Dendrochronology of the Seaside Juniper (Juniperus maritima), Washington State, USA

Seaside juniper (Juniperus maritima) is a recently identified cryptic, rare tree species endemic to the Salish Sea region. This study reports on the first dendrochronological investigation of the species. We sought to determine if seaside junipers are capable of crossdating and to identify correlations between instrumental climate records and radial growth. We collected tree core samples from seaside juniper in five sites throughout the San Juan Islands and nearby mainland in Washington State. We encountered pervasive issues with broken and partially rotten cores. The lobate growth form characteristic of junipers and frequency of missing rings created additional challenges for crossdating samples. Furthermore, most stands were relatively young, with few or no trees that established prior to the early 20th Century. However, samples collected from one of five sites successfully crossdated. Pearson's correlation analysis revealed that the dominant growth-limiting factor of the seaside junipers we sampled was growing-season minimum temperatures in both the prior year and current year. Understanding this climate-growth relationship will aid in the development of a conservation strategy for this rare and endemic species.