Validation and quantification of sap flux variation in coniferous, diffuse-porous, and ring-porous mature trees using the cut-stem method
Abstract
The accurate quantification of transpiration is critical in the analysis of the hydrologic cycle. While sap flux sensors have grown in popularity due to their low cost and practicality, sap flux measurements can display substantial radial, circumferential, and inter-species variation that raise uncertainty in upscaled transpiration estimates. One of the few ways to directly assess whether variability is suitably quantified is to conduct experiments on harvested branches and small trees in which flow is induced by a pressure canister (i.e., the cut stem method). Here we extensively instrumented trees of approximately 10 cm diameter. Custom built 30 mm long probes with three independent temperature sensors were installed in the northwest and northeast directions of Acer saccharum (diffuse-porous), Quercus rubrum (ring-porous), and Tsuga canadensis (coniferous) to quantify both radial and circumferential variation across different xylem types. After collecting field measurements over a week, the instrumented stem segments were harvested and connected to a pressure canister to directly compare the gravimetric flow rate with the sap flux measurements at a range of flow rates. By contrasting field and laboratory measurements taken from the same stem location, we were able to determine whether experiments on harvested trees bare resemblance to in situ conditions. Additionally, we can use such experiments to provide improved guidance on the quantity and placement of probes necessary to account for variability within trees and across species of different xylem types.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2021
- Bibcode:
- 2021AGUFM.H55M0874B