Past the cathode dump

December 26, 2020

As instructions for botanising go, “drive past the cathode dump and walk from there” is one of the more specific pieces of advice that I have ever received. That notwithstanding, we dutifully followed the words of a friend with indepth knowledge of Southland’s flora, Jesse Bythell, when setting out to explore Tiwai Peninsula’s coastal plant communities.

I was particularly keen on seeing the nationally threatened sand iris, Libertia peregrinans, which I had only viewed once in the wild before (also on the Southland coastline). Often, when looking at plant lists for a given area, I steel myself for the possibility that a species may be very sparse or difficult to locate in the wild.

In this case, any such illusions were dispelled well before we had made it anywhere near the cathode dump, as we found considerable numbers of Libertia peregrinans (pictured below, within the dunes on the southern coast) on the margins of shrubland and amongst grass by the side of the access road leading to the well-known aluminium smelter at Tiwai.

Aside from very healthy populations of Libertia peregrinans and other coastal species like Pimelea lyallii and Raoulia aff. hookeri, a notable feature of Tiwai is the presence of species normally found in montane areas growing at sea level – including the mat-forming coprosma shown in the images below, Coprosma petriei. This attractive species wends its way through both gravelled areas and sand dune, often blending with other diminutive native herbs (such as Leptinella pusilla) to create tapestries of foliage.

Another resident of the mountains, Olearia nummulariifolia, plays a much more conspicuous role in various areas of Tiwai, where it is the dominant species of shrublands that act as a stepping stone towards the natural forest type that would have formerly covered much of the peninsula.

The bright green mounded canopies of Olearia nummulariifolia (frequently intermingled with prickly mingimingi – Leptecophylla juniperina) are punctuated by windshorn tōtara that serve as the advance guard for a future forest cover here. Particularly significant stands of tōtara dune forest endure on the coast to Invercargill’s west (not far from Tiwai), demonstrating the role that tōtara plays in the establishment of forest in even the most exposed environments.

Whilst ambling along the dunes lying beyond the fabled cathode dump, I was on high alert for a winged member of these dune communities – one that I had wanted to see in the wild for a long time. I have previously written in this journal about a genus of moths called Notoreas, which are closely associated with our native daphnes (Pimelea spp., which serve as their larval food plants).

Taking their already excellent generic name on to a whole new level, entomologists gave a species from the Southland coast the title of Notoreas casanova, in reference to its beautiful mottled colouration (and its “charm”, as noted within the species’ description). In the few places where it occurs, N. casanova is associated with the attractive sand daphne pictured below, Pimelea lyallii, on which the species breeds and the larvae feed.

At Tiwai, I saw one specimen flitting through the dunes, and despite a spirited chase with camera in hand, I failed to get a closer look at this beautiful moth. However, our next day at Fortrose Spit (one of three known sites for the species) was far more fruitful in this respect, with several specimens of Notoreas casanova having the decency to stay still for long enough for me to photograph them (including the handsome chap in the image above).