TANE 29, 1983

FOREST AND SCRUBLAND ZONES OF THE WAITAKERE RANGE, AUCKLAND

by A. E. Esler Botany Division, DSIR, Private Bag, Auckland

SUMMARY

For nearly a century the forests of the Waitakere Range were subjected to the destructive influences of timber milling, burning and clearing for farming. Resulting zones of forest and scrubland are mapped and explained.

THE PAST

The nature of the vegetation of the Waitakere Range before milling began in earnest in the middle of last century is undocumented. The coastal fringe had been influenced by Maori occupation but elsewhere the land was "entirely covered with luxuriant forest" (Cheeseman 1872).

Forest dominants Accounts of the milling industry (e. g. Diamond and Hayward 1980) indicate that large quantities of kauri (Agathis australis) grew in the region, and many photographs show kauri logs of moderate size not comparing with gigantic logs hauled from some other kauri forests. Kauri was widely distributed rather than in separate pockets of . Cheeseman listed kauri, kahikatea (Podocarpus dacrydioides) and rimu () as the species extensively milled, totara (P. totara) and matai (P. spicatus) as being milled "to a small degree". However, it seems certain that puriri (Vitex lucens) was removed, and also miro (P. ferrugineus) which was probably a more abundant species than matai. Northern rata () was mostly left standing. Many have persisted and indicate a moderate population of this species, and a general distribution. Cheeseman asserted that tawa ( tawa) "... probably forms three-fifths of the forest". It is now in fairly low numbers in spite of being logged lightly if at all, and also a potential to regenerate if felled. I believe that Cheeseman may have over-estimated its significance. My concept of the early vegetation is of a kauri-northern rata-rimu forest over most of the range, kauri being aggregated in some parts and in others interspersed with rimu and northern rata, these 3 species far outnumbering totara, Hall's totara (P. hallii), miro, matai and tawa. Local conditions may have favoured kahikatea (saddles, terraces and wet slopes), taraire (B. tarairi) and (Dysoxylum spectabile)

109 (gullies) in quite large numbers, and some pukatea (Laurelia novae• zelandiae) (stream margins). The mapou, (Myrsine australis), rewarewa ( excelsa), and kohuhu (Pittosporum tenuifolium) that Cheeseman regarded as common, and tanekaha (Phyllocladus trichomanoides), may have been principally in secondary forest induced by local catastrophes; likewise also perhaps hinau () and mangeao (Litsea calicaris).

Forest patterns The patterns of forest vegetation in the Waitakere Range were probably not distinct, there being no major geological discontinuities or effective altitudinal variations. Undoubtedly there were aggregations of kauri, but not necessarily on ridges as is commonly supposed. In some places the versatile rimu may have been in high concentrations, but totara, matai and miro were not plentiful enough to characterise any forest stands. Kahikatea, which Cheeseman surprisingly placed among the three important timber species, normally reaches its fullest development on wet alluvial soils. It most likely occurred near mouths of streams and was near to many of the mills. The distribution of tawa and taraire is unknown but tawa was plentiful enough to receive special mention by Cheeseman. It is strange that taraire, a component of kauri forest at Waipoua and other places, and plentiful in remnants north and south of Auckland, was a minor component.

Successional status There is a temptation to regard whatever vegetation patterns that had developed as the end point of sorting of species to match local habitats over thousands of years. This succession had not reached the hypothetical natural stable end point - the "climax". The land had not undergone any major geological change for thousands of years but the vegetation could have been influenced by early Maori fires to induce kauri dominance within the last 1 000 years. The kauri remnants today, though perhaps not typical, give no indication of perpetuation of kauri. Where mature kauri trees have toppled in recent decades, broad-leaved species have given kauri seedlings little opportunity to replace the fallen trees. Removal of kauri by logging may have simply replaced the slow natural phasing out of kauri.

