New measurements of soil water content with a neutron probe in drought conditions

This summer, 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. These new measurements carried out during a period of severe drought (14/08/2018) will complete the range of measurements required to calibrate the soil water content sensors (CS616 – Campbell Scientific) installed in the OPTMix plots (see also here) .


Article published: Better predicting sessile oak and Scots pine growth in a changing climate

An article has just been published in “Agricultural and Forest Meteorology” on the growth of sessile oak and Scots pine. The goal of this work was to integrate climatic variables into models to better predict growth in the context of climate change. This work was performed using IGN data and ring-width data collected in the OPTMix plots.

Vallet, P. and T. Perot (2018). “Coupling transversal and longitudinal models to better predict Quercus petraea and Pinus sylvestris stand growth under climate change.” Agricultural and Forest Meteorology 263: 258-266. doi: 10.1016/j.agrformet.2018.08.021


  • Large-scale NFI data provide growth models including silvicultural effects.
  • Tree rings data provide models for annual modulation of growth by climate.
  • Coupling both models allowed to develop climate-dependent stand growth models.



Climate change has swept away the former general principles of long-term stability in forest productivity. New types of models are needed to predict growth and to plan forest management under future climate conditions. These models must remain robust for silvicultural practices and variations in climate. In this study, we present a new type of model development to achieve these goals. Our study focused on pure and mixed stands of Quercus petraea and Pinus sylvestris in central France. We used National Forest Inventory (NFI) data: respectively, 525 and 548 pure plots of Quercus petraea and Pinus sylvestris, and 68 plots of mixed species. We also used 108 tree cores from an experimental site of the same species. The cores cover the period from 1971 to 2013, making a total of 4572 individual annual increments. We coupled two types of models. One was developed with NFI data (transversal data). This model takes into account mean diameter and stand density effects on stand growth. It includes a set of biophysical factors accounting for stand fertility. The other one was developed with the data from tree cores (longitudinal data), and provides a climate modulation thanks to the correlation between ring width and yearly climate. The model with tree core data reveals the influence of December to July rainfalls on yearly variability in stand growth for Quercus petraea and of May to August rainfalls for Pinus sylvestris. We obtained a coupled model that allowed us to project growth up to 2100 for all the different IPCC scenarios but one; the model was outside its area of validity beyond 2060 for the RCP 8.5 scenario.

Article published: The effect of deer browsing and understory light availability on stump mortality and sprout growth capacity in sessile oak

An article presenting results on the effect of deer browsing and understory light availability on stump mortality and sprout growth capacity in sessile oak has just been published in Forest Ecology and Management. The work was carried out on parts of the experimental facility OPTMix. The article is the result of work carried out by two Master student projects: Jessica Maurize’s Master 1 (University of Perpignan Via Domitia) in 2015 and Master 2 by Kamel Zouaydi (University of Lorraine) in 2016.

Mårell, A., Hamard, J.-P., Pérot, T., Perret, S., Korboulewsky, N. 2018. The effect of deer browsing and understory light availability on stump mortality and sprout growth capacity in sessile oak. Forest Ecology and Management 430:134-142. doi: 10.1016/j.foreco.2018.08.015

Red deer (left) and roe deer (right) browsing resprouts on the OPTMix experimental study plots.

Graphical abstract


  • Deer browsing increased stump mortality of sessile oak even at low deer densities.
  • Deer browsing inhibited sprout growth of sessile oak even at low deer densities.
  • Sprout growth increased linearly with increasing understory light availability.
  • Stump survival declined linearly with greater parent tree diameter.
  • Increased understory light availability did not compensate for deer impacts.



