基于仿真理论确定缓冲特性曲线方法的研究

本论文探索了一条确定缓冲特性方法的新途径，通过测定缓冲材料的静态特性与一次动态；中击数据为基础，建立数学模型，利用最小二乘法进行误差分析，并使用Madab/Simulink软件仿真出缓冲特性曲线。这种方法得出的缓冲特性曲线准确性高、试验周期短，待理论成熟必将成为今后缓冲材料特性测试的主要方法。     

Smallholder perceptions of agroforestry projects in Panama

The potential effects of agroforestry systems on conservation and development have been well documented. Panama has seen a substantial rise in the number of projects with an agroforestry component in the 1990s. There has been insufficient research on the actual impacts of these projects on smallholders and of farmers' attitudes towards these systems. This study explores the perceived socioeconomic and environmental impacts of five agroforestry projects in Panama. A total of 68 smallholders were administered semi-structured interviews. In addition, 13 agroforestry experts from NGOs, government departments and research institutes were interviewed, and their responses were compared with those of the smallholders. While the projects led to an increase in the standard of living by providing wood products and fruit for domestic consumption, farm income levels generally remained unchanged. This was due primarily to limited market development, the lack of marketing organizations and poor access roads. In terms of environmental impacts, the farmers' responses suggested a slight decline in slash-and-burn agriculture, and an increase in tree planting activities. Some environmental benefits were observed by farmers, including reduced soil erosion, increased soil fertility, and improved quality and quantity of water sources. Nevertheless, slash-and-burn agriculture was still the norm for the majority of farmers. Most farmers continued to harvest wood from primary and secondary growth to meet their domestic wood requirements, rather than relying on trees planted in agroforestry projects. The main obstacles preventing increased agroforestry adoption included insufficient agroforestry extension, inappropriate project design or management (such as top-down management approaches, and the use of food incentives), smallholders' economic constraints, and larger policy issues. Recommendations are proposed to improve project design and management, and to address the economic and policy constraints. This revised version was published online in June 2006 with corrections to the Cover Date.     

Impact of harvesting and logging slash on nitrogen and carbon dynamics in soils from upland spruce forests in northeastern Ontario

The potential impact of timber harvesting in the boreal forest on aquatic ecosystem water quality and productivity depends in part on the production of nutrients within the soil of the harvested catchment. Nitrogen supplied by organic matter decomposition is of particular interest because of the important role that N plays in biotic processes in surface waters, and in forest nutrition in general. Logging slash quality and input to the forest floor has the potential to influence N availability after harvest on clearcut sites. Net production of organic and inorganic-N and microbial biomass C and N concentrations were determined during a 90-day laboratory incubation at constant temperature and moisture. Incubated soils included F horizon and shallow mineral soil horizons (0-5 cm) from unharvested and full-tree harvested (2 and 12 growing seasons since harvest) boreal forest sites at the Esker Lakes Research Area (ELRA), in northeastern Ontario, Canada. In an ancillary experiment, black spruce foliage was added to unharvested forest floor material after 30 days during a 90-day laboratory incubation to simulate the influence of logging slash from full-tree harvesting on C and N dynamics. Twelve-year old clearcut F horizon material released on average 75 and 5 times more -N and 3 and 2 times as much inorganic-N than soil collected from unharvested and 2-year-old clearcuts, respectively. This increase in -N accumulation during the incubation was accompanied by decreases in both exchangeable -N and microbial biomass C and N levels. Net daily changes in microbial biomass N were significantly related to organic and inorganic-N accumulation or loss within the F horizon. Mineral soil release of inorganic-N was lower than release from the forest floor. Nitrate-nitrogen accumulation was lower, and -N accumulation was higher in mineral soil from unharvested sites when compared to 12-year-old clearcuts. Calculated harvest response ratios indicated that incubated mineral soil from the 12-year-old clearcut sites released significantly greater amounts of -N than 2-year-old clearcuts. Incorporation of black spruce needles into F horizon material reduced the production of organic and inorganic-N and increased microbial biomass N. Laboratory incubations of F horizon and shallow mineral soil from 12-year-old clearcuts suggested that these boreal soils have the capacity for increased inorganic-N production compared to uncut stands several years after harvesting. This has the potential to increase N availability to growing boreal forest plantations and increase N leaching due to greater -N levels in the forest soil.     

