Fire is increasing, both in its use as a landscape management tool and in the form of unplanned wildfire. Forest managers use fire-effects models to understand how these fires influence forest structure, yet tree mortality remains a component of fire-effects that remains difficult to predict. Many models lack species-level information related to physiological stress response, and thus often fail to accurately predict post-fire tree mortality. In particular, fire-effects models could benefit from an increased understanding of a tree’s ability to withstand post-fire drought. Our project seeks to fill this void by providing information about post-fire vulnerability to drought for two widespread conifer species with contrasting fire response strategies, Ponderosa pine (Pinus ponderosa; a fire resister) and Lodgepole pine (Pinus contorta ssp. latifolia; a serotinous species). Specifically, we asked if trees that survive low-intensity fire are more vulnerable to post-fire drought than trees outside of burned areas. To assess this, we compared cavitation resistance (P50) , stem-specific hydraulic conductivity (Ks), and native percent loss of conductance (PLC) in both field and lab settings using a simulated heat-plume experiment.
Results/Conclusions
P. contorta had higher rates of hydraulic conductivity and lower rates of embolism compared to controls (P < 0.05). Conversely, P. ponderosa exhibited the opposite trends of reduced hydraulic conductivity and higher rates of embolism (P < 0.05). Cavitation resistance was not different between burned and unburned trees for either species (P > 0.05). These patterns lead us to two main conclusions (1) that low intensity fires have diverse effects on post-fire hydraulic function in co-occurring pine species, and (2) that resistance to drought-induced cavitation is not reduced by exposure to low intensity fire conditions. Furthermore, we hypothesize that the differences observed between P. ponderosa and P. contorta in the present study might be due to differences in life history strategies between these species. For example, it is possible that increased hydraulic conductance post-fire may facilitate release of canopy stored seed banks in serotinous P. contorta. Finally, general agreement between results from actual (field-based) and simulated (lab-based) fire events suggest a robust lab-based model that can be used to explore fire effects on plant hydraulic function in future studies.