Upscaling ozone flux in forests from leaf to landscape

Although stomatal conductance for ozone (O₃) correlates with leaf to air water vapor difference (VPD_LA) at the leaf level, uncertainty in up-scaling to the whole tree level can be overcome by means of sap flow measurements at the tree trunk. Further up-scaling to the stand level is possible by relating whole tree O₃ flux to silvicultural and/or tree-allometric data. In such a way, canopy conductance and O₃ uptake can be related to ground surface area. When normalized, canopy conductance is demonstrated to follow a functional relationship to VPD_LA across several forest ecosystems thus allowing a generalization of model approaches. Further up-scaling to the landscape level, however, needs further investigations due to differences in the response of canopy conductance to environmental drivers in forest stands and grassland ecosystems, respectively.