Tree canopy and herb layer transpiration in three Scots pine stands with different stand structures

Abstract

To evaluate the impact of herb layer structure on the transpiration of Scots pine ecosystems in north-eastern Germany, we measured tree canopy and herb layer transpiration in three stands. Parameters of tree hydraulic architecture were measured and their drought stress monitored. Despite striking differences in ecosystem structure, combined tree and herb layer transpiration was equal for all three sites. Transpiration rate per needle area and tree canopy transpiration were least at the site dominated by the tall grass species Calamagrostis epigeios. Pine pre-dawn water potential in the Calamagrostio-Cultopinetum sylvestris was never lower than in the Myrtillo-Cultopinetum sylvestris, indicating that severity of competition of ground vegetation was not much different. Huber values, xylem hydraulic conductance and leaf-specific conductance of pine were least in the Calamagrostio-Cultopinetum sylvestris. Thus, pine transpiration rate might have been adjusted to lower tree hydraulic conductance and the herbaceous species used the water left by the trees.