Climatology - Research - GES
Sustainable futures of Australian temperate forests
An investigation of coupled carbon, water and energy exchanges from hourly to centennial time scales.
- Project Overview
- Location and Sites
- News and Media
- Useful Links
Australia's forests are a critical natural resource that must be sustainably managed. We will determine the uptake/release of carbon from old growth and regrowth forests and assess the water budgets of the Melbourne water catchment at Wallaby Creek, Victoria, Australia. We aim to understand the current cycles of carbon, water and energy and how these may change over time (hours to centuries). We will integrate our observations with state-of-the-art models to improve our predictions of how forests will respond to change. This will aid our management of forests and forested catchments to ensure sustainable and viable water resources and optimise carbon sequestration. The project is funded from 2004 to 2006.
The full project proposal can be found here (PDF).
The Location and Sites
The site is located at in the Mountain Ash forests (Eucalyptus regnans) of the Wallaby Creek Catchment near Kinglake in Melbourne, Australia.
There are three sites within the Wallaby Creek catchment representing various times since fire.
|300 year old||80 year old||20 year old|
Mountain Ash Forests (Eucalyptus regnans)
| || |
native forests are an important component of the Australian landscape,
comprising 164 million ha or around 21 per cent of the continent
landmass. Temperate open forests cover an area of ~ 5.5 million ha,
which is five times greater than the area of plantation forests and
therefore represent a potentially important carbon sink [RAC, 1992].
Temperate open forests are also economically important for the forestry
industry and are significant in providing areas for recreation and
maintaining the health/biodiversity of the crucial in sustaining
the amount and quality of drinking water (e.g. Maroondah catchment,
Melbourne). For these reasons it important to understand how our
forest assets may develop into the future. This important ecosystem
is biocomplex and has physical, biological and chemical (biogeochemical)
cycles that are coupled across different time scales. Cycles of energy
are essential in driving photosynthesis and determining climate and
water use. Biogeochemical cycles of carbon, water and nitrogen are
important for provision of freshwater, carbon sequestration and forest
production. In order to understand how Australian forests will develop
in the future we must know how these cycles and the forest as whole
will respond to changes in climate, extreme climate events, ecological
succession and human disturbance which all occur on different time
scales. Unfortunately we have limited understanding of these complex
systems at differing spatial and temporal scales [Nikolov &
The fundamentals of the carbon cycle
within forests are relatively well understood. Previous inventory
based estimates have shown the net uptake of carbon of the ecosystem
as a whole (Net Ecosystem Exchange or NEE - the net carbon gained
by the ecosystem through photosynthetic production minus respiration
from plants and soil) decreases with stand age and in old growth
forests, carbon cycling is often assumed to be in equilibrium [Carey
et al., 2001; Hollinger et al., 1994]. However, young trees are believed
to be a net carbon sink because they rapidly sequester carbon as
they grow [Kaiser, 2000; RAC, 1992]. Inverse modelling of carbon
fluxes shows that Northern Hemisphere old growth forests are a stronger
sink of CO2 than calculated from previous inventory studies [Martin
et al., 2001] (In Australia we currently do not have a network that
allows us to resolve these fluxes using this method). The reasons
for high carbon uptake by old growth forests is uncertain, but it
has been suggested that high rates of leaf and root turnover contribute
to permanent soil carbon pools [Dixon et al., 1994; Schulze et al.,
2000]. Therefore old growth forests, in addition to the important
role in biodiversity conservation, provide a large carbon store and
may act as a carbon sink, keeping carbon dioxide out of the atmosphere
[Carey et al., 2001]. Australia's current carbon inventory shows
that growth, harvesting and regrowth in managed native forests and
plantations has been a net carbon sink for greenhouse gases of 75.8
Mt in 1999 [AGO, 2001]. The role of native open forests in the carbon
inventory is uncertain, although they have the potential to contribute
a significant carbon sink given their large areal coverage. To reduce
this uncertainty, investigations of the carbon cycle in native forests
and how it may change with stand age and differing management are
The cycle of water within a forest is
important and is determined by tree water use, evaporation and runoff.
