Dr. Sheppard uses tree rings to reconstruct environmental conditions of the past and/or to monitor modern-day environmental change:
The dating of Sunset Crater of northern Arizona, long thought to have erupted in A.D. 1064, is being re-examined. This research began by focusing on a more recent cinder cone, Parícutin of central Mexico, where results suggest dendrochemical increases in sulfur and phosphorus during the eruption. With modern calibration now established, dendrochronological attention is turning to Sunset Crater itself. A substantially different date of eruption of Sunset Crater would be a truly important contribution to Southwest archaeology. Initial results are promising, and we are hopeful that additional funding will be generated through archaeology, volcanology, and geosciences granting programs.
The existence of multiple, concurrent clusters of childhood leukemia (e.g., Fallon, Nevada; Sierra Vista, Arizona; and Calvine-Florin, California) is a unique research opportunity: Is there any environmental issue held in common by these places that might be linkable to leukemia? Trees associated with the clusters have been sampled and measured in order to monitor temporal changes in urban settings. Dendrochemistry of trees in Fallon indicates that tungsten increased there in the mid 1990s, about the time of onset of the cluster of childhood leukemia in Fallon. This research has included other data types, including soil, inhalable dust, and even lichens. Results from all data types confirm that airborne tungsten is high in Fallon relative to that of other Nevada towns or the outlying desert in general.
General Pollution Studies:
Understanding the ramifications of the anthropogenic doubling of fixed nitrogen in the atmosphere is considered one of the great research challenges of ecology. Fieldwork has been initiated in the mountains of southern California to investigate the effects of changing nitrogen availability on tree growth. These mountains are in the air pollution plume of greater Los Angeles, and as such they receive enhanced quantities of fixed nitrogen. Long-term ring-width patterns might demonstrate tree responses to this extra nitrogen. Soil nitrogen should also be a key variable in this research. Tree and soil samples have been collected across microsites in an effort to associate tree vigor with soil nutrient availability. This sampling scheme is relatively unusual for dendrochronology, but it incorporates basic fundamentals of tree and site selection as well as of soil formation factors.
Image Analysis Innovations:
The practical and expedient use of image analysis in dendroclimatology of conifer species has been a long-standing goal. Recent efforts have been made to solve sample preparation issues of heartwood discoloration. Once quantitative image analysis of conifers is fully operational, it will be applied to strategic sites in the American Southwest, where summer rainfall is important for many stakeholders.