Relationships between regional climatic patterns, wood anatomy and hydraulic architecture of conifer species in the western US.

PROJECT SUMMARY OVERVIEW: The proposed research will investigate climatic signals recorded in wood anatomical features of western US conifer species in relation to two leading climatic modes, the Pacific DecadalOscillation (PDO) and the El Niño-Southern Oscillation (ENSO). Our main objectives are 1) todefine the tree anatomical response associated with long- and short-term growthvariations driven by decadal and inter-annual climatic oscillations, in particular the hydraulic acclimation exhibited during positive/negative phases of the Pacific Decadal Oscillation and during El Niño/La Niña events; and 2) to evaluate the potential of intra-annual tree-ring anatomy as a proxy to be integrated into dendroclimatic reconstructions. During the three years of the project, we will generate century-long time-series of anatomical features (i.e., cell size and cell-wall thickness) for five target regions of the western US, from the moisture-limited environments of the American Southwest and Great Basin to the temperaturelimited Pacific Northwest. A total of 12 sites will be sampled by targeting climate-sensitive conifers (mostly Pseudotsuga menziesii, Pseudotsuga macrocarpa, and Pinus ponderosa). Tree-ring measurements and most of the anatomical measurements will be performed at the University of Nevada-Reno. Wood parameters will also be analyzed on a subset of increment cores through a Confocal Laser Scanner Microscope, in collaboration with the German Research Centre for Geosciences in Potsdam. INTELLECTUAL MERIT: This research falls under the P2C2 program as it attempts to answer the question “How have regional climates, including temperature, precipitation-evaporation, climate modes (e.g. ENSO, NAM, monsoons) and extreme climate events (e.g. droughts, floods, tropical storms), varied and interacted on seasonal to longer timescales?”. We propose an integrated, multi-proxy approach to dendroclimatic reconstructions based on the combined analysis of anatomical and tree-ring responses. In order to distinguish long-term patterns from emerging climatic trends, the calibration of tree-ring proxies with instrumental records needs to describe the mechanistic relationship between regional climate and tree hydraulic architecture. To date, wood anatomical features have been used as proxies for dendroclimatic reconstructions at limited spatial and temporal scales, and no studies have focused on the relationships between long-term intraannual hydraulic adjustments and regional climatic patterns in the western US. The proposed project, by developing and utilizing a much larger dataset than previous investigations, will also make possible to assess the effect of sample size on the variability of climatic signals reconstructed using wood anatomy. BROADER IMPACTS: In the arid and semi-arid environment of the Western US, water is the main limiting factor for forest ecosystems, plant communities, and human socio-economic systems. Improved understanding of past inter-annual and decadal dynamics of PDO and ENSO variability in the Western US will benefit land managers and policy makers as they prepare for the sustained drought events projected under climate change scenarios. This project includes an international collaboration with Dr. Ingo Heinrich of the Humboldt-University Berlin. A graduate student will use this project to develop his/her research, and multiple undergraduates will be trained and mentored during the proposed study. Besides web-based dissemination activities included in the Data Management Plan, the project team will collaborate in producing peer-reviewed scientific papers, oral and poster presentations at national and international conferences, and informational seminars. The PI teaches undergraduate and graduate level classes at UNR, where the student population is constantly increasing in number and diversity, and its members will benefit from the application of results obtained by the proposed activity. Finally, the project will contribute to K-12 STEM education by training high school science teachers, selected from a pool of applicants to become Summer Research Fellows and develop curriculum modules for their classes.