Site factors affecting black ash ring growth in northern Minnesota

Black ash (Fraxinus nigra) is a species used for basketmaking by several Native American Tribes in Eastern North America. In recent years, there has been a decline in availability of quality ‘basket trees’, and the purpose of this study was to determine what site characteristics allow for the growth of appropriate ring widths required for black ash splints used to make baskets. Three ecosystems – lowland wet forest (2 study sites), upland mesic forest (2 study sites) and a series of woodland ponds (4 study sites) – were studied on the Chippewa National Forest in northern Minnesota. At each study site 4–16 plots, each 5-m in radius, were centered on a subject black ash tree. On each plot basal area of all trees and environmental variables such as herbaceous vegetation, composition and structure were measured. On the lowland study sites, volume of soil in hummocks on which single trees grew was also measured. Regression was used to relate ring width to environmental variables. Tree DBH had a significant positive influence on ring width for upland and woodland pond sites (R2 = 51.0%, p < 0.001; R2 = 42.0%, p = 0.031, respectively). Percent cover of herbaceous vegetation showed a significant negative impact on 5-year ring growth on the lowland sites (R2 = 59.9%, p < 0.001) but no significant trends for uplands or woodland ponds. Thus, it seems likely that these herbs, principally sedges, limit tree growth on lowland sites, where total soil volume available for roots is extremely limited by high water tables.