ECART - Do retention trees remain efficient for forest biodiversity conservation in a climate change context?

At the forest-atmosphere interface, tree crowns are the first to be exposed to sunlight: from above if they are in a closed stand, and over their entire height if they are isolated or on the edge of the forest. Their defoliation may alter the spatial structure of the forest microclimate. We hypothesize that the partially defoliated crowns of dying trees reduce the buffering effect of forest cover on the microclimate of the understory, as well as the temperature and humidity differences between the inner and outer crowns.  

The project aims to:

• Describe the stratification of microclimates and communities in trees (little-known aspects in tree crowns), 
• Identify the factors that may influence this stratification, with hypotheses on the health status, species, position of the tree in the center or edge of the island, and size of the island,
•  Carry out the methodological developments necessary for acquiring canopy data.

Approaches

The project is based on three ecological questions and three methodological questions.

From an ecological perspective, how are micrometeorological variables (air temperature and relative humidity) and epiphytic biodiversity (bryophytes, lignicolous fungi) structured in the canopy and on the trunk, depending on whether the oak trees are healthy or dying (question E1), on sessile oaks vs. pedunculate oaks (question E2), on sessile oaks at the edge vs. in the center of the block, and depending on the size of the block (question E3)?

 From a methodological point of view, data acquisition required the prototyping and deployment of a system for measuring microclimatic variables at eight points on the tree along a double vertical gradient (four points along the trunk) and horizontal gradient (four points in the crown, two in the inner crown and two in the outer crown). This autonomous system measured and transmitted data remotely once every hour for a year: the DC prototype, a wired system based on the daisy-chaining principle, was deployed on all sampled trees (question M1) and compared on one of the trees with the wireless mPi solution (question M2). Finally, a test of automatic bryophyte and fungus spore sensors, potentially useful for canopy inventories, was carried out as proof of concept (question M3)

Preliminary results

Health gradient data were collected in 2024 on six pairs of healthy/dying oak trees in closed mature stands (Vierzon and Tronçais state forests). Question E2 will be addressed using bryological data from the trunk base only. Data on 20 trees in the center or on the edge of islands is currently being collected (2025-2026) in the Vierzon, Orléans, and Saint-Palais state forests. The micrometeorological variables for 2024 were analyzed using generalized linear models with mixed effects (effects of position in the tree, health status, or their interaction), as was bryological richness (effects alone or in interaction with position, health status, and micrometeorological variables). The composition of bryophyte communities was analyzed using canonical correspondence analysis.

These initial results were discussed on December 3, 2025, at a workshop bringing together project partners, forest managers (4 CNPF, 2 DSF, 7 ONF), other researchers from INRAE (URFM, ISPA, PIAF, LESSEM) and other institutes (EDYSAN laboratory – University of Picardie). The contributions of the various disciplines made it possible to identify valuable insights, areas for improvement (experimental design, formulation of hypotheses, or data processing methods), gaps (variables not taken into account in the sampling), and resources to be mobilized. Many issues remain to be studied in order to assess how climate change and tree decline influence the effectiveness of retention practices and identify the most appropriate practical recommendations.

Participants

INRAE units involved

• UR EFNO - Unité de recherche Écosystèmes Forestiers
• URZF - Unité de recherche Zoologie Forestière
• UMR BIOGECO - Biodiversité Gènes et Communautés
• UMR ISPA - Interactions Sol Plante Atmosphère
• USC Ecodiv-Rouen - Étude et compréhension de la biodiversité - CNRS / Université de Rouen Normandie
• UE PAO - Unité expérimentale Physiologie Animale de l'Orfrasière

Partners

• ONF - Office national des Forêts
• CNPF - Centre National de la Propriété Forestière
• DSF - Département Santé des Forêts