Collaborative Proposal: Forest Carbon-water interactions in relations to the North American Monsoon climate system

区域气候影响着半干旱的美国西部的森林生长和水资源利用。这些山地森林依靠冬雪和夏雨提供的水分。这些水是由不同的气候系统提供的。北美季风气候系统每年都会在美国西南部发生。它通过从加利福尼亚湾向北移动的几乎每天都有雷暴的方式带来夏季降雨。冬天的雪来自于长期的风暴，这些风暴起源于加利福尼亚海岸外的太平洋上空并向东移动。来自这些不同气候系统的水具有不同的化学成分和时间。利用树木年轮，本研究项目将深入了解森林生长和水利用如何响应过去的气候变化，以及季节某一部分（如冬季或夏季）的变化如何影响随后季节的森林生长和水利用。该地区的积雪减少，冬季气温升高，干旱加剧。因此，了解水分供应的变化如何影响这些森林的生长是很重要的。了解干旱如何控制森林生长不仅对预测自然资源生产，而且对预测和控制森林火灾频率至关重要。这项研究将为一个名为“森林对气候变化反应的指纹”的展览做出贡献，该展览将在亚利桑那大学的树木年轮研究实验室和生物圈2校区举行。这项研究将包括培训两名博士后研究员和众多本科生，重点是从亚利桑那大学庞大的西班牙裔和美洲原住民学生群体中招聘。这项研究将探讨在过去50年中，在任何给定年份，夏季或冬季降水量的变化是否分别与前一个冬季或下一个夏季的降水量负相关，以及这些相关影响是否以可预测的方式影响了森林木材生产和水循环。研究人员将研究树木如何在冬季或夏季降雨量极低的年份调动储存的糖资源来维持木材生产和水循环，以及储存的糖的使用在多大程度上缓冲了冬季或夏季极端干旱的影响。该项目将设计新一代数学模型，以更好地预测冬季与夏季降水的变化如何影响森林木材生产和水资源利用，以及在多年干旱之后是否存在维持木材生产的限制。这项研究将利用先进的技术分析从单个树木年轮中提取的纤维素中的稳定同位素。研究的主要部分将集中在20世纪60年代和70年代产生的树木年轮上，当时原子弹试验在大气中产生了放射性14C的峰值，随后被纳入树木中。14C提供了一种可检测的示踪剂，有助于确定树木中储存的糖的年龄，以及在树木年轮和木材生产中对这些标记糖的利用。新的理论将被开发出来，为理解和预测树木如何从大气中吸收稳定的碳和氧同位素到它们的木材中提供基础。所有数据将被存入国际树木年轮数据库，该数据库由美国商务部、国家海洋和大气管理局管理，并已被用于许多多国合作，以了解气候如何控制森林生态系统的健康和活力。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Regional climate affects the forest growth and water use in the semi-arid western US. These montane forests depend on water from winter snow and summer rain. This water is provided by different climate systems. The North American Monsoon climate system occurs each year across the southwestern US. It delivers summer rain through near-daily thunderstorms that move northward from the Gulf of California. Winter snow comes from longer-term storms that originate above the Pacific Ocean off the coast of California and move eastward. Water from these different climate systems have different chemistry and timing. Using tree rings this research project will provide insights into how forest growth and water use has responded to past climate variation and how variation in one part of the season (e.g., winter or summer) influences forest growth and water use in the following seasons. This region has experienced reduced snow packs, warmer winter temperatures and an increase in droughts. Therefore, it is important to understand how the change in water availability is affecting the growth of these forests. An understanding of how drought controls forest growth is crucial to not only predicting natural resource production, but also predicting and controlling forest fire frequencies. The research will contribute to an exhibit entitled: 'The Fingerprints of Forest Responses to Climate Variation', in The Laboratory of Tree Ring Research and at the Biosphere 2 campus at the University of Arizona. The research will include the training of two post-doctoral fellows and numerous undergraduate students, with an emphasis on recruitment from the large Hispanic and Native American student populations at the University of Arizona. This research will explore whether variation in the amount of summer or winter precipitation over the past fifty years, in any given year, is negatively correlated with the amount of precipitation during the previous winter or the following summer, respectively, and whether those correlated influences have affected forest wood production and water-cycling in predictable ways. Researchers will examine how trees mobilize stored sugar resources to sustain wood production and water cycling during years with extremely low winter or summer rainfall, and the degree to which the use of stored sugars differentially buffers the effects of extreme winter or summer drought. This project will design a new generation of mathematical models to better predict how variation in winter versus summer precipitation influences forest wood production and water use, and whether there are limits to sustaining wood production following multi-year droughts. The research will utilize advanced techniques in the analysis of stable isotopes in the cellulose extracted from individual tree-rings. A major part of the studies will focus on tree rings produced during the 1960's and 1970's, when atomic bomb testing produced an atmospheric spike of radioactive 14C that was subsequently incorporated into trees. The 14C provides a detectable tracer that facilitates determination of the age of stored sugars in trees and the utilization of those tagged sugars in the production of tree rings specifically, and timber generally. New theory will be developed to provide a foundation for understanding and predicting how trees incorporate stable isotopes of carbon and oxygen from the atmosphere into their wood. All data will be deposited in the International Tree Ring Data Bank, which is administered by the US Department of Commerce, National Oceanic and Atmospheric Administration, and which has been used in numerous multi-national collaborations on understanding how climate controls the health and vigor of forest ecosystems.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.