Coppice forestry is a conventional silvicultural practice that takes advantage of a tree’s capacity to respond to disturbances by sprouting. Sprouting capacity is determined by many intrinsic and extrinsic factors such as parent tree age/size, understory light availability and deer browsing, which, under closed canopy conditions are important limiting factors for stump survival or sprout growth. However, the combined effect of potentially confounding abiotic and biotic factors on stump survival and sprout growth remains elusive, even more so under closed canopy conditions. This study aims to quantify the effect of deer browsing on stump mortality and sprout growth under closed-canopy conditions and to compare this effect with other known determinants. Here we show that stump survival and sprout growth in sessile oak (Quercus petraea Matt.) depend on deer browsing, understory light availability and the diameter of the parent tree. By studying paired fenced-unfenced plots, we confirmed that deer browsing decreased stump survival and inhibited sprout growth. Furthermore, by taking advantage of a gradient in understory light availability in monospecific and mixed stands of sessile oak and Scots pine (Pinus sylvestris L.), we showed a clear positive linear relationship between sprout growth and light availability. This relationship explained the observed differences among stand composition types. Finally, we found that increased understory light availability did not compensate for losses due to deer browsing. In the absence of deer browsing, our results demonstrate that sessile oak stumps regenerate well under closed-canopy conditions and maintain a moderate sprouting capacity at least until the age of 70–80 years old. Partial thinning could therefore be a potential tool to renew light-demanding tree species such as sessile oak in mixed high-forest stands. Nevertheless, we do not recommend coppicing sessile oak under closed canopies unless the oak stumps are protected from deer browsing and understory light availability is optimized as much as possible despite closed-canopy-management objectives.

Monitoring soil microbial activity

Promoted by Stéphane Bazot from UMR 8079, Laboratory Ecology, Systematics and Evolution of Paris-sud University, a team led by Gaëlle Vincent came to OPTMix in March and mid-June for two campaigns to monitor soil microbial activity. Soil samples were taken for structural analyzes of the communities of bacteria, archaea and fungi. To complete, soil respiration measurements were coupled for the campaign in June to characterize this part of the carbon cycle as a function of stand density.

At the same time, the Irstea team associated with Sébastien Gogo, from ISTO Orléans, measured soil respiration with large chamber in mixed stands like last year. In addition to the inter-annual variation, the measurements will allow inter-device comparison.



The Research and Development department of National Forest Office comes to visit OPTMix

The research activities carried out on the OPTMix device were presented as part of the annual meeting of the “Research Development and Innovation” (RDI) of the National Forest Office (ONF) on May 30th and 31st, 2018.

70 people from the RDI network came to visit the experimental plots around 4 workshops:

Workshop 1: Water resource, depth of acquisition and transpiration of water by mixed stands in a context of severe water stress (Philippe Balandier and Jordan Bello)

Workshop 2: Natural regeneration interacting with wildlife (Anders Marell and Yves Boscardin)

Workshop 3: Growth and productivity, equipments, sensors and data collected (Thomas Perot and Camille Couteau)

Workshop 4: Plant diversity, nutrient consumption by trees and nutrient cycling (Yann Dumas, Nathalie Korboulewsky and Céline Pradier)

Thank you to all people who helped to prepare these days.





OPTMix joins the CLIMATICK project

OPTMix joins the network of the CLIMATICK project which starts in June 2018. OPTMix becomes the 10th site with a monthly monitoring of tick activity after that of ONCFS in Bazes (Pyrénées).

see also here

Summary of the CLIMATICK project (Isabelle Lebert, INRA UMR EPIA)

Le changement climatique modifie la phénologie la distribution des tiques et en conséquence la distribution des maladies liées aux tiques.

Les objectifs du projet CLIMATICK sont de :

  • Projeter les modèles spatiaux et temporels de l’activité future des tiques indigènes et exotiques dans le scénario RCP (« Representative Concentration Pathways » ou « Profils représentatifs d’évolution de concentration »),
  • Proposer des adaptations de la stratégie de communication, de la surveillance et de la gestion environnementale pour améliorer la prévention vis-à-vis des tiques.

Le projet CLIMATICK met l’accent sur le risque actuel représenté par les tiques indigènes (Ixodes ricinus) et ses pathogènes les plus menaçants pour la santé humaine et animale mais également sur les nouveaux risques liés aux tiques exotiques des régions plus chaudes potentiellement invasives, comme Hyalomma marginatum, vecteur de CCHF (virus de la fièvre hémorragique de Congo-Crimée), établi dans le sud de la France. À l’aide de données observationnelles et expérimentales longitudinales, des modèles mathématiques dynamiques et statistiques seront développés pour étudier l’activité des tiques en tenant compte des variables météorologiques, des populations hôtes et de la répartition des forêts en lien avec les changements climatiques. La projection dans le climat futur sera faite pour 2050 et 2100.

