Wetland or Pasture - An expert's guide to identification and delineation of wetlands in New Zealand
Identification and delineation of wetlands in New Zealand is a rapidly changing field. New regional and national policies are coming into effect to protect remaining areas of wetland, and sometimes what looks like pasture turns out to be a wetland.
Wetlands are defined in the Resource Management Act (RMA) as permanently or intermittently wet areas, shallow water and land water margins that support a natural ecosystem of plants and animals that are adapted to wet conditions.
The proposed Natural Resources Plan for Greater Wellington (pNRP; July 2019 decision version) excludes damp gully heads, wetted pasture, and pasture with patches of rushes. But it does not give specific guidance on how to distinguish these from wetlands.
The definition of natural wetlands in the pNRP also states that, because of the rarity of wetlands in the Wellington Region, all natural wetlands will meet the definition of significant natural wetland1; which triggers a number of objectives and rules in the pNRP to protect wetlands.
The National Policy of Statement for freshwater management (NPS FM) came into effect on 3 September 2020 and sets out guidance as to what constitutes a wetland and on how a wetland should be identified and delineated3. Wetlands should be assessed on their current plant diversity (regardless of whether indigenous or exotic species) and the proportion of the area that is dominated by plants that prefer wet soils/conditions. Plant species are ranked on how much they like wet feet from must live in water (obligative) to can’t stand wet feet (upland). If more than 50% of the vegetation cover consists of species that love or tolerate wet soils then the area is considered to be a wetland.
If the vegetation comprises a relatively even mix of upland and wetland species, then soil types and hydrology should also be taken in to account to determine if an area is wetland. A key point to note is that a wetland need not be dominated by indigenous species, or by species that are considered to be wetland obligates (those species with a less than 1% chance of found growing in a dry area).
The NPS FM definition of natural wetland excludes areas of improved pasture that are dominated by exotic pasture species and subject to temporary rain-derived water pooling. But it does not give further specific guidance on how to determine this.
A workshop was held by the Ministry for the Environment on 24 February 2021 to clarify some of the issues around the identification of wetlands. The draft Guidance on Wetland Definitions (MfE 2021) clarifies that wetlands unintentionally induced through man-made activities, and wetlands in a degraded condition, are also included as ‘natural inland wetlands’ and there is no minimum size. Geothermal areas, and wetlands in the coastal marine area are excluded. Guidance is provided on temporary rain-derived water pooling, and work is underway on a method to assess the dominance of exotic pasture species.
Greater Wellington Regional Council (2020) has proposed a pragmatic approach to reduce confusion about what constitutes pasture with rushes (pNRP) or improved pasture (NPS FM). This is to assess whether a putative wetland area is dominated by plants that were established and maintained for livestock production. An area of pasture should have a minimum of 50% cover of pasture species.
Pasture species are those that are included in recent publications from the New Zealand Grassland Association as pasture or forage species. This does not include some species that were used as pasture species historically such as creeping bent (Agrostis stolonifera).
Creeping bent is considered to be a Facultative Wetland species (FACW; estimated probability 67–99% occurrence in wetlands) and is known to persist in wet ground, and to occur in areas of wetland that were never farmed. So, although an area may look like a pasture (e.g. lots of creeping bent) the species composition may indicate that it is wetland.
While this approach provides more guidance about what is wetland and what might be wet pasture, it often needs fieldwork to determine if an area is dominated by wetland or pasture species.
Contact Astrid for assistance with the mapping and assessment of areas of potential wetland or expert advice on the implications of the recently released draft guidance (MfE 2021).