on a specific date and three days later. In June, graminoid- and shrub-dominated habitats showed the greatest rates of NDVI increase in response to the high air temperatures, while forb- and lichen-dominated habitats were less responsive. In August, the NDVI was more responsive to variations in the daily average temperature than spring greening at all sites. For graminoid- and shrub-dominated habitats, we observed a delayed decrease of the NDVI, reflecting a prolonged growing season, in response to high August temperatures. Consequently, the annual C assimilation capacity of these habitats is increased, which in turn may be partially responsible for shrub expansion and further increases in net summer CO2 fixation. Strong interannual differences highlight that long-term and noninvasive measurements of such complex feedback mechanisms in arctic ecosystems are critical to fully articulate the net effects of climate variability and climate change on plant community and ecosystem processes

Short-term impacts of the air temperature on greening and senescence in Alaskan Arctic plant tundra habitats

Abstract Climate change is warming the temperatures and lengthening the Arctic growing season with potentially important effects on plant phenology. The ability of plant species to acclimate to changing climatic conditions will dictate the level to which their spatial coverage and habitat-type dominance is different in the future. While the effect of changes in temperature on phenology and species composition have been observed at the plot and at the regional scale, a systematic assessment at medium spatial scales using new noninvasive sensor techniques has not been performed yet. At four sites across the North Slope of Alaska, changes in the Normalized Difference Vegetation Index (NDVI) signal were observed by Mobile Instrumented Sensor Platforms (MISP) that are suspended over 50 m transects spanning local moisture gradients. The rates of greening (measured in June) and senescence (measured in August) in response to the air temperature was estimated by changes in NDVI measured as the difference between the NDVI on a specific date and three days later. In June, graminoid- and shrub-dominated habitats showed the greatest rates of NDVI increase in response to the high air temperatures, while forb- and lichen-dominated habitats were less responsive. In August, the NDVI was more responsive to variations in the daily average temperature than spring greening at all sites. For graminoid- and shrub-dominated habitats, we observed a delayed decrease of the NDVI, reflecting a prolonged growing season, in response to high August temperatures. Consequently, the annual C assimilation capacity of these habitats is increased, which in turn may be partially responsible for shrub expansion and further increases in net summer CO₂ fixation. Strong interannual differences highlight that long-term and noninvasive measurements of such complex feedback mechanisms in arctic ecosystems are critical to fully articulate the net effects of climate variability and climate change on plant community and ecosystem processes

Distribution of hunter groups and environmental effects on moose harvest in Interior Alaska

Thesis (M.S.) University of Alaska Fairbanks, 2018Moose (Alces alces) is one of the most valuable wild game resources in Interior Alaska. In recent years, residents of rural indigenous communities have expressed concern that climate change and competition from non-local hunters are challenging local moose harvest opportunities. I collaborated with wildlife agencies and village tribal councils to co-design two studies to address rural community hunter concerns. The first study assessed the spatial and temporal distribution of local and non-local hunter groups to examine areas of potential competition. The second study addressed changing environmental factors and their impacts on moose harvest. Although competition among local hunters or among non-local hunters certainly occurs, competition between local and non-local hunters, or between resident and non-resident hunters is a more common and reoccurring issue. Local hunters are those who hunt in the area in which they reside whereas non-local hunters travel away from the area they reside to hunt. I assessed hunting patterns by local and non-local hunters in a remote hunting region near the interior villages of Koyukuk and Nulato to quantify moose harvest overlap between these two user groups to assess potential competition. I used Alaska Department of Fish and Game (ADFG) moose harvest records to develop a relative competition index that identified locations and time periods within the hunting season where the greatest overlap occurred from 2000-2016. I determined that the highest competition occurred between 16-20 September (i.e., peak harvest period) and was concentrated predominantly along major rivers. To decrease overlap and mitigate potential competition between hunter groups we recommend providing information on competition hotspots to hunters, or lifting the no-fly regulation in the Koyukuk Controlled Use Area with the caveat that hunting with the use of aircraft must occur 1.6 km from the Koyukuk River corridor. These actions may provide hunters information on how to re-distribute themselves across the landscape and allow hunters to use areas away from rivers, where most harvest currently occurs. Additionally, climate change and seasonal variability have anecdotally been documented to impact moose hunting opportunities. Specifically, warm temperatures, delayed leaf drop, and fluctuating water levels are concerns expressed by some local hunters. I quantified changes in temperature, leaf drop, and water level near Koyukuk and Nulato and the subsequent relationships between these environmental variables and the total number of moose harvested using linear regression models. I used temperature data, gauging station data (i.e., water level), remote sensing data (i.e., leaf drop analysis), and ADFG moose harvest records and explored previously untested hypotheses and to quantify relationships from 2000-2016. I concluded that non-local hunter harvest success was more dependent than local harvest success on environmental conditions. Non-local harvest significantly increased with higher water levels from 6-10 Sept (p=0.02), 11-15 Sept (p=0.02), and 16-20 Sept (p<0.01), and decreased with warmer temperatures in the same three time periods (p<0.01, p=0.02, p<0.01, respectively). Local harvest increased with higher water levels from 16-20 Sept (p<0.01). These results quantitatively show that environmental factors do impact hunter success. I speculate that local hunter harvest success is less dependent on environmental variability because they have the ability to harvest opportunistically, rely more heavily on the resource, and reside near the hunting area. This ability to opportunistically hunt and adapt may give them an advantage over non-local hunters as environmental conditions shift with climate change.Chapter 1: Introduction -- Chapter 2: Assessing moose harvest patterns to address hunter competition -- Chapter 3: Quantifying effects of environmental factors on moose hunting success -- Chapter 4: Conclusion

Variation in Tundra Plant Traits Across a Latitudinal Gradient

High latitude regions are warming faster than most regions. Studies documenting change in plant cover due to warming have reported that graminoids, deciduous shrubs, and evergreen shrubs are increasing in some regions of the Arctic, but not at others. Mixed responses to warming have caused researchers to shift towards an emphasis on functional traits of individual species rather than their growth forms. This thesis focuses on ten measured plant functional traits for twelve arctic species at three regions spanning a latitudinal gradient in northern Alaska (Utqiaġvik, Atqasuk, and Toolik Lake). We compare mean trait values across the three regions for each species and find considerable variability within a growth form. Quantification of intraspecific variation (ITV) in the three populations showed high amounts of variation for some traits (\u3e50% for normalized difference vegetation index (NDVI) and photosynthetic capacity (Amax)) but not for other traits (\u3c15% for plant height, leaf area, specific leaf area (SLA), leaf thickness, and leaf dry matter content (LDMC)). Amount of ITV also varied across regions. To better understand why trends in plant cover and functional traits vary across regions, change in cover (measured three times from 2008 to 2018) was also compared with observed trait values (measured in 2018) for twelve dominant species. Canonical correspondence analysis (CCA) suggested a relationship between change in species cover and functional traits. Species increasing in cover were associated with photosynthetic capacity (Amax) and species decreasing in cover were associated with LDMC. Investigation of community-weighted trait means (CWM) showed that whole community rather than species-specific trait values may be more indicative of future change. CWM changed significantly over time for all traits at Utqiaġvik and Atqasuk, but not Toolik Lake. Non-significant results in direct cover-trait relationships also suggest that multiple traits rather than a single trait may be responsible for shifts in plant cover, supporting a multidimensional approach to future trait-based studies. Additionally, studies investigating the impact of warming on vegetation that incorporate ITV will be able to provide more accurate predictions for future change