Soil erosion is a natural process that has been accelerated in New Zealand by deforestation and unwise land use practices (for example, overgrazing). Accelerated erosion is the most serious and the least reversible of soil degradation problems.
The main forms of erosion in New Zealand are:
Hill country is defined as all Class V, VI, VII and VIII land from the NZ Land Resource Inventory (NZLRI) with D slopes and above (more than 16 degrees), below an altitude of around 1000 metres above sea level.
Hill country erosion decreases the productivity of farms. Although vegetation returns within a few years on an eroded site, growth is generally less productive than before because the underlying soil is thinner and holds fewer nutrients.
After hill country slip erosion, pasture production takes around 20 years to recover to within 70-80% of its pre-erosion levels. In severely eroded areas only a few stress tolerant weeds may survive. After repeated erosion, sites may become barren.
In promoting the concept of land use to land capability in the hill country, Government’s policies focus on areas that are at risk of mass movement and fluvial erosion.
Streambank erosion, also a significant form of erosion in the hill country, is being addressed through the riparian management work being undertaken by the Ministry.
Surface erosion, while a significant problem in some regions, occurs largely outside the hill country.
Downstream, debris causes rivers to aggrade, increasing flood risk. Erosion can also contribute to many water quality problems such as loss of aquatic habitat and increased sediment loads.
Regions with hill country land prone to erosion include: Waikato, Bay of Plenty, Gisborne, Hawkes Bay, Taranaki, Manawatu-Wanganui, Wellington, Tasman and Marlborough. Together they have approximately 7,075,000 hectares at risk of erosion (1993). 48% of that risk area is being farmed (State of the Environment Report 8:53)
Decades of research and experience have provided us with techniques to reduce the impacts of erosion on pastoral land. These include:
The short-term costs of soil conservation to farmers include soil conservation work and possible loss of production when stock is excluded from newly established plantings. The major benefits include:
The Ministry for the Environment and the Ministry for Agriculture and Forestry have jointly funded the Soil Conservation Technical Handbook published by the New Zealand Association of Resource Management. This handbook is a valuable resource for anyone dealing with soil erosion or landslips.
Last updated: 17 September 2007