国外发展中国家水产养殖中的环境问题

对调查所获的亚洲、非洲和南美洲的20个国外发展中国家最常见的水产养殖状况、所产生的不利影响和急需的对策支持等数据进行了分析。结果显示,目前的养殖品种至少有90种,表现出较高的多样性。亚洲的水产养殖活动最为明显。除泰国外,所有国家的食粮型养殖品种均高于商业型养殖品种。水产养殖带来的对环境最主要的不利影响为废水污染、环境破坏、药物残留和亲苗掠夺;逃逸灾害、疾病扩散、饵鱼滥捕和生物误捕次之。为消除这些不利影响,这些发展中国家迫切需要在技术更新、科学研究、教育培训和政策扶持等对策方面得到有效的支持。     

Responses of cycads with different life histories to the impact of plant collecting: simulation models to determine important life history stages and population recovery times

Collection of plants and seeds from wild populations threatens a large number of cycad species. We investigated to what extent individual life history stages contribute to population growth (λ) and compared two species with major differences in life histories in the African genus Encephalartos: Encephalartos cycadifolius, a highly persistent grassland species that resprouts after fire, and Encephalartos villosus, a relatively fast growing, non-sprouting forest species. Several harvesting scenarios impacting different sized individuals were simulated to determine the sensitivity of the two functional types to harvesting. In both species λ was most sensitive to changes in abundance of adult plants. The harvesting of seeds had minimal impact on population growth rates, whereas harvesting of adult plants led to rapid population decline. This response from two very different functional types suggests that the conservation of adult plants is critical for all cycad species. Despite similar responses to adult mortality, the two species had substantially different population growth rates. This determined recovery time after harvesting of adult individuals. Encephalartos cycadifolius is typical of highly persistent plant species associated with low levels of recruitment and unable to recover from even small losses of adults within a reasonable conservation time frame (<100 years). Our results suggest that the ability to recover from loss of individuals is an important factor that should be considered when assessing the vulnerability of wild populations to threats.     

Grizzly bear response to human development and activities in the Bow River Watershed, Alberta, Canada

Few studies have reported the effects of multiple human activities on grizzly bears, Ursus arctos. We document the degree of grizzly bear response to various human developments as a function of multiple interacting variables based on observed median distances to roads, trails and development features in a landscape where human presence is widespread. Female grizzly bears remained further than males from paved roads regardless of habitat quality or time of day. Males were found closer to paved roads when within or adjacent to high quality habitat and during the period of least human activity. The combination of traffic volume and highway configuration, however, overrides a bear’s attraction to high quality habitats for high-speed, high-volume, highways. Avoidance of busy transportation corridors was strongest in the adult segment of the population. Bears were found closer to trails during the human inactive period when within high quality habitat and further from trails when distant to high quality habitat. Our data indicated an inverse relationship between the sexes in response to vehicles and traffic noise compared to the response to human settlement and encountering people. Female bears were found further away than males in relation to vehicles and traffic noise, yet found closer than males to human settlement and places where people may be encountered. Those males that were more willing to exploit high quality habitat near roads, did so at night and where hiding cover was present. Adult females were the most risk-averse cohort, choosing to avoid humans instead of seeking out high quality habitats. Adult female grizzly bears were influenced most by human activities and development. Management agencies must maintain access to high quality habitat, especially for adult females, and create new opportunities to support the reproductive potential of the population.     

Characterizing stand-replacing disturbance in western Alberta grizzly bear habitat, using a satellite-derived high temporal and spatial resolution change sequence

