EFFECTS OF 76 HZ ELECTROMAGNETIC-FIELDS ON FOREST ECOSYSTEMS IN NORTHERN MICHIGAN - TREE GROWTH

Since 1984, the possible effects of extremely low-frequency electromag netic (EM) fields generated by a 76 Hz communication antenna on the gr owth and productivity of four deciduous and one coniferous species hav e been studied in the Upper Peninsula of Michigan. Results from two re search sites are discussed here: one site near an antenna element and a control site located 50 km from the communication system. Growth mod els for individual tree diameters were developed for northern red oak (Quercus rubra), paper birch (Betula papyrifera), aspen (Populus tremu loides with a few individuals of P. grandidentata), and red maple (Ace r rubrum). A growth model for individual tree height was developed for young red pine (Pinus resinosa). Average differences between the obse rved and predicted growth were calculated for each growing season and then compared between the study sites and across the study periods to evaluate changes in growth patterns which could be attributed to EM fi eld effects. For aspen and red maple, the results showed a stimulation of diameter growth at magnetic flux density levels of 1 to 7 milliGau ss; height growth of red pine was increased at about the same exposure levels. There are no clear indications of an EM field effect on total annual diameter growth for either of the other two species.