Two areas were sampled, one of native Quercus ilex forest and another of reforested Pinus nigra and pinaster, each covering around 25 ha and 39 predefined sampling points to allow later geostatisical analysis. At each point the BENCHMARKS sampling protocol was used to take at least 1 undisturbed and 1 composite sample. We had several challenges, like finding and distributing sampling locations between teams in an area without phone network, and taking undisturbed samples in stony soils. Moreover, most sampling areas were very remote and could only be reached by foot, crossing (densely) vegetated steep slopes. Another challenge was to keep the samples cool while carrying them up- and downhill during warm spring weather

A detailed preparation and coordinated team work was key to the success. To prepare for the foreseen challenges we rented two 4-wheel drive cars that could bring us to a 30 minutes walking distance from the centre of the sampling locations. We bought many 30 L cooler bags that could be carried as backpack to transport the samples, and made balanced sampling teams. Finally, we managed to finish the sampling in about 18 hours fieldwork with a team of 8 people. Several days later, three people of the team (Efraín, Antonio and Mistral) had to return to repeat several sampling points because, after preparing the samples in the laboratory and removing stones, we did not have enough soil matrix for all the analysis needed for some specific samples, thus they spend one more day of fieldwork. The processing in the laboratory to distribute the samples among all the European teams was also challenging and could be done by a team of 5 people during 3 days. The experience taught us that anticipation and preparation combined with a good team spirit, and a well-deserved local dinner in the beautiful nearby village of Nerpio, were key to the successful campaign.