The first European visitors to New Zealand created a new wave of major environmental impact. New crop plants such as potatoes were introduced from the time of James Cook’s voyages in the late 18th century. Māori grew potatoes widely by the early 1800s, clearing more forest and bracken to make way for gardens.
As Europeans settled in New Zealand, they brought more changes to the remaining forests, animal diversity and landscape stability. Along with immigrants came new animals, crop plants, parasites and diseases. The remaining lowland forests and scrubland were burnt, drained, logged and cleared for farms and cropping. By 2005, forest cover was reduced to 24.8% of the total land area.
Forest seen as unsuitable for farming or other development was selectively logged. Large conifer species such as rimu (Dacrydium cupressinum), mataī (Prumnopitys taxifolia), tōtara (Podocarpus totara), kahikatea (Dacrycarpus dacrydiodes) and kauri (Agathis australis) were taken, significantly changing the forests. Later, beech forest (Nothofagus species) was felled and exported for wood chips. In the 1970s and 1980s, large areas of conifer–broadleaf forest, particularly on the West Coast, were clearfelled for timber and replanted with introduced pine (Pinus radiata).
The settlers drained large wetland and swamp areas, converting them for farming or towns. By the early 2000s, only 10% of New Zealand’s original wetlands remained.
When the settlers cleared the bush for farming, they removed tree stumps and the protective cover of ferns and scrub – unlike the 13th-century deforestation, which left these in place. The loose soils in hilly areas became very vulnerable to erosion, especially during heavy rain. This can trigger massive slips, and the runoff to rivers carries high sediment loads. Over time, river mouths and estuarine systems have become silted up, and mangroves have spread extensively in some silted areas of northern New Zealand.
By the 2000s, more than 30,000 plant species had been introduced to New Zealand. At least 2,166 had become naturalised – they can survive and reproduce without human help. Some early introductions rapidly became irrepressible weeds – such as gorse (Ulex europaeus) which spread from shelter belts and hedges. Others, such as Scotch broom (Cytisus scoparius), wattles (Acacia species) and hawthorn (Crataegus monogyna), have spread more slowly, but are now major weeds.
Some woody species such as contorta pine (Pinus contorta) have spread into alpine areas, even growing above the treeline (the natural limit for native trees) because of their greater tolerance for cold. Coastal sand dune habitats have been altered dramatically, with native plants like pīngao (Desmoschoenus spiralis) being replaced by marram grass (Ammophila arenaria) and tree lupin (Lupinus arboreus). Herbaceous hawkweeds (Hieracium species) have taken over some grasslands, reducing them to wasteland, and are spreading into forests and along creeks.