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Understory forest plants are often limited by shade from the canopy above them. Many such species therefore make use of a shade avoidance strategy referred to as “phenological escape” to access ephemeral light availability during periods when the canopy above them is open (e.g., in early spring). In this primer, we review past literature on phenological escape and related topics. We discuss (1) the physiological importance of this shade avoidance strategy, (2) the effects that climate change may have on species performance via changes in phenological escape, (3) the potential for climate change to result in phenological mismatch related to shade avoidance, and (4) the potential avenues of future research in this area of study. Phenological escape is an important strategy used by spring-active plant species ranging from spring ephemeral wildflowers to deciduous tree seedlings, allowing them to assimilate 50%–100% of their annual carbon budgets before the canopy closes above them. Access to spring light, and thus success of this shade avoidance strategy, is projected to change in response to climate change. Change in access to light, and therefore change in spring performance, likely depends on functional group (woody vs. nonwoody plants), continent, and other geographic and environmental drivers. 

The herbaceous layer accounts for the majority of plant biodiversity in eastern North American forests, encompassing substantial variation in life history strategy and function. One group of early‐season herbaceous understory species, colloquially referred to as spring ephemeral wildflowers, are ecologically and culturally important, but little is known about the prevalence and biogeographic patterns of the spring ephemeral strategy. Methods: We used observations collected by the Global Biodiversity Information Facility (GBIF) to quantify the ephemerality of 559 understory forb species across eastern North America and classify them according to a continuous ephemerality index (ranging from 0 = never ephemeral to 1 = always ephemeral). We then used this information to model where ephemeral forbs were most common across the landscape with the goal of identifying geographic and environmental drivers important to their distributions and ranges. Results: Only 3.4% of all understory wildflower species were spring ephemerals in all parts of their range, and 18.4% (103 species) were ephemeral in at least part of their range. Spring ephemerals peaked in absolute species richness and relative proportion at mid latitudes. Conclusions: Spring ephemeral phenology is an important shade‐avoidance strategy for a large segment of the total understory species in temperate deciduous forests. In North America, the strategy is relatively most important for forest understories at mid latitudes. The definitions of spring ephemerality we provide here serve as an important ecological context for conservation priorities and to evaluate responses of this biodiverse group to future environmental change.