Dune lands

June 8, 2013

“Plants don’t grow on dunes; dunes grow on plants”

Gillian Rapson

As I walked around a beautiful reserve on the Manawatu coastline, my guide on this occasion, Jill Rapson, told me the above quote. This simple statement is the perfect summation of the manner by which sand dunes are formed, and is a very useful piece of advice for anyone involved in their revegetation – for it is better to plant sand-binders low and let dunes form over and through them, rather than inserting them on top of these shifting structures.

My visit to this rare remnant was concerned as much with what grows between the dunes as the communities that bedeck their sides. In the damp habitats that develop between dunes, two species that are only found along the lower west coast of the North Island grow within a dynamic environment.

The rarest of the two is the critically endangered Pimelea actea, pictured above and below, which is only found at two sites on the Manawatu coast (and is in imminent danger of extinction). The other species, Seliiera rotundifolia, is pictured at the bottom of this journal entry, where more is written about it.

Pimelea actea is a relatively short-lived subshrub that was only recently described as a distinct species. It has a delicate appearance (as exhibited by the seedling in the images above, to the right), and produces translucent, whitish berries after the appearance of its white flowers. It was satisfying to find 7 to 8 seedlings around the larger of the two plants that were already known within the reserve, especially considering that the overall wild population of P. actea comprises fewer than 60 individuals.

Another native daphne (as the members of Pimelea are commonly known) that endures in this reserve is Pimelea villosa (syn. P. arenaria) – an attractive, spreading shrub that is increasingly rare on New Zealand’s main islands (good numbers persist on the Chatham Islands). The bluish foliage of P. villosa forms a beautiful association with the orange stems of sand coprosma (Coprosma acerosa), another spreading shrub that has declined majorly on our coastlines over the last century.

When we see ‘wild’ places like this, there is often an unseen element that lies behind their formation (and indeed, their survival) – namely, the interventions of committed individuals (both professional ecologists and volunteers). Without the efforts of people like Jill Rapson (and others associated with this remnant), several of the images shown within this journal entry would look profoundly different. For example, the Coprosma acerosa and Pimelea villosa pictured above would be overrun with weeds like pink ragwort (Senecio glastifolius).

One of the finer details within this powerful landscape is the creeping groundcover, Selliera rotundifolia. Friends of mine have an impressive native garden in which they grow a large range of native plants (including alpines and some of the smaller members of our flora). With regards to Seliiera, they have commented that its less enthusiastic growth habit (although it still gives dense cover) makes for better association with plants that might be overwhelmed by more vigorous groundcovers (like Selliera radicans).

At the time of my visit (at the beginning of winter), S. rotundifolia was in fruit. The yellow fruits (pictured below), which are produced in great abundance, look somewhat like miniature quinces. S. rotundifolia seemed to be well adapted to a wider range of habitats than S. radicans, and is quite common throughout this area.