The Level I monitoring provides an annual overview on forest condition based on a 16x16 km grid and covers around 6000 plots in Europe and beyond.

Besides the annual tree crown condition assessments, the Level I monitoring also includes assessments of soil condition, the foliar nutrient status of trees, the diversity of ground vegetation and general information on living trees and deadwood at irregular intervals.

Tree crown condition

Annual defoliation and tree damage assessments on Level I plots have proven to be a valuable tool for detecting the status and trends of tree condition in Europe.

Soil condition

There are clear correlations between the deposition of air pollutants and forest soil chemistry. Soil condition is essential for many organisms living in the soil and for forest functions like water storage and filtering. Nutrient imbalances in the soil are linked to tree condition.

More than 5000 ICP Forests Level I plots were monitored in two forest soil surveys across Europe. The first took place between 1986 and 1996 and the second between 2004 and 2008 under the Forest Focus Regulation (EC No. 2152/2003). A third transnational soil survey is planned for the upcoming years.

Foliar nutrient status of trees

Changes in environmental conditions may affect foliar nutrient concentrations. The monitoring of tree nutrition is thus essential for assessing forest condition. A foliar survey in the 1990s has covered appoximately 1400 plots. A number of countries are carrying out repeated foliar surveys.