Alan F. Mark

Altitudinal variation in stomatal conductance, nitrogen content and leaf anatomy in different plant life forms in New Zealand

SummaryThis study is part of a series of investigations on the influence of altitude on structure and function of plant leaves. Unlike most other mountain areas, the Southern Alps of New Zealand provide localities where physiologically effective moisture stress occurs neither at high nor at low elevation, but the changes in temperature and radiation with elevation are similar or even steeper than in most other regions. In comparison with results from other mountains, where moisture may impair plant functioning at low elevation, this study allows an estimation of the relative role of water for the expression of various leaf features typically associated with alpine plants. Maximum leaf diffusive conductance (g), leaf nitrogen content (LN), stomatal density (n) and distribution, as well as area (A), thickness (d) and specific area (SLA) of leaves were studied. Three different plant life forms were investigated over their full altitudinal range (m): trees, represented by Nothofagus menziesii (1,200 m), ericaceous dwarf shrubs (1,700 m), and herbaceous plants of the genus Ranunculus (2,500 m). In all three life forms g, LN, and n increased, while SLA and A decreased with elevation. Recent investigations have found similar trends in other mountains from the temperate zone, but the changes are larger in New Zealand than elsewhere. Herbs show the greatest differences, followed by shrubs and then trees.It is concluded that g is dependent upon light climate rather than water supply, whereas SLA and related structural features appear to be controlled by the temperature regime, as they show similar altitudinal changes under different light and moisture gradients. The higher leaf nitrogen content found at high elevations in all three life forms, suggests that metabolic activity of mature leaves is not restricted by low nitrogen supply at high altitude. In general, the leaves of herbaceous plants show more pronounced structural and functional changes with altitude than the leaves of shrubs and trees.

Late Pleistocene and Holocene vegetation history, Central Otago, South Island, New Zealand

Pollen diagrams from upland blanket bogs and mire‐pool complexes on the southern Garvie Mountains and the Old Man Range, and from a sag pond mire on the slopes of the Kawarau Gorge, record the vegetation history of the last 12 000 years in Central Otago, the driest region of New Zealand. During the late‐glacial/early Holocene these subalpine sites supported grassland/shrubland vegetation. Trees or tall scrub were absent. Tree ferns became increasingly common in the early Holocene, most likely as small stands in damp, sheltered locations. At 7500 yr B.P. a coniferous forest of Prumnopitys taxifolia, Dacrycarpus dacrydioides and Podocarpus abruptly replaced the previous grassland communities at lower altitudes, while a coniferous scrub of Phyllocladus alpinus and Halocarpus bidwillii formed the upper treeline. The reafforestation of Central Otago and adjacent regions was completed 2000 years after podocarp‐dominant forest began to occupy coastal regions. The delay is attributed to drier climates in the inte...

The high-alpine vegetation of Central Otago, New Zealand

Summary Extensive areas of dwarfed, tundra-like vegetation, mostly beyond the upper limit of the low-alpine snow tussock grassland, are described from 10 mountain ranges in Central Otago. Environmental data from one representative range indicate that, despite a moderate latitude and altitude, summer temperatures, wind, and snow cover in this vegetation zone are comparable in severity with most high-alpine areas overseas. Four major habitat-physiognomic types are recognised: fellfield, herbfield, cushion, and snowbank. They differ both in physiognomy and flora, while their habitats are differentiated by lithology, altitude, exposure and/or duration of snow cover. Fellfield, being essentially lithologically controlled, is the most distinct type and dominates those ranges with either greywacke or weakly or non-foliated schists, as these tend to fracture into angular blocks. Partially active large stone nets may be present. On the remaining ranges, all with strongly foliated schist, fellfield occurs locally a...

Of mast and mean: differential-temperature cue makes mast seeding insensitive to climate change.

Mast-seeding plants often produce high seed crops the year after a warm spring or summer, but the warm-temperature model has inconsistent predictive ability. Here, we show for 26 long-term data sets from five plant families that the temperature difference between the two previous summers (ΔT) better predicts seed crops. This discovery explains how masting species tailor their flowering patterns to sites across altitudinal temperature gradients; predicts that masting will be unaffected by increasing mean temperatures under climate change; improves prediction of impacts on seed consumers; demonstrates that strongly masting species are hypersensitive to climate; explains the rarity of consecutive high-seed years without invoking resource constraints; and generates hypotheses about physiological mechanisms in plants and insect seed predators. For plants, ΔT has many attributes of an ideal cue. This temperature-difference model clarifies our understanding of mast seeding under environmental change, and could also be applied to other cues, such as rainfall.

Flowering, seeding, and seedling establishment of narrow-leaved Snow Tussock, Chionochloa Rigida

Summary The infrequent flowering years of the narrow-leaved snow tussock appear to depend on abnormally high temperatures during the long-day period of summer in the season before flowering. Physiological induction then occurs and morphological initiation of the inflorescence may take place during autumn, or it may be delayed until early spring, i.e., for about eight months. IntenSity of flowering increases with the duration of high temperatures during the inductive period when daylength exceeds about 14 hnurs. Even so, considerable variation in the intensity of flowering occurred both between sites and between individual tussocks at a site. In their flowering response the plants appear to be insensitive to differences in light intensity. Inflorescence development resembles that already described for the genus. It is increasingly delayed at higher altitudes, but is not subject to control by daylength. Floret size and seed weight decrease significantly with altitude. Seed set and viability are usually sati...

