Monitoring of Forests Indicates Decrease of Important Elements in Tree Nutrition of Main Tree Species across the Czech Republic and Slovakia over the Long Term

: Authors analysed foliar nutrition data from the ICP Forests (International Co-operative Programme on the Assessment and Monitoring of Air Pollution on Forests) monitoring network in two neighbouring Central European countries: the CZ (Czech Republic) and SK (Slovakia). Authors evaluated altogether seven coniferous (six Norway spruce and one Scots pine) and six broadleaves (five European beech and one Sessile oak) in intensively monitored plots. The longest time series cover more than 20 years (1995-2017 in CZ; 1995-2013 in SK). The data show a significant decrease of the concentration of major nutrients, mainly P and K. On roughly half of plots, the concentration of P is near or below the deficiency limit (1.2 g·kg -1 ), the concentration of K has dropped by 10% to 50%, especially in stands of broadleaves during the evaluated period. Over time P and K have shown significantly decreasing trends on one third of the evaluated coniferous plots and a similar situation has occurred on broadleaf plots. Both countries differ in Mg trends － there is a decrease of Mg concentration in needles in SK compared with Czech coniferous plots. On the other hand, in beech leaves there is a decrease of Mg in both countries, and in CZ the trend over time for Mg is significant. The observed changes in nutrition level with stable or slightly increasing N concentration and with a drop in phosphorus and base cations have led to nutrient imbalance, especially between N and P.