The Scientific Reserves of Auckland University. I
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TANE 29, 1983 THE SCIENTIFIC RESERVES OF AUCKLAND UNIVERSITY. I. GENERAL INTRODUCTION TO THEIR HISTORY, VEGETATION, CLIMATE AND SOILS by G. M. Thomas and J. Ogden Department of Botany, University of Auckland, Private Bag, Auckland SUMMARY The University reserves at Swanson, Huapai, Oratia, Anawhata and Leigh are described and mapped. An introduction to the history of each reserve is followed by a brief outline of the main sources of information relevant to the climate, geography and soils of the area. Topography and vegetation cover are related, and the latter is described in more detail. INTRODUCTION The University of Auckland owns or administers a number of scientific reserves, four of which are located in the Waitakere Ranges, west of Auckland City (Fig. 1). The reserves at Swanson, Huapai, and Oratia are examples of kauri (Agathis australis) dominated forest in various stages of regeneration from Leptospermum scrub, with small areas of mature forest. At each the forest canopy also contains podocarp and broadleaf components. At Anawhata and Leigh the reserves also include Leptospermum scrub, but are characterised by regenerating coastal forest with pohutukawa (Metrosideros excelsa) and puriri (Vitex lucens), and a small "ricker" kauri stand at Leigh. In this account the first three reserves (Swanson, Huapai and Oratia) are dealt with in some detail, while the two coastal reserves are briefly covered. This emphasis reflects the amount of ecological research by members of the University staff, Field Club and graduate students which has been carried out in the different areas. Our emphasis is on the vegetation but we have cited the main references dealing with climate and soils. Unreferenced statements are based on the field experience of the authors, or derived from unpublished statements and letters in the files of the University. This paper should be read in conjunction with Ogden (1983 - this volume) which gives more detailed quantitative accounts of the vegetation. SWANSON Swanson State Forest 31 is located 27 km west of Auckland City in the eastern foothills of the Waitakere Ranges near the township of 143 KILOMETRES Fig. 1. Map of the Waitakere Ranges showing the positions of four of the scientific reserves administered by Auckland University. 144 Swanson (Grid reference: Ql 1/497794; NZMS 260 Sheet Qll, Waitakere, 1st Edition, 1979). The property occupies 20. 45 ha on the west side of Tram Valley Road (Fig. 2). This was the first land to become available to the University for use in field studies. It was then Crown land, but was set aside in 1921 for use by the School of Forestry (established in 1924). With the transfer of the school to Canterbury University College in 1931, the control and Fig. 2. Map of the Swanson reserve. 145 management of the forest reverted to the Botany Department of the University on the understanding that an annual report be made to the Forest Service concerning the state of the reserve and its utilisation by the University in the preceding 12 months. Meanwhile, under Professor Corbin's occupation of the Forestry Chair (from 1926) the building which still occupies the site was completed in 1928 from timber donated to the School by local sawmillers. It comprises a large living room, kitchen, and four bunkrooms, each with four bunks. Electricity is not connected. A feature of this building is the handsome fireplace with its splendid mantelpiece cut from an ancient blackened kauri log long-buried in a swamp. The hut is situated at the end of Tram Valley Road, where it is nestled into a stand of kanuka (Leptospermum ericoides). The Swanson Reserve and hut have been the base for much teaching and research in plant ecology and taxonomy. The following theses or project reports deal in total or part with aspects of the vegetation and are available in the Biological Sciences Library of the University of Auckland. Mirams (1951) studied the factors involved in the natural regeneration of kauri. Aspects of kauri growth, particularly those related to light and temperature, were investigated experimentally by Bieleski (1955). A physiological approach was emphasized in the work of nitrogen fixation in forest Utter by Bucha (1975). Germination and early seedling establishment of Leptospermum scrubland were studied by Mohan (1980). West (1980) gives seed collection data from Swanson and compares them with similar data from Tiritiri Matangi Island. She draws conclusions about native forest regeneration generally. Chambers (1952a) presents a detailed quantitative description of the ecology of the bryophytes and lichens at Swanson and some interesting early photographs of the Swanson hut and adjacent area. An artificial key to the vascular plants common in the Swanson area was constructed by Silvester (1963) and is a useful aid to plant identification. CLIMATE The regional climate and weather have been described by Kidson (1950). Rainfall records are kept by the Department of Waterworks of the Auckland City Council and the New Zealand Meteorological Service collects data from Kumeu