Regional variation in forest health under long-term air pollution mitigated by lithological conditions

Abstract

Forest defoliation and discoloration have been monitored extensively in Europe over the past decade, yet the number of published studies seeking to interpret these data in light of environmental parameters such as lithology and airborne pollution are few. In this study we summarize and compare data on defoliation and discoloration of Norway spruce dominated stands from three regions of the Czech Republic that differ in their lithology. In the Šumava and Krkonoše regions these measures increased over the monitoring period, which is interpreted as an effect of residual soil acidification. At Beskydy, a general stability in forest health parameters was observed. Regional differences are attributed to underlying lithography—the greater calcium carbonate content of the flysch bedrock at Beskydy provides better buffering against acid deposition. These results are supported by evidence of similar trends in atmospheric pollution (ambient air concentrations and deposition) between Beskydy and the Krkonoše region and higher sulphur inputs than at Šumava. Stand elevation and age, collected as explanatory variables, did not affect this interpretation. Additionally, in the Krkonoše region forest health data were examined for four soil type categories (extreme, acidic, enriched and nutritive) specific to forest conditions in the Czech Republic. Simple time series analysis of defoliation and discoloration demonstrated that extreme and acidic soils accounted for the majority of the increasing trend of forest decline in Krkonoše. However, multivariate non-linear regression analysis using elevation and stand age revealed that defoliation was not significantly different between acidic and nutritive soil type categories; rather, this was an artefact of the experimental design. The implications of the research are that acidic and nutritive soil type categories respond similarly to acid deposition while enriched, the most nutrient rich type category is most resistant. As such our results support the interpretation that lithology is a factor mitigating forest decline in Norway spruce dominated forests in the Czech Republic. Our results have implications for zonation strategies like those being used in Krkonoše National Park which seek to prescribe specific restoration measures based upon abiotic factors for acid-damaged forests.