R. B. a Plant Communities of the Steepland Conifer- Broadleaved Hardwood Forests of Central Westland, South Island, New Zealand
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Sonderdrucke aus der Albert-Ludwigs-Universität Freiburg ALBERT REIF R. B. ALLEN Plant Communities of the Steepland Conifer- Broadleaved Hardwood Forests of Central Westland, South Island, New Zealand Originalbeitrag erschienen in: Phytocoenologia 16 (1988), S. 145 - 224 Phytocoenologia 16 (2) 145-224 Stuttgart-Braunschweig, May 18, 1988 Plant communities of the steepland conifer-broadleaved hardwood forests of central Westland, South Island, New Zealand by A. REIF, Bayreuth, and R. B. ALLEN, Christchurch with 8 photos, 20 figures and 5 tables Abstract. This paper presents a phytosociological classification of the conifer-broadleaved hardwood forests in central Westland, South Island, New Zealand. The analysis was made using the BRAUN-BLANQUET approach. Because this approach has rarely been applied in New Zealand, syntaxa were not named using BRAUN-BLANQUET nomenclature. The following community groups and communities were distinguished: 1. The Melicytus ramiflorus community group contained shrubland and low statured forest (c. 4-12 m tall) on disturbed sites up to c. 750 m altitude: — The Melicytus ramiflorus — Carpodetus serratus community (A) was frequently found on lower faces, on terraces, in gullies, and in canopy gaps. Soils were recent to weakly de- veloped and contained fine earth. Most relevēs were from schist and greywacke areas. — The Coriaria arborea community (B) was sampled in a few schist areas adjacent to streams. 2. The Prumnopitys ferruginea community group contained 3 communities: — The Dacrycarpus dacrydioides community (C) was c. 20-30 m tall forest. It occurred locally on poorly drained sites, usually terraces, up to c. 300 m a.s.l. (above sea level). — The Dacrydium cupressinum community (D) was c. 15-30 m tall forest. It was found on sites up to c. 600 m a.s.l., on stable ridges, upper faces, and terraces. This community was most frequent in granite areas. — The Prumnopitys ferruginea — Coprosma lucida community (E) was c. 15-25 m tall forest. It was found frequently in schist and greywacke areas up to c. 750 m, mainly on ridges and upper slopes of faces; it was infrequent in granite areas. 3. The Hoheria glabrata community group contained 2 communities: — The Hoheria glabrata community (F) (canopy c. 5-10 m tall) occurred on disturbed sites, often in gullies and on lower faces. It was found above c. 600 m. It was infrequent in granite areas. — The Plagianthus betulinus community (G) was a low statured (10-12 m tall) forest. It was found locally on silty alluvial river terraces subject to cold air drainage. 4. The Libocedrus bidwillii community group contained 2 communities: — The Libocedrus bidwillii — Myrsine divaricata community (H) was c. 10-25 m tall forest. It was found frequently between c. 650 and 850 m. — The Dracophyllum traversii community (I) was stunted forest and shrubland (canopy between c. 5 and 15 m). It was encountered frequently between c. 850 and 1200 m, mainly on stable sites (ridges and upper faces). 5. The Halocarpus biformis community group contained the — Halocarpus biformis — Gahnia procera community (J) and was mostly stunted forest and shrubland (canopy c. 1-8 m). It was found locally on stable sites with developed soils. 6. The Hebe salicifolia community group contained 2 communities occurring at all alti- tudes. Both communities were seral vegetation often establishing on primary sites: 10 Phytocoenologia 16 0340-269X/88/0016-0145 $ 20.00 0 1988 Gebrüder Borntraeger, D-1000 Berlin • D-7000 Stuttgart 146 A. Reif R.B. Allen — The Raoulia tenuicaulis community (K) was an open community with low ground cover dominated by small herbs. Most frequently it was found on river terraces. — The Hebe salicifolia community (L) was dominated by herbs and small shrubs (up to c. 2 m tall). It was found mainly on rocky sites in schist and greywacke areas. Using 28 species groups, further partitions could be made to 43 "sub-units", including subdivisions, types and subtypes. The floristic relationships of the community types were transformed into a hierarchical arrangement. Variation in species composition was dominantly related to altitude, and disturbance resulting in soil differences. Different frequencies of disturbance can be related to landscape stability and topographic position: In schist areas, disturbances of soil and vegetation were frequent, and low-statured seral communities and tall forests frequently were found in a small-scale vegetation pattern. In granite areas, the canopy is more uniform, with few areas of seral vegetation. These large-scale differences in landscape stability and vegetation can be related to different intensities of canopy mortality. Mortality of canopy trees is higher in schist areas than in granite areas. This may be a con- sequence of differential browse pressure by introduced brush-tailed possums (Trichosurus vulpecula Kerr.). 