Quantifying ozone uptake and its effects on the stand level of common beech (Fagus sylvatica L.) in Southern Germany

Stand level O₃ fluxes were calculated using water balance calculations for 21 Common beech (Fagus sylvatica L.) stands and O₃ data from 20 monitoring stations in Southern Germany. For this intention, the daily loss of water by evapotranspiration per stand area was set against the daily O₃ uptake. During the last 30 years, O₃ uptake ranges between 0 and 187 mmol ha^-1 d^-1 per stand area. Cumulative O₃ uptake (CUO₃), ranging between 0.1 and 0.7 mmol m^-2 yr^-1 per stand area, shows increasing trends since 1971 with considerably greater values at high altitudes. Effects in radial growth were used to derive an initial approximate critical threshold value for O₃ impacts on the vitality and growth of mature beech stands in Southern Germany. It is concluded that this concept of O₃ flux estimation in combination with dendroecological analyses offers both a site specific and regional applicable approach to derive new critical levels for O₃. Water balance calculations can be used to estimate long-term O₃ uptake at the stand level and in combination with tree-ring data to derive new critical threshold values.