Data from: Hedging at the rear edge: Intraspecific trait variability drives the trajectory of marginal populations in a widespread boreal tree species

Rear-edge populations at the warm margin of species distribution are
small, isolated and face environmental conditions at the limit of species
bioclimatic envelope. Intraspecific phenotypic variation contributing to
the persistence of peripheral populations is expected to become
increasingly important under future climate conditions in order to avoid
local extirpation where range shifts lag behind climate change velocity.
We investigated the putative role of intraspecific phenotypic variation
for the maintenance of rear-edge populations of fire-prone jack pine
(Pinus banksiana), an obligate pyriscent boreal species. We assessed
whether variation in cone serotiny is associated with the population
trajectory of marginal stands located south of the boreal biome, in the
temperate forest where natural wildfires are infrequent and unpredictable.
To this end, we estimated stand-scale serotiny, minimal age and tree size
structure in 26 jack pine stands from the rear edge (n = 17 sites) and the
core (n = 9 sites) of the species’ range in eastern Canada. On average,
rear-edge jack pine populations are less serotinous albeit more variably
compared to range-core populations where serotiny is more uniformly high.
Rear-edge stands are generally older and display reverse J-shape tree size
structure indicative of a multi-aged demographic equilibrium, whereas
range-core stands are younger and show a unimodal stand structure
depicting a single aging cohort generally lacking interfire recruitment.
Eco-evolutionary dynamics shifts from a dependency on wildfires in
range-core populations to stands that can regenerate and persist without
recurrent fires at the rear edge, where stand-scale serotiny reaches
values below 85%. Synthesis: Unlike range-core populations, rear-edge jack
pine populations can locally rely on a dual life-history strategy to
ensure both steady recruitment during fire-free intervals and successful
postfire regeneration. This capacity to cope with infrequent and
unpredictable fire regime should increase the resilience and resistance of
jack pine populations as global changes alter fire dynamics of the boreal
forest. More generally, unique intraspecific phenotypic variation in
rear-edge populations contributes to long-term species persistence in
marginal environmental conditions that might scale up with global changes.
The conservation of rear-edge populations and their genetic legacy appears
crucial for the resilience of species.