Erosion susceptibility classification and analysis of erosion risks for plantation forestry – response to Marden et al.

Abstract

In a recent paper in this Journal, 'Should detailed terrain stability or erosion susceptibility mapping be mandatory in erodible steep lands?' (Marden et al., 2015), Mike Marden and colleagues call for 'improved quantitative erosion and hazard identification and risk management methods that can be widely applied across New Zealand.' They note that improvements are 'required at both a "reconnaissance" scale (e.g. 1:50,000 or greater) for use at a national level to underpin for example further development of the NES for plantation forestry... to more detailed mapping for use at an operational scale (e.g. 1:5,000 to 1:10,000) as a prerequisite for roading, harvesting and replanting operations.' They also note that an Erosion Susceptibility Classification (ESC) developed for the National Environmental Standard (NES) for plantation forestry (Bloomberg et al., 2011) 'is a start, but it has a number of limitations including': • 'The poor definition of potential erosion used as the metric for defining erosion susceptibility • Misclassification of the potential erosion severity of some Land Use Capability Units • A scale (1:50,000) unsuited for operational use and ESC errors that result from the scale limitations.' I agree with most of what they say, but in my opinion they did not provide enough explanation of why the ESC developed by Bloomberg et al. (2011) has limitations. They also devote most of their paper to an explanation and justification of detailed erosion susceptibility mapping, and do not adequately place this in the context of erosion risk management, whether for plantation forestry or rural land use generally. Without this risk management context, the rationale for improvements to erosion susceptibility mapping is not clear.