Article published: Budburst date of Quercus petraea is delayed in mixed stands with Pinus sylvestris

An article has just been published in the “Agricultural and Forest Meteorology” journal presenting the influence of Scots pine on sessile oak spring phenology. The authors showed that budburst date of Quercus petraea is delayed in mixed stands with Pinus sylvestris.

The article is available until March 16, 2021 here:


Climate change is impacting temperate tree species phenology, especially the timing of budburst, which is mainly driven by air temperature. However, interactions with biotic or other environmental factors also influence the timing of budburst and are usually overlooked. We studied the influence of forest stand composition on the budburst date of adult trees belonging to two species: sessile oak (Quercus petraea, Matt. (Liebl.)) and Scots pine (Pinus sylvestris, L.). We monitored their budburst dates for seven consecutive years at 18 experimental plots located in central France. We compared the budburst dates of oaks and pines growing in monospecific stands with those of their counterparts in an oak-pine mixture. Our results show that sessile oak budburst date in mixed stands with Scots pine was delayed by 2.2 days on average (SE = 0.6) compared to its budburst date in monospecific stands. In years with early budburst, the delay was more pronounced – up to four days. For Scots pine, our results showed no difference between budburst dates in monospecific and mixed stands. We hypothesize that the persistent foliage of the Scots pine in the mixed stand intercepted a part of the solar radiation, which affected the temperature perceived by the oak buds, thereby delaying the heat accumulation needed for sessile oak budburst. This effect may be of interest for the management of sessile oak in the context of global warming. In the future, sessile oak may experience more frequent frost damage due to an earlier budburst. Managing sessile oak with an evergreen species could limit late frost damage to some extent by delaying budburst. Stand composition must obviously be taken into account when monitoring the phenology of temperate tree species and to enable robust comparisons of phenological events for a given tree species at different sites.

OPMTix annual meeting, 14 january 2021

The annual meeting of the project took place on 14 January, 2021 at INRAE, research unit EFNO, Nogent-sur-Vernisson, France. The meeting was held by videoconference.

The morning was devoted to oral presentations. For the French versions of the presentations, please contact Nathalie Korboulewsky (see contact page).

Artificial intelligence techniques for the detection of animals in forest


The article can be downloaded here:


An artificial vision software that contain image processing and deep learning functions has been developed to detect animals on videos recorded by camera traps in forests. Monitoring by camera traps is used on the OPTMix experimental facility in the Orléans forest to estimate wild ungulate pressure (roe deer, red deer and wild boar) on study plots. Scientists and conservation biologists use camera traps to monitor wildlife populations and biodiversity. Automatic image processing that count animals and identify species could facilitate and improve the use of camera traps in biodiversity monitoring programs and make the methodology accessible to a greater number of end users.

OPTMix annual meeting, you can download the presentations

The presentations made during the OPTMix annual meeting on January 9 and 10, 2020 are available by clicking on the download link below for a period of 30 days:

OPMTix annual meeting, 9, 10 and 13 january 2020

The annual meeting of the project will take place on 9, 10 and 13 January, 2020 at Irstea (INRAE) Nogent-sur-Vernisson.

French version of the meeting annoucement and full program for the 9 and 10 of january


Article published in “Notre Forêt”, the journal of Regional Forest Ownership Center Ile-de-France Centre-Val de Loire

The journal “Notre Forêt” of the Regional Forest Ownership Center Ile-de-France Centre-Val de Loire has just published an article presenting the OPTMix device and the first results obtained about the effects of tree mixing on tree growth, water resource, mineral nutrition and biodiversity.

Korboulewsky, N., P. Balandier, Y. Dumas, M. Gosselin, A. Marell and T. Perot (2019). « OPTMix scrute la mixité en forêt. Qu’apporte le mélange d’essence face aux changements globaux ? » Notre Forêt 88(septembre): 4.

The full article is available here

Article published: Stand growth and structure of mixed-species and monospecific stands of Scots pine (Pinus sylvestris L.) and oak (Q. robur L., Quercus petraea (Matt.) Liebl.) analysed along a productivity gradient through Europe

An article has just been published in the journal “European Journal of Forest Research” about stand growth and structure of mixed and monospecific stands of Scots pine and Sessile oak. This work was based on plots set up along a productivity gradient in Europe. OPTMix is one of the plots used in this study.

