Tree-ring Growth and Suppression Dynamics for Sugar Maple (Acer saccharum) in the Presence of Inter- and Intra-specific Competition

Northern Wisconsin and the Upper Peninsula of Michigan have been greatly impacted by a history of large-scale logging, resulting in a loss of old-growth forests. Land use and increased deer browsing have changed forest dynamics such that previously logged areas, especially those formerly dominated by the shade tolerant eastern hemlock (Tsuga canadensis), are being replaced by sugar maples (Acer saccharum). We analyzed secondary forests’ growth rates and suppression for Acer saccharum trees in monotypic and heterogeneous stands. We hypothesized that Acer saccharum will have lower growth rates with more suppression in homogeneous stands full of conspecifics, when compared to heterogeneous stands of deciduous and coniferous trees. Our survey sites were located at the University of Notre Dame’s Environmental Research Center within the Ottawa National Forest in Michigan’s U.P. Sampling consisted of stand mapping, inventorying and increment core extraction within three 0.05-ha plots. Stands were chosen to sample across a compositional and age gradient including an Acer saccharum monoculture and two compositionally heterogeneous and uneven-aged plots. If our hypothesis is correct, sugar maple trees in competition with conspecifics will have lower growth rates, which may increase mortality, create canopy gaps, and allow other species to take root. Alternatively, sugar maples may have lower growth rates in the presence of other species, or there may be no species-dependent change in growth rates at all. In any case, understanding sugar maple growth rates can help explain current species assemblages, and predict the future trajectory of species dominance and competition within the Northwoods.