How resilient is boreal forest vegetation growing on acidic podzols to the environmental change caused by alkaline kiln dust pollution? How adaptive is the vegetation, when species pool and time for dispersal do not limit? How constant is the species niche breadth along the soil pH gradient?Location
Region of 30 km around the Kunda cement plant, northern Estonia (59°30′ N, 26°32′ E), which has been continuously polluted last 140 years.Methods
We sampled 20 forest stands on sandy gleyic podzols at various distances from the pollution source, leeward and windward of prevailing winds. Data processing: principal components analysis for gradient generalization, indicator species analysis for grouping species along the pollution gradient and generalized linear model analyses to estimate species reaction to pollution, considering covariates.Results
The impact of alkaline dust accumulated over a century persisted despite resolute reductions of pollution. Forest soil conditions changed 10 km leeward and 5 km windward from the source: the litter pH level changed from 3.6 to 4.5 in unpolluted forests to 7.1–7.4 in the heavily polluted forests, and soil Ca content increased ten-fold. Soil alkalization has induced a remarkable succession from typical boreal vegetation toward vegetation of boreo-nemoral or calcareous habitats. We detected a linear increase of species richness from habitats on acidic soils (unpolluted) to newly formed alkaline soils (polluted habitats), reflecting the species pool composition and size, which is known to be large for calcicolous species. The establishment of several endangered calcicolous species shows the lack of dispersal limitation and points on their narrow soil pH niche. The niche breadth of species along the pH gradient varied among species, but only a few species appeared to be pH generalists.Conclusions
Species ranking along the pH and/or Ca gradients indicates (1) the existence of different ecological guilds in terms of ecological niche use, and (2) the formation of a new community is dictated by the tolerance level of each species. This supports the individualistic community assembly rule suggested by Gleason. We find that such polluted regions with disturbed communities have high scientific value as long-term ecological experiments, but this might lead to conflict between the peculiar biodiversity complex and human well-being.
Soil alkalization of the pine forest's in northern Estonia caused by cement kiln dust pollution has induced a succession from typical boreal vegetation toward vegetation of boreo-nemoral habitats. The establishment of calcicolous species shows their lack of dispersal limitation; species filtering success is determined by a critical level at the one end of the niche breath along the limiting gradient.