Effects of snow on reproduction of perennial Thalictrum dioicum: Plants survive but seedlings fail to recruit with reduced snow cover

Abstract

Premise: Future reductions in snow cover are expected in temperate climates, likely leading to more soil-freezing events and damage to plant tissues. However, whether and how plants can compensate for this damage may depend on the timing of damage and on plant allocations to seed size and number. We need more information about how seed production, germination, and seedling recruitment might respond to changes in snow cover.

Methods: We manipulated snow cover over three seasons in a common garden experiment with four treatments: (1) "control," where snowpack was left unmanipulated throughout the winter season; (2) "late addition," where snowpack was experimentally increased at the end of the winter season in order to delay the onset of spring; (3) "late removal," where snowpack was experimentally reduced at the end of the winter season in order to advance the onset of spring; and (4) "freeze," a consistent removal treatment, where snowpack was experimentally reduced following every substantial snowfall in order to induce freeze-thaw events in the soil. In all treatments, we measured survival, growth, reproduction, and recruitment of a native perennial herb, Thalictrum dioicum.

Results: Reduced snow cover minimally influenced adult survival. Instead, individuals that experienced reduced snow cover throughout the winter produced more massive seeds, whereas individuals that experienced a single snow removal at the end of the season produced less massive seeds. Seedling recruitment was lower in the removal treatments than in the control, as a result of failure to germinate in the freeze treatment and seedling mortality in the late removal treatment.

Conclusions: Both reduced snow cover throughout the winter and a single late snow removal in the spring reduced seedling recruitment, but for different reasons, suggesting that a holistic approach to the life cycle is needed to understand responses to shifting climates.

Keywords: Ranunculaceae; allocation; climate change; germination; life history; seed size; snow cover; trade-off; winter.