Pretzsch, H., M. Steckel, M. Heym, P. Biber, C. Ammer, M. Ehbrecht, K. Bielak, F. Bravo, C. Ordóñez, C. Collet, F. Vast, L. Drössler, G. Brazaitis, K. Godvod, A. Jansons, J. de-Dios-García, M. Löf, J. Aldea, N. Korboulewsky, D. O. J. Reventlow, A. Nothdurft, M. Engel, M. Pach, J. Skrzyszewski, M. Pardos, Q. Ponette, R. Sitko, M. Fabrika, M. Svoboda, J. Černý, B. Wolff, R. Ruíz-Peinado and M. del Río (2019). « Stand growth and structure of mixed-species and monospecific stands of Scots pine (Pinus sylvestris L.) and oak (Q. robur L., Quercus petraea (Matt.) Liebl.) analysed along a productivity gradient through Europe. » European Journal of Forest Research. doi: 10.1007/s10342-019-01233-y


Past failures of monocultures, caused by wind-throw or insect damages, and ongoing climate change currently strongly stimulate research into mixed-species stands. So far, the focus has mainly been on combinations of species with obvious complementary functional traits. However, for any generalization, a broad overview of the mixing reactions of functionally different tree species in different mixing proportions, patterns and under different site conditions is needed, including assemblages of species with rather similar demands on resources such as light. Here, we studied the growth of Scots pine and oak in mixed versus monospecific stands on 36 triplets located along a productivity gradient across Europe, reaching from Sweden to Spain and from France to Georgia. The set-up represents a wide variation in precipitation (456–1250 mm year−1), mean annual temperature (6.7–11.5 °C) and drought index by de Martonne (21–63 mm °C−1). Stand inventories and increment cores of trees stemming from 40- to 132-year-old, fully stocked stands on 0.04–0.94-ha-sized plots provided insight into how species mixing modifies stand growth and structure compared with neighbouring monospecific stands. On average, the standing stem volume was 436 and 360 m3 ha−1 in the monocultures of Scots pine and oak, respectively, and 418 m3 ha−1 in the mixed stands. The corresponding periodical annual volume increment amounted to 10.5 and 9.1 m3 ha−1 year−1 in the monocultures and 10.5 m3 ha−1 year−1 in the mixed stands. Scots pine showed a 10% larger quadratic mean diameter (p < 0.05), a 7% larger dominant diameter (p < 0.01) and a 9% higher growth of basal area and volume in mixed stands compared with neighbouring monocultures. For Scots pine, the productivity advantages of growing in mixture increased with site index (p < 0.01) and water supply (p < 0.01), while for oak they decreased with site index (p < 0.01). In total, the superior productivity of mixed stands compared to monocultures increased with water supply (p < 0.10). Based on 7843 measured crowns, we found that in mixture both species, but especially oak, had significantly wider crowns (p < 0.001) than in monocultures. On average, we found relatively small effects of species mixing on stand growth and structure. Scots pine benefiting on rich, and oak on poor sites, allows for a mixture that is productive and most likely climate resistant all along a wide ecological gradient. We discuss the potential of this mixture in view of climate change.


New measurements of soil water content with a neutron probe

On 1 and 2 July 2019, new measurements of soil water content were carried out by Cyril Dejean (Irstea G-EAU unit in Montpellier) on the OPTMix plots using a neutron probe. This work was carried out under intermediate soil moisture conditions in order to complete the range of measurements required to calibrate the soil water content sensors (CS616 – Campbell Scientific) installed in the OPTMix plots (see also here).


Set up of 144 automatic band dendrometers

144 automatic band dendrometers (DRS26 SDI12 sensor, Environmental Measuring Systems) are being installed in low and medium density plots. These sensors will allow us to follow trees response to drought and other stressful events (pathogen attack for example) and to compare the species response (sessile oak and Scots pine) according to stand density and stand composition.

On each plot, the sensors were connected to the data logger with a single cable and the data are recorded every 30 minutes (see below for an example on a Scots pine plot).





UR SOLS research unit came to visit OPTMix on June 24, 2019

30 people from INRA’s UR SOLS ( research unit came to visit the OPTMix experimental plots on June 24, 2019. After a general presentation by Philippe Balandier, the scientific studies were presented in little workshops:

  • Water resource and sensors (Jordan Bello and Camille Couteau);
  • Tree growth and biodiversity (Thomas Pérot and Marion Gosselin);
  • Understorey dynamics, ungulates and soil (Anders Marell and Yann Dumas).