Nature and conservation

Whanganui National Park was gazetted in 1986. The park protects one of the largest remaining tracts of lowland forest remaining in the North Island, and it provides habitat for a wide variety of native wildlife.

Of all of New Zealand’s national parks, Whanganui is most closely associated with human settlement. It is dissected by the Whanganui River, the longest continually navigable river in the country. Although the bed and waters of the river are not included in the park, the river is an integral part of the area and provides an important access way into and through the area.

Western tributaries of the Whanganui have eroded through mudstone (papa) which has created spectacular gorges, bluffs and a maze of intricate ridges and V-shaped valleys. Streams and rivers scattered throughout the park are an important habitat for the whio (blue duck), an endemic torrent duck admirably suited to river life.

Vegetation

Whanganui National Park contains extensive stands of podocarp-hardwood lowland forest, an ecosystem that is greatly under-represented in the New Zealand conservation estate. This extensive forest comprises many different communities reflecting changes from north to south, riverside to high ridges.

Kāmahi and tawa are a common canopy species and the understorey is rich in ferns, from 10 m tall mamaku to delicate filmy ferns. Large podocarps include rimu, mīro, tōtara on ridges and faces. Kahikatea and mataī are more prominent in the lower river terrace and alluvial flats as is the nīkau palm. Large northern rata occur throughout the park forming a spectacular display in mid summer.

Dry ridges are a distinct habitat with black beech over twiggy shrubs. Autumn orchids are also commonly seen on these ridges. Silver and hard beech can also be found in the park. The steep riverbanks are another distinctive feature and are a haven for some of the park’s more vunerable plants, like hutu, fuchsia and the rare daisy brachiglottis turneri.

Outside the core area of forest, fragmented patches remain, with areas of grassland, regenerating bush and some exotic vegetation. The Mangapurua Valley, where patches were farmed but abandoned prior to 1942, shows the greatest degree of modification within the park. Some of the valley is still in rank pasture and a few fruit trees and roses are reminders of past gardens, while the edges are regenerating kānuka/ mānuka and silver fern forest.

Introduced plants are mostly limited to riverbanks, walking tracks and heavily disturbed areas, but weeds that are a problem in some areas include buddleia, wattles, willows, Japanese honeysuckle, pines, Japanese walnut and to a lesser extent gorse and Himalayan honeysuckle.

Wildlife

The isolated reaches of the Whanganui River valley support a range of birds. The greatest concentration of birdlife in the park is in the area most intensively managed to reduce the effects of exotic pests. Common species that can be seen include fantails, grey warblers, silvereyes, tomtits, robins, bellbirds, kererū/kūkupa, tūī and whitehead. Migratory cuckoos are heard in spring and early summer. Kākāriki and kākā are present in very low numbers in the mature forest of the Matemateaonga Range and possibly the Heao catchment. Rifleman, yellow-crowned käkäriki and New Zealand falcon are seen regularly.

The park is home to the largest population of North Island brown kiwi in New Zealand with several thousand birds present. The blue duck/whio inhabits the clean fast-flowing river habitats in the park with the most significant populations on rivers bordering the park.

Eighteen species of native fish inhabit the Whanganui River, which is also rich in eels, lamprey, koura (freshwater crayfish) and black flounder. Long-tailed bats are in more open habitats of the park such as river trenches and forest edges. Although less commonly spotted, larger populations of short-tailed bats occur in the dense bush. There are likely to be a number of rare invertebrate species in the park, although they have not yet been extensively studied.

Threats and management

Introduced animals – especially goats, deer, pigs, possums, stoats and rats – have had a major impact on the park’s vegetation and wildlife. Possums cause damage to native forests by targeting their preferred species, sometimes causing local extinctions. In addition to leaves, possums also eat flowers, fruit, buds, fungi, insects and bird eggs and chicks. Possum control in Whanganui National Park has improved the condition of a range of plant species, including the iconic northern rata.

Feral goats and deer are another major environmental pest in the park. They browse vegetation, prevent regeneration and degrade land that adds to erosion. Goat control is achieved by hunting, and populations within target areas of the park have been significantly reduced. As above, the areas receiving pest management have the richest flora and fauna.