Article published: Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect

An article has just been published in the “Journal of Applied Ecology” journal dealing with the effect of mixing tree species on forest productivity. This article shows that two species mixed stands have a greater productivity stability over time than comparable monospecific stands. Mixed stands would buffer the destabilizing effect of temperatures on growth, which would lead to a greater stability in the productivity of mixed stands compared to monospecific stands.

The OPTMix plots contributed to the data of this article based on 261 plots across Europe (87 triplets) of monospecific and mixed stands (beech – Scots pine; sessile and pedunculate oak – Scots pine; spruce – Scots pine).

del Río, M., H. Pretzsch, R. Ruiz-Peinado, H. Jactel, L. Coll, M. Löf, J. Aldea, C. Ammer, A. Avdagić, I. Barbeito, K. Bielak, F. Bravo, G. Brazaitis, J. Cerný, C. Collet, S. Condés, L. Drössler, M. Fabrika, M. Heym, S.-O. Holm, G. Hylen, A. Jansons, V. Kurylyak, F. Lombardi, B. Matović, M. Metslaid, R. Motta, T. Nord-Larsen, A. Nothdurft, J. den Ouden, M. Pach, M. Pardos, C. Poeydebat, Q. Ponette, T. Pérot, D. O. J. Reventlow, R. Sitko, V. Sramek, M. Steckel, M. Svoboda, K. Verheyen, S. Vospernik, B. Wolff, T. Zlatanov and A. Bravo-Oviedo (2022). « Emerging stability of forest productivity by mixing two species buffers temperature destabilizing effect. » Journal of Applied Ecology n/a(n/a) DOI: https://doi.org/10.1111/1365-2664.14267.

Abstract:

  1. The increasing disturbances in monocultures around the world are testimony to their instability under global change. Many studies have claimed that temporal stability of productivity increases with species richness, although the ecological fundamentals have mainly been investigated through diversity experiments. To adequately manage forest ecosystems, it is necessary to have a comprehensive understanding of the effect of mixing species on the temporal stability of productivity and the way in which it is influenced by climate conditions across large geographical areas.
  2. Here, we used a unique dataset of 261 stands combining pure and two-species mixtures of four relevant tree species over a wide range of climate conditions in Europe to examine the effect of species mixing on the level and temporal stability of productivity. Structural equation modelling was employed to further explore the direct and indirect influence of climate, overyielding, species asynchrony and additive effect (i.e. temporal stability expected from the species growth in monospecific stands) on temporal stability in mixed forests.
  3. We showed that by adding only one tree species to monocultures, the level (overyielding: +6%) and stability (temporal stability: +12%) of stand growth increased significantly. We identified the key effect of temperature on destabilizing stand growth, which may be mitigated by mixing species. We further confirmed asynchrony as the main driver of temporal stability in mixed stands, through both the additive effect and species interactions, which modify between-species asynchrony in mixtures in comparison to monocultures.
  4. Synthesis and applications. This study highlights the emergent properties associated with mixing two species, which result in resource efficient and temporally stable production systems. We reveal the negative impact of mean temperature on temporal stability of forest productivity and how the stabilizing effect of mixing two species can counterbalance this impact. The overyielding and temporal stability of growth addressed in this paper are essential for ecosystem services closely linked with the level and rhythm of forest growth. Our results underline that mixing two species can be a realistic and effective nature-based climate solution, which could contribute towards meeting EU climate target policies.

Article published: With increasing site quality asymmetric competition and mortality reduces Scots pine (Pinus sylvestris L.) stand structuring across Europe

An article has just been published in the “Forest Ecology and Management” journal dealing with the stand structuring of monospecific Scots pine forests. This article shows that the stand structuring decreases with site quality because of mortality and asymmetric competition processes. The OPTMix plots contributed to the data of this study based on 90 Scots pine stands.

Pretzsch, H., A. Bravo-Oviedo, T. Hilmers, R. Ruiz-Peinado, L. Coll, M. Löf, S. Ahmed, J. Aldea, C. Ammer, A. Avdagić, I. Barbeito, K. Bielak, F. Bravo, G. Brazaitis, J. Cerný, C. Collet, L. Drössler, M. Fabrika, M. Heym, S.-O. Holm, G. Hylen, A. Jansons, V. Kurylyak, F. Lombardi, B. Matović, M. Metslaid, R. Motta, T. Nord-Larsen, A. Nothdurft, C. Ordóñez, J. den Ouden, M. Pach, M. Pardos, Q. Ponette, T. Pérot, D. O. J. Reventlow, R. Sitko, V. Sramek, M. Steckel, M. Svoboda, E. Uhl, K. Verheyen, S. Vospernik, B. Wolff, T. Zlatanov and M. del Río (2022). « With increasing site quality asymmetric competition and mortality reduces Scots pine (Pinus sylvestris L.) stand structuring across Europe. » Forest Ecology and Management 520: 120365 DOI: https://doi.org/10.1016/j.foreco.2022.120365.

