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

The timing of spring phenology represents 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 exist, indicating that this trade-off is largely untested empirically. Here, we present a 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, predictions indicate that advances in spring phenology do not affect the lethal frost risk under light and moderate warming scenarios. This is likely due to the reduced temperature sensitivity, consistent with trade-off predictions. By contrast, in the high-warming scenario, the freezing safety margin is predicted to expand (by ~1.7 °C), resulting in a lower lethal frost risk. This expansion may compensate for the diminished freezing resistance predicted under extreme warming. Our findings challenge the conventional view that 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.