Pasture to shrublands - the impact of land-use change on carbon storage
What is the problem?
The abandonment of grazed pasture and consequent invasion of native woody vegetation is taking place in many areas of marginal farmland in New Zealand. This is due to changes in land tenure, the economic climate, communal decisions, growth in carbon farming, and as a response to extensive erosion. The major species that naturally regenerate on abandoned pasture are kānuka and mānuka, and although we know a lot about the mature, older abandoned lands, there is a dearth of information on the early stages of growth of shrubs.
New Zealand’s commitment to the Kyoto Protocol requires us to report on the carbon storage of major land uses. Knowledge about changes in carbon stores can be used to reduce our carbon liability. Changes in land use, especially in areas with strong summer drought, can also affect evaporation rates and water storage.
How did we approach resolving the problem?
We measured the amount of carbon gained each year and its distribution in a well-watered pasture in North Canterbury. At the same time we directly measured the evaporation of water from the abandoned pasture. The removal of animals increased carbon by at least 10 times. However, this new carbon was very susceptible to change and fluctuated seasonally. In addition we continuously measured the environmental conditions that controlled the gain and loss of carbon, on an hourly basis, allowing us to model the effects of climate on carbon exchange.
Who has adopted our innovation?
These results are now being used by the Ministry for the Environment (MfE), and for Montreal Process reporting by the Ministry for Primary Industries (MPI), the Canterbury Regional Council (ECan) and the National Institute for Water and Atmospheric Research (NIWA).
What impact has this innovation had on adopters?
These results can now be used for carbon accounting of dryland pastures and to take into consideration changes in New Zealand land use. They can also be used to model carbon storage in the early phases of abandonment and allocation of carbon credits. These models can be employed for national-scale carbon estimates and thus effectively increase the precision of these estimates of carbon storage.
Our direct measurements of carbon gain and evaporation losses from dryland grazed pasture and abandoned fields can be used to determine the effects of changing vegetation on water use, and surface evaporation rates. These data are being used to model water use across areas that are vulnerable to drought and will allow better decisions to be made on water allocation and extraction.
This work has led to closer ties with NIWA to investigate the greenhouse gas consequences of changing from a dryland pasture to intensive dairying and has increased our understanding of the effects of land-use change on both carbon storage and water use efficiency.
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Brown M, Whitehead D, Hunt JE, Clough TJ, Arnold GC, Baisden WT, Sherlock RR 2009. Regulation of soil surface respiration in a grazed pasture in New Zealand. Agricultural and Forest Meteorology 149: 205–213.
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