主催：JST/CREST，Vrije University, ALTERRA, IBPC

No description available.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniversitet, 2005. / Härtill 5 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2006. / Härtill 6 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2008. / Härtill 4 uppsatser.

Thesis (M.S.)--Brigham Young University. Dept. of Integrative Biology, 2006. / Includes bibliographical references (p. 27-34).

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.

The aim of this study was to determine if the occurrence, thalli length and cover of the epiphytic lichens Alectoria sarmentosa, Bryoria capillaris and Usnea dasypogea differ between sites with inland and coastal climate in Norrbotten county, Sweden. The trunk and branch diameter of the Picea abies trees, on which the lichens were inventoried, were measured as well. B. capillaris was the most common lichen species in both habitats. B. capillaris and A. sarmentosa had significant higher percentage occurrence in inland sites, while the occurrence of U. dasypogea was higher in the coastal sites. For B. capillaris, the percentage cover per branch was also higher in inland than in coastal sites. No significant difference in thallus lengths were found for any species. Obtained climate data suggest that humidity is higher inland, which is favourable for B. capillaris. Litterateur suggest that of all studied species, B. capillaris is the most common species in colder climates while A. sarmentosa is an intermediate and U.dasypogea is a lichen species normally occurring in warmer climates, which might explain their observed occurrence pattern outcome of the study. Linear regression was executed as well where only A.sarmentosa had significant and positive relationships to branch diameter. Other studies support the correlation with branch diameter but not with trunk diameter.

Peatland ecosystems are important as natural climate regulators for their capacity to store carbon over long-time scales. Carbon cycling in peatlands in the boreal ecozone of Canada has been more widely studied than the boreal shield of Ontario, where peat depths are thinner and peatlands spatially smaller. The reliance on fill and spill hydrologic connectivity makes the water table dynamics of peatlands in Ontario’s Eastern Georgian Bay (EGB) region of the Ontario shield ecozone sensitive to rain and drought periods. The drying of wetlands in the EGB region decreases moss productivity and increases the ecosystem’s vulnerability to wildfire through an increase in the water table depth. In an effort to understand how peatlands respond to interannual climate variability and wildfire, we examined the role of regional climate patterns on growing season CO2 exchange from an Ontario shield peatland and completed a post-wildfire assessment of CO2 exchange patterns in a recently burned peatland for the first and second year post-wildfire. Using the eddy covariance technique, we analyzed 5-years of growing season CO2 exchange data from 2016 to 2020 from an unburned peatland and 2-years of growing season CO2 exchange data from a burned peatland (2019-2020) in EGB. Plot-scale CO2 exchange measurements were also completed within the burned peatland jointly with abiotic variables and vegetation community surveys. Water table depth was identified as an important variable to explain total summer CO2 uptake (GPP) and net ecosystem exchange (NEE), where years of considerable rainfall maintained a water table near the peat surface and perpetuated high vegetation productivity. Summer total ecosystem respiration (ER) was greatly influenced by preceding winter and spring air temperature, with warmer winter air temperatures leading to summers of increased total ER. Warmer winter air temperatures also initiated water flow across the landscape, thus reviving plant and microbial activity following snow cover. These findings have important implications for the function of these shallow Ontario shield peatlands in a warming climate, where decreased water availability with projected increased temperatures and evapotranspiration leaves peatlands at risk of a net loss of C over the summer with lower water table. In the burned landscape, there was lower GPP in the summer (2019) compared to the wet summer of 2020, however the burned landscape continued to act as a net CO2 sink for the summer season of both years. The rapid recovery of vegetation across the wildfire-disturbed landscape has important implications for the function of these peatlands over time, with the ability for continued carbon uptake and reinstating peat accumulation processes. / Thesis / Master of Science (MSc)

With widespread increases in air temperature, it is expected that the temperature of aquatic ecosystems will also increase, especially at high latitudes. Warmer streams and rivers could have severe, direct impacts on cold-adapted aquatic fauna but may also indirectly influence species by reducing the amount of suitable habitat. Yet, increases in air temperature alone ara potentially insufficient to cause stream warming, which is also influenced by a range of other factors that govern the energy balance of individual stream reaches. Here, I used long-term water temperature data from seven streams in the Krycklan Catchment Study (KCS) to ask whether there are recent trends in warming, and to evaluate how catchment properties regulate the sensitivity of streams to air temperature change during summer. Mann Kendall trend analysis at one headwater site showed that there has indeed been a warming trend in the KCS, but only during a brief time-window in early summer. Across, KCS sites, air temperature-water temperature regressions highlighted notable variation in the thermal sensitivity of streams depending on their catchment features. Finally, observations during extreme warm and dry years did not indicate strong responses in terms of stream temperature. In fact, extreme low-flow conditions seem to reduce the downstream propagation of warm lake water during these events. Collectively, my results suggest that ongoing climate changes in the boreal region have not had dramatic influences on stream temperature, although future changes occurring around the snowmelt season are likely.