Opportunities to manage sediment from forestry more effectively in the Marlborough Sounds and contributing catchments

Authors: Stephen C. Urlich
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2020, Issue N.Z.J.For. 65(2) 2020, pp 28-35, Aug 2020
Publisher: New Zealand Institute of Forestry

Abstract: Soil disturbance associated with earthworks and harvesting of radiata pine (Pinus radiata) has caused erosion and run-off into the coastal waters of the Marlborough Sounds (the Sounds) and resulted in excessive deposition of fine sediment onto estuarine and subtidal benthic habitats. Ecological consequences have included habitat damage and species loss, alteration of ecological interaction networks and associated biogeochemical processes, and loss of resilience from ongoing disturbance. The causes and consequences of forestry’s contribution to excessive sedimentation in the Sounds’ coastal ecosystems are reviewed in this paper. Despite awareness of these issues, the regulatory response over the last 45 years has been largely ineffectual. This now includes the Proposed Marlborough Environment Plan 2020 (PMEP, 2020) where greater stringency available under the National Environmental Standards for Plantation Forestry (NESPF) has been exercised. However, this focused on the management of diffuse sources from surface processes through the provision of coastal setback controls of greater distance than required by the NES-PF. Greater stringency has not been applied to the major sources of sediment delivery, which are mass failures generated by erosion-prone gullies, gully-heads and steep side-slopes. Stricter harvesting controls and the requirement for replanting management plans that retire these source areas would significantly reduce sediment production and promote sediment retention. An update of the NZ Land Resources Inventory is also needed to improve the NES-PF Erosion Susceptibility Classification (ESC), as the predominant High ESC designation in the Sounds does not reflect the likely widespread occurrence of Very High ESC landforms.