, Volume 133, Issue 1, pp 1–9

Web-FACE: a new canopy free-air CO2 enrichment system for tall trees in mature forests

  • Steeve Pepin
  • Christian Körner

DOI: 10.1007/s00442-002-1008-3

Cite this article as:
Pepin, S. & Körner, C. Oecologia (2002) 133: 1. doi:10.1007/s00442-002-1008-3


The long-term responses of forests to atmospheric CO2 enrichment have been difficult to determine experimentally given the large scale and complex structure of their canopy. We have developed a CO2 exposure system that uses the free-air CO2 enrichment (FACE) approach but was designed for tall canopy trees. The system consists of a CO2-release system installed within the crown of adult trees using a 45-m tower crane, a CO2 monitoring system and an automated regulation system. Pure CO2 gas is released from a network of small tubes woven into the forest canopy (web-FACE), and CO2 is emitted from small laser-punched holes. The set point CO2 concentration ([CO2]) of 500 µmol mol–1 is controlled by a pulse-width modulation routine that adjusts the rate of CO2 injection as a function of measured [CO2] in the canopy. CO2 consumption for the enrichment of 14 tall canopy trees was about 2 tons per day over the whole growing season. The seasonal daytime mean CO2 concentration was 520 µmol mol–1. One-minute averages of CO2 measurements conducted at canopy height in the center of the CO2-enriched zone were within ±20% and ±10% of the target concentration for 76% and 47% of the exposure time, respectively. Despite the size of the canopy and the windy site conditions, performance values correspond to about 75% of that reported for conventional forest FACE with the added advantage of a much simpler and less intrusive infrastructure. Stable carbon isotope signals captured by 80 Bermuda grass (Cynodon dactylon) seedlings distributed within the canopy of treated and control tree districts showed a clearly delineated area, with some nearby individuals having been exposed to a gradient of [CO2], which is seen as added value. Time-integrated values of [CO2] derived from the C isotope composition of C. dactylon leaves indicated a mean (±SD) concentration of 513±63 µmol mol–1 in the web-FACE canopy area. In view of the size of the forest and the rough natural canopy, web-FACE is a most promising avenue towards natural forest experiments, which are greatly needed.

Elevated CO2 Exposure Forest ecology Global change Stable carbon isotopes 

Copyright information

© Springer-Verlag 2002

Authors and Affiliations

  • Steeve Pepin
    • 1
  • Christian Körner
    • 1
  1. 1.Institute of BotanyUniversity of BaselBaselSwitzerland
  2. 2.Ministère des Ressources naturelles, Forêt Québec, Direction de la recherche forestière, e-mail: steeve.pepin@mrn.gouv.qc.ca, Tel.: +1-418-6437994 ext. 390, Fax: +1-418-6432165Sainte-Foy (Québec)Canada

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