Naturally rare and threatened

Aotearoa is home to over 70 naturally rare ecosystems - places that make up a tiny amount of the total area of New Zealand but can hold incredible amounts of biodiversity.

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Naturally rare ecosystems happen when there are distinct environmental conditions within a geographically small area; whether it is the underlying rock, the soil chemistry, the climate in the region and/or the local effects of volcanic, geothermal, river, or ocean activities.

Braided riverbeds, coastal turfs, shingle beaches, salt pans, volcanic lahars, tarns and cushion bogs are all examples of naturally rare or naturally uncommon ecosystems in Aotearoa.

These specific landscapes, soil chemistries and conditions have given rise to unique flora and fauna that live in these places. So what you get is a set of rare, endemic (found only in Aotearoa), plants and animals dependent on specific ecosystems and restricted to very small areas.

And many of these are threatened.

In the Waitaki Valley area of North Otago limestone ecosystems are rare and in decline. When it breaks down, the limestone rock produces rich fertile soil good for farming, and the stone itself is quarried for building. So the land has been extensively modified, and the areas suitable for limestone endemic plants has shrunk.

One of the biggest problems for the limestone-soil specific plants is non-native grasses such as Chewings fescue. The grasses smother the plants, blocking out light, sucking up all the moisture and building big impenetrable root mats that stop new plant seedlings from establishing. The low growing natives just can’t compete, and so their numbers have been dwindling.

At the back of the Department of Conservation’s Oamaru field station DOC ranger Tom Waterhouse has been growing these limestone endemic plants in a nursery. But as science advisor Dr. Clement Lagrue explains, the longer-term issue is where to put them. Intensive monitoring and hand weeding have saved the plants from extinction for now, but to allow them to flourish a habitat ‘reset’ might be what is required.

University of Otago Botany Masters student Jacinta Steeds is trying to investigate what scale of reset is needed. She is running a field trial on small plots of land to look at what type of weed removal works best.

Working with Te Rūnanga o Moeraki and their biodiversity restoration team Whiria te Waitaki, Tom, Clement and Jacinta hope to develop a plan to safeguard the future of this rare and threatened ecosystem.

To learn more

• Visit the New Zealand Plant Conservation Network website. Plants discussed in this episode include: Gentianella calcis subsp. calcis, Lepidium sisymbrioides and Carmichaelia hollowayi.
• Listen to John Barkla discuss the issues facing rare native plants, in Favourite plants.