Advancing frost dates have reduced frost risk among most North American angiosperms since 1980

Abstract

In recent decades, the final frost dates of winter have advanced throughout North America, and many angiosperm taxa have simultaneously advanced their flowering times as the climate has warmed. Phenological advancement may reduce plant fitness, as flowering prior to the final frost date of the winter/spring transition may damage flower buds or open flowers, limiting fruit and seed production. The risk of floral exposure to frost in the recent past and in the future, however, also depends on whether the last day of winter frost is advancing more rapidly, or less rapidly, than the date of onset of flowering in response to climate warming. This study presents the first continental-scale assessment of recent changes in frost risk to floral tissues, using digital records of 475,694 herbarium specimens representing 1,653 angiosperm species collected across North America from 1920 to 2015. For most species, among sites from which they have been collected, dates of last frost have advanced much more rapidly than flowering dates. As a result, frost risk has declined in 66% of sampled species. Moreover, exotic species consistently exhibit lower frost risk than native species, primarily because the former occupy warmer habitats where the annual frost-free period begins earlier. While reducing the probability of exposure to frost has clear benefits for the survival of flower buds and flowers, such phenological advancement may disrupt other ecological processes across North America, including pollination, herbivory, and disease transmission.

Stronger Spring Phenological Advance in Future Warming Scenarios for Temperate Species With a Lower Chilling Sensitivity

“…However, earlier spring phenology may lead to higher frost risk at the beginning of the growing season. A trend toward an earlier last frost date may result in stable or even decreased frost risk ( Dai et al, 2013 ; Park et al, 2021 ). A recent study demonstrated that the late-spring frosts increased more in Europe and East Asia than in North America, and in the future, 35% and 26% of Europe’s and Asia’s forests will be increasingly threatened by frost damage ( Zohner et al, 2020b ).…”

The growing and vital role of botanical gardens in climate change research

“…Similarly, plants will generally not replace flowers damaged by late frosts and will lose fitness. Using data from botanical gardens and other locations and herbarium specimens, Zohner et al (2020) and Park et al (2020) examined that risk of late-season frost to young leaves and flowers in scenarios of future climate, finding that risk is increasing in Europe and Asia but is declining in North America.…”

“…(2020) and Park et al . (2020) examined that risk of late‐season frost to young leaves and flowers in scenarios of future climate, finding that risk is increasing in Europe and Asia but is declining in North America.…”

“…Frost damage can limit species ranges (native and nonnative) and can severely harm crop and horticultural species. Studies have shown that the risk of frost is changing differently in different locations – declining in North America, but increasing in Europe and Asia – as a result of climate change (Park et al ., 2020; Zohner et al ., 2020). However, these results are based only on trends in phenology and the dates of last frost in the spring; they lack data on frost tolerance for different species that is important for assessing frost risk.…”

Phenological Sensitivities to Climate Are Similar in Two Clarkia Congeners: Indirect Evidence for Facilitation, Convergence, Niche Conservatism, or Genetic Constraints

“…The first is represented by detailed studies of individual species in which the sensitivity to long-term mean climatic conditions and/or to inter-annual variation in climate is estimated, and some report interactions between predictor variables that affect phenological behavior (Robbirt et al 2011;Gaira et al 2011Gaira et al , 2014Matthews and Mazer 2016;Ellwood et al 2019;Love et al 2019;Petrauski et al 2019;Banaszak et al 2020;Pearson et al 2021). The second category comprises synthetic studies of multiple species and higher taxa, aiming to detect general similarities and differences among taxa or communities with respect to their phenological responses to climatic factors that vary over time or space (Primack et al 2004;Miller-Rushing et al 2006;Houle 2007;Gallagher et al 2009;Diez et al 2012;Panchen et al 2012Panchen et al , 2017Diskin et al 2012;Calinger et al 2013;Li et al 2013;Mazer et al 2013;Hart et al 2014;Park 2014;Davis et al 2015;Kharouba and Vellend 2015;Rawal et al 2015;Munson and Long 2017;Park and Schwartz 2018;Jones and Daehler 2018;Mazer 2018, 2019;Berg et al 2019;Pearson 2019;Kopp et al 2020;Park, Ramirez Parada, and Mazer 2020;Reeb et al 2020). A few studies in both categories have begun to investigate sources of intraspecific variation in phenological sensitivity (Matthews and Mazer 2016;…”