Water turnover in species rich and species poor deciduous forests: xylem sap flow and canopy transpiration The importance of plant diversity for ecosystem functioning has been one of the central research topics in ecology during the past 15 years. While much research has focused on the role of species diversity for plant biomass and plant productivity in grasslands much less is known how tree species diversity and tree identity influence ecosystem processes. The amount of water consumed by forest stands through transpiration is an important ecosystem function which determines the water loss through deep seepage and groundwater yields. Until recently the dependence of canopy transpiration on tree species diversity or functional diversity and tree species identity has not systematically been investigated. Starting in 2005 stem xylem sap flux measurements using the constant heating method after Granier were conducted synchronously in the Hainich National Park in six temperate broad leaved forest stands differing in tree diversity (1 to > 5 tree species) ...