Long-lived trees provide multi-millennial records of the principle environmental factors associated with annual tree growth, such as precipitation and long-term climate oscillations. Dendrochronologists have established that some Southwestern conifer trees, including Douglas-fir, ponderosa pine, and Rocky Mountain juniper, can live to old ages in certain forest settings. Previous research on the remote lava flows at El Malpais National Monument (EMNM) and Cibola National Forest (CNF) located near Grants, New Mexico set the stage for this project. Here, conifers largely comprise a stunted woodland that harbors pockets of exceptional old-growth trees, some trees being over 2,000 years in age. The lava flows are, in effect, island ecosystems that exhibit a very different flora than the surrounding landscape which has a different substrate.
Doctoral student Mark Spond, under the supervision of Professor Henri Grissino-Mayer, will use cross-dated Rocky Mountain juniper samples collected from the lava formations at EMNM and CNF to assess multi-scale relationships between monthly and seasonal climatic factors and Rocky Mountain juniper growth of the past 2,000 years. This study also investigates relationships between Rocky Mountain juniper growth at EMNM/CNF and within and between 10-year climate patterns (e.g., El Niño-Southern Oscillation and the Pacific Oscillation) and regional weather patterns (e.g., North American Monsoon). Smaller-scale vegetation dynamics within the old-growth woodlands at EMNM are assessed by the creation of permanent study plots, compilations of age structure data, and comparisons of repeated photographs. The results of this research will answer both theoretical and applied questions: Which climate variables correlate best with Rocky Mountain juniper growth? What is the average rate of annual growth for Rocky Mountain juniper? What relationships exist between Rocky Mountain juniper growth and climate patterns? What changes in vegetation can be observed in the old-growth mixed-conifer woodlands of EMNM between the 1940s and the present? And finally, can Rocky Mountain juniper tree-ring data aid in providing an expanded framework for water resource availability in the American Southwest, an area prone to extremes in hydrologic properties?
This research will assist local and regional government officials in developing policies that can effectively address such issues as water allocation, invasive vegetation treatment, prescribed burn schedules, wildfire management, and other management issues in western New Mexico. Currently, the International Tree-Ring Data Bank (ITRDB) does not include Rocky Mountain juniper tree-ring data from the American Southwest. Rocky Mountain juniper chronologies produced by this doctoral dissertation research will be submitted to the ITRDB. Findings will be shared with land management officials and the broader scientific community through the dissertation, several professional presentations, and peer-reviewed journal articles. This research will also be incorporated into educational programs for K-12 students and teachers, conservation organizations, and government officials in Tennessee and New Mexico, using the successful model of the University of Tennessee's GK-12 Earth Project, funded by the National Science Foundation. The Principal Investigators of this research are committed to involving underrepresented groups in all phases of their project, and have successfully recruited several female undergraduate students to assist on this project.