Climate-Change Effects on Alpine Plant Biodiversity: A New Zealand Perspective on Quantifying the Threat

Abstract New Zealands alpine region is populated by many (∼613) species of vascular plants with a high endemism (∼93%). To investigate the potential impact of climate warming, we used species-area relations to estimate current and projected vascular plant floras and tested model sensitivity scaling from the whole world to small alpine regions. Within their limitations, these models show that if the present mean temperature of ∼0.6°C higher than in 1900 were maintained, together with a large pool of exotic species, 40–70 species of native plants could become at risk. With a rise of 3°C, an approximate expectation for the following 100 yr, the total New Zealand alpine vascular flora could reach ∼550–685 species and lose 200–300 indigenous alpine species, the rest being exotic. Fragmentation of alpine areas could, over millennia, favor speciation, but in the short term, the loss of ∼80% of existing alpine islands will severely increase extinction risks. These model projections will be modified by downward extension of species through unplanned vegetation destruction, or following deliberate vegetation clearance to create habitats favorable to alpine species, as well as through a number of other as yet unquantified factors. These projections are not predictions of extinctions but rather broad probabilities of risk to a whole flora.

Will loss of snow cover during climatic warming expose New Zealand alpine plants to increased frost damage

If snow cover in alpine environments were reduced through climatic warming, plants that are normally protected by snow-lie in winter would become exposed to greater extremes of temperature and solar radiation. We examined the annual course of frost resistance of species of native alpine plants from southern New Zealand that are normally buried in snowbanks over winter (Celmisia haastii and Celmisia prorepens) or in sheltered areas that may accumulate snow (Hebe odora) and other species, typical of more exposed areas, that are relatively snow-free (Celmisia viscosa, Poa colensoi, Dracophyllum muscoides). The frost resistance of these principal species was in accord with habitat: those from snowbanks or sheltered areas showed the least frost resistance, whereas species from exposed areas had greater frost resistance throughout the year. P. colensoi had the greatest frost resistance (−32.5°C). All the principal species showed a rapid increase in frost resistance from summer to early winter (February–June) and maximum frost resistance in winter (July–August). The loss of resistance in late winter to early summer (August–December) was most rapid in P. colensoi and D. muscoides. Seasonal frost resistance of the principal species was more strongly related to daylength than to temperature, although all species except C. viscosa were significantly related to temperature when the influence of daylength was accounted for. Measurements of chlorophyll fluorescence indicated that photosynthetic efficiency of the principal species declined with increasing daylength. Levels of frost resistance of the six principal alpine plant species, and others measured during the growing season, were similar to those measured in tropical alpine areas and somewhat more resistant than those recorded in alpine areas of Europe. The potential for frost damage was greatest in spring. The current relationship of frost resistance with daylength is sufficient to prevent damage at any time of year. While warmer temperatures might lower frost resistance, they would also reduce the incidence of frosts, and the incidence of frost damage is unlikely to be altered. The relationship of frost resistance with daylength and temperature potentially provides a means of predicting the responses of alpine plants in response to global warming.

Causes of the species-area relation: a study of Islands in Lake Manapouri, New Zealand

The species-area relation consistently found among islands has given rise to the Random Placement hypothesis, the Habitat Diversity hypothesis and the Equilibrium hypothesis. In an attempt to test the Equilibrium hypothesis, twenty-three islands in Lake Manapouri, new Zealand were sampled for richness of vascular plant species

High-alpine environments and primary production on the Rock and Pillar Range, Central Otago, New Zealand

Abstract Cushion and herbfield communities, characteristic of the Central Otago high-alpine zone, are subjected to severe environments : persistent strong winds, low air and soil temperatures with many freeze-thaw cycles during the 5-month growing season, and moist frost-active soils. Sites in herbfield experience somewhat higher temperatures and lighter winds, and have deeper soils with greater profile development and higher organic content than cushion sites. Compared with alpine communities of similar physiognomy from the Northern Hemisphere, the snow-free season is very long, about 6 months, and plants grow, at least intermittently, throughout much of this period. Annual net above-ground production of herbfield (208–255 g m−2) is about twice that of cushion vegetation (126 g m−2) where very high stem densities compensate for the extremely small production of individual stems. Annual productivity is somewhat higher than for many physiognomically similar communities overseas but the longer growing seaso...

Comparative leaf morphology spectra of plant communities in New Zealand, the Andes and the European Alps

Leaf morphology of native vegetation has often been interpreted as a sensitive indicator of environmental conditions, presumably as a result of natural selection. If environmental pressures act as a selective force on community leaf morphology, then we would expect a high degree of similarity in similar environments, regardless of biogeographic origin of the flora. A comparative study of full regional floras of alpine vascular plants was undertaken to test the sensitivity of leaf morphology to macro‐environmental conditions. Five alpine sites and one lowland (control) site were selected in southern New Zealand spanning 1.5° latitude and 2323 m. Three sites with equivalent alpine environments were selected in South America across a 60° latitudinal and 4200 m altitudinal span with subtropical forest used as a control. A further alpine site from the European Alps was included as an outlier. Twenty leaf parameters were obtained for 2143 taxonomic entities x sites. Both the mean and the frequency distribution ...