Collaborative Research: Biophysical and Ecological Constraints on Maximum Tree Height:Insights From the Three Tallest Tree Species.

合作研究：最大树高的生物物理和生态限制：来自三种最高树种的见解。

• 批准号: 0445277
• 负责人: George Koch
• 金额: --
• 依托单位: Northern Arizona University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2005
• 资助国家: 美国
• 起止时间: 2005-01-01 至 2008-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0445277&HistoricalAwards=false
• 关键词: Collaborative; Research; Biophysical; Ecological; Constraints

BIOPHYSICAL AND ECOLOGICAL CONSTRAINTS ON MAXIMUM TREE HEIGHT:INSIGHTS FROM THE THREE TALLEST TREE SPECIESGeorge W. Koch1 and Stephen C. Sillett21Northern Arizona University and 2Humboldt State University Organisms of great size hold an inherent fascination for humans, and the evolutionary and biophysical determinants of extreme size have long intrigued biologists. Among trees, at least three species (redwood, Douglas-fir, and mountain ash) have exceeded 110 meters (" 360 ft) height in the past. Today, redwood alone reaches such heights, heavy logging having greatly reduced the number of tall individuals of all three species. The rarity of giant trees, and uncertainty regarding the threats of continued logging and predicted climate change, underscore the need for this new study of Earth's tallest trees, which seeks to answer fundamental questions regarding the height limits of terrestrial plants. Trees grow tall where soils are moist and competition for light places a premium on height growth. Current research supports the view that constraints on water delivery to the treetop slow and eventually halt height growth as trees grow taller. Gravity may constrain height growth by reducing water pressure within the conducting system of taller trees, which in turn increases water stress to leaves and reduces rates of photosynthesis. Convincing evidence of lower photosynthesis in tall trees is lacking, however, because most studies have been limited to trees less than half of the maximum-recorded height of the species. In this study, the researchers will access the crowns of trees from 50% to 100% of maximum height in order to compare water stress, photosynthesis, and height growth among individuals of different heights for the three tallest trees species, which grow in temperate rainforests in northern California and Australia. They will also use tree ring growth records to understand how these long-lived (400 to 2000 yr) species have responded to past climate variation and how they may be impacted by future climate change. Insights from this study will have implications for other scientific disciplines. A long-standing question in ecosystem ecology concerns the cause of the apparent decline in net primary productivity as forest stands grow and age, which may include hydraulic constraints on photosynthesis, a primary focus of this study. Furthermore, forests of tall trees are storehouses of biodiversity, and the study will strengthen the infrastructure for continued long-term monitoring and ecological research in the state and federal reserves that seek to protect the remaining giant trees and their dependent biodiversity. The problem of tree top death of redwoods in state and federal reserves is a high priority of park managers, and this study may shed light on the causes of this phenomenon and whether it may be exacerbated by climate change. The study contributes to human resources in a number of ways: it strengthens ongoing outreach to high school biology classes that will access real-time data on environmental conditions in tall trees for teaching purposes; it supports the thesis research of three graduate students; and it provides support for involvement of undergraduate students in laboratory-based research activities, including plant physiology studies and state-of-the-art analyses of stable isotope composition of leaves, a powerful index of water stress in plants. Both partner institutions have large enrollments of Native American students and programs for their involvement with research. These students and those from other underrepresented groups will be sought for involvement in this study.

最大树高的生物物理和生态限制--来自三种最高树种的启示Koch 1和Stephen C.北亚利桑那大学和洪堡州立大学巨大的生物体对人类有着内在的吸引力，而极端大小的进化和生物物理决定因素长期以来一直吸引着生物学家。 在树木中，至少有三种（红木，道格拉斯冷杉和山灰）在过去已经超过110米（360英尺）的高度。 今天，只有红杉能达到这样的高度，大量的砍伐已经大大减少了这三个物种的高大个体的数量。 巨树的稀有性，以及持续伐木和预测气候变化威胁的不确定性，强调了对地球上最高树木进行这项新研究的必要性，该研究旨在回答有关陆生植物高度限制的基本问题。在土壤潮湿的地方，树木长得很高，对光线的竞争会促进树木的高度生长。 目前的研究支持这样一种观点，即随着树木的长高，对向树梢输送水的限制会减缓并最终停止树木的高度生长。 重力可以通过降低较高树木的传导系统内的水压来限制高度生长，这反过来又增加了对叶子的水分胁迫并降低了光合作用的速率。 然而，缺乏令人信服的证据表明高大树木的光合作用较低，因为大多数研究都局限于不到物种最高记录高度一半的树木。 在这项研究中，研究人员将从最大高度的50%到100%访问树冠，以比较三种最高树种不同高度个体之间的水分胁迫，光合作用和高度生长，这些树种生长在北方加州和澳大利亚的温带雨林中。 他们还将利用树木年轮生长记录来了解这些长寿（400至2000年）的物种如何对过去的气候变化做出反应，以及它们如何受到未来气候变化的影响。 这项研究的见解将对其他科学学科产生影响。 生态系统生态学中一个长期存在的问题是，随着林分的生长和老化，净初级生产力明显下降的原因可能包括光合作用的水力限制，这是本研究的主要焦点。 此外，高大树木的森林是生物多样性的仓库，这项研究将加强州和联邦保护区的持续长期监测和生态研究的基础设施，以保护剩余的巨树及其依赖的生物多样性。 州和联邦保护区红杉树顶死亡的问题是公园管理者的高度优先事项，这项研究可能会揭示这种现象的原因，以及它是否可能因气候变化而加剧。 这项研究以多种方式促进人力资源：它加强了目前对高中生物课的外联，这些课将为教学目的获得关于高大树木环境条件的实时数据;它支持了三名研究生的论文研究;它为本科生参与实验室研究活动提供支持，包括植物生理学研究和叶片稳定同位素组成的最新分析，这是植物水分胁迫的有力指标。 这两个合作机构都有大量的美国土著学生和项目，让他们参与研究。这些学生和其他代表性不足的群体将被要求参与这项研究。