Plant communities of the steep land conifer-broadleaved hardwood forests of central Westland, South Island, New Zealand
Reif, A.; Allen, R. B.
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 developed and contained fine earth. Most relevés 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 Hoberia glabrata community group contained 2 communities: - The Hoberia 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-Gabnia 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 altitudes. Both communities were seral vegetation often establishing on primary sites: - 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 consequence of differential browse pressure by introduced brush-tailed possums (Trichosurus vulpecula Kerr.).