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 trees. Cheeseman listed kauri, kahikatea (Podocarpus dacrydioides) and rimu (Dacrydium cupressinum) 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 (Metrosideros robusta) was mostly left standing. Many have persisted and indicate a moderate population of this species, and a general distribution. Cheeseman asserted that tawa (Beilschmiedia 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 kohekohe (Dysoxylum spectabile) 109 (gullies) in quite large numbers, and some pukatea (Laurelia novae• zelandiae) (stream margins). The mapou, (Myrsine australis), rewarewa (Knightia 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 (Elaeocarpus dentatus) 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 tree (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 Huia 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 plants 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.