Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2001. / Härtill 4 uppsatser.

Diss. (sammanfattning) Umeå : Sveriges lantbruksuniv., 2001. / Härtill 4 uppsatser.

Area burned in boreal forests is increasing due to climate change effects and regional increases in fuels due to a history of successful fire suppression. An increase in area burned threatens valuable resources and infrastructure in timber resources areas and communities. The ecological integrity of protected areas may also be threatened if fires increase in frequency and size beyond what would have occurred prior to effective fire suppression and the effects of climate change. Fuel management is one strategy being tested by fire management agencies and researchers to address these concerns. However the pattern of fuel management that best regulates area burned has yet to be determined. This thesis investigates random fragmentation of highly flammable fuels in the boreal forests of North-western Ontario. A case study of Quetico Provincial Park is used. Using the fire growth simulation model, Prometheus, I tested whether, under extreme fire behaviour conditions, fuel isolation (FI) and fuel conversion (FC) were effective at reducing average area burned in the park. Through the simulation of over 21,000 large fires, I determined that FI and FC are effective in significantly reducing area burned for this case study. Based on these findings, random FI and FC should be studied further on a regional basis and as a prescriptive, proactive method of reducing area burned in boreal forests.

Area burned in boreal forests is increasing due to climate change effects and regional increases in fuels due to a history of successful fire suppression. An increase in area burned threatens valuable resources and infrastructure in timber resources areas and communities. The ecological integrity of protected areas may also be threatened if fires increase in frequency and size beyond what would have occurred prior to effective fire suppression and the effects of climate change. Fuel management is one strategy being tested by fire management agencies and researchers to address these concerns. However the pattern of fuel management that best regulates area burned has yet to be determined. This thesis investigates random fragmentation of highly flammable fuels in the boreal forests of North-western Ontario. A case study of Quetico Provincial Park is used. Using the fire growth simulation model, Prometheus, I tested whether, under extreme fire behaviour conditions, fuel isolation (FI) and fuel conversion (FC) were effective at reducing average area burned in the park. Through the simulation of over 21,000 large fires, I determined that FI and FC are effective in significantly reducing area burned for this case study. Based on these findings, random FI and FC should be studied further on a regional basis and as a prescriptive, proactive method of reducing area burned in boreal forests.

Forests play an important role in the net ecosystem exchange of CO2 in terrestrial ecosystems. Soil respiration is often the major source of CO2 in forests and is greatly influenced by climatic variability and management practices. Spatial and temporal variations of soil respiration have been examined in a chronosequence (60, 30, 15, and 1 year-old) of temperate, afforested, white pine (Pinus strobus) forest stands in Southern Ontario, Canada, in order to investigate any age related differences. Spatial and temporal variations of soil respiration in a 74 year-old boreal, mixed-wood forest in Central Ontario, was also studied and compared with results from the 60 year-old, temperate, white pine, forest stand, in order to investigate any climate related differences. Soil CO2 flux, temperature, and moisture were measured for one year (June 2003 to May 2004, inclusive, for the chronosequence study, and August 2003 to July 2004, inclusive, for the boreal-temperate study). In all stands, temporal variability of soil respiration followed the seasonal pattern of soil temperature, reaching a minimum in winter and maximum in summer. Temporal variability of soil temperature was able to explain 80 to 96% of the temporal variability in soil respiration at all stands. Spatial variability in soil respiration was also observed at all stands and the degree of this variability was seasonal, following the seasonal trend of mean daily soil respiration. Spatial variability of some soil chemical properties was highly correlated with the spatial variability of soil respiration, while litter thickness was not. The location of soil respiration measurement with respect to tree trunks may also help to explain some of the spatial variability in soil respiration. Across the chronosequence, the highest mean daily CO2 efflux was observed during the growing season for the 15 year-old-stand (5.2 ± 1.3 to 0.4 ± 0.2 μmol CO2 m^-2 s^-1), which was comparable to the 60 year-old-stand (4.9 ± 1.3 to 0.2 ±0.1 μmol CO2 m^-2 s^-1), but higher than the 30 year (3.8 ± 0.9 to 0.2 ± 0.0 μmol CO2 m^-2 s^-1) and 1 year (2.9 ± 0.9 to 0.3 ± 0.3 μmol CO2 m^-2 s^-1) old stands. From boreal-temperate comparison, it was observed that mean daily soil respiration rates for the boreal stand (6.9 ± 1.7 to 0.5 ±0.1 μmol CO2 m^-2 s^-1) were higher during the growing season compared to the 60 year-old temperate forest stand. Understanding temporal and spatial variability of soil respiration and how it is controlled is essential to improving forest ecosystem carbon budget assessments, and subsequently, the global carbon budget. This study will contribute direct observations necessary for improving and validating forest ecosystem CO2 exchange models. / Thesis / Master of Science (MSc)

