Long-term effects of smelter pollution at Sudbury, Ontario, on forest community composition

Abstract

Forest communities were quantitatively analyzed along a south-southeast transect from a large, 70- to 80-year-old smelter complex near Sudbury, Ontario. None currently exist within 3 km SSE of this smelter. At distances of up to 8 km, pockets of remnant forest communities of various sizes occur, mainly on protected slopes and in valley bottoms. Most hilltops are bare of vegetation, denuded of soil, and blackened from the effects of sulfur dioxide fumigations. Beyond this distance, the forests are more or less continuous, although there are still some bare hilltops as far as 15 km from the smelter. The forests which do occur are relatively depauperate in terms of tree diversity and biomass at the closer sites. Similar effects on the ground flora are also documented, although the forest canopy appears to be more greatly affected than the ground flora. Certain species are widely distributed in the inner polluted areas, while others, notably conifers and such ground flora components as bracken fern and most lichens and bryophytes, are absent from sites closer to the smelter.Some changes in the plant communities close to the Copper Cliff smelter have occurred subsequent to the building of a tall (380 m) smokestack in 1972. These have mainly occurred at sites where soils remain, where residual soil toxicity is not excessive, and where midsummer drought is not severe. Colonization has largely involved the spread of such pioneer grasses as Agrostis hyemalis var. tenuis, A. stolonifera var. major, and Deschampsia caespitosa, and more vigorous growth of certain surviving woody species. The recovery of denuded, blackened hilltops, essentially a primary succession on naked Precambrian bedrock, will be a much slower process.