Preliminary site-quality evaluation tools for the hardwood forests of central Ontario

Abstract

There are currently no locally-derived, quantitative site-quality evaluation tools available for major tree species in the tolerant hardwood forests of central Ontario. To estimate potential site productivity, site-index curves from the Lake States and a preliminary set of site-form curves for sugar maple are currently being used. Whether these tools are applicable to central Ontario is of concern. The use of site index as a site-quality evaluation tool in uneven-aged mixed-species stands is also questionable. It is also possible site form may not be a valid measure of forest site quality in these types of stands either. A random sample of 62 pure and mixed-species stands with a variety of age-class structures in central Ontario yielded stem analyses data and stand structure information for sugar maple (Acer saccharum Marsh.), American beech (Fagus grandifolia Ehrh.), yellow birch {Betula alleghaniensis Britton) and red oak (Quercus rubra L.). An exploration of height-growth patterns for each species as a function of age and diameter revealed pronounced differences in shape (polymorphism) of height-age curves for all species with changes in site quality. Polymorphism was also evident for suppressed vs. free-growing sugar maple trees, and for sugar maple growing in even- vs. uneven-aged stands and pure vs. mixed-species stands. Differences were less pronounced in height-diameter curves for all species. Preliminary height-growth and site-index equations and curves were developed for sugar maple, American beech, yellow birch and red oak. The central Ontario data, and curves from this study, were then used to examine the applicability of site-index curves for these species from the Lake States to central Ontario. The Lake States curves were shown to differ substantially from those developed in this study, and were inaccurate in application to data from central Ontario. A preliminary assessment of age and stand structure and species mixture impacts on sugar maple height-growth and site index, and forest floor chemistry, revealed no significant differences in sugar maple site index between stands of different composition or age-class structure, and minor differences in forest floor chemistry between stands of different species composition. Preliminary height-growth and site-form equations and curves were also developed for these species. The curves for sugar maple were used to validate existing preliminary curves for sugar maple in Ontario. The curves in this study differed substantially from the preliminary curves and the existing curves were shown to be inaccurate in application to data from this study. An examination of site form as a site productivity measure in uneven-aged, mixed-species stands using data from this study revealed it was unrelated to site index, basal area or ecological variables known to affect forest site quality for these species.