Highlights
• The study based on 90 mature Scots pine stands along a productivity gradient across Europe.

• Growth partitioning became more asymmetric and structuring with increasing site quality.

• Mortality eliminated predominantly small trees with increasing site quality.

• We found the highest size variation on poor sites and the lowest on rich sites.

• As a result stand structure became more homogeneous with increasing site quality.

Abstract
Heterogeneity of structure can increase mechanical stability, stress resistance and resilience, biodiversity and many other functions and services of forest stands. That is why many silvicultural measures aim at enhancing structural diversity. However, the effectiveness and potential of structuring may depend on the site conditions. Here, we revealed how the stand structure is determined by site quality and results from site-dependent partitioning of growth and mortality among the trees. We based our study on 90 mature, even-aged, fully stocked monocultures of Scots pine (Pinus sylvestris L.) sampled in 21 countries along a productivity gradient across Europe. A mini-simulation study further analyzed the site-dependency of the interplay between growth and mortality and the resulting stand structure. The overarching hypothesis was that the stand structure changes with site quality and results from the site-dependent asymmetry of competition and mortality.

First, we show that Scots pine stands structure across Europe become more homogeneous with increasing site quality. The coefficient of variation and Gini coefficient of stem diameter and tree height continuously decreased, whereas Stand Density Index and stand basal area increased with site index.

Second, we reveal a site-dependency of the growth distribution among the trees and the mortality. With increasing site index, the asymmetry of both competition and growth distribution increased and suggested, at first glance, an increase in stand heterogeneity. However, with increasing site index, mortality eliminates mainly small instead of all-sized trees, cancels the size variation and reduces the structural heterogeneity.

Third, we modelled the site-dependent interplay between growth partitioning and mortality. By scenario runs for different site conditions, we can show how the site-dependent structure at the stand level emerges from the asymmetric competition and mortality at the tree level and how the interplay changes with increasing site quality across Europe.

Our most interesting finding was that the growth partitioning became more asymmetric and structuring with increasing site quality, but that the mortality eliminated predominantly small trees, reduced their size variation and thus reversed the impact of site quality on the structure. Finally, the reverse effects of mode of growth partitioning and mortality on the stand structure resulted in the highest size variation on poor sites and decreased structural heterogeneity with increasing site quality. Since our results indicate where heterogeneous structures need silviculture interventions and where they emerge naturally, we conclude that these findings may improve system understanding and modelling and guide forest management aiming at structurally rich forests.

A new internship on forest regeneration begins on OPTMix plots

Matias Bentkowski is carrying out his internship at the EFNO unit of INRAE. The aim is to study the impact of summer drought on tree regeneration. The field experiment is done using the OPTMix research facility. It consists of measuring water stress and the annual growth of seedlings of Scots pine and Sessile oak under different natural conditions (competition with understory vegetation, level of lighting due to the forest cover, pressure of browsing and fraying by deer). The field measurements will take place during 3 months (June, July and August). The tree seedlings will be regularly measured throughout the summer period. The aim is to estimate the impact of different natural factors on forests regeneration.

“Where is the student?”. Photo taken by Guilhem Parmain during a field trip on the OPTMix device

 

water stress measurement using a porometer. Photo taken by Matias showing the device used for field measurements

 

Study of tree crowns complementarity

In mixed forests, complementarity can be expressed by a differentiate use of space between species so that each species makes the best use of the light resource according to its photosynthetic capacities. This spatial differentiation between species is possible thanks to plasticity in crown architecture. Thus many articles report an increase in the extent and the volume of the crowns in the mixtures compared to the monospecific stands, but with a significant tree species and size tree effects. We wanted to know if the effect of the mixture on tree crown architecture was also observed on the OPTMix plots between sessile oak and Scots pine and to see if there was a relationship with the amount of litter and the nutritional status of the trees.

We therefore carried out measurements of the height of the first living branch and the radius of the crowns according to the “vertical sighting method” (Preuhsler, 1979), to calculate the projection surface and the volume of the crowns of 75 pines and 75 oaks. Several Master trainees did this measurement campaign. The operator effect on the crown measurements will also be studied. A comparison with previous crown data collected in 2017 will be made if possible.

OPTMix annual meeting: January 25, 27 and 28, 2022

The OPTMix annual meeting will take place on January 25, 27 and 28, 2022 by videoconference.

For more information please contact Nathalie Korboulewsky.

