Fig. 3
From: Phosphorus nutrition of beech (Fagus sylvatica L.) is decreasing in Europe
Trends in foliar N/P ratio on individual plots (gray lines) and the positive common trend (thick black line). The range of harmonious N/P ratios (dashed lines) is indicated for a reference (Mellert and Göttlein 2012). The common trend was significant at p < 0.001 (linear mixed effects model: y = 0.083x + 20.131; in the model x = 0 is in the year 1991)