Habitat relationships and survivorship of tree seedlings in hemlock-hardwood forest

Abstract

This study was designed to determine (i) if newly germinated and older seedlings of different tree species occupied different microhabitats in the understory of mature hemlock forest; (ii) if different aged seedlings of the same species occupied different microhabitats; and (iii) if initial survivorship of newly germinated seedlings is correlated with microhabitat. In June 1987, 13 environmental variables were measured around different aged individual seedlings of Acer rubrum, Acer saccharum, Betula lutea, Prunus serotina, and Tsuga canadensis. Seedlings of A. rubrum and T. canadensis occupied habitats with more coniferous litter than seedlings of A. saccharum and P. serotina. Different aged seedlings of A. rubrum generally were found in similar habitats, but these microhabitats were different from randomly located samples. Younger seedlings of T. canadensis occupied habitats with significantly shallower litter layers and more coniferous litter than older seedlings and random points. Habitat structure and survivorship of newly germinated seedlings of B. lutea and A. rubrum was monitored from June to September 1988. Initially, A. rubrum had a higher mortality rate than B. lutea. For both species, survivorship was significantly greater in habitats with shallower litter and less woody debris. These differences disappeared later in the growing season. These results imply that seedlings occur in different microhabitats, that habitat differences occur for different aged seedlings, and that microhabitat does initially affect seedling survival. Thus, studies of older seedlings and saplings do not completely incorporate the regeneration strategies of some species. In addition, the "plant's eye view" approach provides a useful method for quantifying habitat factors that affect species distributions both within and between communities. Key words: habitat structure, hemlock forest, litter depth, survivorship, tree seedlings.