Fertilization Fails to Increase Diameter Growth of Sawlog-size Northern Hardwoods in Upper Michigan

Five hundred individual, sawlog-size crop trees in a selectively managed northern hardwood stand were fertilized with 2.61 kg (5.75 lbs) of N-P-K fertilizer per tree in June 1970. The stand is predominantly sugar maple (Acer saccharum Marsh.) growing on a deep silt loam soil of good site quality. Three- and six-year diameter at breast height (dbh) and basal area growth were analyzed by treatment and diameter class. Fertilization did not increase dbh or basal area growth during either measurement period. Mean annual dbh growth of both fertilized and control trees was 0.41 cm (0.16 in.); trees in all diameter classes grew at essentially the same rate. Nearly half of the study trees grew 2.54 cm (1.0 in.) or more during the 6-year period, and fertilization did not change this proportion. Natural supplies of nutrients in good hardwood soils appear adequate for rapid growth of these species. Periodic cuttings maintain superior growth rates and contributes to efficient nutrient cycling. Fertilization is not recommended on sites like this because growth responses are not likely to justify costs.