Field Notes From Plant Explorations: Juniperus occidentalis of the Yolla Bolly Explored

Field Notes From Plant Explorations: Juniperus occidentalis of the Yolla Bolly Explored | Papers w/ Robert Adams

Juniperus occidentalis of the Yolla Bolly Explored | Papers w/ Robert Adams

Late in the summer of 2009 I re-visited an isolated population of junipers in the Yolla Bolly-Middle Eel Wilderness. The visit was inspired by Robert Adams after he read a blog post of my first visit to the trees. At the time, the population was believed to be Juniperus grandis based on habitat type and other morphological characteristics. After collecting the specimens and sending them to Baylor University for study Dr. Adams published two papers last month on these populations and their relationship to other junipers of the west. He graciously named me as a co-author for my collecting and final editing skills—otherwise the work was all his.

The papers are:

Geographic variation in the leaf essential oils of Juniperus grandis and comparison with J. occidentalis and J. osteosperma. Phytologia 92(2):167-185.
Geographic variation in nrDNA and cp DNA of Juniperus californica, J. grandis, J. occidentalis and J. osteosperma (Cupressaceae). Phytologia 92(2):266-276.

While the DNA and essential oil comparisons verified the Yolla Bolly junipers are Juniper occidentalis they did not clarify the relationship of Juniperus occidentalis to Juniperus grandis. Unusual similarities were found between occidentalis populations of Oregon and Northern California and grandis populations of the San Bernardino Mountains. As Dr. Adams states in his conclusions, some questions were answered with the research but more questions remain—further study is needed.

Juniperus occidentalis Range Map in northwest California

I created this range map after visiting the Yolla Bolly and observing several new, undocumented populations.

As viewed from the ridgeline west of Mount Linn looking northward the populations of western juniper generally grow just east of the ridgelines on sandy soil. Notice the image names the trees as Sierra juniper, which Dr. Adams proved to be wrong.

Other Resources: