Cost benefit analysis of riparian planting options for freshwater coastal streams in Horowhenua : ngā utu kia piki te Mauri o ngā wai a Parawhenuamea : a thesis presented in partial fulfilment of the requirements for the degree of Master of Environmental Management, Massey University, Manawatū, New Zealand
Freshwater ecosystem health is an important policy priority in New Zealand, recently highlighted by the government’s launch of the ‘Freshwater Reform 2013’. One practical way of improving freshwater ecosystem health is riparian planting. In this context, the aim was to develop and apply a cost benefit analysis (CBA) methodology to evaluate riparian planting options for restoring five freshwater coastal streams of importance to iwi/hapu in the Horowhenua, drawing on two distinct disciplines – freshwater ecology and economics.
Essential to this CBA methodology was an explicit evaluation of a desired policy outcome. Accordingly, attention was given to assessing what constitutes the desired policy outcome that is ‘freshwater ecosystem health of coastal streams’. This assessment was based on developing a detailed understanding of the attributes that must managed to achieve ‘freshwater ecosystem health’ including: in-stream temperature, periphyton, sediment, water flows, ecological connectivity, nitrate and ammonia, key fish species and stream invertebrates. The CBA methodology then focused on developing a new systems framework (interrelated ecosystem ‘biophysical structures’, ‘processes’ and ‘functions’) for assessing the ecological role of riparian vegetation in improving freshwater ecosystem health.
Non-market economic values required for CBA calculations were then derived using a benefit transfer method. Data from three study sites (Karapiro South Waikato, Hurunui Canterbury, and Canterbury) based on ‘choice experiment’ values were evaluated for their suitability for use in the policy site (Horowhenua). The suitability of data from study sites for use in the policy site applied the Welch T test and Wilcoxon rank sum, using ‘personal income’ as the assessment criterion. Over 100 hundred planting scenarios were then tested by CBA, with almost all having positive net present values for both 5m and 10m width planting options.
The study concludes with a discussion of the practical and policy implications of these findings, and highlights the limitations of this study and how these can be overcome in future research.
Keywords: Indigenous, ecosystem health, freshwater coastal streams, riparian, environmental cost benefit analysis, benefit transfer.