Rain timing, not warmth, drives California wildflower bloom cycles
Bontrager M, Worthy SJ, Leventhal L, Maloof JN, Gremer JR
Phenology
Native wildflowers in California's hills bloom on rain's schedule, not the calendar's, and this study confirms that first-rainfall timing tells you more about where a plant sits in its life cycle than spring warmth does.
Scientists used old pressed plant specimens from museum collections to reconstruct the complete weather each plant lived through, from germination to the day it was collected. They found that plants that received early, plentiful rain were further along in flowering, and this pattern held across many related species, suggesting it's a shared inherited trait. But even with full rainfall histories in hand, they couldn't reliably predict how many seeds a plant would produce, pointing to other players like pollinators or neighboring plants as the missing piece.
Key Findings
Precipitation onset and total amount were stronger predictors of phenological stage than temperature across all 14 Streptanthus annual species studied
Earlier rainfall was associated with greater phenological advancement, a relationship that showed significant phylogenetic signal, meaning it is evolutionarily conserved across related lineages
Climate variables explained very little of the variation in estimated reproduction, suggesting seed set is governed by factors beyond growing-season weather
chevron_right Technical Summary
Researchers reconstructed the full-season weather that pressed herbarium specimens actually lived through, then asked which climate factors explain how far along in flowering a plant was when it was collected. Rainfall timing and total amount predicted phenological stage better than temperature across 14 annual wildflower species, but climate explained seed production far less well.
Abstract Preview
Original paper
Specimen-tailored 'lived' climate reveals precipitation onset and amount best predict specimen phenology, but only weakly predict estimated reproduction across a clade.
Herbarium specimens are widely distributed in space and time, thereby capturing diverse conditions. We reconstructed specimen 'lived' climate from knowledge of germination cues and collection dates...
open_in_new Read full abstractAbstract copyright held by the original publisher.
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