For much of the 20th century there was a widespread assumption in New Zealand farming circles that agriculture and native plants do not mix. In part, this assumption stemmed from times when farmers needed to clear native forest to develop their farms, and from the belief that native trees grew too slowly to be of value.
Some farmers protected stands of native trees on their land by fencing them off from stock, but for most farmers fencing was too expensive and stock had access into the native vegetation. Over time, unprotected stands of native trees succumb to wind damage and animal browsing, and die off. Islands of dying forests surrounded by a sea of grass were common sights throughout New Zealand for most of the 20th century.
Cabbage trees under attack
Cabbage trees are hardy survivors and one of the few native trees that can resprout after fires and browsing by animals. It was common to see one or more cabbage trees standing in a paddock of sheep or cattle. In the 1980s many rural cabbage trees began to die – at first only those near Auckland, but within 10 years trees all over the North Island and the top of the South Island were affected. They were victims of deadly bacteria carried by a sap-sucking insect.
In the 1970s and 1980s, following recognition that much of New Zealand’s biodiversity was being lost from its lowlands, farmers and conservations began to recommend protection for remnant stands of forest on farmland. In 1977 the government set up the Queen Elizabeth II National Trust, which protects natural and cultural features on private land through binding agreements with landowners. By 2008 there were 3,388 covenants covering a total of 105,282 hectares. The majority of covenanted land (85%) contains native trees – usually in a forest remnant or a stand of regenerating growth, but sometimes isolated trees in a dryland habitat.
Sustainable agriculture on hill country
Since the 1970s many hill country farmers have planted trees to control erosion, and have profited from having well-managed woodlots or forestry blocks on some of their land. Their successes have encouraged neighbouring farmers to adopt similar practices.
With the removal of government subsidies to farmers in the 1980s, many gave up developing the steeper and less-productive areas of their farm. Some discovered they could manage their stock better and reduce their overall costs by fencing off steep land and letting it revert to bush.
The majority of farms have waterways within or at the boundaries of their properties. Since the 1990s regional councils have encouraged farmers to prevent stock from damaging the banks of waterways and polluting streams with effluent. They recommend fencing off waterways and planting the margins to a width of 5 metres or more with trees and shrubs.
Willows or poplars along waterways can cause problems because they grow into large, unwieldy trees that become expensive to maintain and remove. Native trees and shrubs provide more manageable alternatives, especially alongside farm creeks and ponds. Flax, cabbage trees and native shrubs are initially planted to provide a quick cover, then slower-growing trees such as kahikatea and ribbonwood are introduced to provide long-term protection for the waterway.