Grahams Bush Botanical Information (1988)

A top-down description:

From across the Old Mount Cargill Road from the Organ Pipes track entrance, the top section of the walk is very steep, but now relieved by an excellent set of steps. For much of the descent into the gully the walk passes through dense stands of manuka and kanuka. Both have small pointed leaves. Most of the trees are of even size and height. This implies they are even aged and grew up at about the same time. Equally important is the fact that no young kanuka is growing beneath the adult trees. In places many other species of native trees and fauna are growing. This is because kanuka seed needs light to germinate and not enough filters through the canopy. Other seed such as lemonwood is not so light-demanding. These young plants will eventually grow up through the kanuka to become a new forest canopy.

The widespread dominance of the blotchy-leaved pepperwood tells us more of the forest’s history. It is very unpalatable to stock and generally thrives when stock eats out the other plant species. Until recently stock have been common in this bush.

It is also interesting to note how dry this slope is. This stands in sharp contrast to the cooler gully at the bottom of the hill. A bridge spans the creek here, about 20-30 minutes from the carpark. Beyond this are more mature patches of forest.

Fuchsia (with orange bark) predominates in this valley, while little kanuka can been seen. A good variety of ferns thrive here in the moist conditions, the most distinctive of which are the tall tree ferns. The one with milky-coloured frond stalks is the silver tree fern.

Just 2-3 minutes beyond the bridge is a clearing. From it the hill just descended is apparent. More of the story becomes obvious. The whole hillside is of an even aged kanuka. Above nearer the road one sees old macrocarpas.

Kanuka and manuka often thrive after fire or in areas cleared either by humans or nature. Could it be that this hillside was once cleared, and that maybe the macrocarpas indicate an old homestead site – a base for a farm now abandoned and reverting to native forest?

In such a role kanuka is a successional species; i.e. it thrives after disturbance allows light into the forest floor. In time it gets over-topped by other forest species and becomes replaced with more mature forest.

An example of this mature forest that once covered this hill and what will once again be seen is 10 minutes further down the track.

One cannot fail to be impressed by the huge boles in the rimus (with hammer bark) and miros (with soft green leaves and dark mossy trunks). These giants are survivors of a once extensive podocarp forest that covered most of the Dunedin district. Fortunately their poor shape precluded their being logged for timber and consequently they now serve as a seed source to re-vegetate the reserve in podocarps. The dominant trees forming the forest canopy in this area are kanuka.

A second small patch of these trees occurs a little below the second bridge. Beyond them further evidence of the impact of humans on the area is seen – hawthorns growing in the forest! These exotic trees from Europe add a new shade of green to the forest each spring. Being deciduous, like so many continental trees, they lose their leaves in summer and grow a new set in spring. In New Zealand the only common tree with this habit is the fuchsia – the orange shaggy-bark trees. Like kanuka, fuchsia is one of those successional species. Their roles are very similar but they fill them in different locations – fuchsia preferring damper cooler sites.

– Adapted from DoC hard-copy information sheet