Using sap flow sensors to monitor tree water uptake: challenges and opportunities
Friday 2nd October at 14:00
Water is a resource crucial for the survival and growth of trees. Understanding water relations and how changes in water availability may affect the growth and survival of trees across spatial and temporal scales is critical to gain insights in the future of forests. Sap flow sensors allow estimating tree water flow in vivo using heat as a tracer. The relative simplicity of the various sap flow methods and the affordability of the associate sensors and their easy deployment has made them the most widely used approach to estimate tree-level water fluxes. Together with other measurements of tree biomass, leaf area and growth, sap flow sensors can provide data with a high spatial and temporal real time resolution, vital to assessing the impacts of edaphic and climatic conditions on the establishment, survival and productivity of trees and associated forest ecosystems. In a first study, we evaluated and quantified the impact of changes in soil water availability, modulated by rooting depth and topography on leaf area and sap flow of 15-year-old trembling aspen and white spruce trees planted on a reclaimed site. Results indicate that scaling water fluxes from an individual tree to the stand-level is complex and require a deeper understanding of trees’ physiological responses to variation in edaphic conditions. Additionally, obtaining an accurate quantification of water flow in large trees is critical, but we currently lack direct calibrations of sap flow methods for large trees. In a second study, we quantified the uncertainty associated with the use of sap flow sensors in a large tree by directly comparing sap flow rates to gravimetric measurements using the cut-tree method on a large mature trembling aspen tree. Overall, this work highlights that sap flow sensors are a crucial tool that can help to improve our understanding of the spatial and temporal dynamics of trees’ water relations in connection with edaphic and climatic conditions, however they should be used with caution particularly for large trees.