Great Barrier Island

February 27, 2014

I have wanted to visit Great Barrier Island for a long time, to view its striking landscapes and distinctive ecologies in person. Three plants are entirely restricted to the island, whilst a number of other plants that are found there have limited distributions beyond Great Barrier. For anyone interested in native plants, the tracks leading to the summit of Hirakimata/Mt Hobson count as the most fascinating areas.

Geologically, Great Barrier Island shares its history with the volcanic ranges of the Coromandel Peninsula. This is clear to see around Windy Canyon (pictured above), where rhyolitic outcrops form an impressive sight. Massive sheets of climbing rata cling to the sheer faces of these cliffs, upon which the sprawling Great Barrier kanuka (Kunzea sinclairii, pictured below) also makes its home.

When we encountered Kunzea sinclairii in the heathland above Windy Canyon, I was surprised at how silver the leaves of this Great Barrier endemic are. Another distinctive plant of the island, Epacris sinclairii, was coming into bloom at the time of our visit. Aside from Great Barrier, this compact shrub is only found in the upper Kauaeranga Valley (near Thames).

It differs from the closely-related Epacris pauciflora by having a more squat growth habit. The new leaves exhibit a particularly vibrant shade of green, as shown in the photograph below (taken in forest nearer the summit).

As we entered the base of the cloud forest that surrounds the summit, I saw some of the finest specimens that I have viewed of an attractive, small tree of northern New Zealand, called Toronia toru (pictured above). Toru (as it is commonly known) is one of just two members of the protea family that are present in New Zealand. It is found in many parts of the upper North Island, growing in infertile habitats.

Although one often wishes for sunny weather when walking in forest and scrub, the cloudy and mildly drizzly conditions that we encountered were perfect for experiencing the full range of foliage colour in the heathland (which comes alive under these light and moisture levels). It also provides a vivid demonstration of the conditions that make these areas so distinctive. Standing like a sentinel on the Hauraki Gulf, the highest points of Great Barrier are often wrapped in clouds – thereby creating a form of ‘cloud forest’.

A particularly common element of the understorey of this cloud forest is Coprosma dodonaeifolia (shown below), an understated shrub that we have planted on many occasions. It is most similar to Coprosma lucida, from which C. dodonaeifolia differs by having narrower leaves (hence its species name, which compares the foliage with akeake) and a more compact growth form.

Because we have only ever planted specimens that were grown in relatively open conditions, I was surprised by the variation in the appearance of C. dodonaeifolia (which is pictured in fruit below) in different habitats. Plants growing in open conditions on the island (for it grows in the heathland and amongst scrub as well) look almost unrelated to the forest-dwelling specimens. It was especially interesting to note that shrubs growing in difficult, infertile spots often bore mottled leaves (in various shades of red, green and fawn) which were reminiscent of the leaves of tawheowheo (Quintinia serrata) in equivalent habitats.

An unexpected delight as we walked near the summit was the appearance of the cobalt-blue fungus, Entoloma hochstetteri. This remarkable fungus, which appears on our $50 note and is the subject of Maori legend (connecting it with the kokako’s wattles), is not uncommon in our forests. However, I had never seen it in person before, despite having wanted to for years.

In addition to the special plant communities of Hirakimata/Mt Hobson, I was especially keen to visit the eastern beaches of Great Barrier Island. The extensive dunes on this coast still contain good numbers of both of our major sand-binders, Spinifex and pingao, which form beautiful patterns as they go about their work (as pictured below).

Of even more significance in a regional context is that this is the last place in the Auckland region where sand tussock (Poa billardieri, formerly Austrofestuca littoralis) grows (shown below). With its tawny colour and fine, upright leaves, it is perhaps most readily compared with Poa cita (silver tussock) or the more rigid tussocks of Austrostipa stipoides.

Finally, Great Barrier Island possesses an impressive form of nikau, which we regularly specify for gardens. As demonstrated below, the Great Barrier nikau attains longer, more luxuriant fronds than the majority of mainland forms (an attribute that was recognised many years ago by nurserypeople who brought this form into cultivation).