Timely and accurate mapping of anthropogenic and natural disturbance patterns can be used to better understand the nature of wildlife habitats, distributions and movements. One common approach to map forest disturbance is by using high spatial resolution satellite imagery, such as Landsat 5 Thematic Mapper (TM) or Landsat 7 Enhanced Thematic Mapper plus (ETM+) imagery acquired at a 30 m spatial resolution. However, the low revisit times of these sensors acts to limit the capability to accurately determine dates for a sequence of disturbance events, especially in regions where cloud contamination is a frequent occurrence. As wildlife habitat use can vary significantly seasonally, annual patterns of disturbance are often insufficient in assessing relationships between disturbance and foraging behaviour or movement patterns.The Spatial Temporal Adaptive Algorithm for mapping Reflectance Change (STAARCH) allows the generation of high-spatial (30 m) and -temporal (weekly or bi-weekly) resolution disturbance sequences using fusion of Landsat TM or ETM+ and Moderate Resolution Imaging Spectroradiometer (MODIS) imagery. The STAARCH algorithm is applied here to generate a disturbance sequence representing stand-replacing events (disturbances over 1 ha in area) for the period 2001-2008, over almost 6 million ha of grizzly bear habitat along the eastern slopes of the Rocky Mountains in Alberta. The STAARCH algorithm incorporates pairs of Landsat images to detect the spatial extent of disturbances; information from the bi-weekly MODIS composites is used in this study to assign a date of disturbance (DoD) to each detected disturbed area. Dates of estimated disturbances with areas over 5 ha are validated by comparison with a yearly Landsat-based change sequence, with producer's accuracies ranging between 15 and 85% (average overall accuracy 62%, kappa statistic of 0.54) depending on the size of the disturbance event. The spatial and temporal patterns of disturbances within the entire region and in smaller subsets, representative of the size of a grizzly bear annual home range, are then explored. Disturbance levels are shown to increase later in the growing season, with most disturbances occurring in late August and September. Individual events are generally small in area (<10 ha) except in the case of wildfires, with, on average, 0.4% of the total area disturbed each year. The application of STAARCH provides unique high temporal and spatial resolution disturbance information over an extensive area, with significant potential for improving understanding of wildlife habitat use.     

Growth effects of thinning damage in a Corsican pine (Pinus laricio Poiret) stand in central Italy

Damage to residual stand after partial harvesting or thinning may lead to serious economic losses in terms of both timber quality at the final harvest, and tree growth reduction. Logging damages and their effect on tree growth were studied in a long term experiment on Corsican pine in central Italy. Damage frequency, agent (felling, skidding), position (root damage, stem base, between 0.3 and 1 m a.g.l., >1 m a.g.l.) and severity (light, severe) and tree growth were measured after selective thinning from below and at 10 years after the treatment. In detail, we aimed at: monitoring mechanical damages to trees at the end of thinning and after 10 years; and assessing stand stability, growing stock, ring width and basal area at 10 years after the thinning. The thinning removed about 20% of volume, 38% of trees and 26% of basal area. The basal area decreased from 56 m² ha⁻¹ to 42 m² ha⁻¹ but after 10 years it increased again to 56 m² ha⁻¹. Immediately after thinning, 13.6% of the standing trees was damaged, out of these 36.17% showed severe injuries. Damages to standing trees were mainly due to skidding. Ten years after thinning, the percentage of damaged trees was about 17%, out of which 86.67% showed severe wounds. An increase of damaged trees and of trees with severe wounds was observed suggesting that a deeper knowledge on long-term effect of logging damages is needed. This study did not highlight any effect of logging damage on tree growth. In fact, no difference in ring width was recorded between damaged and undamaged trees.     

Testing a key assumption of wildlife buffer zones: is flight initiation distance a species-specific trait?

The distance at which animals flee an approaching predator is known as the ‘flight initiation distance’ (FID). Wildlife managers use FID to develop buffer zones to reduce human impacts on wildlife. Many variables have been demonstrated to influence FID leading one to question whether it can be viewed as a species-specific trait. We tested this critical assumption for developing buffer zones by experimentally approaching eight species of shorebirds found at six sites around Botany Bay, 15 km south of Sydney, Australia. Botany Bay encompasses a range of human impacted areas, from urban developments with high levels of human presence, through to National Parks and wildlife protection areas where human presence is significantly lower. We found that both species and site influenced the distance birds flew away from an approaching human. Importantly, however, there was no significant statistical interaction between site and species demonstrating that ‘flighty’ species were consistently flighty while more tolerant species were consistently tolerant. Taken together, these results suggest that FID can therefore be viewed as a species-specific trait for these shorebirds. The great variability in FID suggests that wildlife managers should be somewhat conservative in developing buffer zones, but they can use previously published FID data for a given species as guidelines for setting buffer zones.     

论道路建设的生态环境影响与生态道路建设

近20年来,我国道路建设取得了辉煌的成就,但在其建设水平和规模巨大提高的同时,道路建设对生态环境的不利甚至负面影响也在不断加深和扩大。从生态学的角度,综合分析了道路建设对生态环境的影响,即:(1)对土、水、气、声、热等无机环境的影响;(2)对植物、动物等生命系统的影响;(3)对景观格局、过程等的影响。在此基础上运用“生命周期”概念分析并提出建设生态道路应在规划设计、建设施工、道路运营等阶段分别采取相应措施,从而达到建设和谐生态道路的目的。