Sexual Regeneration of Black Ash (Fraxinus nigra Marsh.) in a Boreal Floodplain

Abstract

-In northwestern Qu6bec, black ash (Fraxinus nigra Marsh.) is found mostly in floodplains bordering lakes and rivers. In this habitat, population dynamics are largely controlled by spring water level, and sexual regeneration is more abundant in sites less exposed to flooding. The hypothesis tested in this study is that sexual regeneration of black ash in sites slightly exposed to flooding is influenced by fluctuations of spring flood water level. The age structure of two sapling populations (<5 cm DBH) was analyzed using models assuming a constant (exponential function) and decreasing mortality (power function) with age. Both models were useful in describing the age structure of the saplings. The constant mortality model was selected and analysis of the residuals showed that the populations responded in different ways to climate during the 1914-1989 period. While regeneration is correlated with summer and annual precipitation in population A, it is correlated with winter precipitation in population B. Abundant sexual regeneration in both black ash stands suggests that moisture conditions are sufficient to assure constant sexual regeneration, which is, however, diminished during dry years.