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21.
In Life Cycle Assessment (LCA), carbon dioxide (CO2) emissions from biomass combustion are traditionally assumed climate neutral if the bioenergy system is CO2 flux neutral, i.e. the quantity of CO2 released approximately equals the amount of CO2 sequestered in biomass. This convention is a plausible assumption for fast growing biomass species, but is inappropriate for slower growing biomass, like forests. In this case, the climate impact from biomass combustion can be potentially underestimated if CO2 emissions are ignored, or overestimated, if biogenic CO2 is considered equal to anthropogenic CO2. The estimation of the effective climate impact should take into account how the CO2 fluxes are distributed over time: the emission of CO2 from bioenergy approximately occurs at a single point in time, while the absorption by the new trees is spread over several decades. Our research target is to include this dynamic time dimension in unit-based impact analysis, using a boreal forest stand as case study. The boreal forest growth is modelled with an appropriate function, and is investigated under different forestry regimes (affecting the growth rate and the year of harvest). Specific atmospheric decay functions for biomass-derived CO2 are then elaborated for selected combinations of forest management options. The contribution to global warming is finally quantified using the GWPbio index as climate metric. Results estimates the effects of these practices on the characterization factor used for the global warming potential of CO2 from bioenergy, and point out the key role played by the selected time horizon. 相似文献
22.
地形环境因素对塔河林业局人为森林火灾发生的影响 总被引:1,自引:0,他引:1
应用1974年—2009年间人为火的空间地理坐标,结合研究地的基础地理信息及矢量化林相图,应用ArcGIS10.0中的空间分析工具和SPSS19.0的逻辑斯蒂回归模型深入分析地形环境因素对人为火发生的影响。研究结果表明"到铁路距离"对人为火的影响显著,其次,在1∶1和1∶3选取随机点条件下人为火发生分别与"优势树种"和"林型"显著相关。本文研究显示在运用"随机点"方法进行相关性分析时,随机点选取数量对模型拟合结果有一定影响。 相似文献
23.
Hudson’s Bay Company records were used to estimate the 1786–1911 annual number of moose (Alces alces andersonii) and caribou (Rangifer tarandus caribou) involved in trade by northern Ojibwa natives to the company post at Osnaburgh House (51°10′N 90°15′W) in northwest Ontario,
Canada. The human population for the early 19th century, and the number and severity of human starvations from 1786 to 1911
were estimated. The extent of forest fires in the region around Osnaburgh was documented using a “fire-day” index computed
from Hudson’s Bay Company journals and using qualitative archival information. It is argued that the human population was
too small to have caused the observed early 19th century moose and caribou population decline solely through predation. Likewise,
severe early 19th century famines were caused by climatic factors rather than by declines in moose and caribou numbers. Habitat
change caused by increased forest fires correlates with the observed decline of caribou, while moose increased and subsequently
collapsed as winter shelter was destroyed. A burgeoning human population, sustained during winter food shortages on potatoes
donated by the Hudson’s Bay Company, then kept ungulate populations to low levels until the late 19th century. Only then did
maturing forests and a new outbreak of fires provide renewed habitat for resurgences of, respectively, caribou and moose. 相似文献
24.
25.
Understanding the effects of climate change on boreal forests which hold about 7% of the global terrestrial biomass carbon is a major issue. An important mechanism in boreal tree species is acclimatization to seasonal variations in temperature (cold hardiness) to withstand low temperatures during winter. Temperature drops below the hardiness level may cause frost damage. Increased climate variability under global and regional warming might lead to more severe frost damage events, with consequences for tree individuals, populations and ecosystems. We assessed the potential future impacts of changing frost regimes on Norway spruce (Picea abies L. Karst.) in Sweden. A cold hardiness and frost damage model were incorporated within a dynamic ecosystem model, LPJ-GUESS. The frost tolerance of Norway spruce was calculated based on daily mean temperature fluctuations, corresponding to time and temperature dependent chemical reactions and cellular adjustments. The severity of frost damage was calculated as a growth-reducing factor when the minimum temperature was below the frost tolerance. The hardiness model was linked to the ecosystem model by reducing needle biomass and thereby growth according to the calculated severity of frost damage. A sensitivity analysis of the hardiness model revealed that the severity of frost events was significantly altered by variations in the hardening rate and dehardening rate during current climate conditions. The modelled occurrence and intensity of frost events was related to observed crown defoliation, indicating that 6-12% of the needle loss could be attributed to frost damage. When driving the combined ecosystem-hardiness model with future climate from a regional climate model (RCM), the results suggest a decreasing number and strength of extreme frost events particularly in northern Sweden and strongly increasing productivity for Norway spruce by the end of the 21st century as a result of longer growing seasons and increasing atmospheric CO2 concentrations. However, according to the model, frost damage might decrease the potential productivity by as much as 25% early in the century. 相似文献
26.