Ce projet est financé par le métaprogramme ACCAF (Adaptation au Changement Climatique de l’Agriculture et de la Forêt) sur 3 ans (mai 2018 avril 2021). CLIMATICK est un un projet pluridisciplinaire dont l’UMR EPIA est le coordinateur (Karine Chalvet-Monfray) et l’UMR ASTRE le co-coordinateur (Laurence Vial). D’autres équipes sont impliquées dans le projet INRA (BIOEPAR, BIPAR, CEFS, Agroclim, Territoires, Merial et Anses Nancy).

Ce projet est la suite de deux projet CCEID et CCEID-transfert (métaprogramme ACCAF de 2014 à 2018). Ils ont permis :

  • Projet CCEID : de mettre en place un réseau d’observatoires sur l’activité et la dynamique des populations de tiques sur une longue période et de développer des modèles associés de prévision des risques. Une collecte de tiques a lieu tous les mois depuis 2014 sur 8 sites en France. Sur chaque site, la collecte est réalisée sur 10 transects de 10 m² chacun. Une station météorologique est installée par site : température à 2 mètres, température dans la litière, humidité relative… L’identification et la conservation des tiques se font à l’INRA.
  • Projet CCEID-transfert : de transférer le modèle issu de CCEID dans l’application Fleatickrisk pour valorisation le travail réalisé

L’IRSTEA (Nogent sur Vernisson) dans le cadre de leur dispositif expérimental OPTMix rejoint le réseau d’observatoires dans le projet CLIMATICK et devient le 10ème site de suivi mensuel de l’activité des tiques, après celui de ONCFS à Bazes (Pyrénées).


Monitoring and collecting ticks on the OPTMix experimental site

Project partners: INRA Auvergne-Rhône-Alpes – VetAgro Sup, UMR Epidémiologie des maladies animales et zoonotiques (EPIA)

The monitoring of tick populations on the OPTMix experimental facility in collaboration with INRA is part of the CCEID project (Climate change and the risk of wildlife-borne infectious diseases emergence in agricultural and forest landscapes) within the ACCAF (Adaptation agriculture and forestry to climate change) research program of INRA. OPTMix is one of several sites in the CCEID project whose objective is both to set up a network of long-term monitoring sites of the population dynamics of vectors (ticks) and reservoirs of pathogens (rodents) and to develop associated risk prediction models.

The collection of ticks will take place every month in plots with conventional silviculture (with a relative density index, RDI, around 0.7). On each plot (plots O200-O214-O216), the collection of ticks is carried out on 10 transects of 10 m² each. Other data collected on the OPTMix site will help to study the relationship between tick population dynamics and environmental variables such as climate (data from the metrological station), understorey vegetation (vegetation surveys), rodent populations (trapping of small mammals) and wild ungulate populations (camera traps).

Identification and conservation of ticks are done by INRA. Conserved ticks will later on be analysed for pathogens.

The start and the end of transects are marked by wooden sticks painted in orange (see second picture below).

People involved (see first picture below): Yves Boscardin (Irstea), Valérie Poux (INRA UMR EPIA), Adélie Chevalier (Irstea), Isabelle Lebert (INRA UMR EPIA), Anders Mårell (Irstea)


OPTMix participates in the creation of a bryophytes database of the Loiret department.

Inventories of bryophytes carried out on the OPTMix device contributed to the production of a database on Loiret bryophytes. An article published in the Symbioses journal (bulletin of the museums of the region Centre – Val de Loire) presents this work.

Dumas, Y. and P. Boudier (2018). “Bryophytes loirétaines : bilan des connaissances actuelles.” Symbioses 35-36: 35-46.

