Aspects of the ecology of two species ofPassiflora(P. mollissima(Kunth) L Bailey andP. pinnatistipulaCav.) as weeds in South Island, New Zealand

Abstract

Vegetation invaded by two species of passionfruit (Passiflora mollissima and P. pinnatistipula) was examined at several sites in South Island, mostly containing small forest remnants of angiosperm species such as Melicytus ramiflorus and Macropiper excelsum. Several aspects of the regeneration of these Passiflora species were examined and the results generally reflected those of intensive studies of the same species conducted in Hawaii. Seed germination in the laboratory was continuous over an 8 month period from sowing, and in the wild this allows seeds to accumulate in the soil seed bank. Germinable seeds and seedling numbers, however, were of a similar magnitude to those of native angiosperms at the sites, and they do not reach the very large numbers of some woody weeds. Seedling growth was c. 10 cm over a seven month period at two sites at 300 m a.s.l., which is towards the upper altitudinal limit of Passiflora species. Stem cuttings readily establish in both a glasshouse and a shadehouse. As stems frequently become buried and fragmented on steep slopes, their regeneration may assist in the localised spread of the plant, and also in the re-establishment of plants on a wide range of sites after mechanical control operations. Establishment of Passiflora species is restricted to areas of high light levels and soil disturbance such as forest clearings and road cuttings in the absence of dense herbaceous growth. Small forest and scrub remnants with high edge-to-area ratios are therefore particularly vulnerable. Passiflora species are relatively new weeds which are probably still expanding their range, and they can be expected to increase, assisted by human activity, particularly adjacent to highways.