Many plant populations are shifting in both phenology and distribution in response to climate change. In the process, different life history stages are likely to shift at different rates, and locally adapted traits may become maladaptive in new environmental contexts. Understanding how these temporal and spatial shifts interact is important for predicting how plant populations will be affected as the climate continues to rapidly change. We used reciprocal seed and seedling transplants in the field and common garden experiments in the greenhouse to measure early life stage phenology and establishment success of four wildflower species (Aquilegia coerulea, Erythronium grandiflorum, Geranium richardsonii, and Helianthella quinquenervis). We measured success of seeds and seedlings transplanted to low (2900 m), mid (3200 m), and high (3500 m) elevations within the current ranges of these species along a subalpine gradient in the Rocky Mountains in Colorado, USA. We tested whether germination and early growth phenologies are environmentally determined or whether they reflect adaptation to particular elevations.
Results/Conclusions
For transplanted seeds, germination success was greatest at high elevation and lowest at mid elevation. Similarly, survival of transplanted seedlings was greatest at high elevation and lowest at mid elevation. Thus, at early life stages, these species performed best at high elevation, regardless of origin. The low success of seeds and seedlings at mid elevation, where soils were driest, suggests these sites may act as a barrier to upward migration. Under common garden conditions in the greenhouse, seeds from mid elevation exhibited the earliest germination and the fastest development time from seed to juvenile plant. Advanced germination phenology and accelerated development of seedlings originating from mid elevation may reflect adaptation to locally dry conditions, enabling plants to become established before soil moisture declines. As high elevations become more favorable for plant establishment, upward migration of plant populations from lower elevations may be impeded by dry conditions along subalpine gradients.