Keller WB Heneberry J Leduc J Gunn J Yan N 《Environmental monitoring and assessment》2006,115(1-3):419-431
We used multiple linear regression analysis to investigate relationships between late-summer epilimnion thickness, transparency, lake area, acidity and summer weather conditions in a large ($n = 116$) multi-year data set for 9 small Boreal Shield lakes. Dissolved organic carbon (DOC) was the best individual predictor of late summer epilimnion thickness ($r^{2} = 0.69$). Total chlorophyll~$a$, the number of days between ice-out and late-summer stratification, and lake area collectively explained an additional 14% of the variation in epilimnion thickness. The three attributes of summer weather that we examined, mean daily temperature, mean daily wind speed, and mean daily hours of bright sunshine, did not add to the predictive ability of our regression model. Lake acidity also did not add directly to the predictive ability of the model, likely because DOC concentrations already reflected the effects of pH. Our study supports an increasing body of evidence indicating that the dominant effects of climate change on lake thermal structure in small lakes will be through effects on processes that affect lake transparency. 相似文献
27.
Boreal forests in Sweden are exploited in a number of ways, including forestry and reindeer husbandry. In the winter, reindeer
feed mainly on lichens, and lichen-rich forests are a key resource in the herding system. Commercial forestry has mainly negative
effects on reindeer husbandry, and conflicts between these two industries have escalated over the last century. This article
reviews the effects of modern forest management practices on the winter resources available for reindeer husbandry. Forestry
affects reindeer husbandry at both the stand level and the landscape level and over various time scales. Clear-cutting, site
preparation, fertilization, short rotation times, and forest fragmentation have largely resulted in a reduced amount of ground
growing and arboreal lichens and restricted access to resource. This article also discusses alternative forestry practices
and approaches that could reduce the impacts of forestry on reindeer husbandry, both in the short and long term. 相似文献
28.
Arctic Climate Tipping Points 总被引:1,自引:0,他引:1
There is widespread concern that anthropogenic global warming will trigger Arctic climate tipping points. The Arctic has a
long history of natural, abrupt climate changes, which together with current observations and model projections, can help
us to identify which parts of the Arctic climate system might pass future tipping points. Here the climate tipping points
are defined, noting that not all of them involve bifurcations leading to irreversible change. Past abrupt climate changes
in the Arctic are briefly reviewed. Then, the current behaviour of a range of Arctic systems is summarised. Looking ahead,
a range of potential tipping phenomena are described. This leads to a revised and expanded list of potential Arctic climate
tipping elements, whose likelihood is assessed, in terms of how much warming will be required to tip them. Finally, the available
responses are considered, especially the prospects for avoiding Arctic climate tipping points. 相似文献
29.
Cumulative Industrial Activity Alters Lotic Fish Assemblages in Two Boreal Forest Watersheds of Alberta,Canada 总被引:1,自引:0,他引:1
We evaluated the cumulative effects of land use disturbance resulting from forest harvesting, and exploration and extraction
of oil and gas resources on the occurrence and structure of stream fish assemblages in the Kakwa and Simonette watersheds
in Alberta, Canada. Logistic regression models showed that the occurrence of numerically dominant species in both watersheds
was related to two metrics defining industrial activity (i.e., percent disturbance and road density), in addition to stream
wetted width, elevation, reach slope, and percent fines. Occurrences of bull trout, slimy sculpin, and white sucker were negatively
related to percent disturbance and that of Arctic grayling, and mountain whitefish were positively related to percent disturbance
and road density. Assessments of individual sites showed that 76% of the 74 and 46 test sites in the Kakwa and Simonette watersheds
were possibly impaired or impaired. Impaired sites in the Kakwa Watershed supported lower densities of bull trout, mountain
whitefish, and rainbow trout, but higher densities of Arctic grayling compared to appropriate reference sites. Impaired sites
in the Simonette Watershed supported lower densities of bull trout, but higher densities of lake chub compared to reference
sites. Our data suggest that current levels of land use disturbance alters the occurrence and structure of stream fish assemblages. 相似文献
30.
Haitao Wu Yongguang Yin Zhongsheng Zhang Xuehui Zhang Yuan Xin Yong Cai Xinbin Feng Shuxiao Wang Huan Zhong Ping Li 《环境科学学报(英文版)》2022,119(9):50-58
Soil macroinvertebrates as ecosystem engineers play significant, but largely ignored, roles in affecting mercury (Hg) cycle by altering soil physical-chemical properties. Ant is likely expanded into boreal mires with climate warming, however, its impacts on Hg cycle remained poorly understood. We compared total Hg (THg) and methylmercury (MeHg) contents in soils from antmounds (Lasius flavus) and the nearby ambient in a boreal mire in Northeast China. The present work seeks to unravel factors that controlling MeHg levels in case of ant appearance or absence. The average THg was 179 µg/kg in the ant mound and was 106.1 µg/kg in nearby soils, respectively. The average MeHg was 10.9 µg/kg in the ant mound and was 12.9 µg/kg in nearby soils, respectively. The ratios of MeHg to THg (%MeHg) were 7.61% in ant mounds and 16.75% in nearby soils, respectively. Ant colonization caused THg enrichment and MeHg depletion, and this change was obvious in the 10-20 cm depth soil layer where ants mainly inhabited. Spectrometry characteristics of soil dissolved organic matter (DOM) exert a stronger control than microorganisms on MeHg variation in soils. A structural equation model revealed that the molecular weight of DOM inhibited MeHg irrespective of ant presence or absence, while humification conducive to MeHg significantly in ant mound soils. Microorganisms mainly affected Hg methylation by altering the molecular weight and humification of DOM. We propose that the effects of ant colonization on MeHg rested on DOM feature variations caused by microorganisms in boreal mires. 相似文献