Le Bray (LB) is a mandatory site in the Ecosystem part of the project. The site is located approximately 20 km SW from Bordeaux (latitude 44°42' N, longitude 0°46' W, altitude 61 m) in a 16 ha maritime pine stand (Pinus Pinaster Ait.) planted in 1970. The trees are distributed in parallel rows along a northeast–southwest axis. The mean tree height is about 21 m. The inter-row spacing is 4 m and stand density is about 360 trees per hectare.

An equipped 40 m high scaffolding is set up in the middle of the stand (Figure below) surrounded by similar stands, except in the northwest direction where there had been a clear-cut at about 200 m from the tower following the storm of December 1999 (Figure below).

The site is also remarkably flat. The understorey consists mostly of grass (mainly Molinia coerulea L. Moench). The clumps of grass are about 0.7 m high in early summer: they partly remain in winter, depending on frost. The soil is a sandy and hydromorphic podzol, with dark organic matter in the first 60 cm. A layer of compacted sand, barely penetrable by the roots, is located at a depth of about 80 cm. Inorganic sand lies below this layer. The water table level reaches the soil surface during most winters, and in summer it is generally from 120 to 200 cm depth.

The EC system consists of a 3D sonic anemometer (Solent R2, Gill Instruments, Lymington, Hampshire, UK) set up at 41.5 m, coupled with an Open Path CO2/H2O InfraRed Gas Analyzers (IRGA) LI-7500 (LICOR, Lincoln, NE, USA). Data acquisition is made at 20.8  Hz.

The CO₂ profile is also measured with a LI-800 (LICOR, Lincoln, NE, USA) at 0.06, 0.48, 1.60, 2.80, 4.80, 8, 15.40, 17, 19, 23, 30, 35 and 41 m and the temperature and moisture profile is measured using home-made psychrometers at 1.60, 2.80, 4.80, 8, 15.40,  19, 23 and 40 m.

At the tower top, meteorological measurements are taken every 10 s and averaged every half hour. Detailed instruments are summed up in the Table below. At the moment, net radiation is calculated but will be directly measured soon. Rainfall is measured at 24 m on another tower, just above the top of the trees. Soil temperature is measured at four different locations and eight depths: 0.01, 0.02, 0.04, 0.08, 0.16, 0.32, 0.64 and 1 m using home-made thermocouples, i.e copper-constantan soldered joints coated with waterproof paint. Soil water content measurements are taken at 0.05, 0.23, 0.34 and 0.8 m depth. The data are recorded on CR10X, CR21X and CR23X Campbell dataloggers (Campbell Scientific, Logan Utah, USA).

table VI.5.1-a : Description of meteorological measurements done and instruments used at Le Bray site