SCC - Swiss Canopy Crane project - lastest news

Forest Discovery: Trees Trade Carbon Among Each Other

Forest trees use carbon not only for themselves; they also trade large quantities of it with their neighbours. Botanists from the University of Basel report this in the journal Science. The extensive carbon trade among trees – even among different species – is conducted via symbiotic fungi in the soil.

It is well known that plants take up carbon dioxide from the air by photosynthesis. The resulting sugar is used to build cellulose, wood pulp (lignin), protein and lipid – the building blocks of plants. While growing, the tree transports sugar from its leaves to the building sites: to the branches, stems, roots and to their symbiotic fungi below ground (mycorrhizal fungi).

Carbon dioxide shower for trees

Dr. Tamir Klein and Prof. Christian Körner of the University of Basel together with Dr. Rolf Siegwolf of the Paul Scherrer Institute (PSI) now report, that this sugar export goes further than previously thought. In a forest near Basel the researchers used a construction crane and a network of fine tubes to flood the crowns of 120 year old and 40 meter tall spruce trees with carbon dioxide that carried a label. The researchers used carbon dioxide that, compared to normal air, contains less of the rare and heavier 13C atom.

While this modification made no difference for the trees, it allowed the botanists to track the carbon through the entire tree using an atomic mass spectrometer. This way they were able to trace the path of the carbon taken up by photosynthesis from the crowns down to the root tips. The researchers found the labelled carbon not only in the roots of the marked spruce trees. The roots of the neighbouring trees also showed the same marker, even though they had not received labelled carbon dioxide. This included trees from other species.

«Forest is more than the sum of its trees»

The only way the carbon could have been exchanged from spruce to beech, pine or larch tree – or vice versa – is by the network of tiny fungal filaments of the shared mycorrhizal fungi. Understory plants which partner up with other types of fungi remained entirely unmarked. The research group called the discovered exchange of large quantities of carbon among completely unrelated tree species in a natural forest «a big surprise».According to the researchers, the discovery questions the concept of tree individuality with regard to the single largest constituent of the biosphere, tree carbon. Furthermore, the results of the study funded by the Swiss National Science Foundation add a new dimension to the role of mycorrhizal fungi in forests. «Evidently the forest is more than the sum of its trees», comments Prof. Christian Körner the findings.


Klein T, Siegwolf RTW, Körner C (2016) Belowground carbon trade among tall trees in a temperate forest. Science 352:342-344, DOI 10.1126/science.aad6188


Lay Summary in Deutsch (pdf)

Lay Summary in English (pdf)

Beitrag in UNINEWS (link)





Ein 45 m höher Kran erlaubt Forschung in den Baumkronen eines Naturwaldes; A 45 m tall tower crane permits working in the forest canopy of a natural mixed forest (Hofstetten, SO, near Basel; Foto C. Körner)
Eine Arbeitsgondel hebt ab: das Kronendach ist 30-40 m hoch; A work gondola lifts researchers to the 30-40 m heigh canopy (Hofstetten, SO, near Basel; Foto C. Körner)
Fichtenkronen werden über poröse Schläuche mit erhöhter Konzentration von CO2 Gas beflutet. So werden die Bäume mit einer Isotopen-Markierung infiltriert die man bis in die Wurzeln und zu den Bodenpilzen verfolgen kann; The crowns of spruce trees are exposed to elevated CO2 concentrations by means of porous tubing. This way the trees become infiltrated with an isotope-label that can be traced down to roots and soil fungi (Hofstetten, SO, near Basel; photo C. Körner)

SCC - an overview

In March 1999 a ca. 45 m tall crane was installed in a highly diverse, mature temperate forest at Hofstetten near Basel, 550 m above sea level.
This research tool enabled canopy research in both adult conifers and deciduous trees typical for European forests. With a new type of Free Air CO2 Enrichment, called webFACE, part of this forest is exposed to 530 ppm CO2 since October 2000 (see Pepin and Körner 2002). Tree genera included: Fagus, Quercus, Carpinus, Acer, Tilia, Prunus, Abies, Picea, Pinus, Larix.

The forest has by 2016 an age of 120 years and dominant trees vary between 32 m and 40 m in height. Except for Larix and Picea (which were introduced from slightly higher elevations) all species occur naturally. With the broad leaved evergreen Ilex aquifolium and Hedera helix in the understory the spectrum is ideal for a an assessment of functional aspects of forest biodiversity.
Research was strictly comparative in order to capitalize on this unique species richness. Topics attended by our team included canopy architecture and fuctional leaf attributes, reproductive dynamics and storage reserves in whole tree canopy CO2-enrichment, sapflow and stable isotopes.

