Potential for prescribed fire to promote drought resistance of oak seedlings in a changing climate

by

Tyler K Refsland

Program in Ecology, Evolution and Conservation Biology; C-524 Turner Hall, Urbana, IL; refslan2@illinois.edu

Abstract – Shifts in rainfall patterns due to climate change are expected to increase drought-induced stress and mortality in forests, with widespread, negative consequences for forest productivity. Fire-based management could prove an important tool to mitigate such changes, given that fire often reduces competitor density and increases the root to shoot ratios of top-killed trees. Our objective was to investigate the consequences of prescribed fire on the drought resistance of tree seedlings, the life history stage often most vulnerable to drought and a bottleneck for overstory recruitment. Using clear overhead shelters, we imposed summer drought on Quercus alba seedling populations located in fire-managed and suppressed areas in Shawnee National Forest, IL, USA. We will monitor the leaf gas exchange and growth response of seedlings over the 2014 and 2015 growing seasons. In our first year of drought treatment, we reduced shallow (15 cm depth) mean soil water content by 54% relative to ambient conditions (P < 0.001). Q. alba seedlings experienced reduced rates of photosynthesis (β = -12%, P = 0.17) and stomatal conductance (β = -24%, P = 0.03) under drought relative to ambient conditions. After one growing season, we observed no effect of drought on seedling growth (P = 0.52). Fire management did not mediate the impacts of drought on gas exchange (P = 0.62). Despite its important effects on stand density and seedling morphology, our data thus far suggest that fire-based management may not be an effective strategy for promoting drought tolerance in juvenile oaks.