OPTMix data usage conditions and agreement and data request form

The data usage conditions and agreement forms and a data request form are available on the following page:

Home\Data usage conditions and agreement and data request form\

Article published: Handbook of field sampling for multi-taxon biodiversity studies in European forests

An article has been published in the “Ecological Indicators” journal presenting a handbook to sample biodiversity in European forests. Biodiversity data of the OPTMix device were used in this article which was part of the COST Action BOTTOMS-UP:

Burrascano, S., G. Trentanovi, Y. Paillet, J. Heilmann-Clausen, P. Giordani, S. Bagella, A. Bravo-Oviedo, T. Campagnaro, A. Campanaro, F. Chianucci, P. De Smedt, I. Garcia-Mijangos, D. Matosevic, T. Sitzia, R. Aszalos, G. Brazaitis, A. Cutini, E. D’Andrea, I. Doerfler, J. Hofmeister, J. Hosek, P. Janssen, S. K. Rojas, N. Korboulewsky, D. Kozak, T. Lachat, A. Lohmus, R. Lopez, A. Marell, R. Matula, M. Mikolas, S. Munzi, B. Norden, M. Partel, J. Penner, K. Runnel, P. Schall, M. Svoboda, F. Tinya, M. Ujhazyova, K. Vandekerkhove, K. Verheyen, F. Xystrakis and P. Odor (2021). « Handbook of field sampling for multi-taxon biodiversity studies in European forests. » Ecological Indicators 132. https://doi.org/10.1016/j.ecolind.2021.108266

 

Highlights:

  • Forest multi-taxon studies have similar aims but different sampling protocols.
  • The most sampled taxonomic groups are plants, beetles, lichens, birds, fungi.
  • Soil, litter and canopy resulted as undersampled forest habitats.
  • Sampling units and substrates differed widely within and among taxonomic groups.
  • Sampling methods for stand structure were relatively homogeneous.

 

Abstract:

Forests host most terrestrial biodiversity and their sustainable management is crucial to halt biodiversity loss. Although scientific evidence indicates that sustainable forest management (SFM) should be assessed by monitoring multi-taxon biodiversity, most current SFM criteria and indicators account only for trees or consider indirect biodiversity proxies. Several projects performed multi-taxon sampling to investigate the effects of forest management on biodiversity, but the large variability of their sampling approaches hampers the identification of general trends, and limits broad-scale inference for designing SFM. Here we address the need of common sampling protocols for forest structure and multi-taxon biodiversity to be used at broad spatial scales. We established a network of researchers involved in 41 projects on forest multi-taxon biodiversity across 13 European countries. The network data structure comprised the assessment of at least three taxa, and the measurement of forest stand structure in the same plots or stands. We mapped the sampling approaches to multi-taxon biodiversity, standing trees and deadwood, and used this overview to provide operational answers to two simple, yet crucial, questions: what to sample? How to sample? The most commonly sampled taxonomic groups are vascular plants (83% of datasets), beetles (80%), lichens (66%), birds (66%), fungi (61%), bryophytes (49%). They cover different forest structures and habitats, with a limited focus on soil, litter and forest canopy. Notwithstanding the common goal of assessing forest management effects on biodiversity, sampling approaches differed widely within and among taxonomic groups. Differences derive from sampling units (plots size, use of stand vs. plot scale), and from the focus on different substrates or functional groups of organisms. Sampling methods for standing trees and lying deadwood were relatively homogeneous and focused on volume calculations, but with a great variability in sampling units and diameter thresholds. We developed a handbook of sampling methods (SI 3) aimed at the greatest possible comparability across taxonomic groups and studies as a basis for European-wide biodiversity monitoring programs, robust understanding of biodiversity response to forest structure and management, and the identification of direct indicators of SFM.

 

Article published: Mixed stand at Low density: a solution to face climate change? The case of sessile oak and Scots pine mixture.

An article presenting the main results of Jordan Bello’s thesis defended in March 2019 was published in the latest issue of the journal “Rendez-Vous Techniques” of the National Forest Office:

Article published: What are the advantages and limits of tree species mixture to face climate changes? The contributions of the OPTMix device

An article presenting the latest results obtained on the OPTMix device was published in the latest issue of the journal “Rendez-Vous Techniques” of the National Forest Office:

Monitoring tree dieback of sessile oak and Scots pine

A tree health status scoring campaign was carried out in 2020 on all OPTMix plots on sessile oak and Scots pine tree samples. We used the DEPERIS protocol developed by the French Forest Health Department. A new scoring campaign was carried out in summer 2021. The first analyzes show an increase in the percentage of tree diebacks for Scots pine. This indicator rose from 8% in 2020 to 34% in 2021. This scoring will be continued in future years to monitor the health status of trees in the experiment.