Long-term impacts of land use change at Whatawhata: the story continues

Abstract

The Whatawhata Integrated Catchment Management project is New Zealand’s longest-running beforeafter-control-impact catchment farm system study. The economic and environmental impacts of land use changes have been monitored in the 260-hectare Mangaotama Block over 30 years, before and after land use changes implemented in 2001. Those changes included extensive pine plantation (140 ha), indigenous vegetation restoration (12 ha), poplar planting, livestock exclusion from streams, and shifts in livestock enterprises from breeding to finishing systems. This
paper updates earlier presentations of the impacts of these changes. Longer-term monitoring has assessed the impacts on water quality, indigenous biodiversity, and greenhouse gas (GHG) emissions. Results indicate mixed water quality outcomes. Visual clarity improved and stream temperature declined, in contrast with rising nitrate and total nitrogen concentrations, partially due to reduced stream flow. Catchment annual average sediment loads have decreased while annual average nitrate loads have increased. Biodiversity monitoring shows increased tree regeneration and forest structure improvement in fenced and planted areas. The land use changes also significantly reduced GHG emissions,
primarily through afforestation and lower livestock numbers, converting the catchment farm from a net emitter to a net sink. Soil carbon stocks overall appear to be in decline, though data are limited. These findings provide insights for hill country farmers and policy developers seeking to understand realistic time frames for meeting environmental management goals in the long-term.