Revised extent of wetlands in New Zealand

Wetlands are highly valued and significant ecosystems with a large range of services and functions. To help manage and protect them, it is important to map and monitor their spatial extent and condition. However, wetlands have not yet been comprehensively and reliably mapped at the national level, although elements for mapping national coverage exist in two of our national databases: Waters of National Importance (WONI), and the New Zealand Land Cover Database (LCDB). The extent of freshwater wetlands in WONI was derived by identifying all types of freshwater wetlands, excluding inland saline. The extent of freshwater wetlands in the LCDB was derived by identifying areas with either a wet context, herbaceous freshwater vegetation, or flax. We then combined identified freshwater wetlands from the two databases recognising the superior boundary delineation of LCDB and the superior wetland detection of WONI. The current spatial extent of freshwater wetlands in New Zealand is now calculated at 249 214 ha, or 10.08% of the historical extent, rather than the 7.4% reported by LCDB5 alone. This is at least 5954 ha less than that in 1996. The revised extent of freshwater wetlands is an improvement over either WONI or LCDB because it now includes a more comprehensive set of wetlands over 0.5 ha in area with well-defined boundaries. However, the revised extent does not include small wetlands less than 0.5 ha in area. While adding little to the total area of wetlands in New Zealand, small wetlands have significant ecological value. The National Policy Statement for Freshwater Management mandates the national mapping of the small wetlands down to 0.05 ha, but we suggest their ecological value be considered in land use change decisions only, thereby avoiding the excessive cost of mapping many millions of small wetlands.