Key Points

Natural ecosystems are typically complex and highly variable. Measurements at the Calperum OzFlux site are shedding light on some of that variability, with data revealing cycles ranging from daily to seasonal, and longer. Long term monitoring is also showing how different aspects of the ecosystem respond to perturbations like rainfall, drought and fire; and the lags that occur.

Once natural cycles and environmental responses are understood, it is possible to better identify long term trends through the ‘noise’ of variability.

Some key insights from the Calperum OzFlux site follow.

Atmospheric CO2 concentrations are fluctuating, but trending up.

  • Atmospheric CO2 concentrations are continuing to hit new highs as monitoring continues.

Rainfall is the key driver of the mallee ecosystem at Calperum.

  • Soil respiration (producing CO2) is higher after rainfall.
  • Net Ecosystem Productivity (NEP) lags behind water availability. NEP (the difference between the amount of carbon fixed by plants and that lost through ecosystem respiration) declines in response to dry periods and rises, accumulating carbon, in response to wetter conditions.

Rainfall is often less than evapotranspiration.

  • Stores of soil-water buffer vegetation in times in dry spells.
  • Soil-water recharge to the regional groundwater is very low.

Periodic fires reset ecosystem functions and, along with rainfall, regulate long term productivity and carbon sequestration.

  • Annual carbon accumulation rates vary between years, with ranges from -1 to +2 t C/ha/yr.
  • Bushfires at Calperum may occur around once per 20 – 30 years, and take standing (above ground) biomass from 10 t/ha to 7 t/ha.
  • Assuming that Dry Matter is 50% Carbon, long term carbon sequestration rates (accounting for fires) are around 0.3 t C/ha/yr.

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