Foliar nutrients in Italian forests: results from the 1995-2009 monitoring network sites CONECOFOR

Foliar nutrients in Italian forests: results from the 1995-2009 monitoring network sites CONECOFOR. In 1995, the Italian Forest Service (CFS) established the National Network for Forest Ecosystem Monitoring (CONECOFOR) with the aim to study the ecological interactions among structural and functional components of forest stands. In the 31 permanent plots of the CONECOFOR Network, surveys are carried out including vegetation, trees crown condition, chemistry of leaves and soils, tree growth, atmospheric deposition, climate, microclimate, ozone and biodiversity. These surveys are carried out by CFS in collaboration with several scientific institutions. In such context, IBAF/CNR is specifically involved in the investigation of foliage chemical content. The foliar nutritional status was analyzed in 25 sites, taking as a reference the values published by the ICP-Forests and those published in the literature. The study involved 7 forest species (Quercus cerris, Q. petraea, Q. robur, Q. ilex, Fagus sylvatica, Carpinus betulus and Picea abies) investigating the concentrations of the major macronutrients as nitrogen (N), phosphorus (P), potassium (K), magnesium (Mg), sulfur (S) and calcium (Ca) and the N/P ratio. In beech, N, S and K were found in quite high concentrations, though without showing imbalances due to concentration excesses. Ca and Mg are present in very high concentrations, highlighting the possibility of imbalances, especially in relation to the other nutrients. For these two nutrients, spruce shows substantially balanced conditions as also for N/P ratio. For deciduous Oaks nutrients arewithin the parameters of normality, with the exception of Ca. This has been observed in 4 out of the 6 studied sites, with potential indication of nutritional imbalances related to Calcium. Nutrient concentrations in Holm oak are within the average of published data, except for Ca and Mg of site TOS-1, the former being slightly low, the latter being unusually high, in relation to the peculiar soil Mg content of the above site. Considering the coefficient of variation (CV), the variability of the different elements, taking in account all species, presents the following ranking: K ≈ P > Ca> Mg ≈ N / P > S> N. On those sites presenting the longer time-series (12 out of the 25 studied sites), a more detailed analysis has been performed in order to verify the existence of trends along the monitoring period for each nutrient. Calcium, Mg and N/P show a steady decrease during the considered time span. Such trend is less marked for Ca than for Mg and N/P. Phosphorus and K show an increasing trend while no common trends have been highlighted for N and S. Overall, the study provides relevant data on status and dynamics of nutrients in Italian forest ecosystems