Living life on the edge – plants of screes

Looking at the photos below, you wouldn’t expect these unstable rockslides, called screes, to be home to anything.

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But take the time to look a little closer and you’ll find a number of native New Zealand plants that have adapted to living in just such seemingly inhospitable environments.

Getting close and personal with scree plants. Many scree plants have leaves that are a grayish colour and blend in with the surrounding greywacke rocks. This makes them difficult to see, especially when they aren’t flowering. Photo: Lara Shepherd.

Getting up close and personal with scree plants. Many scree plants have leaves that are a grayish colour and blend in with the surrounding greywacke rocks. This makes them difficult to see, especially when they aren’t flowering. Photo: Lara Shepherd.

In early January I spent a week looking at plants with the Wellington Botanical Society on their summer camp botanising in the Nelson Lakes region.

Members of the Wellington Botanical Society on the Red Hills, near Nelson Lakes. Photo: Lara Shepherd.

Members of the Wellington Botanical Society on the Red Hills, near St Arnaud. Photo: Lara Shepherd.

I’ve never spent much time thinking about what might be growing on the tumbles of rocks cascading down the mountain slopes so when we stepped onto our first scree I was surprised to see that there were actually plants present.

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I later learnt that there are a number of New Zealand plants that can survive on screes and some of these only grow in this habitat. Many of these plants are unrelated to each other but have independently evolved many of the same special adaptations required to survive in this harsh environment.

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Screes aren’t as dry as they first appear. Around half a metre beneath the surface rocks there is a stable finer-grained soil layer through which water constantly seeps downslope. Scree plants have extensive deep root systems that tap into this moist soil as well as anchoring the plant.

Other adaptations such as small, fleshy, hairy and/or waxy leaves slow the evaporation of water from their exposed surfaces.

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One hazard for plants in this environment is scree instability. Some scree plants have leaf and flower stalks that are thin and break off easily, preventing the entire plant from being uprooted if they are caught in a rockslide. If their leaves do break off, or the plant is buried under rocks, they are able to re-sprout from their extensive root systems. Many also die back to a taproot or rhizome in winter when the rocks are most likely to move.

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Vegetable sheep (Haastia pulvinaris) were much more visible than most of the other scree plants. They tended to grow at the top of highest screes in the Nelson Lakes region.

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As well as the flowering plants above we also saw lichens, mosses and even a few invertebrates on screes.

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Screes are most common on the mountains of Canterbury and Marlborough east of the main divide where rainfall isn’t heavy enough to wash the eroding greywacke rocks downhill, so they instead accumulate. Threats to scree plants include introduced pines, and browsing and trampling by introduced mammals such as tahr, goats and occasionally trampers.

7 Responses

  1. Lea Robertson

    Very interesting – thanks Lara. Like the slide-shows with a few excellent photos at a time. What is that cricket?

    Reply
    • Lara Shepherd

      I’m not sure on the identification of the cricket. They were very common on the screes, where they blended in nicely with the rocks.

  2. Leon Perrie

    For anyone on FaceBook interested in the activities of the Wellington Botanical Society, their group page is “Wild plants of Wellington” https://www.facebook.com/groups/322939557873243/

    Reply
  3. Olwen Mason

    How interesting this is! Are the scree slopes a natural phenomenon or are they caused by deforestation or over grazing or both?

    Reply
    • Lara Shepherd

      Thanks Olwen. Screes are a natural feature of our landscape. I read that scientists have examined the weathering patterns of the rocks on some Canterbury screes and determined that the screes have been the same size for hundreds or even several thousand years!

  4. Stuart Nicholson

    I will never just think of a scree slope as only a fast way down a mountain again,:-( Beautiful photos.

    Reply
    • Lara Shepherd

      Thanks Stuart! They are definitely worth a closer look, if you get the chance.

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