Calli Nielsen and Dr. Matthew F. Bekker, Geography
Utah juniper is rarely used by dendrochronologists in tree-ring applications. In the global species database, Utah juniper has a score of 1, which means that it typically only crossdates within its own site, and is therefore not useful in tree-ring research. This mentored research project was conducted to demonstrate that it is a potentially very valuable species. Our preliminary research showed a very high correlation among other juniper sites in Utah, making us confident that if we moved forward, our further results would prove the usefulness of this species. In northern Utah, traditionally used species aren’t available because we are outside of their range, like pinyon and ponderosa pine. Our results may change dendrochronology in the future, by making this previously avoided species, viable.
To begin, we sampled our site, known as South Fork Chalk Creek (SFC). After tree-ring samples were taken we brought them to the lab and sanded them with successively finer grits of sandpaper to remove scratches or imperfections that obstruct our view of the cells which from ring boundaries. We then examined the samples under a binocular microscope, and crossdated the rings. Crossdating is the process of assigning each ring a specific calendar date, based off of a pattern of marker rings (narrow and wide rings) which indicate wet or dry years. In this process, we can identify missing rings, which are rings that the tree never fully generated due to lack of water, sunlight, or oxygen, and also false rings, which are the result of trees starting to shut down and create a ring halfway through the year, then receive necessary nutrients and start growing again, only to form another ring boundary. After dating was complete, we measured the rings to the nearest .001 millimeter using a sliding micrometer. These measurements were input into a computer system which provided a statistical check on the crossdating, and allowed us to create a tree-ring index series for the site. As we have continued to push our chronology back in time, we have been able to incorporate dead wood into our analysis, which allows us to push the record even farther back.
As we have increased our sample depth, we have accumulated data proving that this species is highly sensitive to climate variability. These sensitive rings are valued because they provide us with a clear chronology, as indicated by the obvious marker rings. Our interseries correlation for SFC is very high, at .826, indicating to us that each sample responds similarly and reliably to the climatic variance. The intercorrelation between our site and other juniper sites throughout the West is also very high. With our incorporation of dead wood, we have been able to analyze samples that will extend to at least A.D. 900.
We have found that Utah Juniper is in fact a very useful species in tree-ring research, although it was originally listed as a non-viable species. Utah junipers are highly sensitive to climate, providing very useful data in modeling past climate cycles. They are very old, allowing us to create a long chronology that will provide a more complete picture of variation in water resources in the west.