Trends of Scots pine forest health and element flow changes in the ICP Forests monitoring sites in Latvia

Scots pine (Pinus sylvestris L.) is one of the most widespread and economically most important tree species in Latvia. Scots pine forest health and element flow changes have been monitored in Latvia 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 115 Level I monitoring sites (mostly oligothrophic and mesotrophic Vacciniosa, Myrtillosa and Hylocomiosa forests) and with sampling and analyses of environmental samples at three Level II monitoring sites representing typical Scots pine forests (Myrtillosa) in hemiboreal conditions in Latvia. This study summarizes the background information and presents the trends of forest health, carbon turnover and environment condition in Scots pine forest since 2009. In general, defoliation rate in Scots pine stands remains stable for 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 action of man. Chemical element flows in Scots pine forests in Level II monitoring plots have been 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, interannual variations were rather wide.