Main project
Holm oak (Quercus ilex L.) forests cover about 350 000 ha in southern France where they were traditionally coppiced on short rotations (from 7 to 30 years) for charcoal or tannins production. These coppices have been generally abandoned and under-logged since the second half of the 20th century which resulted in alterations of the forests structure mainly due to ageing and increased the forests sensitivity to perturbations such as pests, fires and drought. Thinning has been regarded as a means-considered as a way to address the structural ageing (Ducrey, 1988) and, more recently, to mitigate the impact of climate change on Holm oak forests (Rodríguez-Calcerrada et al., 2011). Thinning has a positive effect on growth and vigour of seasonally dry forests by decreasing the stand density and leaf area, and therefore releasing the water competition amongst the trees.
The main objective of the study is to assess experimentally the long-term effect of thinning on tree growth and wood production in a Mediterranean Q. ilex coppice.
The thinning experiment started in 1986 and is composed of 15 plots of 1000 m2 each with 45 trees follow-up, divided into 3 blocks. The last clear-cut occurred in 1942 for the blocks 1 and 2, and in 1928 for the block 3. Selective thinning from below (sensu Assman, 1970), which consists in removing the smallest stems to the benefit of the biggest ones, was applied in March 1986 when stems were 44 years old in the blocks 1 and 2 and 59 years old in the block 3. Five thinning intensities were applied corresponding to approximately 0%, 25%, 45%, 60% and 80% of the basal area removed. Each treatment level was applied to a 1000 m² plot and replicated in each of the three blocks. The number of stems that were removed varies between 55%, for T25% and 90% for T80%.
Main project protocol
Four thinning intensity applied in 1986, % basal area removed :
- 24-27%
- 40-45%
- 56-60%
- 77-79%
- three parcel without thinning
Continuous measurement
SF : Sapflow
Ts / Tsol : Soil and trunc temperature
SWC : Soil relative humidity
DBH : Trunk circonference
NDVI : Normalized Difference Vegetation Index
PRI : photochemical reflectance index
Discrete measurements
- DBH in winter : 1985, 1986, 1987, 1988, 1989, 1991, 2013, 2015, 2017
Height : 1985, 1989 - LAI
- DBH : Trunk diameter of circunference (annual)
- LIT : Litterfall (monthly)
- PHENO : Phenology (weekly March -July)
- C : Shoot and leaf growth (annual)
- PB : Leaf water potential (monthly in spring, summer, automn)
- pS : Photosynthesis
- Res : Respiration : soil, trunk, leaves
- CH : Chemistry of green leaves and litterfall
- Delta13C of leaves
Associated projects
Two treatment of the partial rainfall exclusion experiment established in 2003 received a treatment of thinning. The experiment was set up on 100m² plots situated on a flat area, so that lateral flow of water is negligible and replicated three times. The first is submitted to a selective thinning from below with 33% of the basal area removed and the second is thinned and subjected to throughfall exclusion. These two treatments are replicated 3 time.
- one thinning intensity, -30% of the basal area applied during the winter 2002-2003
- 6 parcels of 100m2
- 3 parcel thinning and 3 parcel thinning + rainfall eclusion
Funding
| Date | Project | Origin |
| 2017 – 2020 | INNOV’ILEX | Fonds stratégique de la forêt et du bois. Ministère de l’agriculture. |
| Depuis 2013 | AnaEE | European research infrastructure, EU |
| 2010 – 2014 | ExpeER | EU FP7 N°INFRA-2010-1.1.17 |
| Depuis 2008 | OSU OREME | CNRS, Univ. Montpellier, IRD, IRSTEA |
| 2007 – 2011 | IMECC | EU FP6 n° 026188 |
| 2002 – 2005 | MIND | EU FP6 N°EVK2-CT-2002-000158 |
Selected publications
Gavinet J, Ourcival JM, Limousin JM (2019) Rainfall exclusion and thinning can alter the relationships between forest functioning and drought. New Phytologist doi : 10.1111/nph.15860. (PDF)
Ducrey M, Toth J (1992) Effects of cleaning and thinning on height growth and girth increment in holm oak coppices (Quercus ilex L.). Vegetatio 99-100:365-376. (PDF)
Ducrey M (1988) Sylviculture des taillis de chêne vert. Pratique traditionnelle et problématique des recherches récentes. Revue Forestière Française 40(4):302-313.(PDF)