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Forest Vines to Snow Tussocks: The Story of New Zealand Plants

Linear Succession (Climax)

Linear Succession (Climax) (Fig. 64)

A postulated sequence63,64,65 which leads to the present forests, with their overstorey of scattered podocarps and canopy of flowering trees, is as follows:

Where the previous forest cover is completely removed by such agents as volcanism or fire, the first coloniser is bracken fern (Pteridium
Figure 64 Diagrams illustrating linear and cyclic forest successions. (Reproduced with permission from To Save a Forest—Whirinaki.)

Figure 64 Diagrams illustrating linear and cyclic forest successions. (Reproduced with permission from To Save a Forest—Whirinaki.)

page 107esculentum) followed in order by two small-leaved light demanding species — the shrub manuka (Leptospermum scoparium) and the small tree kanuka (Kunzea ericoides)

Within this association, broader-leaved shrubs and small trees establish, including five-finger (Pseudopanax arboreus), lancewood (P. crassifolius)Coprosma lucida, Pittosporum tenuifolium, juvenile rewa rewa (Knightia excelsa), juvenile kamahi (Weinmannia racemosa), and in moister places the tree ferns mamaku (Cyathea medullaris) and ponga (C. dealbata), mahoe (Melicytus ramiflorus), wineberry (Aristotelia serrata), tree fuchsia (F. excorticata) and pate (Schefflera digitata).

When these broad-leaved plants form a canopy the bracken, manuka and kanuka gradually die out as the light falls below the level required for their continued recruitment. It is at this stage, about 50 years from the beginning of the sequence, when the forest floor is sheltered but still quite well-lit, that the podocarp conifers become established. After a further 50 years or so the podocarps begin to grow above the broadleaf canopy and by the time they form a higher stratum themselves, the lower layer of flowering trees is now dominated by kamahi (Weinmannia racemosa), often initially epiphytic on the ponga tree fern, with scattered rewa rewas (Knightia excelsa), hinau (Elaeocarpus dentatus) and maire (Nestegis cunninghamii and N. lanceolata).

Finally, shade-demanding species enter and tawa (Beilschmiedia tawa) largely replaces kamahi in the forest canopy. The forest floor is now strongly shaded and the podocarps, light-demanding to varying degrees, no longer establish. The podocarp trees which are already present, often in combination with epiphytic northern ratas (Metrosideros robusta), gradually die out and the climax, according to this hypothesis, is a forest with the canopy dominated by tawa and without emergents. The tawa and other shade-demanding species are able to maintain themselves indefinitely until some catastrophic event destroys the forest to initiate a new succession.