Examining the effect on sediment loss by differential pricing in the ETS to encourage land use change on highly erodible land

We defined three land use change scenarios on highly erodible land to examine the effect on sediment loss by differential pricing in the New Zealand Emissions Trading Scheme (NZ ETS) to encourage land use change on highly erodible land (HEL).

There are >1 million hectares (ha) on HEL under pasture, with the highest amount of land in Manawatū–Whanganui, Canterbury, Hawke’s Bay, and Gisborne. There are c. 0.5 million ha on HEL under pines, mostly in Northland and Gisborne. There are c. 0.03 million ha on HEL under PCEF. There are c. 2.2 million ha on HEL under native forest.

Results include:

• Converting pasture to native forest would decrease average annual sediment loads delivered to the stream network by 50 Mt/yr at the national scale; Gisborne and Northland would show the biggest regional decreases.
• Converting pine to native forest would decrease average annual sediment loads delivered to the stream network by 6.1 Mt/yr, mostly in Gisborne.
• Converting pines to permanent exotic carbon forest (PECF) will have minor improvements on erosion rates under current modelling assumptions.
• Look-up tables from the Ministry of Primary Industries (MPI) overestimate pine carbon sequestration and underestimate native carbon sequestration when trees are 30 years old.
• If the NZ ETS price was the same for pine and native trees, the conversion of HEL to natives would greatly increase in many regions.

Recomendations:

• Converting HEL pasture to native forests should be prioritised to reduce erosion across New Zealand, and Gisborne and Northland have the highest priority to have the greatest impact.
• Converting pines to native forests will have a greater impact in Gisborne than other regions.
• MPI look-up tables should be updated to better represent carbon sequestration in pines and native trees; these land covers may also require the same NZ ETS price to be applied to facilitate land resilience.
• Within the NZ ETS there would need to be a mechanism to apply a higher price for natives than pines to HEL land only. This will involve a step that identifies erosion-prone land suitable for planting native trees and incentivises the planting of this land with a higher NZ ETS price for carbon sequestrated by native trees. This could be viewed as an ‘erosion credit’ and may need to be facilitated in a framework outside of the NZ ETS to ensure that on-the-ground impact is made on erosion-prone land.