Ecology of East Harbour Regional Park
Plants growing in East Harbour Regional Park, 1984 (source) [The forest is now 40 years older so many gorse scrub areas have given way to kanuka and manuka, and broadleaf plants]
Topographical map of Eastbourne (Topo Maps)
The Ancestral Forest
In the poor clay soils of Wellington's eastern hills a forest of black and hard beech grows from the shore of Eastbourne, sweeping up over the hills and across into Wainuiomata. It belongs to a forest that grew here over 3 million years ago; a forest of kauri and tropical beeches flourishing in the warmer climates of the time, only to be replaced with subalpine plants when an ice age settled in 2.5million to 30,000 years ago. Eventually after swinging between glacial and subtropical conditions, the earth warmed to present conditions 4,000 years ago.
In Wellington's Living Cloak (1993), Isobel Gabites describes the Hutt Valley 4,000 years ago as more tropical than today, with forests of 'matai, pukatea and a great many fern species' and the Wainuiomata Valley swamp filled with 'rimu, miro, matai and totara'. Cooler and drier conditions from 2,500 years ago to present favoured the beech forest that grows today in the East Harbour Regional Park.
Describing the Ancestral Cloak covering Wellington's land, Gabites offers detailed insights into the growth pattern of Eastbourne's beech forest that only an avid walker and botanist can. Her book allows me understand the ever-changing dimensions of this forest that I have walked through over the last 3 decades, as well as an appreciation of the plants that grow here. I was especially intrigued to learn the top of the subalpine forest's treeline 20,000 years ago was at today's sea level, pretty much the view from my front door! Hard to believe there is so much tectonic and climate disruption in the place where I live.
I have copied excerpts from the book to use in my exegesis as it is so detailed and rich in botanical knowledge. I'm not sure if this is okay despite reference to 'fair dealing for the purpose of private study and research as permitted under the Copyright Act' on the inside cover?....
Wellington's Living Cloak: A Guide to the Natural Plant Communities by Isobel Gabites, 1993. Chapter 4 (pp 65-72)
Hard and Black Beech Forest - "Soil fertility is markedly different on either side of the Wellington faultline. The soils to the east are older, clay-rich, leached of nutrients, and acidic. Yet beech is in its element. Only mountain beech is absent from Wellington; historically, hard, black, silver and red beech have formed forests from the sea of the bushline on these poorer soils."
"Hard beech is particularly well suited to infertile soil. It forms the main forests on the low hills around eastern Wellington, on old river terraces and fans, and reaches higher altitudes in the southern Tararua Range.
Black beech, a small-leaved tree resistant to drought and salt-laden winds but not quite so tolerant of infertile soils, favours dry sites with shallow, rocky soils which will be slightly more fertile. It grows in such places within hard beech forests on the lower hillslopes east of the harbour, and also throughout the southern Taraua Range and the Rimutaka Range. Yet black beech is an enigmatic tree; like manuka, it has the ability ti grow either in dry, rocky soild or in waterlogged soils.
Stark stands of blackened beech trunks on spurs above the Eastbourne bays are evocative of primeval images - all the more startling for being on the doorstep of a city. No wonder last century harbour ferries were laden with Wellingtonians escaping the brash, bleak city for a picnic at Eastbourne. Whereas the windswept hills around Wellington had been denuded, the eastern hills offered a different mood. An additional attraction was that beech forest offered easy access with glimpses of the harbour through its open understoreys, unlike the dense podocarp forests that remained in the Karori hills of the Hutt Valley.
In 1840 William Wakefield's surveyors had divided the beech-clad eastern hills into blacks of 93-130 acres. Attempts to farm the steep hillsides failed; most ended up as government reserves.
Road access, possible after the 1855 earthquake uplifted the Eastbourne coastline, encouraged residential subdivision and by 1879 real estate advertisements were appearing that prompted the attractive bush settings. In truth the forest had been peeled back to the skyline in many bays, and home builders found themselves clearing regenerating scrub and gorse. By the 1920s \, repeated fires had caused gorse to become a real menace.
Without gorse, regeneration after a fire in hard beech commonly begins with manuka. The woody seed capsules are resistant to burning but split in the heat, releasing thousands of light seed, easily dispersed by wind. Initial manuka growth is dense, but self-thinning. After 20 years or so, understorey plants can penetrate the thicket. About 40years after establishment the plants are weakening; light filtering through the thinning canopy allows ferns and understorey layers to develop. Fivefinger, mahoe, rangiora, hangehange, lemonwood, koromiko and coprosmas have a toehold.
After 40 to 60 years manuka is overtopped by this low forest of broadleaved species, which now includes kamahi, rewarewa and pigeonwood. Once overtopped, manuka quickly rots and will not regenerate as it is a light-demanding plant. Rangiora is also eliminated after 50 years or so of being shaded by taller broadleaved species.
Long-lived, shade-tolerant species can occupy sites for long periods, as their seedlings can establish under their own cover. The species are perpetuated, creating a stable vegetation. At this stage it would be hard to tell whether the secondary bush was replacing a previous broadleaved forest or a beech forest, as beech will only re-establish if some mature trees are nearby to provide seed. The presence of shining karamu, mingmingi and prickly mingimingi provide the clue: they are usually associated with beech forest.
