DEPERIS project

Drought vulnerability

Global warming is causing more frequent extreme droughts and heatwaves, which are leading to forest decline. Tree species such as pedunculate oak (Quercus robur), beech (Fagus sylvatica), and spruce (Picea abies) are particularly susceptible to water stress. However, even more resilient species such as Douglas fir (Pseudotsuga menziesii) and sessile oak (Quercus petraea) are also showing signs of weakening in some areas, raising fears of dieback. To monitor how different tree species respond to this climatic context, the Observatoire Wallon de la Santé des Forêts (OWSF) launched the DEPERIS network in 2020, supplementing the European ICP-Forest network. The DEPERIS network tracks tree health by monitoring crown condition and trunk radial increment in forest plots spanning a wide range of bioclimatic and soil conditions. As tree decline can result from various biotic and abiotic factors, detailed data on soil, tree physiology and water use are required to understand the role of drought.

Douglas fir (Pseudotsuga menziesii)

As part of a research agreement between the OWSF and the Université catholique de Louvain (UCLouvain), a dominant Douglas fir tree in two DEPERIS plots (Werbomont and Gouvy) has been fitted with a sap flow sensor, a point dendrometer and a sapwood moisture probe to enable continuous measurement of water use and growth. In parallel, soil water content and soil water potential are measured at three different depths to monitor soil water status. These measurements are complemented by the characterisation of soil hydraulic properties (e.g. retention curves and hydraulic conductivity) and soil texture, as well as by the acquisition of data describing the trees' functional traits (e.g. LAI and root profiles). These data will enable us to pinpoint the stress levels endured by trees subjected to drought and will notably be used to simulate retrospectively edaphic water stress in forests and its impact on tree health. The extension of these measurements to other plots and other species in the DEPERIS network is planned.

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Tree location

The monitored Douglas firs are located in two DEPERIS plots (Werbomont and Gouvy). The satellite image below shows the exact location of the monitored trees.