Forest carbon-water interactions in relation to the North American Monsoon climate system

Monson, Russ
Please categorize the nature of the Source of Support: 
Other Gov
Who is the funding agency?: 
Amount Requested: 
$1 461 004.00
Award Dates: 
Mon, 04/02/2018
Date Submitted: 
Mon, 2017/09/04
Award Amount: 
Salary Support: 
Participants are receiving financial support
University of Utah

Net primary production in montane forest ecosystems in the western US is dependent on precipitation from winter snow and summer rain. The dependence of forest productivity on these water inputs is influenced by climate systems and oscillations, which recur at loosely-predictable frequencies. The North American Monsoon (NAM) climate system occurs annually throughout the southwestern US and produces a gradient in warm-season precipitation that decreases from south-to-north. The coupling of forest productivity to the delivery of winter and summer precipitation will determine how forests in this region respond to future climate changes. In this proposal, a plan is presented to explore past patterns of carbon-water coupling using the stable isotopes of tree rings associated with ponderosa pine forests within the spatial domain of the NAM. Three research aims will be pursued: (1) studies will be conducted at six sites located within the dynamic northern boundary of the NAM to explore how antecedent effects, whereby the climate of one season influences that of the following season, influence woody-biomass production, transpiration processes and intrinsic photosynthetic water-use efficiency (iWUE); (2) studies will be conducted of the reliance of woody-biomass production on stored non-structural carbohydrate (NSC) in response to extreme drought anomalies in the presence or absence of NAM precipitation; and (3) studies will be pursued to develop a new process-based modeling framework that starts from current and stored pools of NSC, combines climatic and biochemical mechanisms of stable isotope fractionation and includes consideration of cambial phenology to determine woody-biomass production and isotopic signals of forest iWUE and needle transpiration processes.
Intellectual Merit:
The proposed research will provide insight into how climate controls the growth of forests and the efficiency with which they utilize water in a region that has experienced reduced snowpacks and an increase in the frequency of drought, yet is home to 12 million residents. The interaction of winter and summer precipitation in supporting ecosystem services is uncertain. The proposed studies will reduce uncertainties by carefully developing reconstructions of past forest-climate interactions within the past 50 years; thus, setting the stage for accurate reconstructions extending back several centuries. Dendrochronology (the study of tree rings) is one of the key disciplines in climate reconstruction activities. The work proposed here will expand the use of dendrochronology and move the discipline closer to an integration of climatology, biogeochemistry, ecosystem dynamics and forest ecophysiology. This will be facilitated through the development of novel approaches that focus on stable isotope tracers and sub-annual investigations of tree ring anatomy, both of which have the potential to reveal seasonal, rather than annual, processes in forest stands. This would be a major advance in improving confidence and creating opportunities to use tree rings to understand forest processes in relation to spatial variability and synchronicity in climate oscillations.
Broader Impacts:
It is not difficult to attract the attention of citizens to the topic of tree rings and their role as 'fingerprints' of past climates, civilizations and natural disasters. Most people have a natural curiosity about how old trees are and how they record the earth's history. An exhibit will be created entitled: 'The Fingerprints of Forest Responses to Climate Change', which will be presented as part of existing docent-focused outreach programs in The Laboratory of Tree Ring Research and at the Biosphere 2 campus at the University of Arizona, which together attract over 50,000 visitors each year. The proposed research will contribute to the training of two post-doctoral associates, which includes a Latin American male, and five undergraduates, two of whom will receive support to conduct two-year independent study projects. All data will be deposited in the International Tree Ring Data Bank, which has been used in numerous cross-national collaborations and is increasingly important as a source for data constraints on climate-carbon modeling at global and regional scales. Participating Co-Is will develop new lectures on tree ring isotope techniques in three summer courses for graduate students.