Post-fire resprouting oaks (genus: Quercus) exhibit plasticity in xylem vulnerability to drought

Resprouting is a key functional trait for species in disturbance prone environments. In many semi-arid environments, woody plants face both fire and drought as recurring disturbances. Past work has demonstrated that oaks inhabiting sky-island forests of the northern Sierra Madre Oriental have differing microhabitat preferences and heavy stem dieback occured during the historic 2011 drought indicating potential xylem failure. These oak species, representing two sections within the genus, are all post-fire resprouters: they can resprout from underground storage organs when fire kills above ground tissue. Resprouts provide an opportunity to examine how functional traits may change as plastic responses to changing environmental conditions. Post-fire resprouts have increased root:shoot ratios relative to adults and therefore have access to more water relative to leaf demand. We expected that if resprouts exhibit plasticity in xylem function, they should favor water transport efficiency over safety: they should have higher maximum xylem conductivity, but greater susceptibility to drought-induced cavitation. We examined four oak species common in the Davis Mountains in west Texas and compared adult physiology with that of resprouts following wildfire. We found that species differed in degree of desiccation avoidance (isohydry) consistent with microhabitat preferences and that the species that were most desiccation tolerant as adults had resprouts significantly more susceptible to xylem cavitation. We found no evidence for a trade-off between efficiency and safety, however.