Forest destruction The man-made catastrophes that befell the early forests were variable in nature and degree but the sources of seeds and spores remained and everywhere the environment favoured the return of forest. This tendency for regeneration, and infertility and adverse topography for farming have maintained native vegetation on just about all parts of the

110 CONSPECTUS OF VEGETATION CHANGES

Fig. 1. Conspectus of vegetation changes in the Waitakere Range.

Ill Waitakere Range. The preoccupation of the loggers for about a century from the 1840s was the extraction of millable logs of favoured timber trees. Because the value of the land was primarily in the timber it could immediately yield there was little regard for matters which concern conservationists today. Pit sawing of trees near at hand gave way to mass conveyance of logs by gravity to established mills when the demand for timber increased. Logs reached the streams by bullock tracks, chutes and rolling roads, and driving dams were used to flush them down the streams to holding dams. Tramways carried logs and sawn timber out of the range. In the process of felling and transport much vegetation was damaged. At a later period logs were dragged by haulers to ridge tops and conveyed to collection points by bullocks or heavy machinery. Trees previously considered to be unsuitable for milling were harvested during a second or third logging. Fire has made a strong impression on the vegetation. Some fires were accidental and destroyed the forest ahead of the loggers. Fires in cut- over forest, whether deliberate or accidental, were fuelled by forest debris, particularly the resinous kauri crowns. The use of fire to clear land for farming is detailed by Levy (1949). Burning continued while pasture was being developed to destroy stumps and secondary growth of tea (manuka, Leptospermum scoparium and kanuka, L. ericoides). Fire alone was inadequate to keep tea tree under control on these infertile soils in a high rainfall area. Repeated burns gave only a temporary clearance. Most of the farmland was eventually abandoned to the tea tree, some of which was harvested for firewood. The human influences on the original vegetation are summarised in Fig. 1. Complexity was added to the vegetation pattern by multiple burning of scrubland, cut-over and standing forest. Burning is the main factor determining present day patterns. Comment on Maori influences Vegetation influenced by Maori activities could not be identified by the methods used in this survey. J. Beever, from her examination of early survey plans, and J. T. Diamond and B. W. Hayward, from archaeological evidence, have indicated to me the general regions not supporting primary forest at the time of European settlement. It seems that the Maori influence was extensive along the west coast (and extended inland a kilometre or more in some places) in areas mapped here as cut-over and Maori-influenced vegetation without tall trees, and as tea tree scrubland. Vegetation near and on the Cornwallis peninsula appears to have been similarly affected. THE PRESENT Unmilled and lightly milled forest Only a small part of the present day Waitakere vegetation is not

112 markedly modified by past felling or burning (see Fig. 2). Kauri Grove Track in the Kitekite Valley runs through a stand of kauri set aside as a private reserve when forest around it was being cleared. The Cascade

Fig. 2. Vegetation zones of the Waitakere Range.

113 Park kauris in the Waitakere catchment were destined to provide about five million super feet of timber before being acquired from the Kauri Timber Company jointly by Auckland City Council and the Crown in 1926. Some dead trees were removed at that time. The largest block with a substantial amount of large kauri lies east of the Huia Stream near the lower dam. It is unclear why this was not completely logged. Over the ridge to the east a block of kauri forest was separated by rough terrain from the mill in the upper Nihotupu and may not have been accessible from the lower reaches. These relic stands may not be the same as the early Waitakere forest but they have the general features of kauri in other districts, except that average trunk diameters may be a little smaller. The stoutest known existing kauri in the Waitakeres grows near the lower Huia dam. It has a trunk diameter of 2. 86 m, is 7 m to the first branch and about 14 m to the second. Some larger trees have been known especially in the upper Nihotupu Valley. Trees 1-2 m in diameter occur in these remnants - about the size of most logs shown in photographs of the milling operations. Kauri trees are close together in some places, and in others interspersed with rimu, miro, totara and northern rata. Unlike Trounson and Waipoua forests there is no low canopy of tawa and taraire between the widely-spaced kauri trees. There are the usual kauri associates - kauri grass {Astelia trinervia), toru (Toronia toru), neinei (Dracophyllum latifolium) and korokio (Corokia buddleioides) but many other species also occur, particularly in the Cascades Park. Here the dominating influence of kauri does not prevail because irregular terrain, past logging operations and Phytophthora (Podger and Newhook 1971) have had an influence.