1. Introduction 1.1. General introduction The New Zealand indigenous forests now cover c. 23% of the country's 270000 km2 area (P. WARDLE et al. 1983). When the first Maori migrants arrived about A.D. 950 (DUFF 1950), forest covered most of New Zealand (MASTERS et al. 1957). During the next 900 years, the indigenous forests were reduced to perhaps half their original area (CAMERON 1962). The Maori population initiated fires which destroyed large areas of forest, mainly in the drier regions (CUMBERLAND 1962; HOLLOWAY 1954). Over the period 1850 to 1950 European settlers removed about half of the remaining forests (CAMERON 1962). The remaining indigenous forests are found mainly in mountainous areas. There is currently little direct anthropogenic influence within these forests. However, most have been, and con- tinue to be, modified by introduced browsing animals (P. WARDLE et al. 1983; J. WARDLE 1984). The indigenous forests fall into two broad categories; beech and conifer-broad- leaved hardwood forests. These are composed of four major physiognomic ele- ments; beeches (Nothofagus species), broadleaved hardwoods (hardwoods other than beeches), kauril (Agathis australis) and conifers other than kauri (COCKAYNE 1928; McKELVEY NICHOLLS 1957). Beech forest dominated by pure beech in the canopy constitutes 46 % of the forested area, and 22 % is made up of forest dominated by mixtures of beeches, conifers, and broadleaved hardwood species (J. WARDLE 1984). The remaining 32 % of forest is dominated by conifer and broadleaved hardwood species. Conifer-broadleaved hardwood forests usually occur in areas with high rain- fall (up to 12 000 mm per year) and mild climates (P. WARDLE et al. 1983). These areas tend to be in western and northern parts of the country (NEW ZEA- LAND FOREST SERVICE 1984). These forests usually have a more complex struc- Nomenclature of generic and common species names in Appendix 1 Steepland conifer-broadleaved hardwood forests of central Westland 147 ture than beech forests, and have affinities with the structure of tropical rainforest, often containing lianes and epiphytic plants (DANSEREAU 1964). By calling the forests "subtropical rainforest", COCKAYNE (1928) recognised these affinities. As latitude increases, the number of species making up the forests seems to de- crease (P. WARDLE 1975,1980c). Canopy tree species and epiphytes in particular decrease in numbers. Species composition also varies with altitude. The conifer-broadleaved hard- wood forests of central Westland represent the general pattern. In this region the dominant canopy hardwood species include southern rata (Metrosideros umbel- lata), kamahi (Weinmannia racemosa), and Quintinia acutifolia. At lower altitudes (< 600 m a.s.l.) these species are associated with the conifers miro (Prumnopitys ferruginea) and rimu (Dacrydium cupressinum; FRANKLIN 1968). Dacrycarpus dacrydioides and Prumnopitys taxifolia are prominent at lower altitudes on fertile, often alluvial, sites. At higher altitudes (> 800 m) these hardwood species occur with the conifers Libocedrus bidwillii and Halls totara (Podocarpus hallii) (COCKAYNE 1928; P. WARDLE 1977). At altitudes above c. 1000 m, conifer- broadleaved hardwood forest gives way to a wide belt of subalpine shrubland dominated by Dracophyllum spp., Halocarpus spp. and the composites (Senecio spp., Olearia spp.), before grading into tussock grassland dominated by Chio- nochloa spp. (EVANS 1970; BURROWS 1977 b; P. WARDLE 1977). Within any altitudinal band, variations in species composition reflect different environmental factors, such as geological substrate (J. WARDLE 1974), geomor- phic processes (P. WARDLE 1977, 1980a), and variation in soil development (CUTLER 1960; P. WARDLE 1977). All these factors are interrelated. In central Westland, forest patterns reflect site history, and often cannot be related in an obvious way to existing environmental conditions (P. WARDLE 1964). The removal of forests by glaciation and the subsequent slow immigration by beech have been used to explain the absence of beech and dominance of faster migrating conifer-broadleaved hardwood forest species (COCKAYNE 1928; WIL- LETT 1950). On a local scale factors such as high natural erosion rates (CUTLER 1962), high rainfall intensities and strong winds result in frequent disturbance. Relationships have been drawn between disturbance and the maintenance of canopy species (e.g., HUTCHINSON 1928; P. WARDLE 1980a). Some authors have related discontinuous size (age) distributions of species to recent climatic change (HOLLOWAY 1954; P. WARDLE 1978 a), but these may also be significant- ly influenced by disturbances such as windthrow and