Improving the economic and environmental performance of a New Zealand hill country farm catchment: 4. Greenhouse gas and carbon stock implications of land management change

ABSTRACT

An integrated catchment management project was established at the Whatawhata Research Centre in the late 1990s to study the implications of land use and management change for a typical New Zealand hill country pastoral farm system. The main changes implemented on the 296 ha Mangaotama block in 2001–2002 included production forest plantation (147 ha), indigenous riparian planting (8 ha); intensification of livestock enterprises and spaced-tree planting. The purpose of this study was to estimate the greenhouse gas (GHG) balance for the catchment farm, incorporating recent measurement and modelling over a 100-year period (excl. soil carbon). The changes reduced the GHG intensity of the livestock enterprises from 25 to 15 kg CO₂-e kg⁻¹ product and turned the system from a net emission source (c. 1 kt CO₂-e y⁻¹) into a long-term net sink (−353 kt CO₂-e y⁻¹). This was mainly due to planting of Pinus radiata with high carbon assimilation rates, compared to the smaller areas and slower assimilation rates of indigenous trees (currently 5–17 t CO₂-e ha⁻¹y⁻¹). Based on 100-year mean tree carbon stocks, it was estimated that the area of pine forestry required to achieve net zero emissions would be in the order of 36% of the catchment farm.

KEYWORDS:

• Carbon (C)
• simulation model
• pasture
• forestry
• Whatawhata

Acknowledgements

The catchment project was a large multi-year, multi-agency project and the participants are acknowledged in Dodd et al. (2008a, 2008b, 2008c). The Whatawhata farm is now owned by Tainui Group Holdings and we thank them and the farm manager Shane Hill for ongoing access to the site. We thank Liz Curry and her team (Tonkin + Taylor consultants) for field data collection in the indigenous forest remnants. This study was funded by a subcontract from NIWA as part of the Strategic Science Investment Fund (SSIF) resourced ‘Long-term Stream Response to Sustainable Land Management’ Project. The constructive suggestions of the journal reviewers are acknowledged.

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

This work was supported by National Institute of Water and Atmospheric Research.