Dendroecological assessment of the complex causes of decline and recovery of the growth of silver fir ( Abies alba Mill.) in Southern Germany

• Published in: Forest ecology and management 2009-02, Vol.257 (4), p.1175-1187
• Main Authors: Elling, Wolfram, Dittmar, Christoph, Pfaffelmoser, Klaus, Rötzer, Thomas
• Format: Article
• Language: English
• Subjects: Abies alba; Air pollution; Animal and plant ecology; Animal, plant and microbial ecology; Biological and medical sciences; climatic factors; Cultivation of silver fir; decline; Decline of growth; dendrochronology; Dendroecology; edaphic factors; equations; Fir decline; forest trees; Forestry; Fundamental and applied biological sciences. Psychology; Growth modelling; growth models; growth rings; Growth trends; Recovery of growth; Silver fir; soil water content; sulfur dioxide; Synecology; Terrestrial ecosystems; tree growth; tree mortality
• ISSN: 0378-1127; 1872-7042
• DOI: 10.1016/j.foreco.2008.10.014

Causes of decline and silver fir ( Abies alba Mill.) mortality in Central Europe have been controversially discussed for a long time. This contribution details a comprehensive dendroecological investigation of two basic and alternative hypotheses that explain the decline by either climatic influences or by SO 2 pollution as the primary factors. Growth reduction between the 1960s and 1980s as well as the recovery of growth during recent decades have be seen as a response to complex interactions of multiple factors. Herein, we undertake a multidisciplinary evaluation of a broad database, representing the long-term growth of 1010 firs from 51 sites, long-term climate records as well as data assessing the long-term pollution situation in Southern Germany. The results provide clear evidence that SO 2-immissions play a key role in decline and that tree growth corresponds with the regional and temporal pattern of SO 2 pollution. Calculations with a new complex growth model indicate that tree-ring widths of fir at many sites were more influenced by SO 2 than by any other growth-determining factor during the second half of the last century. Strongest coherence between measured and modelled ring widths are found if – in addition to temperature, available soil water content, heavy frost events and long-term growth trends – the site-specific trend of SO 2 pollution is included. Both the immediate response to SO 2 pollution and the quick recovery of fir since the beginning of the 1980s after the decrease of SO 2 emissions indicate a direct impact of SO 2 in gaseous form and not via the soil in terms of soil acidification. Tree-ring widths document that radial growth response occurs at air concentrations above 10 μg SO 2 m −3 (annual average), which can be thought of as a critical threshold for silver fir health. Since the beginning of the 1980s, increasing growth trends have been observed which predominantly result from decreased SO 2 pollution in most parts of Central Europe, although climate change, fertilization by nitrogen deposition and a reduced tree-to-tree competition are also relevant factors. The drastic reduction of SO 2 emission during the recent decades significantly improved the environmental conditions for fir. Consequently, an increased cultivation of silver fir on suitable sites is recommended.