Establishing a Multi-Century, Annual-Resolution Climate Record from the Northeastern Caribbean

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At middle and high latitudes, dendrochronology has provided some of the most valuable annual-resolution climate records available, most of which significantly extend our knowledge of climate back into time well before periods with instrumental records. In contrast, few dendroclimatological records from low latitudes exist, because tropical trees rarely produce reliable annual rings that allow dendrochronological research. This research project builds on the finding that Pinus occidentalis Swartz, the native pine of the Caribbean island of Hispaniola, produces excellent rings that are moisture-sensitive. This species provides a valuable proxy precipitation record, but only when it grows at the very highest-elevation and moisture-stressed sites within its range, near 3,000 meters in elevation, in stabilized blockfields, and on cliffs. The investigators have collected wood samples (cores and a few sections of living trees, plus sections of dead trees and remnant wood) from 120 specimens. Initial work on small subsets shows promising potential. This award supports analyses of these samples through surface preparation, computer-measurement of rings under magnification, and statistical analysis of the chronologies including comparison with modern climate data. Fire scars are abundant in the stands sampled, and the species' fire response will be analyzed to assess the potential of the species to yield sub-seasonal fire history information for these Caribbean highlands. Rare pieces of subfossil remnant wood are found in fire-protected bare-rock spots within the stands, and the investigators will try to determine the age distributions of floating chronologies from such specimens using radiocarbon dating in order to estimate the ultimate potential record length from these and similar sites. Finally, the award will help fund ongoing efforts to improve public-outreach activities at the University of Tennessee's Laboratory of Tree-Ring Science. These efforts include helping school children and others discover the excitement of tree-ring research.The importance of this project stems from the fact that Pinus occidentalis grows at tropical latitudes, a region that has not witnessed the development of tree-ring-based climate records as have more temperate locales. In geographic terms, the nearest published dendroclimatological record is 1,700 kilometers to the northwest in an extra-tropical location. As awareness of the importance to human society of climate and climate change increases, the scientific impetus to improve understanding of tropical climate dynamics continues to grow. This project will provide the first terrestrial proxy record of precipitation from a tropical region that is closely connected in climatic terms to the North American mainland. It also will enhance educational efforts to inform students and the public about the processes and outcomes of tree-ring research.