The effect of an integrated catchment management plan on the greenhouse gas balance of the Mangaotama catchment of the Whatawhata Hill Country Research Station : a thesis presented in partial fulfillment of the requirements for the degree of Master of Science in Ecology at Massey University, Manawatu, New Zealand

Abstract

An integrated catchment management plan implemented in the Mangaotama catchment of the Whatawhata Research Station in 2001 demonstrated that Pinus radiata forestry on marginal land, along with conservation measures and intensification could produce a win-win outcome for economic output and the environment. However, greenhouse gas mitigation was never fully considered. This research investigated the effect of the plan on the land’s greenhouse gas balance and carbon stocks between 2000 and 2011. Historical records, modelling with OVERSEER and CenW, literature values and field measurements were used to account for CO2, CH4, and N2O from the four main land-use types: pasture, native forest, pine, and native plantings. The original land-use would have emitted a net 10.99 Gg CO2e over 10yrs, whereas the new land-use sequestered a net 47.26 Gg CO2e in its first 10yrs. The total carbon stocks rose by 15.9 Gg C. Forestry conversion of almost half the area explained most of this effect. Agricultural intensification increased per hectare emissions from pasture, but overall pasture emissions were lowered by over half due to the reduction in livestock numbers. The native plantings had a small impact due to the small area planted and their slower growth compared with pines. Soil carbon was lost under all land-uses, except possibly in grazed native forests, but these conclusions were hampered by a scarcity of samples. Uncertainty also surrounded the modelling of the pine forest in complex terrain, which is not yet adequately captured in CenW. A preliminary look at carbon trading suggested that it could strongly undermine the viability of the original farm system, but it could also help to fund the expensive transition to the new land-use. Overall, it was found that in addition to the benefits already shown by the integrated catchment management plan, it was also an effective way of mitigating climate change.