The relationship of the soil seed bank and understory vegetation in old-growth northern hardwood–hemlock treefall gaps

Abstract

In mature northern hardwood forests, small treefall gaps constitute an important mode of compositional and structural change within the long return time of larger catastrophic disturbances. The soil seed bank and patterns in vegetation layers are described in this disturbance regime context. In these small treefall gaps, herbaceous and woody vegetation species present are similar to those of forest understory plots, differing primarily in abundance. Seed bank communities are compositionally more similar among gaps than forest understory plots, but vegetation similarity is equal among forest plots and among gaps. Seed bank-vegetation similarity is greater among forest plots than in gaps. Seed bank strategies differ among the plant species characteristic of the differing forest layers. Dominant canopy tree species (Acer saccharum, Tsuga canadensis, Betula alleghaniensis) are not an important component of the seed bank. Bird-dispersed shrub and herbaceous species and ant-dispersed herbs are important in the seed bank, especially in gaps. In particular, based on gap seed bank response, it appears that understory shrub abundance and pattern within the forest change with the time since large-scale disturbance, in accordance with species adaptations to the size and increase in number of small treefalls in the mature forest. These species patterns may relate to the patchy nature of resource availability that develops, especially that of nitrogen, which is controlled by the canopy species–gap mosaic. Key words: treefall gaps, soil seed bank, disturbance, northern hardwoods, old growth, succession, shrubs.