Effects of gamma radiation on biomass production of ground vegetation under broadleaved forests of Northern Wisconsin

Effects of gamma irradiation (10,000 Ci ¹³⁷Cs source) for one growing season on biomass production of ground vegetation under northern Wisconsin aspen and maple-aspen-birch forests and on an abandoned logging road were evaluated during and one year after irradiation. No significant changes in production were determined during the irradiation year. One year later three distinct zones—semi-devastated, herbaceous, and original forest—developed along the radiation gradient. Biomass production under forest canopies decreased significantly in the semi-devastated zone, increased significantly in the herbaceous zone (primarily responding to additional light), and remained unchanged under the original forest. Logging road vegetation responded similarly but the changes were restricted within higher radiation doses. At comparable levels of radiation, production of species of the logging road vegetation was affected less than that of species under forest canopies. Such a trend was predictable from the generally smaller interphase chromosome volumes, ICV's, of the species on the logging road and from their ability to survive in severe habitats.