Scaling up from shifting-gap mosaic to geographic distribution in the modeling of forest dynamics

Abstract

Shifting-gap mosaic is incorporated into the dynamic model of size-structured forests along geographic gradients. In the model named SAL(size-age-location), a forest at a geographic location has a patch-age structure, which approximates the shifting-gap mosaic, and a tree-size structure in each patch of the forest. Growth and recruitment occur in each patch and are regulated by patch-scale crowding in terms of upper basal area. Seed production depends on the basal area density of mother trees at the forest scale. Seeds are dispersed to neighboring locations of the geographic landscape. After a century-long “warming” treatment, a resident forest zone prevented, over several millennia, an invading forest zone from achieving a steady-state range of geographic distribution. Introducing the gap mosaic into the model did not make substantial changes in the response of latitudinal forest zones to the warming treatment, but only moderately accelerated the migration speed of invader species. Temporal fluctuation in seed production without interspecific synchronization, or the lottery effect, did not facilitate the migration of invader species at all.