Environment – Dune diversity

The Tawharanui sand dunes are full of geological and biodiversity changes. An example is the fact that researchers doing core samples discovered that in the 14th century, a tsunami swept over the dunes.

Also, the sand dune face on Ocean Beach is constantly active with storm erosion creating steep cliffs.

Long trails of spinifex grasses restore these cliffs to a natural slope by capturing wind-blown sand and returning it to a gentle dune slope until the next storm hits. The dune face adjacent to the Anchor Bay car park is repairing itself, after Auckland Council removed a clay cap undermining it, and TOSSI volunteers planted spinifex. Also, the access steps diagonal to the face have been shifted to reduce direct erosion.

The mid-dunes have lush rolling muehlenbeckia that is fairly free of weeds, thanks to passionate Tossi volunteers who spent years removing yellow lupin, Apple of Sodom and purple groundsel. A small team still monitor the dunes for these species. Sand coprosma acerosa has been fenced to protect it from the rabbits, and pingao grass has also been planted and fenced. A professional weed team employed by council has addressed freesia flowers left in another area by earlier residents.

The endemic shore skink (Oligosoma smithi) lives in the mid-dunes and some have been taken from Tawharanui to be established on Tiritiri Matangi and Rotoroa Islands. For many early years Tossi nursery volunteers were careful not to accidentally release the more common plague (rainbow) skink eggs into the dunes. However, more recently, on a warm spring morning I was entering the dunes from the campground and right before me were 40 to 50 small newly-hatched plague skinks sunning themselves on the muehlenbeckia. There was nothing I could do about it. The question is, “What effects do these fast-breeding plague skinks that lay eggs have over the endemic shore skink that produce three or four young?”

Common copper butterflies Lycaena species (such as L.salustius, L. rauparaha, and L. feredayi) rely on muehlenbeckia as the primary host for larvae. Only once over the years have I had the delightful experience of finding myself among them. I might have been in an aviary of butterflies as they silently fluttered around.

Soon after the pest proof-fence was completed, the New Zealand dotterel (tuturiwhatu) took to nesting in the mid-dunes. Finding their nests for monitoring proved extremely difficult as the incubating bird could sneak off the nest and use the cover of spinifex, popping up some metres away calling cheerily as if trying to lead us away from the nest site. Over the last seven years, tuturiwhatu have stopped nesting in the dunes. Cameras showed that rabbits constantly disturbed incubating birds and the heat these days seems excessive in the dunes.

The dunes at Tawharanui have the potential for being among the most pristine sand dunes in New Zealand if the rabbits were eradicated and rare plants given the opportunity to grow there without getting eaten.