L’O3HP (Oak Observatory at the OHP) interdisciplinary and experimental approaches to study Mediterranean forest functioning under climate change

The need to improve our understanding of the functioning of Mediterranean forests in the light of their future evolution, has led to the elaboration of a program concerning the Downy Oak forest. It's one of three major species of importance in the region of the French Mediterranean, and covers more then 250.000 ha in the Provence-Alpes-Cote-d'Azure (PACA) Region.

This program is complementary to pioneer programs at Puechabon for Holm Oak, installed and run by the CEFE in Montpellier, and at Roquefort la Bedoule for Aleppo Pine, installed and run by the INRA Avignon.

The O3HP program is managed and coordinated by a consortium of the IMBE/OSU-PYTHEAS/ECCOREV and is strongly supported by the Institute for Ecology and Environment (INEE) of the CNRS. The installation of the dedicated field site and laboratory has further received substantial financial support by the PACA Region and the Conseil Général des Alpes de Haute Provence.

The central installation consists of an experimental field site, situated at the research center of the Observatory of the Upper-Provence (OHP, UMS CNRS Pythéas) at Saint Michel l'Observatoire, close to Forqualquier in the Alpes of the Upper-Provence. The site is thus named O3HP (« Oak Observatory at the OHP »).

The O3HP is built-up of several elements installed in a 80-year old forest dominated by Downy Oak (Quercus pubescens) mixed with some Montpellier Maple (Acer monspessulanum) :

 1. Scaffolding for canopy access, installed in a shape of a cross. Each arm is 10 m long with platforms at two levels (0.8 m & 3.5 m) giving access to the shade and the sun crown without perturbating the ground layer.

2. A rain exclusion device covering about half of the core plot (300 m²): The roof is opened and closed by retractable covers, intercepted rain is collected in an underground water reservoir. On the experimental plot, this allows to apply a precipitation scenario close to what models predict for the end of the 21st century, which means a reduction in annual rainfall of about 30% to 40%. The exclusion and the adjacent control plot can therefore be studied in terms of their biodiversity and ecosystem functioning in order to understand the impact of climate change for this type of Mediterranean ecosystem.

3. An environmental sensing network (atmospheric and soil temperature and humidity in the vertical profile, photosynthetically active and global radiation, precipitation, sap-flow, stem growth, etc.)

The O3HP has high scientific potential as its commonly used in a pluridisciplinary way by several local laboratories, and as it's open to any scientific collaboration. This associates atmospheric physicians with astrophysicians, ecophysiologists and ecologists, with strong interactions in between the staff of the OHP and the ones of the laboratories engaged in ecological or environmental sciences such as the IMBE, CEREGE, CEA Cadarache.

Two CNRS employees are decicated specifically to the O3HP, a reserach engineer (IR), and an engineer assistant (AI).

Several research teams, local and national, have ongoing research projects at the O3HP. Several topics have and are being addressed, some in the context of PhD theses; studies of:

- meso and microclimate

- the geochemical cycle

- emission and content of secondary plant metabolites

- efficiency of photosynthesis and nutrient turnover

- plant water relations

- pheology, growth, and annual course of cambial activity

- carbon stock of the ecosystem

- abundance and evolution of the microbial community of the soil and the phyllosphere

- genetic diversity

- zoological community


Prof. Thierry GAUQUELIN, IMBE, principal investigator of the ’O3HP, thierry.gauquelin (at)


 Participating Institutions

Environnement et
Durable (CNRS-EDD)