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.

京都大学 / 新制・課程博士 / 博士(地球環境学) / 甲第24059号 / 地環博第222号 / 新制||地環||42(附属図書館) / 京都大学大学院地球環境学舎地球環境学専攻 / (主査)准教授 岡田 直紀, 教授 柴田 昌三, 教授 德地 直子 / 学位規則第4条第1項該当 / Doctor of Global Environmental Studies / Kyoto University / DGAM

An example of watershed disturbance activity undertaken to gain access to the oil sands is large scale mining in the Athabasca basin, Alberta, Canada. One of the remedial activities of this disturbance is the reclamation of the disturbed lands. In the process of reclamation, the overburden soil is placed back into the mined pits and reformed with soil covers (alternatively called reconstructed watersheds). In the design process of reclamation, a major concern is hydrological sustainability, which includes the soils ability to store enough moisture for the water requirements of vegetation growth and land-atmospheric moisture fluxes. Typically, the goal of the reclamation is to restore the disturbed watersheds, so that they mimic the natural watersheds in terms of the ecological sustainability. Therefore, a comparative evaluation of the hydrological sustainability of the reconstructed watersheds with natural watersheds is required.<p>The considered reconstructed watershed in this study (the flat top of the South Bison Hill, Fort McMurray, Alberta, which is about 6 years old) constitutes a thin layer of a peat-mineral mix (20 cm thick) overlying an 80 cm thick secondary (glacial till) layer on the shale formation, mimicking the natural soil horizons of undisturbed watersheds. As the reconstructed watershed is located in the boreal forest region, a mature boreal forest (Old Aspen site, about 88 years old) located in the Southern Study Area (SSA), BOREAS, Saskatchewan, Canada, is considered as a representative of natural watershed. The A-horizon with 25 cm of sandy loam texture, the B-horizon with 45 cm-thick sandy clay loam, and the C-horizon with 40 cm of a mixture of sandy clay loam and loam are considered in this study.<p>An existing System Dynamics Watershed (SDW) model (lumped and site-specific) is modified and adapted to model the hydrological processes of the reconstructed and natural watersheds, such as soil moisture, evapotranspiration, and runoff. The models are calibrated and validated on daily time scale using two years data (growing season) in each case. The hydrological processes are simulated reasonably well despite the high complexity involved in the processes of soil moisture dynamics and the evapotranspiration, for both study areas. Using the modified and calibrated models, long term simulations (48 years) are carried out on both the reconstructed and natural watersheds. Vegetation properties are switched between the reconstructed and natural watersheds and two scenarios are generated. Consequently, long term simulations are performed. With the help of a probabilistic approach, the daily soil moisture results are used to address the comparative soil moisture storage capability of the watersheds.<p>The results indicate that the selected reconstructed watershed is able to provide its designed store-and-release moisture of 160 mm (a requirement of the land capability classification for forest ecosystems in the oil sands) for the vegetation and meteorological moisture demands at a non-exceedance probability of 93%. The comparative study shows that the reconstructed watershed provides less moisture for evapotranspiration requirements than the natural watershed. The reconstructed watershed is able to provide less moisture than the natural watershed for both small and also mature vegetation scenarios. A possible reason for this may be that the reconstructed site is still in the process of restoration and that it may take a few more years to get closer to natural watersheds in terms of the hydrological sustainability. The study also demonstrates the utility of the system dynamics approach of modeling the case study under consideration. The future addition of a vegetation growth model to the hydrological model, and the development of a generic watershed modeling technique would be helpful in decision making and management practices of watershed reclamation.