LTER: Long Term Ecological Research at the Hubbard Brook Experimental Forest

哈伯德布鲁克（HBR）长期生态研究（LTER）项目是一个跨学科的研究项目，重点是提高对北方森林生态系统的认识和管理。这些提供生态系统服务的重要自然资源，如碳储存、养分循环、水和空气净化以及野生动物栖息地，受到自然和人为干扰的影响。这些干扰包括气候变化、空气污染、入侵物种和森林采伐，本研究的重点是森林生态系统如何应对这些干扰。尽管对森林生态系统的研究已经有了很长的记录，但《哈佛商业评论》最近对树木如何在生态系统中输送水分、钙在森林健康中的作用、氮在生态系统中的运动以及森林中植物、昆虫和鸟类的相互作用的观察表明，仍有许多未知之处。大部分研究将在哈伯德布鲁克实验森林进行，这是新罕布什尔州白山地区的一个地点，由美国林务局管理。研究小组将测量土壤中保留的氮的形式、树木的生长和死亡、发芽的树苗的命运、凋落物的数量和类型、土壤呼吸速率以及细根对氮和磷添加的反应。他们还将测试森林和大气之间的气体、热量和水蒸气的交换如何响应春季落叶和秋季落叶的时间。有关森林生态系统及其径流的信息将通过森林科学对话项目和科学政策交流项目提供给土地管理者，并将为区域和国家层面的政策和管理决策提供信息。计划中的教育和推广活动，包括为初中和高中学生制定课堂课程，与普利茅斯州立大学合作组织的本科生研究经验项目，通过教师研究经验项目培训教师，以及开发水循环可视化工具Waterviz，将把生态知识带给公众，以及从K-12到研究生院的学生和教师。支撑HBR-LTER项目的概念模型设想了作为生态系统变化驱动因素的三种主要干扰类型：大气化学、气候和生物群。这些驱动因素对地球物理和历史模板的影响，包括基岩、土壤、水文、气候和过去扰动历史的变化。在生态系统内，扰动影响水文、生物地球化学、植被动态和食物网动态的相互作用过程。对大气变化的研究主要集中在过去空气污染的遗留问题上，特别是土壤中钙等营养阳离子的耗竭以及土壤和植被中氮的积累。对气候影响的研究主要集中在观测到的长期蒸散量下降的原因，以及季节变化的时间和持续时间对植物、土壤、微生物、动物和河流生态系统的影响。生物变化的研究主要集中在气候、新植物物种的入侵、森林害虫的入侵和干扰制度的改变等多种相互作用的压力因素引起的森林组成和结构的变化。研究方法包括：利用稳定同位素进行长期野外测量，以更好地确定土壤中氮汇的强度；利用Illumina HiSeq平台对群落DNA进行宏基因组鸟枪测序，初步表征微生物群落组成和功能随土壤深度的变化；通过田间试验，确定养分添加对土壤酶活性、微生物养分库和周转、根际分配和菌根官能团的影响，从而调节养分循环和植物吸收的地下响应；利用林分生态系统碳和养分循环模型、单个树种碳氮参数化模型、生态系统人口统计学模型和多元素限制模型等定量模型进行模拟建模，将数据与实验知识综合起来，识别知识空白，提出假设，预测未来森林行为；以及包括15N核磁共振在内的实验室研究，以更好地确定土壤有机质中保留的氮的形式。教育活动包括在现场接待学校小组，对教师进行科研实践培训，指导本科生的研究项目，并促进研究生的研究。外联活动包括综合哈佛商业评论和其他地方的研究结果，通过圆桌讨论向当地利益相关者传播科学，通过有针对性的媒体向公众传播科学，通过针对具体政策问题的简报和出版物向政策制定者传播科学。

The Hubbard Brook (HBR) Long-Term Ecological Research (LTER) project is an interdisciplinary research program focused on improving the understanding and management of Northern Forest ecosystems. These important natural resources that contribute ecosystem services such as carbon storage, nutrient cycling, water and air purification, and wildlife habitat are impacted by natural and man-made disturbances. Those disturbances include climate variation, air pollution, invasive species and forest harvesting, and this research focuses on how forest ecosystems respond to those disturbances. Despite a long record of research on forest ecosystems, recent observations from HBR of how trees move water through the ecosystem, the role of calcium in forest health, the movement of nitrogen through the ecosystem, and the interactions of plants, insects, and birds within the forest indicate that much is still unknown. Most of the research will occur within the Hubbard Brook Experimental Forest, a site in the White Mountain region of New Hampshire that is operated by the U.S. Forest Service. The research team will measure the forms of nitrogen retained in soils, the growth and death of trees, the fates of germinating tree seedlings, the amounts and types of litter fall, rates of soil respiration, and how fine roots respond to nitrogen and phosphorus additions. They also will test how the exchanges of gases, heat, and water vapor between forests and the atmosphere respond to the timing of leaf out in the spring and leaf fall in the autumn. Information about forested ecosystems and the streams that drain them will be made available to land managers through a Forest Science Dialogues Program and a Science Policy Exchange and will inform policy and management decisions on a regional and national scale. The educational and outreach activities planned, including development of classroom curricula for middle- and high school students, a Research Experience for Undergraduates program that is organized in partnership with Plymouth State University, the training of teachers through the Research Experiences for Teachers program, and development of Waterviz, a water cycle visualization tool, will bring ecological knowledge to the public as well as students and teachers at levels from K-12 to graduate school.The conceptual model underpinning the HBR-LTER project envisions three principal types of disturbance acting as drivers of change in the ecosystem: atmospheric chemistry, climate, and biota. The effects of these drivers play out on geophysical and historical templates that include variation across the landscape in bedrock, soils, hydrology, climate and history of past disturbance. Within the ecosystem, the disturbances affect the interacting processes of hydrology, biogeochemistry, vegetation dynamics and food web dynamics. Research on the changing atmosphere is focused primarily on the legacies of past air pollution, particularly the depletion of nutrient cations such as calcium from the soil and the accumulation of nitrogen in soil and vegetation. Research on the impacts of climate is focused on causes of the observed long-term decline in evapotranspiration at the site and the effects of changing timing and duration of seasonal transitions on plants, soils, microbes, animals and stream ecosystems. Research on biotic change is focused on the changing composition and structure of the forests caused by multiple interacting stressors including climate, new plant species immigrations, invasive forest pests, and altered disturbance regimes. Research methods include: long-term field measurements with stable isotopes to provide a better resolution of the strengths of nitrogen sinks in soils and metagenomics shotgun sequencing of community DNA (Illumina HiSeq platform) to provide initial characterization of how microbial community composition and function vary with soil depth; field experiments to identify belowground responses that mediate nutrient recycling and plant uptake in response to nutrient additions and the ensuing impacts on soil enzyme activities, microbial nutrient pools and turnover, rhizosphere allocation, and mycorrhizal functional groups; simulation modeling with quantitative models such as stand-level ecosystem carbon and nutrient cycling models, a carbon and nitrogen model parameterized for individual tree species, an ecosystem demography model, and a multiple element limitation model to synthesize data and experimental knowledge will be used to identify knowledge gaps, develop hypotheses, and make prediction of future forest behavior; and laboratory studies including 15N NMR to better determine the forms of nitrogen retained in soil organic matter. Education activities include hosting school groups at the site, hands-on training of teachers in scientific research, mentoring undergraduate student research projects, and facilitating research by graduate students. Outreach activities include synthesizing results of research done at HBR and elsewhere, and communicating the science to local stakeholders through roundtable discussions, to the public through targeted media, and to policy makers through briefings and publications addressing specific policy questions.