Elevational adaptation and plasticity in seedling phenology of temperate deciduous tree species

Abstract

Phenological events, such as the initiation and the end of seasonal growth, are thought to be under strong evolutionary control because of their influence on tree fitness. Although numerous studies highlighted genetic differentiation in phenology among populations from contrasting climates, it remains unclear whether local adaptation could restrict phenological plasticity in response to current warming. Seedling populations of seven deciduous tree species from high and low elevations in the Swiss Alps were investigated in eight common gardens located along two elevational gradients from 400 to 1,700 m. We addressed the following questions: are there genetic differentiations in phenology between populations from low and high elevations, and are populations from the upper elevational limit of a species' distribution able to respond to increasing temperature to the same extent as low-elevation populations? Genetic variation of leaf unfolding date between seedlings from low and high populations was detected in six out of seven tree species. Except for beech, populations from high elevations tended to flush later than populations from low elevations, emphasizing that phenology is likely to be under evolutionary pressure. Furthermore, seedlings from high elevation exhibited lower phenological plasticity to temperature than low-elevation provenances. This difference in phenological plasticity may reflect the opposing selective forces involved (i.e. a trade-off between maximizing growing season length and avoiding frost damages). Nevertheless, environmental effects were much stronger than genetic effects, suggesting a high phenological plasticity to enable tree populations to track ongoing climate change, which includes the risk of tracking unusually warm springs followed by frost.

Variation in leaf flushing date influences autumnal senescence and next year’s flushing date in two temperate tree species

“…Buds of oak and beech were formed in late summer, in line with previous studies (55,56). Leaf flushing observations were conducted on the terminal bud of each individual sapling, according to the following phenology scale: (1) undeveloped bud: bud still in winter dormancy; (2) swollen bud: green or elongated bud with broken scales; (3) leaf flushing: leaf bases still hidden in bud scales but leaf tips detached from the bud axis; and (4) leaf unfolded: the entire leaf blade and the leaf stalk were visible.…”

Plastic Responses to Elevated Temperature in Low and High Elevation Populations of Three Grassland Species

“…1). Similarly, a study with seedlings of European deciduous tree species found that high elevation provenances exhibited less temperature-induced plasticity in growth and leaf phenological traits [103], [104]. The authors argued that low plasticity at high elevations was a result of different directional selection for reduced temperature sensitivity and a stronger influence of photoperiodism, which may reduce the risk of damage by unpredictable late spring frost events [105].…”

Past-century decline in forest regeneration potential across a latitudinal and elevational gradient in Canada

“…Tree development and phenology are related to climate through evolutionary controls, influencing the early niche space of trees, with plasticity potentially providing a buffer to maintain fitness (Aitken et al, 2008;Vitasse et al, 2013). Important tree development and phenology events include germination, establishment, bud burst, growth, bud set, leaf senescence, seed fall, and dormancy, among others (Richardson et al, 2013;Walck et al, 2011).…”

“…Environmental effects are estimated to exert greater influence on plasticity than genetics in northern forests (Vitasse et al, 2013), while phenotypic variation reflecting phylogeographic origins (Alberto et al, 2013) is not necessarily adaptive (Duputié et al, 2015). Extreme weather events, such as frost or drought, occurring at critical times during tree development can have strong demographic effects on forests.…”