Jack pine of all trades: deciphering intraspecific variability of a key adaptive trait at the rear edge of a widespread fire-embracer North American conifer.

PREMISE
Understanding mechanisms fostering long-term persistence of marginal populations should provide key insights about species resilience facing climate change. Cone serotiny is a key adaptive trait in jack pine, which shows phenotypic variation according to the fire regime. Compared to range-core populations within the fire-prone boreal forest, low and variable serotiny in rear-edge populations suggest local adaptation to uncommon and unpredictable wildfire regime. We assessed environmental/physiological factors that might modulate intraspecific variation in cone serotiny.


METHODS
We experimentally submitted closed cones to incrementing temperatures followed by seed germination tests to investigate if and how various ecological factors (cone age, branch height, tree size, tree age) are related to cone dehiscence and seed viability in jack pines from rear-edge and range-core populations in eastern Canada.


KEY RESULTS
Cones from rear-edge populations dehisce at a lower opening temperature, which increases with cone age. Cones from range-core stands open at a more constant, yet higher temperature. It takes between 13 and 27 years for cones from rear-edge stands to reach the level of serotiny achieved at the range core. At the rear edge, seed viability is steady (51%), whereas it decreases from 70% to 30% in 20 years at the range core.


CONCLUSION
At the rear edge, we inferred the mechanisms of a bet-hedging strategy ensuring steady recruitment during fire-free intervals and successful postfire regeneration. This capacity to cope with infrequent and unpredictable fire regime should increase the resilience of jack pine populations as global changes alter fire dynamics of the boreal forest. This article is protected by copyright. All rights reserved.