Where regrowth has been subjected to repeated fires, gorse has become the new coloniser. Gorse has the ability to increase nitrogen levels in the soil, which means ir can grow on the infertile soils formerly colonised by manuka. Along with bracken and kamahi, gorse is capable of resprouting afte fire and can oust manuka which depends on seeds for re-establishment
In any case, gorse seeds have a long viability in the soil (up to 60 years) and after a fire there is prolific germination. These is no shortage of seeds: one study showed concentrations of up to 14 million seeds per hectare.
Scrub develops faster with gorse than under manuka because of gorse's lower stature and shorter life span. A forest of fivefinger and kamahi can completely replace gorse in 40 years. The thick leaflitter under gorse also provides an excellent nursery for seedlings, so gorse has gradually gained acceptance as an agent in 'natural' regeneration.
The litter layer and the abundance of dead branches on older plants unfortunately also provide a ready fuel for fires. Further burning of Wellington's hillsides merely ensures the dominance of gorse and spreads it further into new territory.
With a knowledge of growth rates and the recognisable phases of regeneration after clearance, a visitor can estimate ages of scrub, bush and forest areas along the Eastbourne hillsides.
For example, the Kowhai Street track to Butterfly Creek winds up through a scrubland of manuka, kanuka, scattered gorse and a dense mix of fivefinger, mahoe, koromiko, coprosma, lemonwood, rangiora and hangehange. All are about the same height - low enough for good views across the harbour from the track. This section of the ridge had been psature until the 1950s, and the low density of gorse confirms this is the first regrowth since the initial (pre-gorse) burning last century. When our children are our age their views will be blocked by mature bush.
The shallowest, and therefore the driest, soils support a mature forest of black beech and northern rata. There are some superb stands of black beech in Lowry Bay Scenic Reserve where the ground is covered with orchids - Dendrobium cunninghamii, strongly scented Earina autumnalis and some E. mucronata. These usually epiphytic orchids have found just the conditions they like: good drainage but without the threat of prolonged drought.
After fire in black beech forest, kanuka, shining karamu and mingimingi are common in the regenerating scrub; kanuka in preference to manuka because it grows better in the slightly more fertile conditions offered by the shallow clay compared to deep, very weathered clays. Kanuka is relatively uncommon as a colonising species on the eastern soils but it is present in the Eastbourne hills. It is much slower to be replaced than manuka, living 80 years or more on black beech sites. One 125-year-old kanuka has been recorded in Lowry Bay.
Within minutes of the carpark in Williams Park in Days Bay, you can stroll through examples of each of these forest types. As the short track winds up from the duckpond to Korimako Road, it leads you up a gully and onto the sides of a spur.
In the steep-sided gully a dense broadleaved forest forms an arch over your head, but as the slope shallows slightly, hard beech forest becomes evident with rewarewa sharing the canopy. Beneath this, a layer of understorey shrubs includes mingimingi, small and large leaved coprosmas, heketara, hangehange, Neomyrtus pedunculata, ponga and fivefinger.
As you break out onto the spur itself, suddenly the undergrowth disappears and views of the sea can be glimpsed through the clean-trunked black beech stand. A cutting exposes the root system of a beech, revealing the pale, leached clay soil of the spur. There is typically sparse shrubbery of drought tolerant plants such as mingmingi, Coprosma microcarpa, C. rhamnoides, shining karamu, juvenile tree ferns and juvenile rimu, which is often found with black beech. A carpetland of lichens, sedges and orchids is heavily littered with tiny black beech leaves. Of all the delicate textures of the black beech forest, the indigo-berried lily turutu found here must be the daintiest.
If you were to climb up further from Williams Park onto the ridge you would find an unusual forest of beech and northern rata. Here rata is terrestrial, unrestricted to sprawling shrubs on rocky outcrops. The ridge-line track spans the length of Eastbourne, with access tracks from all the bays. By far the most popular walk in the area, however, is to Butterfly Creek. This is a delightful streamside picnic area in the valley immediately behind the hills of Eastbourne township.
Four different access tracks lead the walker up through various ages of secondary growth and from the ridgetop down the other side through a forest of hard and black beech that grows on lichen-encrusted clay banks dappled with kidney fern and hound's tongue, easter orchids and fine-leaved hook sedges. The sparse undergrowth of small leaved coprosmas includes Coprosma crassifoloa, its tiny felted leaves sparingly arranged on divaricating twigs. Towards the valley floor the moister, detrital soils support three ferns, nikau, luxuriant kiekie and supplejack, kaikomako, mahoe and fivefinger.
One of the seasonal pleasures of walking in beech forest is the profusion of fungi to be seen after autumnal rains. All our forest trees harbour mycorrhizal fungi of different types within their roots and beech forests are rich in these associations. The fungi help nourish the trees and in exchange they receive carbohydrates.
Some of the showiest of the beech forest fungi are the Hygrophorus group, but a walk through pines on the Town Belt of the Eastbourne hills will no doubt uncover the rival scarlet caps of Amanita muscaria, trailing off in the direction of their host's roots. There too will be the Suillus granulatus with its slimy brown cap and yellow spongy tissue instead of gills."
Native Plants of the Eastbourne Hills: Status and Conservation Management was published in 2005 by John Sawyer, Biodiversity Conservation Officer Wellington Conservancy. It is a comprehensive summary of the plants, mosses and fungi growing in the hills. their significance and conservation management.