The first CO₂ enrichment experiment with treeline trees

Does the availability of photosynthates (sugar) limit tree growth at the treeline?

An in situ test in the Swiss central Alps using "free air CO2 enrichment" (FACE) may provide an answer. If carbon limitation is a reality, CO2 enrichment should induce sustained stimulation of growth (Handa et al. 2005).

1 - The research site (top center).
1 - The research site (top center).
2 - Larix decidua
2 - Larix decidua
3 - Pinus uncinata
3 - Pinus uncinata

The research site is on Stillberg (Dischma valley, Davos) in a 30 year old treeline afforestation of the Swiss Federal Institute for Forest, Snow and Landscape Research (WSL) and its section on snow and avalanche research (SLF), 2200 m above sea level, 46° N.

Porous tubes emit pure CO2. A computer controls the concentration at c. 200 ppm above ambient (556 instead of 367 ppm at the beginning of the experiment). Strong winds from NW are screened off by a transparent wind break (Hättenschwiler et al. 2002).

4 - CO2 tanks are ...
 4
5 - ... delivered by helicopter.
 5
6 - A 3 weeks gas supply at the helicopter platform.
 6
7 - Pressure regulator, providing CO2 at 6 bar.
 7
8 - The experimental site.
 8
9 - The control and monitoring system regulates the CO2 flow.
 9
10 - Vertical CO2-release tubes are mounted on a hexagonal steel ring, surrounding a 27 year old individual of Pinus uncinata.
 10
11 - The air sample is drawn in through this funnel and pumped to the infra-red gas analyser in the control and monitoring system unit.
 11
12 - Strong winds from NW are screened off by a transparent wind break.
 12
13 - Decomposition trial: known quantities of naturally senesced leaf litter are exposed in mesh covered chambers.
 13
14 - Collection of needle litter by small "litter traps".
 14
15 - Photosynthesis measurements.
 15
Captions
  1. CO2 tanks are ...
  1. ... delivered by helicopter.
  1. A 3 weeks gas supply at the helicopter platform.
  1. Pressure regulator, providing CO2 at 6 bar.
  1. The experimental site.
  1. The control and monitoring system regulates the CO2 flow.
  1. Vertical CO2-release tubes are mounted on a hexagonal steel ring, surrounding a 27 year old individual of Pinus uncinata.
  1. The air sample is drawn in through this funnel and pumped to the infra-red gas analyser in the control and monitoring system unit.
  1. Strong winds from NW are screened off by a transparent wind break.
  1. Decomposition trial: known quantities of naturally senesced leaf litter are exposed in mesh covered chambers.
  1. Collection of needle litter by small "litter traps".
  1. Photosynthesis measurements.