Quantifying uncertainty in the biospheric carbon flux for England and Wales

Summary.  A crucial issue in the current global warming debate is the effect of vegetation and soils on carbon dioxide (CO₂) concentrations in the atmosphere. Vegetation can extract CO₂ through photosynthesis, but respiration, decay of soil organic matter and disturbance effects such as fire return it to the atmosphere. The balance of these processes is the net carbon flux. To estimate the biospheric carbon flux for England and Wales, we address the statistical problem of inference for the sum of multiple outputs from a complex deterministic computer code whose input parameters are uncertain. The code is a process model which simulates the carbon dynamics of vegetation and soils, including the amount of carbon that is stored as a result of photosynthesis and the amount that is returned to the atmosphere through respiration. The aggregation of outputs corresponding to multiple sites and types of vegetation in a region gives an estimate of the total carbon flux for that region over a period of time. Expert prior opinions are elicited for marginal uncertainty about the relevant input parameters and for correlations of inputs between sites. A Gaussian process model is used to build emulators of the multiple code outputs and Bayesian uncertainty analysis is then used to propagate uncertainty in the input parameters through to uncertainty on the aggregated output. Numerical results are presented for England and Wales in the year 2000. It is estimated that vegetation and soils in England and Wales constituted a net sink of 7.55 Mt C (1 Mt C = 10¹² g of carbon) in 2000, with standard deviation 0.56 Mt C resulting from the sources of uncertainty that are considered.     

胶东半岛与辽东半岛现代植被发展趋势研究

通过胶东半岛、辽东半岛及庙岛群岛５２个样地乔木更新层情况的调查,采用主成分分析方法进行样地资料分析,指出现代植被发展趋势的两个阶段：松类—栎类混交林阶段与栎类—松类混交林阶段;生境变化趋势由庙岛群岛的温湿向辽东半岛略暖温和胶东半岛的暖干过渡．     

秦岭南坡旬河流域中上游地区植被演替的初步研究

分析了旬河流域中上游地区三个植被垂直带的植被演替过程，总结了植被演替的特点     

Restoring complex vegetation in urban settings: The case of tidal freshwater marshes

Tidal freshwater marshes have diverse plant communities that vary spatially and temporally due to hydrology, animal activity, and other factors. Development of urban centers along rivers of the U.S. Atlantic coast has reduced the historic extent and quality of these and other coastal wetlands. Because the vegetation of these wetlands is more complex than that of salt and brackish marshes (where restoration of vegetation typical of natural systems has sometimes been successful), restoration of tidal freshwater marsh vegetation is likely to be more difficult, particularly in urban areas. Watershed urbanization alters hydrology, sediment load, propagule availability and composition, nutrient status, and other variables that together create an environment different from that of wetlands in less developed areas, possibly precluding restoration of typical marsh vegetation. Tidal freshwater wetlands were historically extensive along the Anacostia River in Washington, DC, but most of these were lost due to filling, dredging, or hydrologic alteration. Over the last decade, the U.S. Army Corps of Engineers has implemented projects designed to restore tidal freshwater wetlands along the Anacostia, which involved increasing elevation with dredged river sediment and planting native vegetation. To illustrate some of the mechanisms affecting vegetation development in restored tidal freshwater marshes in urban areas, I present a case study on one of these wetlands, Kingman Marsh, that also includes research at another restored wetland and two natural reference sites. Studies by my research groups indicate that the restored wetlands undergo essentially a planting-modified process of primary succession. Low densities of seeds are initially present in the substrate, and prolific seed dispersal into the restored sites results in high initial plant diversity comprised of plantings and ruderal (i.e. weedy) natives and exotics. Seed banks develop rapidly at the restored sites, probably due to colonization and early reproduction by ruderal species. Hydrology and disturbance by non-native animals (including resident Canada goose) are important variables controlling establishment of vegetation in these systems. Recent literature and the case study indicate that the environmental conditions of urban settings impose constraints in restored wetlands that result in plant communities more like those of urban natural wetlands than those of wetlands in less urbanized watersheds. This suggests that rather than design wetland restoration projects with the goal of creating pristine wetland vegetation, restorationists must identify, accept, and if possible capitalize on the ecological constraints of the urban environment in setting achievable and desirable restoration goals.     

