To examine the impacts of carbon dioxide and climate change
on tropical savannas, an experimental facility (OZFACE)
has been established to:
- determine the impacts of elevated carbon dioxide and altered
climate on tropical savanna ecosystems and the enterprises
- quantify the potential for vegetation management practices
to offset greenhouse gas emissions;
- incorporate data into improved assessments of the impacts
of climate change to support management and policy decisions.
The study will provide a better understanding of the impact
that climate change will have on savanna ecosystems. This
will allow the industry and government to develop adaptation
strategies and policies.
At the core of the study is a Free-Air Carbon dioxide Enrichment
(FACE) experiment located in a coastal tropical savanna at
Queensland Nickel Pty Ltd's Yabulu refinery site, north-west
Trends in Climate Change
Human activities have significantly altered the atmosphere
over the last 200 years. The increase in 'greenhouse' gas
concentrations has already led to a warming of the earth (around
0.6°C since 1900) and, as greenhouse gas concentrations
are continuing to increase, the trend of warming will continue
(Houghton JT, Meira Filho LG, Callander BA, Harris N, Kattenberg
A & Maskell K (eds.) 1996 Climate Change 1995: The Science
of Climate Change, University Press, Cambridge).
Almost half of these emissions are buffered by uptake in
the oceans and assimilation into land-based ecosystems. But
the excess emissions accumulate in the atmosphere contributing
to global warming and climate change. Based on current trends,
the earth will warm by 1.4 - 5.8°C this century and there
will be substantial shifts in weather patterns.
Tropical savanna ecosystems will likely be strongly
affected by these changes. There is some understanding
of what the likely impacts will be at the scale of individual
plants (e.g., effects on plant physiology), but we don't yet
know how complex ecosystems, with their many interacting components,
will respond. There are likely to be changes in nutrient cycling,
soil carbon storage, grass production and its nutritive value
as forage, the proportion of woody vs grassy vegetation, and
These will have important implications for the pastoral industry
(the predominant user of savannas), carbon sequestration (and
potential trading of carbon credits) and other aspects of
natural resource management (e.g., management of catchments
draining into the Great Barrier Reef lagoon).
Such changes will produce both opportunities and challenges
for adapting existing land use practices to the altered environments
of the future.
The FACE Facility
To address these issues, a FACE facility was proposed and
constructed in 2001 with the aid of an Australian Research
Council grant. This system allows us to study the effects
of increased carbon dioxide on an unenclosed, intact ecosystem
with a minimum of disturbance.
FACE systems are expensive to operate (particularly in their
usage of carbon dioxide) but capture the natural complexity
of soils, vegetation, microbes, insects and carbon and nutrient
cycles that could not be replicated in glasshouse studies.
The operation of the OzFACE facility would not be possible
without the support of Queensland
Nickel Pty Ltd (QNPL), who provides the carbon dioxide
and electricity together with the infrastructure to supply
these to the site.
The OZFACE facility is operated jointly by CSIRO, Queensland
Nickel and James
Cook University with additional funding support provided
by the Australian
Greenhouse Office, the Australian
Research Council and the Tropical
Savannas Management Cooperative Research Centre. It has
generated collaboration with researchers from other institutions
(e.g., University of Melbourne, Bristol University) and is
the first of its kind in Australia, the first in any tropical
ecosystem, and the first to use an industry.
The FACE Design
The FACE system consists of six rings, each 15 m in diameter.
The vegetation enclosed by two rings is exposed to ambient
CO2 (370ppm), two rings are exposed to a CO2 level of 460
ppm and the remaining two rings are exposed to CO2 concentrations
Within these plot areas, one third of the area is left intact,
one third is clipped to simulate grazing and one third has
nutrients added to simulate higher fertility savanna locations.
Local eucalypt and acacia seedlings have been planted to study
woody-grass dynamics. This is a critical issue in savannas,
in terms of current land management practices and the impacts
of future climate. Plant and soil carbon is being measured
to examine the interaction between rising CO2 and the ability
of these systems to store carbon.
Target CO2 concentrations are achieved by controlling the
amount and location of release of CO2 from different parts
of the ring according to the direction and velocity of the
wind. Carbon dioxide usage is approximately 1.5 tonnes per
day. The experiment is planned to run a minimum of five years
- this time frame is necessary to detect changes in plant
species composition and carbon dynamics.
A range of measurements of ecosystem parameters and responses
are being made at the site. These include vegetation composition,
net primary productivity, forage quality and plant nutrient
pools, soil moisture, soil carbon and nutrients, soil microbial
activity, litter decomposition and various aspects of plant
physiology. Baseline measurements were made at the time of
the facility's construction and these have been followed up
with regular monitoring since.
One ecosystem response that has been rapid is the response
of grass production, with vegetation in the 550 ppm rings
(985 kg/ha) showing an 103% increase in above ground net primary
production relative to ambient controls (484 kg/ha) in the
first full growth season (2001/02) of the study. But this
might have been a short-term enhancement of growth and water
use efficiency in response to the initial application of the
CO2 treatments. In the past growth season (2002/03), which
was very dry, we did not observe any enhanced grass production.
An important aspect of the study will be to test for longer-term
vegetation responses to CO2 (including possible negative effects)
and to examine the interaction of elevated CO2 with natural
variation in rainfall. We predict that elevated CO2 may reduce
the effects of drought periods / rainfall variability on vegetation.
Most other ecosystem properties that are being measured would
be expected to take longer to respond. Our intention is to
continue monitoring changes over the next 3-5 years to determine
these longer-term responses.
We will use information gathered from the FACE study to predict
the likely implications of climate change for the vast tracts
of savanna across northern Australia. This will serve to inform
policy and management decisions dealing with climate change.
>> Rangelands and Savannas