Understanding the ecohydrology of catchments such as the Maroondah
catchment is critical given their role in the provision of potable
water to large urban populations. Basic hydrological processes for
these forests are well understood from comprehensive observations
and modelling work (e.g. [Vertessy et al., 1995] which has included
research on the effect of stand age on water yields [Cornish and
Vertessy, 2001]). However, we do not currently have a good understanding
of how the water cycle is coupled with cycles of carbon and energy
and how these cycles interact over annual to centennial time scales.
Such knowledge is important for the future management of these forests
and catchments given anticipated environmental change.
The energy cycle within the forest is critical in driving photosynthesis,
evaporation, transpiration, heating of the atmosphere and soil. There
is strong coupling between the energy, carbon and water cycles. The
amount of energy that is used in evapotranspiration, heating and
canopy energy storage, as well as the way in which this energy is
partitioned between these fluxes is influenced by the biological
(stand age and species composition) and physical characteristics
(height, canopy structure) of the forest. For extensive forest ecosystems,
this energy flow in turn feeds back to influence climate.
Although several of the individual processes within carbon,
water and energy cycles (photosynthesis, respiration, leaf energy
balance and turbulent exchange within plant canopies) are well characterised
at the leaf level, the complex nature of the coupling between processes
has not been examined extensively [Kull, 2002]. A greater understanding
of microenvironmental forest processes are needed to be able to scale
up from the leaf level to the plant canopy. This is vital if we are
to be able to predict the response of whole forests to environmental
change. It may be best achieved using integrated observations and
ecosystem modelling of the carbon, water and energy balance of forests
at a canopy scale. There have been few measurements of the carbon,
water and energy processes in Australian forests, making it difficult
to both quantify and predict changes with time. Some inventory-style
carbon balance estimates have been made in temperate eucalypt forests
[Keith et al., 1997], but these do not capture the important ecosystem
dynamics and variability.
Recent advances in micrometeorological techniques (namely Eddy Covariance - EC) now allow hourly measurements
of carbon, water and energy fluxes from ecosystems. This technique
is considered the most robust and accurate for measuring fluxes compared
to inventory and inverse modelling approaches [Moncrieff et al.,
1997]. To date, there have been few EC studies of native vegetation.
Hutley et al.  used EC to quantify water and energy balances
of tropical savanna vegetation and Eamus et al.  estimated
the carbon sink strength of tropical savanna derived from short periods
of measurement. Only one study of southern temperate open eucalypt
forests has been conducted, in West Australian Jarrah [Silberstein
et al., 2001], however, carbon exchanges were not measured during
their study, and measurements were short-term only. As a result of
the lack of long-term integrative studies, there is a large uncertainty
regarding the carbon, water and energy cycles of temperate (or any)
Australian forests, particularly in relation to how they may change
with time. Clearly, more rigorous long-term estimates of carbon,
water and energy cycles in temperate open forests across various
time scales are needed. Such studies are of considerable value in
helping to determine the response of forests to environmental change
and quantifying Australia's carbon and water balances.
Many of the processes driving water and carbon fluxes at ecosystem level are strongly dependent on seasonal changes and extremes in climate [Grelle et al., 1999]. Seasonal changes of phenology and biomass production significantly affect rates of water and carbon exchanges. Furthermore, extreme events (extreme temperatures, high wind velocity, drought conditions) are not often captured during short-term field measurements yet these non-average conditions have a strong impact on the hydrological and carbon cycles of terrestrial ecosystems [Baldocchi et al., 1997]. It is therefore critical to examine the response of Australian forests over time scales long enough to be relevant to climatic processes issues (seasonal to interannual to decadal). An improved knowledge of the complex land-atmosphere exchanges of carbon, water and energy is vital at time scales encompassing days, seasons, years, and even decades, as well as over spatial scales from a few kilometres to landscapes and will be a major outcome of this proposal. Such knowledge will provide improved parameterisations for predictive ecosystem models and ultimately aid the sustainable management of carbon and water resources within Australian forests.
