Do longer growing seasons give introduced plants an advantage over native plants in interior Alaska?

Abstract

In interior Alaska, increases in growing season length and rapid expansion of introduced species are altering the environment for native plants. We evaluated whether earlier springs, warmer summers, and extended autumns alter the phenology of leaves and flowers in native and introduced forbs and shrubs in the boreal understory and open-canopy habitats, and whether the responses provide an advantage to either group. We tracked the phenology of 29 native and 12 introduced species over three years with very different spring, summer, and autumn conditions. The native species produced flowers (but not leaves) earlier than the introduced species, and both groups advanced leaf-out and flowering in the early-snowmelt year. However, shifts in phenology between early and late years were similar for both groups. There was no increase in fruit development rate for either group in the warm summer. In contrast, in the year with the extended autumn, the introduced plants extended leaf production and time of senescence much more than native species. While growth form and leaf habit could explain the differences in phenology between native and introduced groups in spring and summer, these traits could not account for differences in autumn. We conclude that in boreal Alaska extended autumns may benefit introduced species more than native ones.