Study Site

The TasFACE experiment is located within the Australian Federal Department of Defence Pontville Small Arms Range Complex (PSARC) at Pontville, SE Tasmania at 42° 42’ S 147° 16’ E (see map). The site is approximately 30 km north of Hobart and is located on a basalt plain at an altitude of 40 m a.s.l. Soil at the site is black basaltic clay and is best classified as a black vertosol. Climate is Mediterranean with a mean annual temperature of 11.6°C and mean annual rainfall of 560 mm, although the site has experienced severe drought since the experiment commenced. The site has a mean windspeed of 2.7 m s -1 at 2 m above ground height.

The TasFACE experiment is established in a flat, reasonably uniform area of lowland Themeda-Austrodanthonia grassland (see photo of grassland). The entire study site is 30 ´ 30 m and contains approximately 60 species, but the grasses Themeda triandra, Austrodanthonia setaceae and Austrodanthonia caespitosa dominate.

Design of the experiment

TasFACE commenced operation in February 2002. The current round of funding covers the period until December 2006.

The TasFACE experiment is a two factor experiment in which vegetation within 1.5 m rings is exposed to either elevated or ambient [CO2] and either ambient temperature or +2 ° C warming. Experimental treatments are replicated three times. There are six ambient and six FACE treated rings, half of which are treated with IR lamps. Thus, there are three rings designated controls and three each of FACE alone, IR alone and FACE+IR in combination (see photo of rings and lamps). [CO2] within the FACE treatment rings is set to 550 µmol mol -1.

The design and control of the FACE treatment are a modification of the POPFACE pure-CO2 injection design. The 1.5 m diameter rings are made of 4.5 m long 20 mm internal diameter PVC pipes with 0.3 mm laser-drilled holes every 50 mm along the outside edge (see photo of a ring).

[CO2] is controlled using a dedicated programmable microprocessor-based control system. Gas is sampled from the centre of each FACE ring using a high velocity air pump and monitored by one of two infrared gas analysers (IRGAs). Pure CO2 is supplied from a 6 t bulk store and CO2 release in each ring is controlled by electropneumatic flow-control valves, dependent upon [CO2] as measured by the IRGA and wind velocity as estimated by a cup anemometer. Fumigation commences at sunrise and ceases at sunset each day. Valves are not closed at high wind velocities, as occurs in some other FACE experiments (see photo of control system)

Warming is provided by a single 240 V 250 W Solid Ceramic Infrared Emitter suspended 1.2 m above the soil surface above the centre of each ring. The IR emitters operate continuously.

System Performance

Climate change experiments are classified as having good control if the [CO2] is within 20% of the set-point for 80% of the time. The temporal [CO2] control of the TasFACE experiment far exceeds this criterion since the central [CO2] is within 20% of the set-point for 97% of the time. Indeed, all FACE rings are within 10% of the set-point more than 85% of the time.

The infrared heaters produce an average elevation in abaxial leaf temperature of 1.98°C, in adaxial leaf temperature of 2.20°C and of shielded air temperature at canopy level of 2.16°C during the growing season. Soil temperature at 1 cm depth is elevated by an average of 0.82°C. Warming varies over the day and is greater during the night. The elevation of air temperature is accompanied by an average decline in relative humidity of 5.1%, which is most pronounced during the night.