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Protecting our precious places

Natural turfs of diverse tiny plants

An update from the Landcare Research Sustaining and restoring biodiversity programme funded by the Foundation for Research, Science and Technology.

Bill Lee from Landcare Research describes the research being undertaken on our turf communities (native lawns) and the factors that maintain them.

One of our most spectacular and distinctive native plant communities is frequently overlooked, literally.

It comprises a species-rich suite of prostrate plants less than five centimetres tall found on coastal headlands, in dune hollows, in riverine and wetland systems, and near tarns and kettleholes in the mountains.

In general, these communities are associated with environmental extremes, usually saline conditions near the coast, and winter submergence elsewhere.

Because of these factors, it is unlikely that they were ever forested in the past but have always been open glades in a woody landscape.

In turfs, the plants are so small that the flowers and fruits often appear enormous – larger than the prostrate leaves.

Nearly 20% of native higher plant species grow in these communities, which nationwide support over 62 threatened and/or uncommon plant taxa.

Recently they were recognised as one of the important originally rare ecosystems of New Zealand.

Interestingly, the turf communities are locally most extensive where they are grazed by birds and nowadays by small mammals such as rabbits and hares, or sheep.

In past times, they must have been dominated by long-extinct birds such as moa, duck, rail, and geese, and it is likely that these played a key role in their evolution.

Turf assemblages attract herbivores because of the nutrient-rich foliage and short accessible vegetation. The proximity of waterways and seasonal ponds also provides escape from predators.

Our turf communities may represent avian grazing lawns adapted to concentrated and persistent feeding by birds, similar to the marsupial lawns in Australia and the famous mammalian grazing lawns in the Serengeti.

We are investigating the origin and maintenance of this distinctive vegetation, particularly the role of native and introduced herbivores.

Using a combination of field and glasshouse experiments, we are attempting to answer the following questions:

  • How important are birds and do they act merely as grazers, or are they critical nutrient sources?
  • How do the turf plants cope with defoliation and what stops many exotic species in adjoining communities from taking over?
  • Is the impact of introduced mammals (e.g. rabbits, sheep, cattle) comparable to that of birds?

The aim is to understand the role of grazers and assist the conservation management of turfy areas.

Covenants protecting turf communities

QEII covenants include some impressive turf communities and we are working at two sites where these are a special feature.

Inland turf

The Ohau Downs kettleholes occupy glacial moraine in the Mackenzie Basin and support extensive seasonally submerged turfs that have in the past been used for playing polo.

In collaboration with QEII High Country Regional Representative Brian Molloy, we are measuring duration and depth of water levels in relation to turf zonation patterns, and what happens to the vegetation when all grazers are excluded.

Ohau Downs Station

Above: At Ohau Downs Station in the Mackenzie Basin, a 1,185ha covenant protects lowland tarn wetland, grassland, and impressive shrubland communities on moraine deposits.

Usually ponded in winter, these depressions are fringed by a zone dominated by pasture grasses, which give way in the centre to turf that is grazed by rabbits and hares.

Inland turf community

Above: The inland turf community showing a suite of creeping herbaceous species - Epilobium komarovianum, Hypsela rivalis and Leptinella maniototo.

Exclosure plot in turf community

Above: An Ohau Downs enclosure plot set in a turf community dominated by the tiny prostrate native herb Epilobium angustum, with its large white flowers.

Coastal turf

Our second covenant, at Smaills Beach near Dunedin, supports salt-tolerant turf mixed with pasture above coastal cliffs.

Here we are attempting to determine the factors that favour turf over pasture, in order to help sustain it.

Early results for a wide range of turfs suggest that these communities are sensitive to grazing, and that grazers appear to restrict encroachment of aggressive pasture species.

Sheep graze across a wide area in and around turfs whereas rabbits and hares are similar to birds in that they appear to favour feeding on turfs. All animals feed on the most nutritious plants.

In coastal turfs, salt spray and grazers combine to sustain the turfs, while elsewhere it is not yet clear whether winter submergence alone will reduce pasture invasion and maintain turfs dominated by these special native plants.

If grazers are essential, one option is to encourage native (paradise shelduck) and naturalised (domestic geese, Canada geese) birds to occupy these systems, as they do naturally at some sites – but confining game birds to refuges in many agricultural areas is a major challenge.

Smaills Beach coastal turf

Above: Rhys Millar’s 2ha coastal herbfield QEII covenant at Smaills Beach near Dunedin protects distinctive exposed coastal turf communities alongside pasture, with Trifolium repens prominent.

The research will assist management of the covenant to ensure that the turf continues to occupy this important site.

Native coastal turf

Above: Native coastal turf with tiny plants of Leptinella dioica, Samolus repens and Selliera radicans forming a dense prostrate cover.

Open SpaceTM Magazine No. 74, November 2008 © QEII National Trust

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