The area and percent of forest designated or managed primarily for the protection and regulation of soil and water reflects the importance of these resources to society, including the trade-offs made between other uses.
New Zealand has significant areas of natural and accelerated soil erosion, but the designation of protection forest land is no longer applied in most management planning. Although forest land is still managed with conservation of soil and water resources as implied objectives, and sometimes as specific objectives, national data on the extent of such management are derived estimates only.
The New Zealand Country Report for the Food and Agriculture Organization’s Global Forest Resource Assessment indicates 6.742 million hectares of indigenous and planted forest have soil and water protection functions. This assumes that nearly all indigenous forests fulfil these roles, although little if any is specifically designated for this purpose.
The annual cost of hill country soil erosion (mainly in pastoral use) is reported to be $100 million to $150 million. These national estimates of the cost of soil erosion and sedimentation in New Zealand are estimated as an order-of-magnitude average annual cost to be $127 million.
Studies of the total economic value of New Zealand’s forest ecosystems and the services they provide have valued erosion control at $2092 million, second only to the production of raw materials. In particular, indigenous forests play a critical role in maintaining soils and preventing sediment loss on land that is often steep and unstable.
Planted forests have also been established for soil and water conservation purposes, although most of the land involved is not formally designated as such. This includes the planting of Aupouri, Woodhill, Santoft and Bottle Lake forests to stabilise sand dunes. The total area of coastal sand dune planting is estimated to be 67 000 hectares, nearly all of which occurred prior to 1990.
More recently, 42 000 hectares of forests have been established through planting or reversion under the government’s Erosion Control Funding Programme (East Coast) (ECFP, formerly the East Coast Forestry Project) for the primary purpose of soil conservation. Some 26 percent of the land on the East Coast is susceptible to severe soil erosion.
The ECFP was established in 1992 to control erosion on the worst eroding or erosion-prone land in this district, and is administered under the Forestry (East Coast) Grants Regulations 1992. It targets 60 000 hectares of the lands at greatest risk, plus immediate surrounding areas. The government provides financial grants for establishing effective tree cover through planting, or encourages natural reversion to indigenous forest.
The Sustainable Land Management (Hill Country) Erosion Programme was established by the government in 2007. It supports projects helping hill country farmers treat erosion-prone land and implement sustainable management practices. The total hill country land area at risk of erosion is about 1.14 million hectares, with 300 000 hectares having a severe to extreme risk. Soil conservation initiatives under this programme, including afforestation, are co-ordinated by regional councils who can apply for funding from an annual pool of $2.2 million.
These programmes recognise that avoiding erosion has significant, long-term benefits beyond the productive capacity of New Zealand’s pastoral and forest lands. In particular, they improve water quality and protect the built environment in rural and urban communities (such as bridges, roads, water supplies and flood banks). In establishing and managing forests individual land owners make decisions around the focus of their land management. Much of the forest on Māori owned land is managed to protect the whenua (land) for future generations so intrinsically incorporates soil and water conservation in the management objectives.
The economic value of reduced erosion due to afforestation using radiata pine on marginal lands has been estimated (in a study of the Gisborne area) to be in excess of NZ $1000 per hectare in perpetuity. The benefits could be even higher for marginal lands that have steeper slopes.
Co-ordinated efforts to manage hill country erosion date from the early part of the 20th century. This work led to the passage of the Soil Conservation and Rivers Control Act in 1941. This Act authorised the establishment of local catchment boards, tasked with co-ordinating soil and water conservation. The boards provided financial assistance to landowners to carry out flood protection and soil conservation works. Many of these works involved tree planting programmes to stabilise slopes and reduce sediment yield.
The catchment boards were rolled into a new regional council structure in 1989 and the focus went on to providing landowners with technical information on and assistance with sustainably managing their properties. In a number of regions, some financial support continued to be available for land management plantings (such as riparian plantings along streams).
Since 2008, progress has been modest in the management of land for soil and water values through further forest establishment under the Erosion Control Funding Programme (East Coast), and initiatives under the Sustainable Land Management (Hill Country) Erosion Programme.
The ECFP was reviewed in 2011 and 2012. Subsequent changes seek to make landowner participation in the ECFP easier, to remove the requirement for a covenant to be registered against the land title, and to streamline grant payments.