Changes in the Abundance of Vascular Plants under the Impact of Industrial Air Pollution: A Meta-analysis

We applied a meta-analytic approach to improve an understanding of the effects of pollution on the primary productivity of terrestrial ecosystems. We identified 73 data sources reporting changes in the abundance of vascular plants (measured as the percentage of ground cover, biomass per unit area, canopy closure and stem basal area) around 75 polluters located in 18 countries (137 effect sizes). The overall effect was negative but varied among the vegetation layers and types of polluters. The strongest detrimental impact on productivity was due to non-ferrous smelters. The abundance of trees was decreased around both acidifying and alkalifying polluters, whereas the abundance of shrubs and field-layer vegetation decreased only near acidifying polluters. Overall, a decline of vegetation was observed in boreal and temperate forests but not in treeless biomes (deserts, tundra or grasslands). The magnitude of the detrimental effects on trees increased with the duration of the polluters?? impact around acidifying polluters but decreased around alkalifying polluters. Adverse effects on the field layer became more severe with increasing community productivity; in combination with the conclusions of previous meta-analyses, this result indicates that diverse and highly productive communities are likely to be the most susceptible to pollution impacts. In general, the pollution effects on the abundance of vascular plants were less detrimental than the effects on their growth and diversity, indicating that primary productivity in polluted ecosystems is maintained by the preferential growth of several pollution-tolerant species.