Seed production and dispersal patterns in populations of Liriodendrontulipifera at the northern edge of its range in southern Ontario, Canada

Abstract

Seed production, viability, and dispersal patterns were examined for populations of Liriodendrontulipifera L. (tuliptree) at the northern edge of its range in Ontario, Canada, to determine whether these factors could account for its locally limited distribution. Seed production was measured by estimating the number of samara cones present in the canopy, and samaras collected in traps were dissected to determine potential seed viability under different stand conditions. Seed-trap collections were used to delineate seedfall patterns around individual tree stems and within high-density stands. Results indicate that seed production in Ontario begins when trees reach approximately 25 cm diameter at breast height and increases with maturity. Large trees often produce more than 2000 cones in good years, a level similar to more southern populations. The proportion of samaras containing filled seed increases with stand density, ranging from approximately 8–10% for isolated trees to over 20% for old-growth, high-density stands. Although low, these values are comparable to those reported elsewhere in the species' range. Seedfall patterns followed a leptokurtic distribution about individual stems. Life-history attributes other than seed viability may therefore be the cause of the restricted distribution and low population levels of L. tulipifera in Ontario.