Habitat origins and microhabitat preferences of urban plant species

Urban vegetation is commonly described as dominated by weedy species that are adapted to human disturbance. In this study, we determined the original (pre-agriculture) habitats of urban plant species sampled quantitatively in the spontaneous vegetation of a university campus in Halifax, Nova Scotia (eastern Canada). We sampled 11 distinct patch types corresponding to different built forms. Differences in vegetation among patch types were related in part to environmental variables such as soil moisture and light availability. The urban vegetation was dominated by species from rocky habitats such as cliffs and talus slopes, with lesser representation from grassland and floodplain habitats. When compared to a null model of species origins based on the global area and species richness of different original habitats, species from rock outcrops and grassland habitats were overrepresented in the urban vegetation. These results contrast with the received view that cities represented highly “unnatural” ecosystems: built form appears to replicate the habitat templates required by rock outcrop species. Urban ecological theory should incorporate the replication of habitat analogs by built forms in addition to the creation of ecologically novel habitats.     

结合相干系数的极化干涉SAR植被高度估计方法研究

阐述了极化干涉SAR成像技术的基本理论,分析了极化干涉SAR的植被散射模型和Cloude三阶段植被高度反演算法。因三阶段法采用多参数初值迭代求解方法,其运算量较大复杂性高,该文提出基于相干系数的高度估计方法。先用干涉相位估计植被高度,再由相干系数幅度估计植被高度对前面相位估计的高度进行补偿,既保证了一定植被高度估计精度,又大大减少了反演算法的运算量,最后用极化干涉SAR仿真数据验证了该方法的有效性。     

黄土高原退化生态系统的恢复重建方略

综观黄土高原植被恢复重建历史，最为流行的观点当属“以古证今”和“以山证原”两种观点。而事实情况是，古代山地的植被分布，只能提供一些植物恢复重建可咨借鉴的旁证资料。对于黄土高原退化生态系统，其植被建设只能立足于现实生态环境条件，适地适树（草）适法，方能有效恢复和重建植被，以发挥其多方面的生态经济功能。植被恢复重建在不同类型区有不同模式，总体应由东南部的以乔灌为主，向西北部的以灌草为主逐步过渡。植被恢复重建目标应是建立与现实生态环境最为适应的人工植被类型。植被恢复、植被重建和植被保护3个方面相辅相成，是黄土高原地区植被建设不可分割的3条主要途径。     

山区高速公路边坡防护的新型技术——植物草毯生态防护技术

通过对比,分析了典型的人工植被、三维植被防护、客土喷播、网袋工程等边坡生态防护技术特点和适用范围。重点介绍一种新型山区高速公路边坡生态防护技术——植被毯技术,阐述了植被毯生态防护技术的防护原理。结合六潜高速公路植被毯边坡防护工程实例,分析了这种防护措施的可行性,对其生物防护的机理、特点、设计原则、施工工艺进行探讨。为山区高速公路边坡的生态防护,尤其是劣性土质和岩质边坡生态防护提供了重要参考。     

Vegetative characteristics of urban land covers in metropolitan Tucson

In this study we developed a methodology that associated land cover categories to aerial photographs. We selected 4, 42-mile (10 km2) study sites within metropolitan Tucson, Arizona for our pilot study. Land uses within these sites covered the range of landscapes found within Pima County, Arizona, although not necessarily in proportions representative of the metropolitan area. We designated land cover categories within the pilot sites based on recent (March, 1990) aerial photographs and developed a geographical information system (GIS) database of these land cover categories. We measured vegetation attributes on randomly selected samples within each land cover category and classified vegetation occurring on specific land cover categories according to the Brown et al. (1979) system. Our land cover classification system was nominal with a hierarchical structure, facilitating organization and providing flexibility for adding new categories.Our results showed that although neighborhood parks contained the greatest vegetated areas within our four study plots, very low density housing (4 acres/house), rivers whose banks were partially stabilized, naturally occurring washes (with no bank stabilization), and natural open space contained the highest percentage of native vegetation. Within our four study sites, low density housing (4 acres/house), rivers with partially stabilized banks, naturally occurring washes (no bank stabilization), and natural open space land cover categories contained the most area that was covered with vegetation providing escape cover.     

沈阳市青年公园使用状况评价研究

城市公园是城市中向公众开放的、以游憩为主要功能,有一定的游憩设施和服务设施,同时兼有健全生态、美化景观、防灾减灾等综合作用的绿化用地。但是,以往的公园改造普遍缺乏对使用者需求的充分重视,致使改建后的公园在使用中效果不佳。针对沈阳市青年公园这一具有代表性的公园为研究对象,分别选取工作日、休息日和节假日中天气晴好的日子进行多次实地考察,运用使用状况评价法（Post Occupancy Evaluation）,以发放调查问卷和访谈等形式对公园使用者的行为特征和使用需求进行分析,提出营造文化氛围,健全服务设施,增设植物景观,无障碍设计,环境管理维护等建议。