and Henderson (No. A64861). Mirams (1951) operated a thermohygrograph in the area for 12 months during the period 1948—1950 and collected data on precipitation, temperature and relative humidity for the same years. GEOLOGY AND SOILS The area was initially described by Hochstetter (1864) but Hayward (1976) gives a more detailed account. The Waitakere Ranges are 146 composed essentially of fragmented andesitic volcanic rocks. The Swanson area is classified as Lower Miocene (Pareora Series) Waitemata Subgroup sedimentary rocks. The typical rocks are friable yellowish-brown feldspathic sandstones interbedded with light-grey to bluish-black thinner mudstones often well laminated in character. They contain few determinable fossils other than Foraminifera. The New Zealand Soil Bureau (1968) describes the soils of the Waitakere Ranges as interzonal brown granular clays arising from the underlying andesitic parent material. A more specific description of the soils at the Swanson property is given by Bucha (1975). The topsoils are relatively thin, averaging 10 cm. They are greyish-brown to brown, friable and moderately to strongly granular in structure. The topsoils merge gently into brown to yellowish-brown, firm to compact subsoils with blocky to prismatic structure. The clays of the lower horizons are dense, highly plastic, fairly sticky when wet and very friable when dry. Mirams (1967) gives information on soil pH and moisture content. TOPOGRAPHY AND VEGETATION The landscape at Swanson is dominated by a ridge running from north to south. This ridge is 76. 2 m above sea level at its lowest point and 121. 9 m at its highest. The Swanson Stream flows from north to south at the foot of the slopes and has an average width of 3 m. It is a freshwater stream with a substrate of small boulders and gravel. The ridge and valley sides are covered in kauri-podocarp-hardwood forest typical of the region. The remaining area comprises scrubland (predominantly Leptospermum), abandoned pasture and swamp. The area has been subject to severe disturbance through kauri logging and fire last century and in the early years of this century, and the forest vegetation is largely serai. However, there is no doubt that some of the vegetation survived both axe and fire: a 120 cm diameter kauri on the ridge up which the main track runs has been estimated at 250 years minimum age (from three cores). The vegetation of the area was first described by McKinnon (1930), but his thesis was never deposited in a library, and two maps signed by him appear to be all that remain. The first gives details of topography and the other boundaries of vegetation types and the location of four quadrats within them. Trevarthen (1962) presents a colourful account of the historical background to the vegetation, including logging and fires. The regenerating vegetation was classified on the basis of time since last fire, and maps illustrate the mosaic pattern of communities produced in response to past disturbance and topography. Trevarthen mentions "three distinct types of bush no more than 100 years old - those of the drier ridge tops, those of the valley walls, the mixed bush proper, and 147 finally the facies that fringes the creek or occupies the very deepest and wettest parts of the valleys". This three-fold distinction may still be useful, although recent ordination and classification studies imply a continuous relationship between the different facies. The ridge tops are occupied by stands of young kauri "rickers" with associated kanuka (Leptospermum ericoides) and tanekaha (Phyllocladus trichomanoides). The ricker stands appear to represent a development from areas which regenerated in Leptospermum scrub following the great fires which swept the area in 1840—50. Subsequent less intense ground fires in the ricker have been tentatively dated from fire scars on the kanuka to 1951 and 1955 (Ogden 1983 - this volume). The ridge top facies gives place rapidly to a more diverse assemblage of species on the slopes, with rewarewa (Knightia excelsa) and maire (Nestegis lanceolata) prominent in the canopy and an understorey of tree-ferns, mahoe (Melicytus ramiflorus) and pigeon wood (Hedycarya arborea). The creek side or valley bottom vegetation is characterised by pu tapu ta weta (Carpodetus serratus), nikau palm (Rhopalostylis sapida) some large kanukas, and small shrubby trees (Coprosma australis, Brachyglottis repanda, etc. ). Although all tree ferns are abundant throughout, Cyathea dealbata is most prominent on the ridges, C. medullaris on the slopes and Dicksonia squarrosa in the valley bottoms. The regeneration process at Swanson - the progressive development of Leptospermum and Agathis dominated communities -was given a comprehensive treatment by Mirams (1951, 1957). The physical features of the site were described in detail and some black and white photographs supplement the account of the vegetation. Mirams surveyed kauri size classes in a series of quadrats. A species list based on these quadrats is included in the appendix to his 1951 paper, and includes 71 species of vascular plants (from 31 families) and 25 species of ferns and allied plants.