The overall objectives of this study
are to understand the complex coupling of carbon, water and energy
cycles within Australia's temperate forests over various temporal
scales in order to assess the impact of future environmental change.
We will measure hourly fluxes of carbon, water and energy above the
forest using the EC technique on a tall tower over a period of more
than 3 years. Concurrent measurements of meteorological variables
and component processes will be made. Our approach is to combine
continuous flux measurements of these cycles on a multi-year time
basis with ecological process interpretation and modelling. This
will allow us to understand the complexity of these systems and incorporate
this into our models to improve future simulations.
The site will be located within the Maroondah Water catchment that supplies Melbourne's drinking water. The catchment is an excellent example of temperate eucalypt forest and is unique because it has intact old growth stands with individual trees as old as 300 years. The forest is primarily Mountain Ash (Eucalyptus regnans) and has been the site of intensive hydrological research. Our proposed research will provide ongoing information on canopy scale water budgets that will be used by the CRC for Catchment Hydrology. In addition, areas of the surrounding catchment are host to commercial clear felling practices. Operations over the past century have subsequently allowed forests to regrow and there are many areas of homogeneous forest of varying age. We will investigate these sites to examine decadal to centennial changes to carbon, water and energy cycles. There are two major project objectives:
Objective 1: To quantify the carbon, water and energy exchanges in a temperate forest and the factors regulating them over hourly to inter-annual time scales.
Objective 2: Establish the carbon, water and energy cycles of different aged forest stands and investigate how they change over successional time scales (decadal to centennial).
Real time data can be found here. For longer time series and quality controlled data please contact the authors.
News and Media
|Video of news report from Channel Ten Melbourne (Monday 12th April 2005)|
|Jason climbing 110m tower on first ascent||Jason (left) and Lindsay (right) on tower|
|Kenichi (left) and Ian McHugh (right) sampling root biomass||Lindsay (left) and Danni Martin (right) taking soil CO2 flux measurements|
|Jason climbing 110m tower on first ascent|
Wood, Stephen (2005) Change in Leaf Area Index (LAI) and Tree Characteristics of Different Age Mountain Ash Stands to Determine Effects on Water Yield . Third year project. PDF 478K.
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Baldocchi, D., E. Falge, L.H. Gu, et al., FLUXNET: A new tool to study the temporal and spatial variability of ecosystem-scale carbon dioxide, water vapor, and energy flux densities, Bul.Am. Met. Soc., 82 (11), 2415-2434, 2001.
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Kaminski, T. and M. Heimann. Inverse modeling of atmospheric carbon dioxide fluxes, Science ,294 (5541), 259a, 2001.
Keith H., R.J. Raison, K.L. Jacobsen. Allocation of carbon in a mature eucalypt forest and some effects of soil phosphorus availability. Plant Soil 196: 81-99, 1997.
Kull, O. Acclimation of photosynthesis in canopies: models and limitations. Oecol 133: 267-279, 2002.
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NLWRA, National Land and Water Resources Audit: Annual report 1999-2000, pp. 34 pp, Canberra, Australia, 2000.
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Peel, M.C., Vertessy, R.A., & Watson, F.G.R. (2002) Generating water yield curves for forest stands in the Thomson catchment for inclusion in the Integrated Forest Planning System. Final report to Natural Resources & Environment, Victoria, 33 pp.
Peel, M.C., Watson, F.G.R., Vertessy, R.A., Lau, J.A., Watson, I.S., Sutton, M.W., & Rhodes, B.G. (2000) Predicting the water yield impacts of forest disturbance in the Maroondah and Thomson catchments using the Macaque model, Cooperative research Centre for Catchment Hydrology, Rep. No. 2000-00/14. Melbourne. 71 pp.
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This project was funded from 2004 to 2006 from the Australian Research Council under project number DP0451247.