Dendroprovenancing instream wood at the watershed scale
Dendroprovenance is a discipline usually linked to dendroacheology or wood commercialization; however, other purposes as inferring the origin of wood in rivers (i.e., instream large wood, LW) are often overlooked. LW in fluvial ecosystems enhances its geomorphology and biodiversity, but also increases potential risk during floods. Thus, knowledge about its source is crucial for understanding LW dynamics and optimizing river and riparian forest management.
This project aims at developing a fingerprinting technique to decipher LW origin in mid-size river catchments (i.e., 1000 – 5000 km2). So far, we tested D/H and 18O/16O stable isotopes coming from the water molecule. They show spatial variations due to fractionation during evaporation-precipitation processes. When a tree takes up water, stores a specific isotopic signal in the cellulose. Since this signal is linked to a location, it may be used to trace LW’s provenance once it has been recruited and transported through the river network.
Our study area is a 50 km reach of the Rhone river, between the Lake Geneva and the Genissiat dam, where all incoming wood material is retained.
Initial results showed significant differences between the two main wood supply areas in the basin, the Arve and the Valserine tributaries; these distinctions were clearer in the most recent tree rings.
Finally, we will analyse other tracers related to geology (i.e., minor and trace elements), and combine them with the isotopic ratios in a multivariate analysis to determine more precisely the origin of the wood. Thereby, we will have developed a new dendroprovenance method that can be extrapolated to other fields, stepping forward in the application of our knowledge about tree rings.