Fig. 4: Geographical distribution of the trend in annual rate of variation for Ca, Mg, and S foliar concentration in mg g−1.

a the entire forests, b Pinus sylvestris, c Picea abies, and d Fagus sylvatica. The estimations are based on neural networks using 80% of the trees with more than five measurements for training and 20% for validation. We replicated the process 1000 times and averaged the results.