Variability and Coherence of Oxygen and Carbon Stable Isotope Ratios of Tree Ring Cellulose in Coast Redwood Between Distant Sites.

Fog water uptake is an important hydrologic input for redwood ( Sequoia sempevirens) trees and is isotopically distinct from rainfall. The utilization of this resource may depend on climatic factors such as precipitation abundance and changes in sea surface temperature. Increment cores from 3-5 redwood trees at 4 sites were cross-dated and δ18O and δ13C of α-cellulose extracted from subdivided annual rings was measured. Trees from southern sites had latewood cellulose over 4‰ more enriched in 18O than trees from northern sites. Inter-annual variation in latewood cellulose δ18O ranged between 2.3 and 3.5‰ for all sites for the 45+ years measured. Correlations of latewood δ18O variation between sites were greatest for those in close proximity to each other (as high as 0.84 for sites 40 km apart). However, some distant sites also showed substantial coherence (r = 0.43 for sites 380 km apart). In general, cellulose obtained from the center of the ring (middlewood) was more depleted in 18O than latewood and is likely to reflect the use of precipitation water in middlewood cellulose. We observed significant correlations between sites for both middlewood δ18O (r as high as 0.64) and the difference between latewood and middlewood δ18O (as high as 0.65). Significant between-site correlations were also observed for the inter-annual variation in δ13C of cellulose for both latewood and middlewood ring segments. These results indicate that inter-annual variation in tree ring δ18O and δ13C is coherent across much of the redwood forest range and that stable isotopes in these tree rings are capturing a common environmental signal and possible physiological response that may provide valuable information regarding hydrologic inputs, climate cycles and tree response for this ecosystem.n