The Transform P1.3 REF “Network of experimental forest plots” project established a network of permanent plots covering the primary forest species and associated silvicultural systems in Portugal. The project will also provide complementary data to that of the National Forest Inventory, enabling Portugal to join the European network of ICP Forest plots and make data available to the national and European scientific communities on the state of Portuguese forests.

ICP Forests monitors the influence of air pollutants, climate change and other stressors on the condition of forest ecosystems at two levels of monitoring intensity. Seven ICP Level II plots were installed under the supervision of ISA. There are four plots of maritime pine, two of cork oak, and one of Portuguese oak. For this type of plots, a pedological characterization and soil sampling at fixed depths are mandatory. In the border areas of each plot, a soil profile was opened, and samples were collected from each horizon for physicochemical characterization. The soil classification followed the World Reference Base for Soil Resources (WRB) 2022. Sampling was also carried out in each plot at depths of 0–10, 10–20, 20–40, and 40–80 cm. Organic and mineral layers were collected at 24 sampling points spaced 5 m apart. Four composite samples were formed for each plot, resulting from the combination of six different sampling points.

This work presents the initial soil monitoring values for these plots according to the following set of parameters:

Carbon and nitrogen – Ctot (total organic carbon), Ntot (total nitrogen);

Nutrients - P, Ca, Mg, K, S, Mn;

Acidity, Exchange characteristics -pH, Carbonates, CEC (cation exchange capacity), BS (base saturation), Exchangeable cations, Exchangeable Acidity, Reactive Fe and Al

Heavy metals - Pb, Cu, Zn, Cd, Cr, Ni, Hg

Physical soil parameters - Particle size distribution and soil texture, Organic layer mass.

The pedological characterisation of the soil in the plots at the profile level will help to identify which types of soil are most prevalent in which types of forest and establish their relationship with the state of the forest, within the framework of the future Portuguese ICP Forest network. The data obtained for each plot will form the basis for studying the effects of the evolution of local conditions with regard to parameters dependent on climatic variations (e.g., the evolution of carbon stock) or sustainable forest management (e.g., the water and nutrient balance). This will enable the soil to be studied in depth, its condition to be evaluated, and soil processes and dynamics to be studied in the long term.