Rapid recovery of stem increment in Norway spruce at reduced SO_2 levels in the Harz Mountains, Germany

摘要

Tree-ring width of Picea abies was studied along an altitudinal gradient in the Harz Mountains, Germany, in an area heavily affected by SO_2-related forest decline in the second half of the 20th century. Spruce trees of exposed high-elevation forests had earlier been shown to have reduced radial growth at high atmospheric SO_2 levels. After the recent reduction of the SO_2 load due to clean air acts, we tested the hypothesis that stem growth recovered rapidly from the SO_2 impact. Our results from two formerly damaged high-elevation spruce stands support this hypothesis suggesting that the former SO_2-related spruce decline was primarily due to foliar damage and not to soil acidification, as the deacidification of the (still acidic) soil would cause a slow growth response. Increasing temperatures and deposited N accumulated in the topsoil are likely additional growth-promoting factors of spruce at high elevations after the shortfall of SO_2 pollution.