Effects of atmospheric fluorides on foliage, and cone and seed production in balsam fir, black spruce, and larch

SIDHU, S. S., and R. J. STANIFORTH. 1986. Effects of atmospheric fluorides on foliage, and cone and seed production in balsam fir, black spruce, and larch. Can. J. Bot. 64: 923-931. Fluoride accumulations and damage symptoms to foliage, cones, and seeds of balsam fir (Abies balsamea (L.) Mill.), black spruce (Picea mariana (Mill.) B.S.P.), and larch (Larix laricina (Du Roi) K. Koch) were monitored at six sites downwind from a phosphorus plant that emitted fluorides during 1982. Atmospheric fluoridation rates ranged from 347.4 pg F . dm-2. week-' (1 1.38 pg F . m-3) at 1.4 km from the fluoride source to 2.5 pg F .dm-2. week" (0.08 pg F . m-7 at 18.7 km. Various degrees of foliar damage (chlorosis, necrosis, needle damage, and defoliation) occurred where fluoride accumulations in the foliage exceeded 20 ppm. This occurred at sites where the fluoridation rates were in excess of 26.0 pg F . dm-2. week'l, and at distances less than 10.3 km downwind from the fluoride source. Reductions in seed size, percent germination, numbers of seeds per cone, number of cones per tree, number of fertile trees, and size reduction, distortion, or mortality of the cones occurred under the same fluoridation rates. Seed output on the windward sides of trees was significantly less than that on the leeward sides. At the most polluted site, seed production in balsam fir, black spruce, and larch, respectively, was reduced to 3.6, 2.6, and 0.0% of that at a control site. All three species in the study are considered to be susceptible to fluoride damage, with respect to both vegetative and reproductive symptoms. Reproductive failure and past mortality of fluoride-damaged conifers have resulted in their replacement by more tolerant hardwood species (e.g., birch (Betula papyrifera Marsh.), alder (Alnus crispa (Ait.) Pursh)) as the dominant forest species in the vicinity of the phosphorus plant.