Cut-over forest Changes in the forest flora following milling were minor but changes in the structure (the way the are arrayed in space) were gross (see diagram). Some of the species were secondary forest plants growing in the light pools created by fallen trees, on banks of streams, on bluffs and on the landslides. This cut-over forest lacks the majestic trees of the undamaged forest but is still an attractive feature of the landscape with its tall northern ratas standing high above an uneven cover of shorter plants. With the ratas are smaller quantities of tawa, rewarewa and the timber trees (mainly rimu) not meeting the miller's standards. The distinctive feature of the canopy is the variety of crown shapes and shades of green. Among the components of the tall shrub layer are pigeonwood (Hedycarya arborea), mahoe (Melicytus ramiflorus), heketara (Olearia rani), kohuhu, mapou, species of Coprosma, tree ferns and nikau palms (Rhopalostylis sapida). The climbers, supplejack (Ripogonum scandens)

114 and kiekie ( banksii), are abundant and together with Gahnia make some cut-over forests very difficult to penetrate. It is forty to one hundred years since these forests were significantly disturbed. In some places it is still not clear which species will eventually dominate. In the older stands rimu is well established and pushing its way through a canopy which casts too much shade for kauri seedlings to endure. Kohekohe would almost certainly become a prominent species but the plants are seriously damaged by opossums before the saplings reach the canopy. The diagnostic feature of this vegetation is the preponderance of secondary forest species with scattered tall emergent trees (mainly northern rata). Vegetation of this kind lies in a broad central belt stretching from the upper Karamatura Valley to the Waitakere catchment with an extension down the eastern slopes of the Range in the region of Opanuku Rd and West Coast Rd. It is mostly on rugged terrain unsuited to farming.

Cut-over and burnt forest The distinguishing feature of this vegetation is the absence of relic emergent northern rata and rimu over a low forest of broadleaved species. A burn after milling would have varied in intensity according to the length of time since milling, the kind of vegetation, the season, the weather, and the topography. It is likely that in conditions most favourable for a fire, no area would have been completely bared, though a very fierce fire would be carried on a dry ridge top, particularly if kauri crowns were present. The gullies would have been least affected. In most places there would have been some recovery from sprouting stumps and germination of buried seeds and seeds carried in from surrounding vegetation. Some species that survived the logging may have been eliminated but a total change of vegetation may have occurred only locally. All tall trees left by the millers would have been killed by the heat but not consumed by the fire. Tree ferns with their ability to resprout may have provided the first tinges of green on the blackened landscape. These are now a fairly prominent feature of this vegetation, some colonies maintaining a firm hold by inhibiting seedlings of competitors by means of a litter of dead fronds. Nikau palms with a single vulnerable bud could tolerate only light fires but they later found congenial habitats for re-establishment on moist concave slopes and along streams. Many species make up the low irregular canopy of these secondary forests but chief among them are pigeonwood, mahoe, heketara, kohuhu, mapou, species of Coprosma, tree ferns and nikau palms. The largest tract of this forest is in the headwaters of streams flowing to the west coast. This is linked by a neck of forest across the range on

115 the north side of West Coast Rd and reaching the heads of streams flowing to the east. At the southern end of the Waitakere Range this vegetation is interspersed with blocks of tea tree.

