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Early needle senescence and thinning of the crown structure of Picea abies as induced by chronic SO 2 pollution. II. Field data basis, model results and tolerance limits
Author(s) -
SLOVIK STEFAN
Publication year - 1996
Publication title -
global change biology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 4.146
H-Index - 255
eISSN - 1365-2486
pISSN - 1354-1013
DOI - 10.1111/j.1365-2486.1996.tb00095.x
Subject(s) - picea abies , canopy , soil water , thinning , pollution , environmental science , karst , crown (dentistry) , litter , precipitation , hydrology (agriculture) , botany , agronomy , ecology , soil science , biology , geology , geography , medicine , paleontology , geotechnical engineering , dentistry , meteorology
Field data on the sulphur and cation budget of growing Norway spruce canopies ( Picea abies [L.] Karst.) are summarized. They are used to test a spruce decline model capable of quantifying effects of chronic SO 2 pollution on spruce forests. At ambient SO 2 concentrations, acute SO 2 damage is rare, but exposure to polluted air produces reversible thinning of the canopy structure with a half‐time of a few years. Canopy thinning in the spruce decline model is highest (i) at elevated SO 2 pollution, (ii) in the mountains, (iii) at unfertilized sites with poor K + , Mg 2+ or Zn 2+ supply, (iv) at low spruce litter decomposition rates, and (v) acidic, shallow soils at high annual precipitation rates in the field and vice versa. Model application using field data from Würzburg (moderate SO 2 pollution, alkaline soils, no spruce decline) and from the Erzgebirge (extreme SO 2 pollution, acidic soils in the mountains, massive spruce decline) predicts canopy thinning by 2–11% in Würzburg and by 45–70% in the Erzgebirge. The model also predicts different SO 2 ‐tolerance limits for Norway spruce depending on the site elevation and on the nutritional status of the needles. If needle loss of more than 25% (damage class 2) is taken to indicate ‘real damage’ exceeding natural variances, then for optimum soil conditions SO 2 tolerance limits range from (27.3 ± 7.4) μg m −3 to (62.6 ± 16.5) μg m −3 . For shallow and acidic soils, SO 2 tolerance limits range from (22.0 ± 5.5) μg m −3 to (37.4 ± 7.5) μ m −3 . These tolerance limits, which are calculated on an ecophysiological data basis for Norway spruce are close to epidemiological SO 2 ‐toIerance limits as recommended by the IUFRO, UN‐ECE and WHO. The observed statistical regression slope of the plot (damaged spruce trees vs. SO 2 ‐pollution) in west Germany is confirmed by modelling (6% error). Model application to other forest trees allows deduction of the observed sequence of SO 2 ‐sensitivity: Abies > Picea > Pinus > Fagus > Quercus. Thus, acute phytotoxicity of SO 2 seems not to be involved in ‘forest decline’. Chronic SO 2 ‐pollution induces massive canopy thinning of Abies alba and Picea abies only at unfavourable sites, where natural stress factors and secondary effects of SO 2 pollution act together to produce tree decline.