Résumé
Sap flow research highlights new perspectives to study in situ root structure of large trees. Several examples demonstrate the ability of the Heat Field Deformation method, HFD, to do this under natural and experimental conditions. Within the latter, localized irrigation, sink- or source-severing trigger sap flow responses that help us to understand the belowground parts of a tree, such as the presence of anastomoses between roots of different trees. The vertical profile of root density, as well as root size around a tree, can be derived from the stem sap flow radial profile. Increase of stem flow due to localized irrigation may be used to distinguish root locations near the corresponding stem sector. Responses of root or stem sap flow when exposing roots using an air-spade or following the severing of roots or branches help us to understand the relationships between different sapwood conducting layers and paths of water between sources and sinks.