After 4 years, we found an immediate and sustained enhancement of carbon flux, but there was no overall stimulation in stem growth and leaf litter production (Körner et al. 2005).

We cooperated with partners from other Swiss institutions (WSL, PSI and others) and colleagues from Germany and Austria. Internationally this project lined up with currently operative crane projects in Panama, Venezuela, Oregon, NE-Australia, and Japan, providing a global network which also included animal sciences. With its sole emphasis on experimental and analytical work in the top of a mature forest, this was the first crane project in Europe, and one out of three globally in a temperate deciduous/mixed forest (the others are in Japan and in Germany). The SCC project first of all seeked to contribute to biodiversity research in forests.



Dr. Günter Hoch (Postdoc), Dr. Tamir Klein (Postdoc), Martin Bader (PhD), Manuel Mildner (PhD), Erwin Amstutz (Technician), Georges Grun (Technician)
Paul Scherrer Institut, Villigen (Dr. R. Siegwolf)
Swiss Federal Institute for Forest, Snow and Landscape Research, Birmensdorf (I. Bucher, F. Hagedorn, P. Schlaeppi)

Global Canopy Programme - a world wide network of scientific studies of forest canopies.
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Altermatt F (2003) Potential negative effects of atmospheric CO2-enrichment on insect communities in the canopy of a mature deciduous forest in Switzerland. Mitt Schweiz Entomol Ges 76:191-199

Asshoff R, Keel SG, Siegwolf RTW, Körner C (2008) Tracing arthropod movement in a deciduous forest canopy using stable isotopes. In: Floren A, Schmidl J (eds) Canopy arthropod research in Europe, Bioform, Nürnberg, pp 327-338

Asshoff R, Zotz G, Körner C (2005) Growth and phenology of mature temperate forest trees in elevated CO2. Global Change Biol 12:848-861

Bader M, Hiltbrunner E, Körner C (2009) Fine root responses of mature deciduous forest trees to free air carbon dioxide enrichmen (FACE). Funct Ecol 23:913-921

Bader MFK, Leuzinger S, Keel SG, Siegwolf RTW, Hagedorn F, Schleppi P, Körner C (2013) Central European hardwood trees in a high‐CO2 future: synthesis of an 8‐year forest canopy CO2 enrichment project. J Ecol 101:1509-1519

Bader MKF, Körner C (2010) No overall stimulation of soil respiration under mature deciduous forest trees after 7 years of CO2 enrichment. Glob Change Biol 16:2830-2843

Bader MKF, Mildner M, Baumann C, Leuzinger S, Körner C (2016) Photosynthetic enhancement and diurnal stem and soil carbon fluxes in a mature Norway spruce stand under elevated CO2. Environ Exp Bot 124:110-119

Bader MKF, Siegwolf R, Körner C (2010) Sustained enhancement of photosynthesis in mature deciduous forest trees after 8 years of free air CO2 enrichment. Planta 232:1115-1125

Cech PG, Pepin S, Körner C (2003) Elevated CO2 reduces sap flux in mature deciduous forest trees. Oecologia 137:258-268

Han Q, Kabeya D, Körner Ch, Hoch G (2011) Leaf traits, shoot growth and seed production in mature Fagus sylvatica trees after eight years’ CO2 enrichment. Annals of Botany 107:1405-1411

Hättenschwiler S, Schafellner C (2004) Gypsy moth feeding in the canopy of a CO2-enriched mature forest. Global Change Biology 10:1899-1908

Hoch G (2005) Fruit bearing branchlets are carbon autonomous in mature broad-leaved temperate forest trees. Plant Cell and Environment 28:651-659

Hoch G, Keel SG (2006) 13C labelling reveals different contributions of photoassimilates from infructescences for fruiting in two temperate forest tree species. Plant Biology 8:606-614

Hoch G, Richter A, Körner C (2003) Non-structural carbon compounds in temperate forest trees. Plant Cell Environ 26:1067-1081

Keel SG, Pepin S, Leuzinger S, Körner C (2007) Stomatal conductance in mature deciduous forest trees exposed to elevated CO2. Trees 21:151-159

Keel SG, Siegwolf RTW, Jäggi M, Körner C (2007) Rapid mixing between old and new C pools in the canopy of mature forest trees. Plant Cell Environ 30:963-972

