SPATIOTEMPORAL PATTERNS IN THE COMPONENTS OF REGENERATION OF 4 SYMPATRIC TREE SPECIES - ACER-RUBRUM, A-SACCHARUM, BETULA-ALLEGHANIENSIS AND FAGUS-GRANDIFOLIA

1 The spatiotemporal patterns of seeds in the seed rain and the seed bank, and of seedlings may have important, ecologically adaptive implications for a species, particularly with regard to natural disturbance and forest dynamics. One may look for specific assemblages of traits corresponding to various 'strategies' of regeneration enabling species to coexist in the face of an ever-changing environment. Species differing in shade tolerance and occupying the same habitat would be expected to have such contrasting assemblages of regeneration traits. 2 Here, I present an analysis of the spatiotemporal patterns of the seeds in the seed rain and the seed bank, and of newly emerged seedlings of Betula alleghaniensis, Acer rubrum, A. saccharum, and Fagus grandifolia. The study covers a four-year period and considers two spatial scales (stand and microsite). The species studied are typical of the hardwood forest of eastern North America and represent an increasing gradient of shade tolerance from Betula to Fagus. 3 Of the traits considered, only seed bank type and grain of dispersion, and seedling and seed bank dispersion patterns were useful discriminators between the four species studied. Shade intolerant species tended to have a persistent, coarse-grained and contagious seed bank, with newly emerged seedlings contagiously dispersed, while shade tolerant species often had a transient, finer-grained and randomly dispersed seed bank, with newly emerged seedlings randomly dispersed. 4 The widely held belief that species must differ in many key-characters in order to coexist has led to the search for coevolved assemblages of regeneration traits for sympatric species. However, when these traits are analysed in detail, few, if any such assemblages can be identified. Environmental heterogeneity in space and in time, from both biotic and abiotic sources, appears to favour the maintenance of some flexibility in the expression of regeneration traits.