Peter Wardle

Biological Flora of New Zealand

Abstract This paper includes information relevant to the ecology of Weinmannia racemosa, a distribution map based on its presence or absence in grid squares, a discussion of the taxonomic relationship to W. silvicola, and bibliographic references to other information.

Distribution of subfossil forest remains, eastern South Island, New Zealand

Abstract The distnbutiOn of subfossil forest remains collected in the eastern part of the South Island of New Zealand 15 outlined. Surface logs, buried wood and charcoals, wind–throw dimples and buried podsols provide convincing evillence of a former widespread forest cover over now–treeless tracts of the South Island. Most of the Wood and charcoals discovered have been identitied, and collecting sites plotted on a map. A broad distinction can be drawn between probable podocarp and beech forest areas.Radiocarbon dates for a number of wood and charcoal samples are presented and most of these point to forest destruction by fire since the advent of man In New Zealand within the last 1.000 years or so.Older dates presented obviously lie outside the period of human occupatIOn of New Zealand and the fires that produced these ancient charcoah are assumed to have originated from mltural causes. The pre~ent vegetallon on former forest sites and the distribution of forest remains in relation to existing forest are ...

An explanation for alpine timberline

Summary Alpine timberline represents the highest altitude at which shoots of woody plants can grow and ripen under the air temperatures which prevail at the height of tree canopies. At higher altitudes, woody plants can occur as shrubs and krummholz, by benefiting from warmer day-time temperatures close to the ground. Inverted timberlines against valley floors are related to nocturnal temperature inversions and repeated daily freeze-thaw cycles. Evidence favouring these interpretations comes from experiments in the Craigieburn Range, New Zealand, in which seedlings of the local timberline species, Nothofagus solandri, and various overseas timberline species were grown in a series of gardens above and below the natural timberline. Although seedlings show decreasing growth with increasing altitude, tree limit is better explained in terms of the ripening of shoots so that they can withstand unfavourable winter conditions, than by the hypothesis relating it to the ability to achieve a positive CO2 balance. Ph...

Engelmann Spruce (Picea Engelmannii Engel.) at Its Upper Limits on the Front Range, Colorado

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.

Evidence for rising upper limits of four native New Zealand forest trees.

Abstract Since the 1860s New Zealand mean air temperatures have risen about 0.5°C, which might be expected to have led to a rise of about 100 m in altitudinal limits of plants. Four tree species were examined at several South Island localities for evidence of such a rise Young silver beech plants have established above the upper limit of mature trees, mostly within the last 60 years. However, as beech timberlines are strongly buffered, few of these young plants occur more than 9 m from the forest margin. Above mountain beech timberlines, which lie in drier climates east of the Main Divide, the “advance zone” is usually less than 7 m wide, and does not include the exposed spurs and northerly faces where timberline ascends highest. Above the limit of mature red beech trees, there is a zone in which younger red beech, up to 150 years old, occur through nearly 30 m of altitude. Scanty data for miro suggest a still wider advance zone. The difference between the potential altitudinal rise of upper limits and th...

Freezing Resistance of Trees of the South Temperate Zone, Especially Subalpine Species of Australasia

Maximal resistance to winter freezing of trees of the South Temperate Zone, especially subalpine trees of Australasia, was assessed. Most of the tree species which grow in lower altitudes were marginally hardy to - 10?. Subalpine and alpine shrubby species such as Podocarpus nivalis, P. lawrencei and Dacrydium bidwillii were the hardiest conifers in New Zealand and Australia, resisting freezing to -20? to -23?. This hardiness was comparable to that of conifers native to the warm temperate or temperate parts of Japan. In Nothofagus, the deciduous, subalpine N. antarctica of South America was the hardiest, resisting freezing at -22?. A New Zealand evergreen timberline species, N. solandri var. cliffortioides was marginally hardy to - 15?. Of the Eucalyptus species, E. pauciflora which forms the alpine tree limit on the mainland of Australia was the hardiest, resisting freezing to - 15? in the leaves. Other high-altitude angiosperm species tested mostly survived freezing to only -10? or -15?. Very hardy tree species that withstand freezing below -30? seem not to have evolved in the Southern Hemisphere, because the mild, oceanic winters did not provide the stimulus, and because hardy northern tree genera, with minor exceptions, have been unable to cross the barrier formed by the tropics.

Primary succession in Westland National Park and its vicinity, New Zealand

Abstract 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. In general, 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 ...

Facets of the distribution of forest vegetation in New Zealand

Summary The altitudinal sequences of vegetation in New Zealand is divided into the following belts, based on floristics (especially the upper limits of species), physiognomy, and broad climatic relationships; warm temperature, cool temperature or montane, subalpine, lower alpine, high alpine, and nival. The boundaries are somewhat arbitrary, except for the subalpine/alpine boundary, which marks the upper limits of trees and large shrubs. The presence or absence of Nothofagus can give very different physiognomy to forest which exist under the same climatic regime, and which are otherwise floristically similar. The competitive ability and abundance of this genus, relative to other components of forest vegetation, increase along environmental gradients that lead away from the moist, mild, fertile “optimum” and in most places where Nothofagus borders beech-free vegetation, it tends to invade the latter. Absence of beech from climatically suitable areas can be related to Pleistocene glaciation, but the rate of...

The regeneration gap of New Zealand gymnosperms

Summary The majority of stands of Dacrydium cupressinum, Podocarpus spicatus and Libo cedrus bidwillii at six localities in the South Island and Stewart Island show a “regeneration gap”, i.e., a paucity of seedlings, saplings, and young trees. This is most evident to the east of the Main Divide and least evident in Stewart Island. Increment borings indicate that the lowest rate of regeneration occurred between 1600 and l800 A.D., if it is assumed that the growth rings are annual. It is suggested that during this time. the area supporting regeneration contracted into the coolest, moistest, and least drought prone parts of the country, and that more recently, it has been expanding again. This is in fair agreement with Holloways hypothesis concern ing the effects of climatic change on South Island forests.

New Zealand timberlines. 3. A synthesis

Abstract An experimental comparison of the native mountain beech (Nothofagus solandri var. cliffortioides) with exotic timberline species, and a study of the configuration of timberline in an alpine valley in relation to topography and microclimate are synthesised with the results of other timberline studies to develop general hypotheses about New Zealand timberlines. Although assimilation and growth in mountain beech decrease with increasing altitude, the abrupt nature and local altitudinal variations of beech timberlines mainly reflect the cold-tolerance limits of its seedlings. Winter death of beech twigs, that can lead to a krummholz form, is aligned with downslope winds, but sensitivity to low temperatures may also be involved. At least some of the tall shrubs that replace beech forest in cirque-form valley heads possess greater cold-tolerance. These shrubs also have endotrophic mycorrhizal associations, in contrast to the ectotrophic mycorrhizas of beech, which may have bearing on their lower statur...