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Exotic species possess abilities to harm the ecosystems they invade. This study assesses the density, frequency and cover of exotic plants in roadside right-of-ways, logged areas and wildfire sites within mixedwood sections of the southern boreal forest of Saskatchewan. A total of 23 exotic species were observed including nine species of Gramineae, seven species of Leguminosae and five species of Compositae. Average density of exotic species in areas recently disturbed by timber harvesting or wildfire was 0.2 stems m−2 with a frequency of 72%. Exotic species adapted for wind dispersal were best represented including common dandelion (Taraxacum officinale), perennial sow thistle (Sonchus arvensis) and annual hawksbeard (Crepis tectorum). Only two exotic species, T. officinale and Canada bluegrass (Poa compressa), were observed in mature forest; both occurred with a frequency of 13% and an average density of 0.002 stems m−2. A total of 22 exotic species was found in the right-of-ways quadrats with an average density of 117 stems m−2 and a frequency of 94%. The most frequently observed exotic species in the roadside right-of-way areas were T. officinale, alsike clover (Trifolium hybridum), S. arvensis, creeping red fescue (Festuca rubra) and smooth brome grass (Bromus inermis). These species are either common agricultural weeds or were part of the original seed mixture used to establish a plant cover in the roadside right-of-ways. 相似文献
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Brian MilakovskyBrent R. Frey Mark S. Ashton Bruce C. LarsonOswald J. Schmitz 《Forest Ecology and Management》2011,261(3):440-446
The boreal mixedwood forest type of the Canadian interior boreal is largely comprised of two dominant tree species: white spruce and trembling aspen (Picea glauca and Populus tremuloides). This forest type is expansive, providing important ecosystem services and economic production, yet such mixtures are difficult to establish after harvests. While aspen resprouts and grows vigorously following disturbance, spruce growth is relatively slow and is often limited by intense competition from associated vegetation, including aspen. To improve management, it is important to understand how environmental and vegetative conditions vary in relation to the competitive-facilitative relationship of spruce-aspen mixtures. In this study white spruce was planted across large canopy openings to determine whether survival and height growth is influenced by position within gap and by differing levels of competing vegetation control of aspen and understory plants. In addition, we addressed the issue of herbivory, which can pose a significant threat to planted spruce seedlings. Within each of four sites, linear gaps were created and five gap positions were recognized spanning the southern and northern forest understories, and southern, center and northern positions within each opening. Three different levels of vegetation management were implemented: a brush saw treatment in which all vegetation was cut to ground level, a mixing treatment in which all vegetation and rootstock was ground up, and a control with no vegetation management. The three herbivory treatments excluded large ungulates, small herbivores (rabbits, hares) or had no herbivore exclusion. Growth and survival of white spruce seedlings were measured for four years (1997-2000). Understory survival was significantly lower than within the gap, with the sheltered southern edge position providing the best initial environmental conditions and or ameliorative cover for spruce establishment. However, after four years the shelter effect starts to be inhibitive relative to center and northern gap positions, suggesting the removal of the canopy is necessary before spruce productivity declines. The optimal vegetation management treatment also changed over the study period. The most intensive treatment (mixing) initially showed a negative influence on survival and growth, but by year four, survival converged to approximately 75% for all treatments, and the mixing treatment produced the best height growth. The growth advantage became most evident in the center gap positions, which initially lagged the brushsaw and control treatments. Lastly, some growth losses from herbivory must be expected in boreal mixedwoods, although not enough to merit control. Results have implications for the timing and intensity of silvicultural treatments for harvesting and planting. 相似文献
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Adoption of a new technology, such as irrigation, is a complex phenomenon. Several factors of economic and social nature contribute to the farm-level decisions affecting adoption. In this study, the role played by attitudes of potential adopters towards irrigation and its subsequent adoption on their farm unit was estimated. Two models were estimated, one incorporating only adopters' socio-economic characteristics, and the other, only their attitudes towards irrigation. Results suggest that adopters' attitude, particularly with respect to economic and environmental effects of irrigation, were significant determinants of their decision to proceed with adoption of irrigation, and have a role to play in adoption of irrigation over and above that explained by socio-economic characteristics. In particular, these results suggest that negative perceptions with respect to economics of irrigation and those related to its detrimental impacts on environmental quality, particularly through soil salinity, may be significant deterrents for adoption of irrigation. The study suggests that planning of large scale water development projects, particularly those involving irrigation, must be cognizant of attitudes of potential adopters. Furthermore, during the planning stages, more attention should be paid to the development of proper educational programs, as well as extension packages, to ensure that potential adopters formulate correct attitudes towards the new technology. 相似文献
