Vulnerability to cavitation of central California Arctostaphylos (Ericaceae): a new analysis

A recent study, 'Influence of summer marine fog and low cloud stratus on water relations of evergreen woody shrubs (Arctostaphylos: Ericaceae) in the chaparral of central California' by M. Vasey, M.E. Loik, and V.T. Parker (2012, Oecologia, in press), presented data on the vulnerability to cavitation of eight Arctostaphylos species. We reanalyzed the vulnerability data presented in this manuscript using a different statistical model and have arrived at different conclusions than those reported previously. We suggest that regional differences have not lead to differentiation in cavitation resistance among populations of an Arctostaphylos species and, contrary to the conclusions of Vasey et al., the xylem of maritime species appears to be "overbuilt" for their current environment and do not appear to be especially vulnerable to water stress. Importantly, data on vulnerability to cavitation are limited for Arctostaphylos species from these sites. More specifically, treatment factors of site and region were not replicated and therefore conclusions drawn from these data are necessarily limited.