Data from: When spring ephemerals fail to meet pollinators: mechanism of phenological mismatch and its impact on plant reproduction

The flowering phenology of early-blooming plants is largely determined by
snowmelt timing in high-latitude and high-altitude ecosystems. When the
synchrony of flowering and pollinator emergence is disturbed by climate
change, seed production may be restricted due to insufficient pollination
success. We revealed the mechanism of phenological mismatch between a
spring ephemeral (Corydalis ambigua) and its pollinator (overwintered
bumble bees), and its impact on plant reproduction, based on 19 years of
monitoring and a snow removal experiment in a cool-temperate forest in
northern Japan. Early snowmelt increased the risk of phenological mismatch
under natural conditions. Seed production was limited by pollination
success over the three years of pollination experiment and decreased when
flowering occurred prior to bee emergence. Similar trends were detected on
modification of flowering phenology through snow removal. Following
snowmelt, the length of the pre-flowering period strongly depended on the
ambient surface temperature, ranging from 4 days (at >7ºC) to 26
days (at 2.5ºC). Flowering onset was explained with an accumulated surface
degree-day model. Bumble bees emerged when soil temperature reached 6ºC,
which was predictable by an accumulated soil degree-day model, although
foraging activity after emergence might depend on air temperature. These
results indicate that phenological mismatch tends to occur when snow melts
early but subsequent soil warming progresses slowly. Thus, modification of
the snowmelt regime could be a major driver disturbing spring phenology in
northern ecosystems.