Dendrochronological potential of Quercus garryana, Saltspring Island, British Columbia

Abstract

Garry oak (Quercus garryana Dougl.) is the cornerstone tree species of one of the most biologically diverse yet threatened ecosystems in Canada. The Canadian Garry oak ecosystem is located only in southern coastal British Columbia and is home to numerous endangered species. This study tests the dendrochronological potential of Garry oak trees near their northern range limit by successfully crossdating a sample from the Crow's Nest Ecological Research Area (CNERA) on Saltspring Island, British Columbia. Forty-five samples were collected from 39 trees to determine accurate age estimates and develop a crossdated tree-ring chronology that spans 180 years (A.D. 1825–2005). Wood anatomy and periodic growth suppression made crossdating challenging. However, distinct marker rings were readily identified on nearly all cores showing a synchronous response among trees to a common radial growth signal. The majority of trees sampled were established during 1860–1880 and 1947–1967. Correlation analyses show that radial growth of Garry oak at CNERA is influenced by both temperature and moisture availability. Our study demonstrates that extraction of high-quality dendrochronological data from Garry oak trees near their northern range limit is possible, so this species should be recognized as having good dendrochronological potential.