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Fire-based management for promoting drought resistance of woody seedlings in a changing climate - Final Report to the Joint Fire Science Program

Author(s): Jennifer Fraterrigo, Tyler Refsland
Year Published: 2016

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. Additionally, the extent, frequency and severity of natural and anthropogenic fires are rapidly changing, highlighting the need to understand the interactive effects of fire and drought on forest productivity and recruitment. Given that fire disturbance often reduces tree density and improves the water relations of resprouting trees, fire tolerant tree species may have higher drought resilience in forests stands that experience periodic fires. Our objective was to investigate the consequences of prescribed fire on drought vulnerability of tree seedlings, the life history stage most vulnerable to drought and a bottleneck for overstory recruitment. Using rainout shelters deployed in the forest understory, we imposed summer drought on in situ and planted populations of Quercus alba seedlings located in periodically burned (three fires since 2002) and unburned sites in Shawnee National Forest, IL, USA. We monitored leaf gas exchange, leaf water potential (Ψpd) and relative growth rate (RGR) of seedlings for two years. Burned sites had approximately twice the light availability (P = 0.05) and seedlings showed 33% higher transpiration rates than those in unburned sites (P = 0.02). The drought treatment reduced 2014 – 2015 mean soil water content (0 - 45cm depth) by 28% (± 9%) relative to controls (P < 0.001). Regardless of burn treatment, drought significantly reduced Ψpd of in situ Q. alba seedlings (P = 0.003), but only post-fire Q. alba resprouts experienced drought-induced declines in max photosynthetic rates (-10%, P = 0.37) and stomatal conductance (-18%, P = 0.16). We observed similar patterns for ex situ Q. alba seedlings, with only those planted in burned sites experiencing drought-induced declines in max photosynthetic rates (-33%, P = 0.28) and stomatal conductance (-35%, P = 0.26). Burned sites had 10-13% greater drought-induced declines in RGR for both in situ (P = 0.58) and ex situ Q. alba seedlings (P = 0.43). These findings indicate that higher light availability and transpiration rates after fire can predispose shallow-rooted seedlings to increased water stress under drought. Forest management under future scenarios of hydroclimate variability should therefore consider the implications of fire on seedling drought tolerance.

Citation: Fraterrigo, Jennifer M.; Refsland, Tyler K. 2016. Fire-based management for promoting drought resistance of woody seedlings in a changing climate. Joint Fire Science Project 14-3-01-16. Urbana, IL: University of Illinois. 19 p.
Topic(s): Fire Effects, Ecological - Second Order, Vegetation, Fire & Climate
Ecosystem(s): None
Document Type: Technical Report or White Paper
NRFSN number: 17051
FRAMES RCS number: 23248
Record updated: Mar 7, 2018