Tea tree scrubland Only the most destructive fires bared the ground sufficiently for the small-seeded pioneers manuka and kanuka to establish. These species probably became important after repeated fires and where farmland had been developed (Esler and Astridge 1974). Invasion by these species would have been hampered initially by lack of local seed sources. Once established, manuka particularly would have been promoted by each successive fire. Kanuka seeds are borne on the branches for a shorter time and are also more vulnerable to destruction by fire. It is usual, for kanuka to eventually prevail over manuka in most places either by prior occupation or competitive replacement, the kanuka being longer lived, taller and possibly more shade resistant in its early life. On the least hospitable sites manuka dominance is shared with small amounts of mingimingi {Cyathodes fasciculata) and akepiro {Olearia furfuracea). For a time while the canopy is closed there is insufficient light reaching the ground to encourage any undergrowth. Later Blechnum capense, Dianella and Gahnia setifolia increase and a shrub layer of hangehange {Geniostoma ligustrifolium), Coprosma arborea, C. lucida and silver tree fern (Cyathea dealbata) develop. Kauri, rimu and tanekaha are now evident as emergents in the older stands. Some kauri established in manuka and had only a little way to grow to reach full light. Mostly, however, kauri entered kanuka stands and flourished where the light was sufficient. It seems that favourable conditions for entry of kauri have not been continuous in time or space. Reliance on wind for seed dispersal into large tracts of tea tree remote from sources of seed may account for fewer rickers than would be expected in some areas. The dense kauri ricker stands which cap many spurs require some comment. Although they occupy relatively small areas their prominent position on spurs has given the impression that these are characteristic kauri sites. It is possible that these rickers could have established after kauri logging without encouragement from fire and tea tree, as there is less suppression by the broad-leaved species than in moister habitats. Rimu invades kanuka stands continuously from the time they approach maturity. It tolerates shading and is able to respond to better illumination as the canopy opens or is breached by the rimu crown. This species is not as conspicuous as kauri at present but is more versatile. Its ability to grow in cut-over forest gives it a territorial advantage over kauri. Tanekaha is a minor feature of secondary forest developing after tea tree and was probably of little significance in the undisturbed forests of

116 the past. It grows with kauri rickers mainly. A significant diversion of the succession is from tea tree to communities of Coprosma arborea up to 15 m tall. The outcome is not clear because few other plants grow beneath the dense canopy. The distribution of tea tree stands coincides fairly closely with areas which J. T. Diamond (see Esler and Astridge 1974) considered to have been farmed, or burnt over by gum diggers. Most of it is within 3 km of the coast. Discontinuity is caused mainly by intervening valleys with secondary forest. Inland stands of tea tree are mostly on ridge tops.

THE FUTURE

Much of the Waitakere Range is covered by the 15 000 hectares of Centennial Memorial Park and water catchments. Its vegetation has some degree of protection from the direct harmful influences of man but fires will occur, and opossums will continue to be the prime animal pest. Natural changes in some communities are quite rapid but the mosaic of vegetation patterns induced by the uncontrolled quest for timber and subsequent management of the land will persist into next century and the century beyond.

ACKNOWLEDGEMENTS

I am grateful for the assistance of J. Beever, R. E. Beever, W. J. Beveridge, J. T. Diamond, B. W. Hayward, E. D. Hatch and P. Wardle. I was fortunate in being able to spend much time in the field with the late A. D. Mead.

REFERENCES

Levy, E. B. 1949: The conversion of rain forest to grassland in . Tuatara 2: 37-51. Diamond, J. T. & Hayward, B. W. 1980: "Waitakere Kauri. A Pictorial History of the Kauri Timber Industry in the Waitakere Ranges, West Auckland. " The Lodestar Press, Auckland. 48 p. Cheeseman, T. F. 1872: On the botany of the Titirangi district of the Province of Auckland. Transactions of the New Zealand Institute 4: 270-284. Esler, A. E. & Astridge, S. J. 1974: Tea tree (Leptospermum) communities of the Waitakere Range, Auckland, New Zealand. New Zealand Journal of Botany 12: 485-501. Podger, F. D. & Newhook. F. J. 1971: Phytophthora cinnamomi in indigenous communities in New Zealand. New Zealand Journal of Botany 9: 625-38.

GEOLOGY

117 8TI