Climatic determinants of plant phenology in vernal pool habitats

The floral phenology of vernal pool plants is little understood despite being a crucial developmental stage for producing seeds and determining population growth rates. Vernal pools are ephemerally aquatic habitats harboring species adapted to predictable seasonal fluctuations between desiccated and inundated conditions; thus, vernal pool plant phenology is predicted to be particularly responsive to interannual climate variability.

For two vernal pool species, Limnanthes douglasii subsp. rosea (meadowfoam), a vernal pool specialist, and Trifolium variegatum (whitetip clover), a generalist vernal pool associate, we characterized flowering onset, termination, and duration in response to interannual variation of winter precipitation and growing degree hours (GDH). We recorded phenology over 7 years from 2016 to 2022 during a period of high climatic variability, which served as a robust data set.

Warmer and drier environmental conditions during early growth periods were strongly associated with advanced floral phenology later in the life cycle for both species. The floral duration of the vernal pool specialist was influenced by position along the inundation gradient, whereas no such pattern was observed for the vernal pool associate.

To our knowledge, this is the first study quantifying the relationship between vernal pool floral phenology and climate, offering insights into how phenology may shift in response to modern climate change.