Methods for ascertaining shallow landslide susceptibility in the harvest planning process

Authors: S Smith, R Visser, M Bloomberg, D Palmer
Publication: New Zealand Journal of Forestry, Volume N.Z.J.For. 2024, Issue N.Z.J.For. 68(4) 2024, pp Pages 38 - 45, Feb 2024
Publisher: New Zealand Institute of Forestry

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Abstract: High-intensity, localised rainfall events present a serious challenge for forest management in New Zealand. These have the potential to trigger shallow landslides and mobilise slash and debris, resulting in discharges onto land and waterways. Regions prone to erosion-triggering weather events, particularly those with steep topography and weak sedimentary rocks, have the greatest vulnerability. However, there is little guidance for New Zealand forest managers about assessing shallow landslide susceptibility at an operational scale. This paper describes a range of methods to assess shallow landslide susceptibility. In New Zealand, the Erosion Susceptibility Classification (ESC) is readily available and identifies at-risk areas but is mapped at a scale too coarse to be useful for operational planning. We review methods that might be more appropriate, including heuristic (expert assessment) and quantitative approaches that have been developed in New Zealand. We also present decision support systems used to define landslide-susceptible areas in the Pacific Northwest (PNW) region of North America for comparison. These employ a combination of heuristic and quantitative approaches. This review does not attempt a critical comparison of these different approaches. It recognises that currently a combination of approaches to assessing shallow landslide susceptibility may provide the most robust information appropriate to New Zealand plantation forestry conditions. However, the opportunity exists for establishing a standardised approach to support harvest planning.

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