New Zealand Journal of Botany abstracts

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The vascular flora of the DSIR study area lower Orongorongo Valley, Wellington, New Zealand

D. J. CAMPBELL

Ecology Division, DSIR
Private Bag, Lower Hutt, New Zealand

Abstract All vascular plants recorded in the lower Orongorongo Valley DSIR study area (1100 ha) are listed with notes on their status and distribution. Of the 501 taxa, 355 are native, 128 are naturalised, and 18 have probably been delib- erately introduced or cultivated. Of the native taxa, 35% are woody plants, but only 75 of these (or 60% of woody native taxa) are common and thus make up the bulk of the vegetation structure. By contrast, less than 9% of the naturalised species are woody plants, and all except two ó gorse and buddleia ó are either uncommon or rare. Annuals comprise 5.6% of all native dicotyledon herbs and 49% of the naturalised dicotyledon herbs. The history of the study area, public use, introduced animals, and tectonic events, particularly the earthquake-induced landslides of the mid-nineteenth century, are out- lined and discussed in relation to the native and adventive flora. Exotic herbivores, especially pos- sums (Trichosurus vulpecula), have greatly reduced the abundance of some plants which were common 30 years ago, including Alectryon excelsus, Fuchsia excorticata, Coriaria arborea, and Pseudopanax arboreus. Some other species, although probably never common, have been brought to the verge of extinction. Naturalised plants ó especially daisies and grasses ó have been able to colonise extensive open habitats created by earthquake slipping in 1855, and the reactivated terraces and river flood plain. If current selection pressures continue, it is predicted that other species such as Metwsideros robusta, Weinmannia racemosa, and Sphaeropteris medullaris will become rare, at least in lowland forest. Spread of Pinus radiata into mid-altitude communities will accelerate as exotic forests to windward mature.

Keywords vascular flora; introduced herbivores; earthquake-induced landslides; floristic Received 21 October 1983; accepted 21 November 1983

Received 21 October 1983; accepted 21 November 1983
New Zealand Journal of Botany, 1984, Vol. 22 : 223-270
0028-825X/84/2202-0223$2.50/0 © Crown copyright 1984

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