Tree-ring growth in a chronically gamma-irradiated forest

Annual tree-ring growth was measured in populations of trees exposed to chronic gamma radiation at a field site in the Canadian boreal forest. Cores from balsam fir, black spruce, jack pine and white birch were collected and ring widths measured during the pre-irradiation period, the irradiation period from 1973 to 1986 and the post-irradiation period until 1992. Cores were collected from various sites with dose rates ranging from background control levels to a maximum of 7.1 mGy h−1. Intercomparisons among different irradiation treatments and among different periods showed some statistical differences, but these could not be consistently attributed to an impact caused by the irradiation. Dose rates less than 2 mGy h−1 did not cause an impact on tree-ring growth for any of the tree species.