Quantifying the trade-off between spring phenology and lethal frost risk: a global meta-analysis

The timing of spring phenology reflects a critical trade-off between growing season extension and frost risk avoidance, the balance of which governs plant fitness and shapes plant species’ distributions. However, few quantitative assessments of the spring lethal frost risk exist, meaning that this trade-off is largely untested empirically. Here, we present the first global meta-analysis encompassing 193 plant species across 126 study sites, finding consistently high freezing resistance (to -12°C) with remarkably low lethal frost risk (safety margin of 17°C) during spring emergence. Under projected climate warming scenarios, predicted advances in spring phenology did not affect the lethal frost risk for two plausible warming scenarios (SSP1-2.6 and SSP2-4.5), this was likely due to reduced temperature sensitivity, consistent with trade-off predictions. By contrast, in the high-warming scenario (SSP5-8.5), the freezing safety margin was predicted to expand (by ~ 1°C), resulting in a lower lethal frost risk, this may compensate for the diminished freezing resistance predicted under warming. Our findings challenge the conventional view of simple-environmental factors moderate spring phenology and highlight the necessity of incorporating biotic factors (e.g., freezing resistance) and biotic processes (e.g., early growth versus frost risk trade-offs) into next-generation phenological models to enhance prediction accuracy under climate change.