The nutritional status of Picea abies (L.) Karst. across Europe, and implications for 'forest decline'.

During the summer of 1986, three year-classes of foliage were sampled from approximately 30-year-old Norway spruce [Picea abies (L.) Karst.] trees at 12 sites from S. W. Germany to N. Scotland. At sites in Germany, where trees were showing symptoms of ‘decline’, samples were taken from trees with ‘good’ crown condition and ‘poor’ crown conditon. The distinction between ‘good’ and ‘poor’ was made on the basis of international protocols for defining crown density and foliar discoloration. There was a wide range in nutrient content (percent dry weight) in apparently healthy trees. Current year foliage had ranges of mean values per site: S(0.07–0.13%), N(0.9–1.4%), K(0.5–0.9%), Ca(0.2–0.7%), and Mg (0.05–0.1%). Ranges were greater for 2-year-old foliage: S(0.09–0.18%), N(1.0–1.8%), K(0.4–0.7%), Ca(0.2–1.4%), and Mg(0.03–0.09%). At sites with trees having ‘poor’ crown condition, there were significantly smaller concentrations of Mg and Ca, and larger concentrations of K in 2-year-old foliage from ‘poor’ trees, compared with adjacent ‘good’ trees. Ratios of nutrient content were more significantly related to crown condition within sites than individual nutrients, especially in older needles. ‘Poor’ crowns were associated with larger ratios of N∶Mg, K∶Mg, S∶Mg, K∶Ca and smaller ratios of S∶K and N∶K. A ‘risk index’ is defined for trees showing no visible ‘decline’ symptoms, based upon nutrient content and nutrient ratios, which may be useful in identifying sites liable to experience deterioration in crown condition.