Bārdule, A., Bārdulis, A., Polmanis, K., Krumšteds, L.L., Butlers, A., Stola, J., Skranda, I., Purviņa, D., Zvaigzne, Z.A., Muižnieks, E., Lībiete, Z., Zvirbulis, U., Kļaviņš, I., Jansons, J. and Lazdiņš, A. 2021. Trends of Scots pine forest health and el

   Scots pine (Pinus sylvestris L.) is one of the most widespread and economically most important tree species in Latvia. Tree health and element flow changes in Scots pine forests have been monitored within the International Cooperative Programme on Assessment and Monitoring of Air Pollution Effects on Forests (ICP Forests) with assessment of crown condition and damaging agents at 70 Level I monitoring sites (mostly oligotrophic and mesotrophic Vacciniosa, Myrtillosa and Hylocomiosa forests) and with sampling and analyses of environmental samples at three Level II monitoring sites (Myrtillosa site type). All sites represent typical Scots pine forests under hemiboreal conditions in Latvia. This study presents the trends of forest health, carbon turnover and environmental condition in Scots pine forests during a 10-year period from 2009 to 2019. In general, defoliation rate in Scots pine stands remained stable during the studied period, with some yearly fluctuations, possibly related to regional insect outbreaks, especially well demonstrated in two Level II plots. The share of damaged trees varied by year from 12.8% to 19% of the total number; the main cause of damage was direct human influence. Flows of chemical elements in Scots pine forests in Level II monitoring plots were relatively stable as well, except the decreasing trend in total N concentration in deposition and SO4-S concentration in soil solution and increasing trends in DOC concentration in soil solution that is in line with common trends in Europe. Carbon input with above-ground litter was relatively stable during the whole period; however, inter-annual variations were rather wide.

Keywords: forests on dry mineral soils, Scots pine, ICP Forests, monitoring, environmental condition, forest health, litter