SAPFLUXNET

Drought-related forest dieback is being increasingly reported worldwide, threating the ecosystem services provided by forests such as climatic regulation, local water balance and carbon sequestration. Hence, understanding the main environmental controls on tree water use and drought vulnerability is essential to address relevant questions posed by the global change-driven enhancement of drought conditions.

Global surveys of drought tolerance traits at the organ level are rapidly increasing our knowledge of the diversity in plant functional strategies to cope with drought stress. However, a comprehensive study of the ecological drivers of tree-level transpiration across the globe would add a new, whole-plant perspective to the worldwide spectrum of hydraulic traits, greatly improving our understanding of drought effects on woodlands. Sap flow measurements using thermal methods have now been applied to measure seasonal patterns in water use and the response of transpiration to environmental drivers across hundreds of species of woody plants worldwide, covering a wide range of climates, soils and stand structural characteristics.

In SAPFLUXNET we will assemble a  global database of sub-daily, tree-level sap flow that will be used to improve our understanding of physiological and structural determinants of plant transpiration and to further investigate the role of vegetation in controlling global water balance. We will collectively analyse sap flow responses to environmental drivers, at time scales from daily to seasonal and annual, using statistical models, time series analysis and mechanistic modelling of water transport in plants. These analyses will yield a set of traits related to physiological regulation of transpiration across species. These traits will be analysed in their ecological context, including taxonomic group, wood anatomy type, climatic and soil variables, tree size and stand structure. We postulate that these transpiration-related traits play a central role in defining whole plant’s vulnerability to drought and hence will show strong coordination with other organ- or plant-level hydraulic traits.

SAPFLUXNET is a global, novel approach to address the ecological drivers of woody plant transpiration at the individual level, the relevant scale to address plant responses to global change and extreme climate events. SAPFLUXNET will thus bridge the ecological scales in global databases of plant traits and networks of ecosystem-level water and CO2 fluxes