The Land Cover Database should not be used on its own to identify wetlands in the Wellington region, whether it is for resource management, ecological or significance assessment purposes.
Abstract: Wetlands are nationally rare in New Zealand as a result of their on-going loss through land development. The Department of Conservation’s natural heritage responsibilities call for the development of a national database for wetlands. A number of regional wetland databases already exist, but the Land Cover Database (LCDB) is considered to have applicability at a national level and has previously been used by several projects to map the extent of wetlands in New Zealand. However, LCDB is based on remote sensing and can produce variable results depending on factors such as scale, image quality, image interpretation and field verification. In this study, we assessed the ability of LCDB (LCDB2) to map wetlands in the Wellington region, by comparing areas identified as ‘wetlands’ with those identified using other information sources. Over 3700 ha of wetlands were assessed, including parts of Lake Wairarapa. We found that LCDB2 underestimated the area of wetlands in the region, with many wetlands not being identified or their boundaries often being inaccurate. LCDB2 is generally more effective at identifying larger wetlands, especially if they include open water, but is less useful for identifying smaller wetlands, particularly in areas dominated by grassland or pasture. This study of the Wellington region indicates that LCDB2 should not be used on its own to identify wetlands, whether it is for resource management, ecological or significance assessment purposes. It is recommended that this analysis is repeated for other regions where good quality wetland databases exist, to ensure that the findings are applicable nationally Updated versions of LCDB are likely to retain similar errors until wetland mapping issues are resolved.
Authored by M. Davis, D. Brown, H. Robertson and L. Chadderton.