1.Why some herbaceous plant species refrain from sprouting in some years is a longstanding puzzle in plant ecology. When vegetatively “dormant”, the plant lives as a rootstock, but does not produce or maintain photosynthetic tissue. During this time, energy may be remobilized from resource reserves, or acquired from mycorrhizal fungi, although the mechanisms are still poorly understood. If vegetative dormancy is adaptive, it may be in response to a harsh environment, to life history costs, or as a bet-hedge against unpredictable environmental variability. 2.We tested whether vegetative dormancy is adaptive via game theoretical analysis of deterministic and stochastic ahistorical and historical life history models parameterized with long-term census data for two long-lived plants, Anemone americana and Cypripedium parviflorum. The ahistorical deterministic model provided a test of the hypothesis that dormancy is adaptive in response to a generally harsh environment and/or short-term life history costs, while the historical model tested whether long-term costs drove the evolution of dormancy. The stochastic ahistorical model provided a test of whether dormancy is a bet-hedging trait. 3.We found that vegetative dormancy is an adaptive consequence of life history costs of growth to survival, and that these costs may be operating under a variable but generally harsh environment. Such costs led to sprouting and survival probabilities that generally increased with size in adults but never reached unity, and decreased with size in juveniles. Historical deterministic models particularly predicted observed sprouting frequencies, while deterministic ahistorical and stochastic models did not, suggesting although the environment is likely stressful and fluctuates between harsh and mild states, short-term costs and temporal stochasticity alone do not explain observed sprouting frequencies. 4.Synthesis. Life history costs can drive the evolution of seemingly paradoxical traits. In particular, growth can lead to survival costs that may become significant in future years. These costs may be incurred via the use of stored reserves that, once used, cannot be used in the next several years. Such costs are the currency favoring the evolutionary maintenance of vegetative dormancy in two distantly related perennial plant species, and may account for dormancy throughout the Plant Kingdom.

Matrices.For.DryadExcel file containing spreadsheet with ahistorical and historical demographic matrices used in deterministic and stochastic invasibility analyses.