Resilience of mixed beech-Scots pine forests to climate change
PI : Ignacio Babeito (UMR 1092 Laboratoire d’Etude des Ressources Forêts-Bois – LERFOB)
Co-applicatnts : Office National des Forets (ONF)
Collaboration : Catherine Collet, François Ningre (UMR Lerfob), Myriam Legay, Alexandre Piboule (ONF)
____________________________
Context — Numerous recent studies have documented the ecological benefits and values provided by mixed-species stands in temperate forests. However, the effects of these mixes are expected to change with corresponding changes to environmental conditions and gradients of resource supply.
Objectives — Our main goal was to increase our understanding of the differences in growth, structure and functioning of trees in mixed vs. pure forests using a well replicated study at the European level. In particular, we asked (i) how does productivity of mixed-stands differ from that of pure stands, (ii) how does crown morphology differ in mixed and pure stands, and (iii), to what degree do both (i) and (ii) depend on the site characteristics?
Approach — We studied the growth of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) in mixed versus pure stands on 32 triplets (pure pine-mixed-pure beech) located along a productivity gradient through Europe, reaching from Sweden to Bulgaria and from Spain to Ukraine. We installed a triplet in the Northern Vosges; we cored 20 dominant trees per plot and species and pooled our data with the rest of the European network. Additionally, we used terrestrial laser scanning (TLS) to obtain high-detail 3-D description of crowns in a subsample of four sites covering the mixture’s distribution area (from Spain to Sweden).
Key results —
- We found a mean overyielding of +12% in mixed stands (Pretzsch et al. 2015).
- This overyielding was independent of the site index, the stand growth and yield, and climatic variables despite the wide variation in precipitation (520–1175 mm year-1) and mean annual temperature (6–10.5 °C) on the sites (Pretzsch et al. 2015).
- Terrestrial laser scanner revealed higher variability in the allometric relationships of beech between diameter and crown parameters in mixed stands for all sites (Barbeito et al. in prep.).
Main findings — Our results point to the complementarity in the use of resources of beech and pine leading to overyielding. The absence of a significant relationship between overyielding and climate variables may result from a balance between the effects of different types of interactions (light-, water- and nutrient related) that all occur in these stands but are important individually under different climatic conditions. The refined crown data obtained with TLS support previous findings that show that trees with a given diameter have contrasting architecture in mixed and pure stands. However, our data are, to our knowledge, the first to generalize this finding for such a wide range of climatic conditions.
Future perspectives —
Two additional papers concerning the data on growth are planned for the winter of 2015 and spring of 2016 (see below papers in prep.). A second paper on TLS data, dealing with the canopy space occupation in mixed vs. pure stands is planned. We would also like to publish a third paper or short communication on the analysis of TLS cloud data using different approaches.
The plots in the Vosges and in other triplets from our European partners will be maintained for at least three more years. Thus, further collaborations within the topic of functioning of mixed forests within the European network are guaranteed. We believe that the question of whether differences in crown architecture are linked to growth or to trees’ resilience to climatic events, and how this balance may be affected by silviculture, merits further consideration. Along these lines, we recently proposed a project for the LabEx ARBRE 2015 call for proposals (SCAN-COMP) that would allow us to pursue these questions.
__________________________
Publications:
Pretzsch, H., del Río, M., Ammer, C., Avdagic, A., Barbeito, I. et al. (36 authors total). 2015. Growth and yield of mixed versus pure stands of Scots pine (Pinus sylvestris L.) and European beech (Fagus sylvatica L.) analysed along a productivity gradient through Europe. European Journal of Forest Research 134: 927-947.
Conferences:
Barbeito, I., Dassot, M. Collet, C. Ningre, F. Canopy space filling in mixed versus pure stands of European beech revealed by terrestrial laser scanning. IUFRO 10th Beech Symposium, Turkey, September 2015.
Barbeito, I., Collet, C., Dassot, M., Ningre, F. Legay, M. Piboule, O. 2015. Croissance et occupation de l’espace par la canopée de hêtre-pin sylvestre en peuplements purs vs. mélangés le long d’un gradient européen. Les forêts mélangées : quel état des connaissances scientifiques ? IRSTEA, Nogent sur Vernisson, June 2015.
Dissemination:
Der Alzenauer Wald in 3D- 6 March 2015. Frankfurter Allgemeine.
Twitter- July 24 (date publication of the paper Pretzsch et al. 2015).
Other:
A Ph.D. candidate from the University of Valladolid (Spain), Sara Uzquiano, is coming for a short visit of 2 weeks in mid-November financed by a Short Term Scientific Mission of the COST action EuMixFor (European Mixed Forests), to learn how to use the software CompuTree (computree.onf.fr) and in particular several functions that were specifically designed within the REMIX project for the analysis of canopies in multi-species complex stands.