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A public mail survey was sent to a sample of New Brunswick (NB) and Saskatchewan (SK) residents in 2007 to investigate their attitudes about controlling two very different forest pests: spruce budworm (SBW) (Choristoneura fumiferana) and forest tent caterpillar (FTC) (Malacosoma disstria). Participants were asked a series of questions related to their knowledge of these pests and their preferences over control options and program extents. SBW was the most widely known forest pest in NB, and FTC was most widely known in SK. Both groups largely supported (at over 80%) controlling future SBW and FTC outbreaks with biological control. They generally agreed that ecologically sensitive areas and wildlife habitat were the top priority that should be protected during the next outbreak of either pest. However, provincial differences in attitudes were found over the rank order of forest-type priorities that should be protected and the rank order of control options. Socio-demographic factors found to positively influence the preferred SBW and FTC control extent included those who had a high level of pest knowledge, those who had family members work in the forest industry, those who were residents in New Brunswick, those who were male, those who were aged 55 and over, those who had an education level beyond secondary school, and those who had household income of $50,000 or more. Results of this study can be used to assist policy makers and forest managers to arrive at publically acceptable pest control policies and make better informed decisions about future pest outbreaks. 相似文献
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Sublethal concentrations of the herbicide chlorpropham caused marked changes in a green alga and some cyanobacteria. Herbicide-treated cells of Chlamydomonas reinhardii were enlarged, contained numerous nuclei and starch bodies, and were surrounded by multilayered envelopes. The herbicide altered the pigmentation of Tolypothrix tenuis by disturbing the relative amounts of the phycobiliproteins c-phycoerythrin and c-phycocyanin. Photosynthesis in Anacystis nidulans and C. reinhardii was inhibited by chlorpropham and the herbicide also reduced the rate of nitrogen fixation by Anabaena cylindrica. 3-Chloroaniline, a metabolite of chlorpropham, was relatively nontoxic. 相似文献
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R. A. Sutherland 《Land Degradation \u0026amp; Development》1989,1(3):199-208
The principal objective of this investigation was to quantify erosion rates for five agricultural fields in three separate study areas in Saskatchewan. The radionuclide tracer caesium-137 (137Cs) was used to quantify net erosion and net deposition within the landscape over a 30-year period. Uneroded (native) sites were used to establish the mean background level of 137Cs in each of the study areas. The assumption being that agricultural sites with 137Cs areal activities greater than the native site were subject to deposition, and sites with 137Cs less than the native control site were subject to erosion. A linear proportionality model was used to convert the loss or gain of 137Cs to net soil erosion or deposition. Results have indicated that accelerated (anthropogenic) erosion has been commonplace on arable land in Saskatchewan, even on near-level fields (< 1.3 degrees). The net integrated sediment output from the five agricultural fields ranged from — 0.6 t th−1 y−1 to — 6.8 t ha−1 y−1 (where negative values represent erosion). What is more alarming is that between 40 and 75 per cent of all sites sampled within individual fields had erosion rates in excess of the generally accepted rate of soil formation (1.0 t ha−1 y−1). Also, in one highly eroded field (Crystal Springs medium sloping site) 65 per cent of the sites sampled exceeded the upper tolerable erosion rate of 11.0 t ha−1 y−1. These results indicate significant degradation of the non-renewable soil resource has occurred over the past 30 years and is still presently active. Land degradation by accelerated erosion would result in reductions in effective rooting depth, soil moisture holding capacity, essential nutrient stores, and would adversely effect the physical structure of the topsoil. The major reason for accelerated erosion on arable land in Saskatchewan is the practice of summer fallowing, where the field is left in a ‘bare’ state and repeatedly tilled every second or third year. During a fallow period, or prior to crop emergence during a cropping year, fields are subject to wind and water erosion. On near-level fields wind would be the dominant transport agent, while on sloping fields inter-rill and rill erosion would be the primary forces of erosion. It is suggested that the appropriate conservation farming response would be to increase application of surface mulches and possibly to decrease the frequency of summer fallowing. Without such efforts long-term sustainable agricultural production in the Prairies of Canada is considered to be a tenuous land use practice. 相似文献
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