Physiological limits -- a possible cause of spruce decline

Dieback of spruce stands was studied in the regions Kysuce and Spi (Slovakia). Possible causes of spruce decline were analysed through observations of the following characteristics: genetic background, provenience, influence of root system, physiological processes (photosynthesis, chlorophyll fluorescence, content of pigments), water stress, climatic conditions, soil condition, immission load, diameter increment, defoliation, and influence of fungal pathogens and insects. Our research results do not allow identifying a single primary cause of spruce decline. Separate factors act in concert, and it is not possible to rank them according to their significance. In general, however, there is an evident strong influence of biotic pests, wind, exhausted soil and impaired physiological fitness since young trees. A special interest was put on monitoring possible influence of drought stress. Across the whole research period we have not recorded noticeable drops in amounts of soil water accessible for plants. Nevertheless, we suppose that importance of this factor will grade, especially in areas relatively rich in precipitation.