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101.
102.
The timing of forestry operations relative to weather conditions is a consideration in applying Forestry Best Management Practices (BMPs). Harvesting during different seasons can result in degrees of soil disturbance, the distribution of logging debris, and potentially future stand productivity. The purpose of this study is to examine the response of loblolly pine (Pinus taeda L.) stands after wet- and dry-weather harvesting combined with three site preparation treatments. A 20 × 20 meter grid was established in fifteen 20-year-old, 3.3-ha loblolly pine plantations in South Carolina. A census of soil physical disturbance and slash distribution was made after harvesting. Growth was measured on 1/125th-ha plots at ages two and five. Dry-weather harvested (DWH) sites were 91% undisturbed, and 9% compressed. Wet-weather harvested (WWH) sites were 41% undisturbed, and 59% disturbed. WWH sites averaged 9% bare soil, while DWH sites averaged 16% with 1 kg m-2 less logging residue; primarily in the form of heavy and light slash. At age five, the green-weight biomass of flat-planted DWH and WWH sites were 13.3 and 12.6 kg tree-1 respectively, and on the bedded DWH and WWH sites were 18.6 and 22.8 kg tree-1. Wet weather harvesting did not seem to adversely affect stand growth, and may have improved it. Due to a prolonged drought, bedding had a larger effect on WWH sites than DWH harvested sites. The effects of droughty conditions may be influencing treatment response on these highly productive sites; however, the long-term effects of harvesting on stand growth remain to be seen.  相似文献   
103.
LANDSCAPE DEVELOPMENT INTENSITY INDEX   总被引:12,自引:0,他引:12  
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104.
The purpose of this study was to design and test a monitoring protocol for marine waterfowl in the central Alaskan Beaufort Sea. The study provides an important case-study of how a long-term monitoring program may be affected by unanticipated human disturbances.Because of its overwhelming and widespread abundance, relatively sedentary behavior, ease in counting, and the extensive historical database, the long-tailed duck (Clangula hyemalis) was selected as the focal species. Two null hypotheses were formulated concerning potential changes in the numbers and distribution of long-tailed ducks in relation to disturbance in an industrial study area, compared to a reference study area located about 50 km to the east.A 9-year historical database (1977–1984, 1989) of long-tailed duck densities and other important data recorded during systematic aerial surveys was analyzed retrospectively using multiple regression techniques. The retrospective analyses determined which of several predictor variables recorded were significantly related to long-tailed duck density. Separate analyses were conducted for two periods: (1) the overall period when long-tailed ducks were present in the lagoon study areas, and (2) the shorter adult male molt period. The results of the two analyses indicated that 57% and 68%, respectively, of the total variation in long-tailed duck density during the two periods could be explained by variables recorded during the surveys. Predictor variables representing habitat, day of the year, time of day, amount of ice, and wave height recorded on-transect during surveys were most closely associated with long-tailed duck density. Measurement error during the surveys, and influences outside the study area such as nesting success in tundra habitats and mortality during migration and in over-wintering areas likely also had strong influences on the results, but these factors were not measurable in our study.Based on results of the retrospective analyses, a long-term monitoring protocol consisting of a program of systematic aerial surveys and an analyses of variance and covariance (ANOVA and ANCOVA) statistical procedure was designed and initially tested in 1990 and 1991. This 2-year testing phase resulted in several revisions to the monitoring protocol. Refinements were made to the original sampling procedures, to the survey schedule, and to the recommended statistical analysis procedures. Results of the ANOVA and ANCOVA indicated that there was no evidence of a change in long-tailed duck densities that could be attributable to disturbance (from any source) in the industrial study area relative to a reference area with no industrial development. Other analyses indicated that the sampling and analysis procedures would be adequate to detect long-term trends in long-tailed duck density and localized disturbance effects, but that the monitoring program should be continued well beyond two years to detect statistically significant changes. As a result, additional aerial surveys of both study areas were conducted again during 1999–2001.Results of the revised ANOVA and ANCOVA of the 1990–1991 and 1999–2001 survey data indicated that the density of long-tailed ducks had significantly declined in coastal lagoons along the central Alaskan Beaufort Sea coast during the study period. In addition, disturbances throughout the barrier island-lagoon systems used by these ducks, including both the industrial and the reference study areas, had significantly increased over the same period. However, because unanticipated disturbances from a variety of anthropogenic sources, and not just industry sources, increased in both study areas, the reference study area was not an effective statistical control. As a result, the decline in long-tailed duck density in both study areas was not attributable to industry-related activities. Although the monitoring protocol described here is an effective method to detect statistically significant changes in long-tailed duck distribution and abundance in the nearshore Alaskan Beaufort Sea, many more years of sampling would be necessary to attribute observed changes to industry-related disturbances.  相似文献   
105.
