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

Lady Lake

Lady Lake

An interesting study was recently carried out at the small Lady Lake in north Westland, New Zealand, in which the relative representation of potential macro-fossils196 and micro-fossils197 in the lake sediments was compared with the representation of the present day flora in the region. Surrounding the lake is kahikatea (Dacrycarpus) swamp forest, conifer broadleaf forest and swamp. With potential macro-fossils it was found that most trees and shrubs were represented. Exceptions were putaputaweta (Carpodetus serratus), Fuchsia excorticata, kaikomako (Pennantia corymbosa), wineberry (Aristotelia serrata) and Coprosma tenuicaulis, which all have leaves that decay readily. Kahikatea was under-represented and there seems no obvious explanation for this. Some trees and shrubs appeared to be better represented in the lake sediments than in the surrounding forest — matai (Prumnopitys taxifolia), Hall's totara (Podocarpus hallii), Phyllocladus aspleniifolius, manuka (Leptospermum scoparium), kanuka (Kunzea ericoides), southern rata (Metrosideros umbellata) and Coprosma propinqua. Forest floor herbs were not represented in the lake sediments although some high herbaceous epiphytes, Lycopodium varium and the orchids Earina and Dendrobium were. This may be because the latter are page 240better situated to fall or to be blown into the lake.

Aquatic and swamp species were poorly represented in the lake litter. Many of them are soft-tissued and decay readily and in the cases of those that are very fibrous, such as Phormium tenax, dead leaves remain attached to the plants and gradually decay.

Some of the litter would be brought into the lake by streams, especially when in flood, some by surface wash during heavy rain, some by direct fall from overhanging plants and some by wind, particularly during gales.

Spores and pollen were sampled from the surface of the lake sediments and from moss cushions. They gave a picture broadly similar to that of the macro-plant remains, but there were some differences. By contrast with the lake litter, Quintinia, Cyathea smithii and kamahi (Weinmannia) were under-represented. The epiphytic orchids were not recorded at all. The two types of remains were in agreement in under-representing Dacrycarpus and sedges. It has been suggested that at least some of the under-representation of these species may be due to the rapid decay of their spores or pollen under lake conditions. Some of these species are well represented in peat where the acid conditions would aid their preservation.