Damage measurements and reproductive outcomes following phenologic delay and floral freezing of a population of Prunus pumila plants

Abstract

There are advantages flowering early in the spring, which include greater pollinator fidelity and longer fruit maturation time. But plant phenology has advanced in recent years making many plants vulnerable to freezing damage from late frosts. To determine the costs and benefits of flowering early in the spring, we exposed Prunus pumila plants to two freezing treatments and a delayed flowering treatment in subsequent years. Data were collected on ovary swelling, fruit production and pollinator visitation on hand-and open-pollinated plants in all treatments. We also measured tissue damage after freeze events. Our results suggest that flowering time and temperature affect reproductive success, with fewer fruits produced after hard freezes. The same was not true for light freezes, which had minimal impact on reproduction. Freezing damage to plants after a hard freeze did affect the number of Dipteran pollinators but not the overall pollinator visitation rate. Despite the clear impact of freezing temperatures on plant reproduction, there were also advantages for flowering early as reproductive output decreased during with delayed flowering. Our findings suggest that Prunus pumila will retain the ability to attract pollinators and produce viable seeds if exposed to false spring conditions that involve a light freeze, but hard freezes may reduce yield by an order of magnitude. Although the advantages to flowering early may outweigh the risk of freezing damage under current conditions, it is possible that flower viability may be constrained under continued climate warming.