Plasticity

We are frequently asked for a definitive figure on the eventual size of plant species, or to confirm information garnered on this subject from the Internet or literature.

As infuriating as the response, ‘It depends’, can be, I would point anyone hopeful of a categorical reply in the direction of New Zealand’s tallest forest tree, kahikatea, growing in windshorn coastal scrub at Te Hapu, measuring approximately the same height as my ten-year old son.

I do expect Henry to eventually outstrip his father’s height (probably too soon for my liking), but he should clearly be no match for kahikatea. An under-achieving kahikatea is not, however, the subject of this journal article – which concerns a native climbing rātā that regularly demonstrates considerable plasticity in its growth form.

The coastline of Te Hapu is a perfect example of Metrosideros perforata‘s ability to mould itself in response to varying conditions, partially due to the general abundance of this rātā throughout an array of differing habitats.

The lefthand image above shows the juvenile form of the plant as it finds purchase on one of the innumerable limestone boulders that are ubiquitous in this landscape – in this case, still nestled within a sheltered aspect. On the right, one can see the billowing form that is typical of the adult stage of this white-flowered rātā when it reaches a place in the sun (which can be as high as 15m or more up the trunks of our forest giants).

Such lofty heights cannot be countenanced in the teeth of the biting westerly gales whose regular appearance is writ large upon the rolling, cloud-like fields of rātā inhabiting slopes and outcrops on this section of the South Island’s northwestern coastal fringe. No – something much better occurs here.

Furrows through which the wind whistles, and inclined planes scythed into perfectly even surfaces, create a vegetative topography – a new ground plane like a green shadow of the stone and earth below.

Nature’s most sublime act of lunacy in this regard is shown in the photo above, left, where a hedge of Metrosideros perforata has developed at the top of a cliff. The clean line at which it meets the pasture behind may betray the thoroughness of sheep, although it is also likely to demonstrate the exact point where it becomes very unwise to place one’s foot.

When one views such compact growth forms, it is easy to misjudge the age of these plants, which are as old as (if not older than) rātā specimens that scale rimu or kahikatea in nearby forests. The trunk on the venerable individual shown above gives a clear indication that the field of foliage appressed upon this massive block of limestone has been developing for many decades.

The lessons that we learn from observing such landscapes, where livestock are yet another influence upon the development of vegetation, are valuable because we work in places that are neither natural nor benign. That said, as I wandered about Te Hapu with my family (camera in hand), I was simply transfixed by the exercise in form that is exhibited so extravagantly in this place.