Regeneration of black ash (Fraxinus nigra Marsh.) in hardwood swamps of the Great Lakes – St. Lawrence Forest Region

Abstract

An inductive, ordination-based approach was used to explore patterns in the microenvironment and natural regeneration of black ash across a range of representative stands in the central Ontario portion of the Great Lakes -St. Lawrence Forest Region (GLSL) near Lake Nipissing, Ontario, Canada. The objective of this study was to describe patterns of regeneration of black ash and determine the associations between multiple indicators of black ash regeneration success and biotic and abiotic factors. Using a randomized sampling design with specific selection criteria, 12 black ash stands were sampled, each with three 400 m2 circular sample plots that contained three 4 m2 sub-plots. A suite of environmental variables such as elevation, topographic wetness index, slope, and soil characteristics (percent moisture, pH, total nitrogen, exchangeable phosphorus, potassium, magnesium) were determined for each stand. Variables capturing regeneration potential, including density, diameter, and height of all germinants, seedlings, saplings and sprouts were also collected. A sample of 15 dominant or co-dominant trees in each stand, as well as numerous black ash seedlings, saplings and sprouts were examined using dendrochronological methods to estimate ages. Principal component analysis ordinations were performed exploring the variation in environment and black ash regeneration variables among the stands. High soil moisture and the presence of canopy gaps, (as indicated by high standard deviation of canopy closure), were key variables associated with greater abundance of regeneration. Black ash was the dominant species in all stands, which were also generally characterized by a common reverse-J diameter distribution. It was observed that black ash in the sapling layer reached substantial ages (up to 60 years), indicating they are capable of withstanding long periods of suppression below the canopy. Collectively, these findings suggest that black ash-dominated stands in the study area are regenerating in multiple cohorts. Based on these patterns, it appears that regeneration in these stands is occurring through gap-phase mechanisms, suggesting single tree selection as the best management option for black ash in the GLSL.