A Survey of Sugar Maple Nutrition in Vermont and its Implications for the Fertilization of Sugar Maple Stands

Can fertilization of sugar maple stands lead to increased diameter growth, better crown conditions, and/or added sugar production? We have wrestled questions like these for over a decade at research sites in northwest Vermont. Recently we have begun to expand our understanding of maple nutrition by examining stands in a wider geographic area. The effectiveness of fertilization depends in large part on soil nutrition. Where nutrients are limiting, and tree vigor is not otherwise affected by conditions such as poor drainage or shallow soils, careful fertilization has, in some cases, improved crown health and radial (diameter) growth. In the early 90's, we compared several sugarbushes in our area with contrasting health, and found that poor stands, those that showed significant crown dieback, had much lower soil and foliar calcium. Three years after addition of lime (about 1.5 tons/acre) and smaller amounts of potassium and magnesium to the deficient sugarbushes, mature trees in these stands had improved crown health and radial growth rates had doubled compared to untreated controls (Wilmot et al., 1996). We have yet to demonstrate improved sugar production with fertilization, although some of our data suggested that sap volume was positively correlated with crown health (Wilmot et al. 1995). The influence of fertilization on the sugar production of mature trees is the subject of a current study at the Proctor Center. We undertook the current survey to characterize soil conditions in Vermont maple stands, to determine to what extent calcium or other nutrients might be limiting. Sampling was carried out during the summers of 1998 and 1999. We collected soils, foliage, and wood cores from 29 stands, both sugarbushes and non-sugarbushes. Because these stands were monitored by the North American Maple Project (NAMP) we also obtained detailed information about the health of these stands over the past decade. At each site we took ten increment cores from trees <11" dbh, five composite foliar samples, each made by pooling leaves from several sun-exposed mid-canopy branches, and five soil samples from each of two depths. NAMP stands are not randomly located, therefore, although this survey covered most of the state, we were not attempting to generalize about the health of sugar maple across Vermont, but rather to characterize tree condition on these various soils.