ABSTRACT: To prioritize sites for riparian restoration, resource managers need to understand how recovery processes vary within landscapes. Complex relationships between watershed conditions and riparian development make it difficult to predict the outcomes of restoration treatments in the semiarid Southwest. Large floods in 1993 scoured riparian areas in the Carrizo watershed on the White Mountain Apache Reservation in east‐central Arizona. We evaluated recovery at three of these sites using repeated photographs and measurements of channel cross sections and stream‐side vegetation along permanent transects. The sites were mapped as lying on the same soil type, had similar streamside vegetative communities, and were similarly treated through livestock exclusion and supplemental seeding. However, the sites and individual reaches within the sites followed strikingly different development paths. Dramatic recovery occurred at a perennial reach where cover of emergent wetland plants increased from 4.7 percent (standard error = 0.8 percent) in October 1995 to 55.5 percent (standard error = 2.7 percent) in September 2001. At several other reaches, geologic and hydro geomorphic characteristics of the sites limited inputs of fine sediment or surface water, resulting in modest or negligible increases in emergent cover. Recovery efforts for highly valued marshlands in this region should prioritize perennial reaches in low gradient valleys where salty sediments are abundant.  相似文献   
106.
为了揭示煤巷顶板围岩承载能力的弱化机理,结合已有的研究成果,建立巷道顶板三向承载梁结构承载弹塑流弱化分析模型,确定三向承载梁结构承载状态的分析方法,提出用围岩塑性区深度、宽度、长度作为评价巷道围岩承载的弱化分析指标,研究围岩性质、支护强度、采动应用等诱导因子对煤巷顶板结构承载能力弱化分析指标的影响规律。研究结果表明:随着围岩强度的提高、支护强度的增加、扰动应力的减小,弱化分析指标呈似线性减小的变化规律,且减幅由大到小排序为塑性区长度Sy,宽度Sx和深度Sz,同时提高围岩强度、支护强度,减小采动作用应力,煤巷顶板弱化分析指标的减小程度显著高于单因子的改善。  相似文献   
107.
Insect outbreaks are a major disturbance factor in Canadian forests. If global warming occurs, the disturbance patterns caused by insects may change substantially, especially for those insects whose distributions depend largely on climate. In addition, the likelihood of wildfire often increases after insect attack, so the unpredictability of future insect disturbance patterns adds to the general uncertainty of fire regimes. The rates of processes fundamental to energy, nutrient, and biogeochemical cycling are also affected by insect disturbance, and through these effects, potential changes in disturbance patterns indirectly influence biodiversity. A process-level perspective is advanced to describe how the major insect outbreak system in Canadian forests, that of the spruce budworm (Choristoneura fumiferana Clem. [Lepidoptera: Tortricidae]), might react to global warming. The resulting scenarios highlight the possible importance of natural selection, extreme weather, phenological relationships, complex feedbacks, historical conditions, and threshold behavior. That global warming already seems to be affecting the lifecycles of some insects points to the timeliness of this discussion. Some implications of this process-level perspective for managing the effects of global warming on biodiversity are discussed. The value of process-level understanding and high-resolution, long-term monitoring in attacking such problems is emphasized. It is argued that a species-level, preservationist approach may have unwanted side-effects, be cost-ineffective, and ecologically unsustainable.  相似文献   
108.
In this paper, we examine the consequences of rapid climate change on lake ecosystems in terms of two main effects: variability effects and magnitude effects. How these factors influence life history selection is considered by focusing upon body size as a quantifiable and strong correlate of life history variation (Pianka 1970, McNab 1980, Charnov 1991). We then consider the relationship between the concept of biological diversity and the diversity of life history strategies in the context of rapid climate change.  相似文献   
109.
大型水利水电工程扰动区植被的生态恢复   总被引:1,自引:0,他引:1  
大型水利水电工程具有防洪、发电、航运等综合效益,是开发治理江河的骨干工程.水利水电工程建设常对项目区自然生态环境带来影响,施工中所产生的岩质边坡、土质边坡、弃土和弃渣等扰动可能导致项目区的生态系统退化、生物多样性丧失、水土流失和地质灾害加剧.扰动区植被生态恢复关系到工程安全运行和其所在区域的可持续发展.以向家坝水电工程为例,研究了大型水利水电工程扰动区植被生态恢复的目标、原则及方法.按生产、生态和社会功能,向家坝水电工程扰动区可划分为工程核心区、服务区和过渡区等3个功能区来系统规划其生态恢复.结合各自的功能需求和干扰特征,各功能区可采取相应的生态恢复技术和配置适宜物种来构建植物群落,形成结构稳定、多样性丰富、具有复合功能的植被景观.还简要评价了向家坝水电工程植被恢复现状,提出一些完善其生态恢复的建议.  相似文献   
110.
不同水温时底泥扰动对不同形态磷分布的影响   总被引:3,自引:0,他引:3  
研究了江南地区典型水温条件下,底泥扰动对上覆水中不同形态磷迁移的影响.结果表明,不同水温条件下,底泥扰动均有利于上覆水中溶解态磷(即溶解性总磷酸盐(DTP),包括溶解性正磷酸盐(DIP)和溶解性有机磷(DOP))向底泥迁移.与对照试验相比,不同水温时的扰动均导致DIP/TP和DTP/TP明显降低.与初始状态(第0天时)相比,扰动导致DIP/TP分别降低了39.61百分点(冬季水温)和17.38百分点(夏季水温),而DTP/TP则分别降低了39.16百分点(冬季水温)和19.06百分点(夏季水温).相反,对照试验中,DTP/TP分别上升了24.90百分点(冬季水温)和23.37百分点(夏季水温).这说明底泥扰动促进了溶解态磷向颗粒态磷(PP)的转化.  相似文献   
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