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Puechabon

Evergreen broadleaved forest dominated by Quercus Ilex
close to Montpellier, France

43°44’30” N
3°35’40" E (tower coordinates)
270 m asl (tower)

Puechabon

Site description

This study site is located in the Puéchabon State Forest on a flat area 35 km North-West of Montpellier in the south of France. It is surrounded by large area of dense forests and open forests and shrublands. Vegetation is largely dominated by the overstorey tree Quercus ilex whose percent cover is greater than 80%. The leaf area index is about 2.9 m2 m-2. Mean tree height is about 5.5 m. In 1999, density of resprouted stem was 8500 ± 600 stems per ha. The percentage of stem with DBH < 4 cm was 11% and 46% for DBH > 7 cm. In 2007, density of resprouted stem was 6304 stems per ha. The percentage of stem with DBH < 4 cm is 7% and 56% for DBH > 7 cm. The above-ground biomass is about 11800 g dry matter m-2.

Understorey species compose a sparse shrubby layer with Buxus sempervirens, Phyllirea latifolia, Pistacia terebinthus and Juniperus oxycedrus and have likely a small contribution to the whole ecosystem functions.

The area has a Mediterranean-type climate. Rainfall occurs during autumn and winter with about 75% between September and April. Mean annual precipitation is 883 mm with a range 550-1549 mm recorded over the previous 16 years. Mean annual temperature over the same period were 13.5 °C respectively.

Landuse

Puéchabon State Forest has been managed as a coppice for centuries and the last clear cut was performed in 1942.

Soil & Geology

This forest grows on hard Jurassic limestone filled with clay soil. Because of the large fraction of rocks and stones in the soil profile available water cumulated over 4.5 m depth averages only 150 mm. Because of this low availability, vegetation undergoes very frequent drought summer stress.

Measurements

Flux tower

Flux Measurements (half-hourly)

  • Carbon dioxide flux
  • Latent heat flux
  • Sensible heat flux
  • Soil heat flux
  • Momentum
  • Friction velocity
  • Tree transpiration (sap flow)

Atmospheric Measurements

  • Water vapor concentration
  • Carbon dioxide concentration
  • Air pressure
  • Atmosphere stability parameter
  • Precipitation
  • Maximum wind speed
  • Precipitation
  • Relative humidity
  • Wind direction
  • Wind speed

Temperature

  • Air temperature
  • Below canopy air temperature
  • Mean sonic temperature
  • Soil temperature
  • Stem temperature at breast height

Radiation

  • Below-canopy photosynthetic photon flux density
  • Diffuse photosynthetic photon flux density
  • Diffuse radiation
  • Direct beam global radiation
  • Global radiation
  • Long wave incoming radiation
  • Long wave outgoing radiation
  • Net radiation
  • Photosynthetic photon flux density
  • Reflected photosynthetic photon flux density
  • Reflected radiation
  • Short wave incoming radiation
  • Short wave outgoing radiation

Others

  • Normalized difference vegetation index (NDVI)
  • Photochemical Reflectance Index (PRI)
  • Soil water content profiles
  • Top soil water content
  • radial growth (yearly)
  • litterfall (monthly)

Manipulation experiments

MeasurementsMethods
Water balance 
Top soil water contentTDR
Plant water statusWater potential (pressure chamber)
TranspirationSapflow (Granier's probe) and leaf gas exchange (LiCor 6400, 1600)
Stomatal conductanceGas exchange (LiCor 6400, 1600)
Hydraulic conductivity and vulnerability to cavitationXyl’em tool (Cochard et al. 2005)
Productivity 
Leaf, root, stem biomass and growthAllometry, automatic dendrometers, dendrochronology
LAI and phenologyLI-2000 and weekly observations
LitterfallTraps
Root growthIngrowth core (only Exp. 2)
PhotosynthesisLeaf gas exchange and fluorescence (LiCor 6400)
Mesophyll conductanceFluorescence (LiCor 6400-40 Leaf Chamber Fluorometer)
RespirationGas exchange (LiCor 6400)
Soil CO2 flux 
Soil respirationAutomatic (Rayment type) and manual gas chamber (LiCor 6400)
CO2 concentration profileMini-IR gas analyzer (Vaisala GMT-220, only Exp. 2)
Soil organic matter 
Humic, fulvic, amino acids, humins, carbohyd., lipidsNear infrared spectrometry
Tissue biochemistry: 
NSC, fiber, lipid, N, P for all tissue and litterfall, Total plant construction cost δ13C: leaf, shoot, stem, rootNear infrared spectrophotometer, NIRS (Joffre et al. 1992) Biochemestry, biomass and elementary cost (Merino et al. 1984) Mass spectrometer
Functional traits: 
Leaf lifespan-leaf age Leaf: area-mass-dry matter-density-thickness-SLA Shoot: diameter-length-mass-volume Root: Specific root length-root diameter-root density Wood densityMonthly and bi-weekly leaf demography Sampling and laboratory analysis Sampling and laboratory analysis Sampling and laboratory analysis Sampling and laboratory analysis

