Thresholds of Vegetation Change Following N Deposition in Southern California Ecosystems

南加州生态系统氮沉积后植被变化的阈值

• 批准号: 0421530
• 负责人: Edith Allen
• 金额: --
• 依托单位: University of California-Riverside
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-03-15 至 2011-02-28
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0421530&HistoricalAwards=false
• 关键词: Thresholds; Vegetation; Change; Following; Deposition

This project will examine the influence of anthropogenic nitrogen (N) deposition on thresholds of vegetation-type conversion caused by invasive annual grasses. Invasive plants have dramatically altered many semiarid ecosystems of the western United States, but N deposition may exacerbate the problem. The conceptual framework for this effort is based on complex systems theory, including modeling non-linear, non-equilibrium dynamics to determine thresholds at which N deposition and fire irreversibly change ecosystems ranging from desert to forest. The impacts of N deposition varies as a function of ecosystem proximity to major N emission sources, meteorology, and soil physical and chemical conditions. N emissions in this region originate primarily from internal combustion engines as nitrate, and secondarily from agriculture as ammonium. This project proposes to identify sources of N deposition, describe atmospheric transport of N, quantify rates of deposition across landscapes, and subsequently determine the N supply rate to vegetation. Biogeochemical, hydrological, fire, and landscape transition models will then be used to show how elevated N and fluctuating precipitation affect grass biomass, the fire cycle, and vegetation change in the different ecosystem types.Methods: The research will have two major components. First, it will describe N deposition to different ecosystems in the southern California air basin. The hydrological, carbon, and nitrogen cycles will be coupled since together they control the movement of N, and interannual variability in vegetation growth. Researchers will examine the relationships between modeled N deposition and vegetation response from 1982 to the present. They will also model N deposition expected in the future as a result of projected urban and agricultural land use changes, comparing possible impacts associated with three urban development scenarios. Second, they will examine vegetation composition along N deposition gradients and resample historic vegetation plots to determine changes in plant diversity, and use remote sensing to detect large-scale vegetation changes. Researchers will measure N inputs, turnover, and losses in soils, and conduct fertilization experiments in desert, forest, and shrubland ecosystems to determine thresholds of change under increased N loading. Vegetation change will be modeled using fire and landscape transition models. These results will be coupled with the atmospheric model to show the effect on vegetation for several N deposition scenarios in 2018.Intellectual Merit: This research will have relevance far beyond southern California since the processes of urbanization and N deposition are occurring around the world, and to a range of ecosystems from arid to mesic. This effort will be one of the few to couple biogeochemical and landscape transition models to show how N deposition, variation in precipitation, and exotic invasions promote non-linear changes in different ecosystem types. The research will promote our understanding of complexity theory by comparing four ecosystem types, each responding with its own threshold and emergent properties to N deposition. Broader Impacts: The research will examine complex dynamics of landscapes impacted by emissions caused by changing human demographics and population growth. The controls on plant invasions and their further impacts are not well known, so the results of this research will have implications for regional planning efforts and for emissions regulations. The educational and outreach components of the project include working with local programs to educate the public and school children about N deposition, organizing a regional conference on N deposition for land managers, legislators, and scientists, and working with federal, state, and local agencies on Habitat Conservation Planning efforts for sensitive species subject to air pollution and invasive species. The project will provide research opportunities for a diverse student population, which will be augmented by advanced seminar courses led by an interdisciplinary research team.

该项目将研究人为氮（N）沉积对植被型转化的阈值的影响。 侵入性植物已大大改变了美国西部的许多半干旱生态系统，但n的沉积可能会加剧问题。这项工作的概念框架基于复杂的系统理论，包括建模非线性，非平衡动力学，以确定n沉积和火灾不可逆地改变从沙漠到森林的生态系统的阈值。 N沉积的影响因生态系统邻近的函数而变化，与主要的N排放源，气象以及土壤物理和化学条件相差。该区域的n排放主要来自硝酸盐内燃烧发动机，其次来自农业作为铵。该项目建议识别N沉积的来源，描述N的大气传输，量化跨景观的沉积速率，并随后确定N供应率的N供应率。然后将使用生物地球化学，水文，火和景观过渡模型来展示不同生态系统类型的n和波动降水升高和波动降水如何影响草生物量，火周期和植被变化。方法：研究将具有两个主要组成部分。首先，它将描述南加州空间中不同生态系统的n沉积。水文，碳和氮循环将耦合，因为它们共同控制N的运动以及植被生长的年际变化。研究人员将研究建模的N沉积与植被反应之间的关系，从1982年到现在。由于预计的城市和农业用地使用变化，它们还将对未来预期的N沉积进行建模，并将可能与三种城市发展方案相关的影响进行比较。其次，他们将检查沿N沉积梯度的植被组成，并重新采样历史植被图，以确定植物多样性的变化，并使用遥感检测大规模的植被变化。研究人员将测量土壤中的N投入，营业额和损失，并在沙漠，森林和灌木丛生态系统中进行施肥实验，以确定N负载增加下的变化阈值。植被变化将使用火灾和景观过渡模型进行建模。这些结果将与大气模型相结合，以显示2018年几种N沉积情景的植被的影响。智能优点：由于城市化和n个沉积的过程在世界各地发生，并且与来自干旱到Mesic的一系列生态系统，这项研究的相关性远远超出了南加州。这项工作将是为数不多的生物地球化学和景观过渡模型之一，以表明N沉积，降水变化和外来入侵如何促进不同生态系统类型的非线性变化。这项研究将通过比较四种生态系统类型来促进我们对复杂性理论的理解，每种生态系统类型都以其自身的阈值和新兴属性响应N。更广泛的影响：该研究将研究受人口统计学和人口增长而导致的排放影响的景观的复杂动态。对植物入侵的控制及其进一步的影响尚不清楚，因此这项研究的结果将对区域规划工作和排放法规产生影响。该项目的教育和宣传组成部分包括与当地计划合作，向公众和学童教育n个沉积，组织n个土地经理，立法者和科学家的区域会议，并与联邦，州和地方机构合作，从事栖息地保护计划的敏感物种的栖息地保护计划工作，以空气污染和侵入性物种。 该项目将为多元化的学生群体提供研究机会，这将由由跨学科研究团队领导的高级研讨会课程增加。