Sectional elevation

January 4, 2023

In the early 1930s, K. G. Mcindoe presented some of the only diagrams ever published of the root systems of native plants, in an article about plants of the Cromwell district. These beautiful line drawings show the improbable depths to which several diminutive species from the South Island’s drier regions send their roots in search of moisture.

In the case of the weeping broom pictured above (the nationally endangered Carmichaelia stevensonii), it was not necessary to dig trenches to observe its root system (the method applied in McIndoe’s study).

The dynamic geology of the Seaward Kaikouras had already obliged to expose one side of its roots, thereby providing an unusual ‘sectional elevation’ of this normally unseen structure. For enthusiasts of plant morphology, I highly recommend zooming in on the righthand side of this image to see how the tree has driven anchoring roots into the slope above it.

This large population of weeping broom occurs at the treeline – at the altitudinal threshold for beech forest and amongst subalpine scrub. I had been here once before, with Winston Dewhirst and other botanically-minded friends, when the Seaward Kaikouras were cloaked in mist – giving an impression of the environmental conditions that contribute towards defining this habitat.

On our second trip, in early December 2022, the skies were clear allowing us to gain a much fuller impression of the population, including giants emerging from the scree in the top right of the image above.

Whether as part of lecturing work (at VUW) or within our practice, there have been many occasions when I have had cause to discuss the efficacy of root structures in addressing or preventing erosion – a matter that should be a topic of major interest for landscape architects (especially in places where historical vegetation cover has been lost).

Yet mystifyingly, there is very little research on the root systems of our native species, and their potential for offering pragmatic solutions to problems of our making. These issues include large-scale topsoil loss caused by hillside erosion, and the deleterious effects of major rain events on river systems in which deforestation has amplified the natural dynamism associated with such places (in contrast with the character of the river cutting shown above, which represents an example of a natural system at work).

This research trip to Marlborough is part of a future book project (with David Straight) about environments and plants. The last two images shown above demonstrate one of the aspects that we will explore within the book – namely, the essential role of dynamism within natural environments in providing opportunities for diversity to occur (and the often beautiful path charted by water).

Whilst the latter offers physical evidence of what happens nearer the headwaters during storm events (like a reverse mould of the stream), the former shows an interesting plant community that occupies the margin of the river’s lower section – where floodwaters generate a more open, sharply-drained habitat for the rare toothed lancewood (Pseudopanax ferox) and leafless clematis (Clematis afoliata).