Northern seeds outperform southern seeds at HD common garden
It is possible that seeds sourced from the south were of a generally
inferior quality than northern seeds, which may be linked to greater
climate-related environmental stresses at lower latitudes. Other studies
have found that climate-based environmental stresses lead to decreased
germination (Moreira de Oliveira et al. 2019, Yi et al. 2019, Ribeiro et
al. 2021), which may help explain our finding that northern seeds
outperform southern seeds at both common gardens.
Our prediction that southern seeds would outperform northern seeds also
assumed that southern populations had adequately adapted to historically
warmer conditions and that these conditions match recent climate
warming. Given the rapid rate of climate change in the region and the
high degree of habitat fragmentation throughout the Klamath Mountain and
Willamette Valley ecoregions (Wilson 1998, Floberg et al. 2004), it is
possible that southern populations may not yet be adequately adapted to
their current climates. Because our study only lasted one growing
season, we may have assessed germination during an abnormal winter that
favored northern-sourced seed. Although a multi-year analysis of
germination was outside the scope of this study, multi-year studies
allow for a more thorough understanding of the mechanisms driving
differential germination and establishment patterns (Rice & Knapp 2008,
Pfeifer-Meister et al. 2012, Merges et al. 2020)