A European network of sessile oak – Scots pine plots to better understand the effect of tree species mixture on forest vulnerability (REFORM project)

One of the objectives of the REFORM project (REsilience of FORest Mixtures, ERA-NET SUMFOREST, see also here) is to set up a European network of forest plots comparing pure and mixed stands of sessile oak and Scots pine in order to determine the role of tree species mixture on forest vulnerability. In this framework, three plots of the OPTMix device will be integrated in the REFORM project. Additional dendrometric data were collected from March 19 to 23 (crown width measurements and cores from 120 trees).

Thank you to Mathias Steckel, PhD student on the project (Technical University of Munich, TUM School of Life Sciences Weihenstephan, Chair of Forest Growth and Yield Science), coming to help us and supervising the operation.

And a big thank to the staff from Irstea Grenoble (UR LESSEM) coming to help us during this week:
Pascal Tardif (team ASTRRE), Eric Mermin (team ASTRRE) and Patrick Vallet (team DYNAMICS)

Article published: Influence of forest tree species composition on bryophytic diversity in mixed and pure pine and oak stands

An article dealing with stand composition effect on bryophyte diversity has just been published in Forest Ecology and Management. This work was partly performed on OPTMix experimental plots during the internship of Deki Fourcin (Master 2, Irstea Nogent-sur-Vernisson). Below are the abstract and key points of the article.

Gosselin, M., D. Fourcin, Y. Dumas, F. Gosselin, N. Korboulewsky, M. Toïgo and P. Vallet (2017). “Influence of forest tree species composition on bryophytic diversity in mixed and pure pine (Pinus sylvestris L.) and oak (Quercus petraea (Matt.) Liebl.) stands.” Forest Ecology and Management 406(Supplement C): 318-329. doi: 10.1016/j.foreco.2017.09.067

The effects of mixed stands on biodiversity are increasingly being studied since they are supposed to offer higher habitat heterogeneity. Nevertheless, for tree-associated diversity, including epiphytes and terricolous species near tree trunks, few studies exist, and still fewer compare mixed stands with each corresponding pure tree species stand. We evaluated and quantified the influence of forest composition on tree-associated bryophyte diversity (species richness, abundance, composition) in mixed and pure oak-pine stands in a French lowland forest. The main explanatory variables for bryophyte diversity at tree-level were the identity of the phorophyte tree species and the mixture type (pure versus mixed). At the plot level, the main explanatory variable was the stand type (pure oak, pure pine and mixed). We also explored the role of other variables including the chemistry of the bryophyte substrates (soil, bark) and water supply (stemflow, throughfall), as well as stand abundance variables (basal area, interfering plant cover). We analyzed data with Generalized Linear Models under Bayesian statistics, to take into account the spatial autocorrelation between plots and any under- or over-dispersion of our data. At the tree-level, bryophyte richness and abundance were higher on oak than on pine. Pine bryophyte richness was higher in mixed compared to pure stands, whereas for oak, mixed stands did not enhance bryophyte richness. At the plot level, mixed stands hosted bryophyte communities of similar richness to those in pure oak stands, whereas pure pine stands were clearly poorer. Our exploratory models suggested strong effects of water supply chemistry (stemflow and throughfall pH or conductivity) and basal area; the latter had a strong quadratic effect on epiphytic richness at the plot level. In terms of composition, three species were more likely to be found on pine phorophytes, seven species clearly occurred more frequently on oaks. Some species were more likely to be associated to pine in mixed than in pure stands, and one species was found more often under pines in pure stands. Therefore, bryophyte diversity at the landscape level should benefit from the simultaneous presence of the three stand composition types – pure oak, pure pine and mixed stands.


  • Bryophyte diversity on and around tree trunks was higher for oak than for pine.
  • Mixed stands enhanced bryophyte diversity for pine trees.
  • At the plot level, mixed stands and pure oak stands had similar bryophyte richness.
  • Nevertheless, some species were more likely to be found on pines.
  • Exploratory models revealed strong effects for basal area and water supply chemistry.

This research was supported by the French Ministry of the Environment (ISCAR and DivClim Projects) and carried out on a part of the OPTMix (Oak Pine Tree Mixture) experimental site (, managed by Irstea and supported by the Centre-Val de Loire region and the French National Forest Office.