The present distribution and ecology of New Zealand plants is discussed from a historical viewpoint. It is suggested that during the Miocene a southern extension of the New Zealand archipelago ~upported a cool temperste flora, which gave rise to the present mountain flora after the onset of orogeny and climatic cooling in the Pliocene. As there wa~ scarcely any simultaneous development of a distinctive flora adapted to the dry conditions which prevail to the east of the mountain axis, Cockayne's opinion that extremely arid Pleistocene climates evoked certain characteristic life forms-notably the divaricating ;uvenile form of some trees-is considered to be substantially incorrect. That these life forms are adapted to still·exi~ting conditions seems more probable.The broader features of present distribution are explllined in terms of Pleistocene glaciation and subsequent climatic amelioration. From the evidence of endemism and discontinuous distribution, it is concluded that Otago and Southland, Nelson and Marlborough, Auckland, the subantarctic regions and the Chatham Islands are areas where much of the present flora survived during the glaciation, whereas the middle portion of the South Island .lnd the south of the North Island were characterised by extinction. Adjustment Ilf the vegetation to post· Pleistocene conditions is still incomplete, and complicated by the effect of continuing climatic fluctuations.
Engelmann spruce is the dominant tree at timberline in the Front Range at approximately 3,350 m elevation; it occurs as krummholz in the forest—tundra ecotone up to about 3,500 m, and occasional individuals are found in the tundra up to 3,730 m. Temperatures decrease with increasing altitude above timberline, whereas wind velocity increases, especially during winter. Winter snow is deeper and persists longer in the forest than in the krummholz above, its depth in the latter tending to remain constant once the lower portions of the plants are packed. Soil temperatures fluctuate widely beneath tundra vegetation in the neighborhood of krummholz plants, whereas under forest variations are small and there is a prolonged period in spring when they remain within 0.6°C (1°F) of freezing point. Krummholz growth forms of spruce arise through death of needles and shoots exposed to the prevailing westerly winds. Even in the summer young exposed needles tend to be somewhat chlorotic, and many show lesions. In winter windward needles dry out, become bleached, and are eventually shed. Certain needles, instead of becoming bleached during winter, turn brown and dry out in early spring. In krummholz, even within a single shoot, sharply contrasting differences develop in winter between leeward needles that show only small seasonal decreases in water content, and windward needles that dry out and die. Desiccation is usually confined to krummholz, mainly affected small needles on stunted shoots and the distal needles of long, robust shoots, but in the winter of 1961—62, following a cold, wet September, it extended to leading shoots of saplings below timberline. Replenishment of water in needles during winter is probably from water stored in sapwood above the snow pack, since sapwood beneath the snow pack remains frozen in both forest and krummholz. Late—lying snow delays the spring growth of seedlings below timberline, but they occur even where snow persists until late in June. Above timberline, spruce seems to be less tolerant of late—lying snow. It is concluded that though the position of timberline is correlated with summer temperatures, dry winter winds are the immediate, though probably not the ultimate, cause of the krummholz growth forms in the forest—tundra ecotone.
This paper concludes a series on the vegetation of Westland National Park with an outline of the development of vegetation on new surfaces. A particularly long succession, well dated over its latest 14 000 years, is taking place on surfaces formed during the fluctuating retreat of low-altitude glaciers. Surfaces have been classed as gravel slopes, alluvial flats, loose boulders, solid bedrock, landslide scars, and talus slopes. IngeneraI, they show a development from open pioneer vegetation, through shrubland and seral forest to "climax forest", and eventually. a deterioration to heathland vegetation where soils change to gley podzols with impervious iron pans. On poorly drained areas, successions lead to infertile swamps.Successions at subalpine and alpine levels are slower and none in the district are older than the end of the last major glaciation. Consequently, they do not reach a stage equivalent to the low-altitude heathlands, except where the former glaciers left scoured bedrock that is still almost bare of soil.Notho/agus menziesii has entered the south-eastem part of the Park, apparently late in post-glacial time. Its rapid colonisation of new surfaces contrasts both with its very slow marginal invasion of other forest communities, and with the delayed entry of native conifers into primary successions where beech is absent.
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