Treatments within the CARBO-Extreme project

Throughfall exclusion experiment (Exp. 1)

In 2003, the throughfall exclusion experiment was set up on four 140m² plots (14 x 10m) situated on a flat area, so that lateral flow of water is negligible:

  1. control (control, C),
  2. throughfall exclusion (dry, D),
  3. thinned (thinned, T)
  4. thinned and subjected to throughfall exclusion (dry-thinned, DT)

On the dry and dry-thinned plots, throughfall exclusion was achieved using 14 m long and 0.19 m wide PVC gutters covering 33% of the ground area under the Quercus ilex canopy, with the aim to exclude 33% of throughfall. On the control plot and the thinned plot, identical gutters had been set up upside down so that the albedo and the micro-climate of the forest understorey were the same in all plots. The leaf area index (LAI) was 3.1m² m-² in the controls plots and 1.6 m² m-² in the thinned plots. In the control plot, rainfall partitioning into interception loss, throughfall and stemflow was respectively 30.9%, 56.6% and 12.5% of the total precipitation. Thinning reduced the stem basal area by 33% and the total interception loss by 34.6%. Given the rainfall partitioning, the throughfall exclusion was found to remove 19% of total precipitation, which was confirmed by soil water content measurements.

Rainfall exclusion experiment (Exp. 2)

In 2007, a rainfall exclusion experiment was established on the site and included 3 plots of 195 m² each (15 m x 13 m, 2 x treatment, 1 x control). The experiment was designed to exclude 100% of rainfall on different forest plots at different periods of the year, without changes in other meteorological variables such as incident radiation, temperature and vapor pressure deficit. Rainfall exclusion was achieved trough a mobile rainfall shelter of 15 m x 13 m standing above the canopy on 60 m long rails. The two exclusion plots were situated at each extremity of the rails, the middle part serving as a parking position for the shelter in the absence of rain. The control plot was situated 20 m aside, in the east direction of the exclusion plots.

Two rainfall exclusion treatments were defined

  • an extreme autumn-winter drought with no rainfall for 6 months, from July to December 2008 (autumn exclusion treatment). In this treatment, the soil water shortage increased while atmospheric demand was decreasing.
  • an extreme winter-spring drought with no rainfall for 6 months, from February to July 2009 (spring exclusion treatment). In this treatment, soil water shortage increased while atmospheric demand was increasing.

Related projects

  • IMECC (Infrastructure for Measurements of the European Carbon Cycle) 2007-2011 (UE)
  • DROUGHT+ (drought + vulnerability assessment of Mediterranean ecosystems) 2007-2010 (ANR)
  • Nitro-Europe 2006-2011 (UE)
  • CARBOEUROPE-IP 2004-2009 (UE)
  • MIND 2002-2005 (UE)
  • CARBOFOR 2002-2005 (GICC)
  • CARBOEUROFLUX 2000-2003 (UE)
  • MEDEFLU 1998-1999 (UE)

Pictures

Puechabon1 Puechabon2 Puechabon3 Puechabon4 Puechabon5 Puechabon6 Puechabon7 Puechabon Rainshelter

Contact

Serge Rambal
Richard Joffre
Dream CEFE-CNRS (UMR 5175)
1919 route de Mende
34293 Montpellier cedex 5 France
serge.rambal@cefe.cnrs.fr
richard.joffre@cefe.cnrs.fr
web page of experimental site

References

Misson, L., Rocheteau, A., Rambal, S., Ourcival, J-M., Limousin, J-M., Rodriguez, R. (2009) Functional changes in the control of carbon fluxes after 3 years of increased drought in a Mediterranean evergreen forest? Global Change Biology (in press).

Limousin J.-M., Rambal S., Ourcival J.-M., Joffre R. (2009). Reply to comment by Llorens et al. "Modelling rainfall interception in a Mediterranean Quercus ilex ecosystem: lesson from a throughfall exclusion experiment". Journal of Hydrology, 365: 142-143.   Limousin J.-M., Rambal S., Ourcival J.-M., Rocheteau A., Joffre R., Rodriguez-Cortina R. (2009). Long-term transpiration change with rainfall decline in a Mediterranean Quercus ilex forest. Global Change Biology,15: 2163-2175.

Lavoir A.-V., Staudt M., Schnitzler J. P., Landais D., Massol F., Rocheteau A., Rodriguez R., Zimmer I., Rambal S. (2009). Drought reduced monoterpene emissions from the evergreen Mediterranean oak Quercus ilex: results from a throughfall displacement experiment, Biogeosciences, 6, 1167-1180, 2009.


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