Keel SG, Siegwolf RTW, Körner C (2006) Canopy CO2 enrichment permits tracing the fate of recently assimilated carbon in a mature deciduous forest. New Phytol 172:319-329

Klein T, Bader MKF, Leuzinger S, Mildner M, Schleppi P, Siegwolf RTW, Körner C (2016) Growth and carbon relations of mature Picea abies trees under 5years of free-air CO2 enrichment. J Ecol 104:1720-1733

Klein T, Siegwolf RTW, Körner C (2016) Belowground carbon trade among tall trees in a temperate forest. Science 352:342-344, DOI 10.1126/science.aad6188

Körner C (2002) Basel canopy crane, Switzerland. In: Mitchell AW, Secoy K, Jackson T (eds) Global canopy handbook. Global Canopy Foundation, Oxford, pp 42-46

Körner C (2003) Carbon limitation in trees. J Ecol 91:4-17

Körner C (2003) Ecological impacts of atmospheric CO2 enrichment on terrestrial ecosystems. Phil Trans R Soc Lond A 361:2023-2041

Körner C (2004) Through enhanced tree dynamics carbon dioxide enrichment may cause tropical forests to lose carbon. Phil Trans R Soc Lond Ser B-Biol Sci 359:493-498

Körner C (2005) Wald, Biodiversität und CO2 - Überraschungen sind sicher. Naturwissenschaftliche Rundschau 58:61-69

Körner C (2006) Forests, biodiversity and CO2: surprises are certain. Biologist 53:82-90

Körner C (2013) A mature forest canopy in a CO2-rich future: An experiment at the Swiss Canopy Crane Research Site In M. Lowman et al. (eds.), Treetops at Risk: Challenges of Global Canopy Ecology and Conservation, Springer NY. pp 141-145

Körner C, Bader M (2010) Der Wald in einer CO2-reichen Welt. Lehrmittelverlag Kanton Solothurn, Solothurn

Körner C, Zotz G (2003) Cranes in temperate forests; Basel, Switzerland. In: Y Basset, V Horlyck, SJ Wright (eds) Studying forest canopies from above: The International Canopy Crane Network. Smithsonian Tropical Research Institute and UNEP, Panama. pp 67-70

Leuzinger S, Hartmann A, Körner Ch (2011) Water relations of climbing ivy in a temperate forest. Planta 233:1087-1096

Leuzinger S, Körner C (2007) Tree species diversity affects canopy leaf temperatures in a mature temperate forest. Agric For Meteorol 146:29-37

Leuzinger S, Körner C (2007) Water savings in mature deciduous forest trees under elevated CO2. Glob Change Biol 13:1-11

Leuzinger S, Vogt R, Körner C (2010) Tree surface temperature in an urban environment. Agricultural and Forest Meteorology 150:56-62

Mildner M, Bader MKF, Baumann C, Körner C (2015) Respiratory fluxes and fine root responses in mature Picea abies trees exposed to elevated atmospheric  CO2 concentrations. Biogeochemistry 124:95-111

Mildner M, Bader MKF, Leuzinger S, Siegwolf RTW, Körner C (2014) Long-term C-13 labeling provides evidence for temporal and spatial carbon allocation patterns in mature Picea abies. Oecologia 175:747-762

Pennisi E (2005) Sky-High Experiments. Science 309:1314-1315 (26 August 2005)

Pepin S, Körner C (2002) Web-FACE: a new canopy free air CO2 enrichment system for tall forest trees in mature forests. Oecologia, 133:1-9

Schädel C, Blöchl A, Richter A, Hoch G (2009) Short-term dynamics of non-structural carbohydrates and hemicelluloses in young branches of temperate forest trees during bud break. Tree Physiology 29:901-911

Schleppi P, Bucher-Wallin I, Hagedorn F, Körner C (2012) Increased nitrate availability in the soil of a mixed mature temperate forest subjected to elevated CO2 concentration (canopy FACE). Glob Change Biol 18:757-768

Steinmann K, Siegwolf RTW, Saurer M, Körner C (2004) Carbon fluxes to the soil in a mature temperate forest assessed by 13C isotope tracing. Oecologia 141:489-501

Zotz G, Pepin S, Körner C (2005) No down-regulation of leaf photosynthesis in mature forest trees after long-term exposure to elevated CO2. Plant Biology 7:369-374.