Garden favourites may threaten native bush

Waimarino Bulletin, Volume 3, Issue 50, 27 May 1986, Page 10

Garden favourites may threaten native bush

The problem of noxious plants as a threat to farm land is well known in rural areas. Less well known are plants, many former garden favourites, which threaten native forest. In the Waimarino disturbed areas of Tongariro National Park are particularly vulnerable. In this article, the first of two, Martin Nicholls, landscape architect with the Department of Lands and Survey, gives a personal view of the problem of invasive exotic plants. __

Many are aware of the problem of noxious plants and the threat of old mans beard to native forests. It is the lesser known species, garden plants not usually thought of as a threat which I wish to highlight here. Periwinkle, especiallyVinca major. This is commonly known as a variegated ground cover creeper. Its reversion to the vigorous, dark green form is a particular threat to the forest. It is easily identified as a vigorous smothering ground cover creeper. Its leaves are glossy and evergreen, and borne in pairs along the stem. They are oval or ovate, similar in shape to those of a privet. It has attractive purple or bluish flowers whose petals lie flat. They are often borne abundantly in early summer. Gardeners who know this plant and how it can spread are usually keen to remove it. It often finds refuge in shady forgotten places under hedges or trees. It can smother out any ground vegetation up to eye level. This is an indication of its threat to our indigenous forests. It is already present along the Mangawhero River, from Ohakune to Raetihi and in waste areas adjacent to Tongariro National Park. Honeysuckle (Lonicera spp.) is a vigorous climber. It should not be confused with another forest weed, (Leycesteria formosa) which is a soft-wooded shrub. The invasive properties of old mans beard are similar to honeysuckle. In fact the two can be easily confused from a distance during the growing season for their

habit of growth and method of smothering the forest canopy. Honeysuckle can spread far and wide from its initial source by surface rooting runners and pieces which break off and are spread by water or animals. Its black fruit are also eaten by birds which drop the seeds elsewhere. I have found seedlings in even dense forest. These will sit, growing slowly. until the canopy opens up. Then they grow vigorously to form a nucleus for widespread invasion into surrounding forest. The leaves are very sweetly scented and the plant is often cultivated for this purpose. It was, and still is, a popular arbour vine. While it is not a threat in the Waimarino at present it could take hold to form a nucleus of invasion in warmer parts of the national park. Suitable sites could include areas near the railway line and the outskirts of Ohakune Junction along Old Station Road. Privet (Ligustrum japonicum and L. ovalifolium) is a popular hedge plant. It seems an unlikely threat to the forest. However, near Thames the giant species, L. lucidum (tree privet) has spread so fast that it has replaced indigenous forest species which initially harboured it. The smaller species mentioned are a threat to the forests in cooler climates. Seedlings of privet are quite common in forests marginal to residential areas. They grow rapidly in clearings but in the Waimarino are generally not vigorous enough to compete with

indigenous hardwood species. , The two species are easily identified by their dull green leaves borne in pairs along the stem. The leaves are generally small, wavey at the margins and semi-deciduous. Flowers are small and creamy and are borne in dense paricles. Fruit are black and occasionally eaten by birds. Cotoneaster. This group of plants is a major threat to regenerating stands of native bush in the Waimarino. It appears to have a particular liking for our acidic ash soils and the cool, moist climate of the region. The shrub grows in open localities, but can be codominant in predominantly manuka communities. Cotoneaster is a popular garden shrub and is noted for its abundant bright red to scarlet berries. The major concern with these species is their potential to invade rehabilitated areas along the rail deviation before indigenous vegetation can establish properly. Barberry (Barberis vulgaris & B. darwinii) The latter, or Chilean barberry, was until recently a registered noxious plant in the Waimarino. It deserved this classification. Its capacity to spread along forest margins and streams is considerable. It is easily identifiable, especially in spring by its abundantly produced, brightorange flowers. It is an attractive shrub and for this reason and for its glossy, dark-green, spiny

leaves, it was popular as a garden shrub. As it is relatively unpalatable to animals it has a competitive advantage in national parks and reserves where wild animal population are a problem. It can grow in a dense and smothering habit and is very hard to kill with conventional herbicides. It tolerates shade to some extent so it can persist in bush reserves. Chilean barberry loves the cool Waimarino climate which closely resembles its natural habitat. This is a plant which, while not on the noxious plants register here any longer, should not be grown. Despite its obvious ornamental value it should be removed from the home garden. It is on marginal farmland in the Horopito to Makatote areas where Chilean barberry is a potential threat to crown reserves and state forest parks. The common or European barberry (B. vulgaris) should not be overlooked. It too grows well in the Waimarino and is speading. It is not classified as a noxious plant but garden or hedge row escapes should be controlled. Common barberry is seldom cultivated now in the Waimarino, but residents are asked to be aware of the plant and remove it when ever it is seen. In next week's article I will describe the problem of old man's beard and ways of controlling invasive exotic plants.