Rowan P. Buxton

Sphagnum in peatlands of Australasia: Their distribution, utilisation and management

In comparison to the northern hemisphere, Sphagnum peatlands are an unusual andinfrequent component of the Australasianlandscape. Most peatlands in Australasiaare primarily composed of eitherRestionaceous or Cyperaceous peats. Sphagnum peatlands in Australia and PapuaNew Guinea/Irian Jaya (now West Papua) arelargely located in montane and alpineenvironments, but also occur down to sealevel in New Zealand and as moss patches onsome subantarctic islands. Fire is a majordeterminant of the characteristics ofpeatlands in Australasia. Peatlandmanagement in Australasia is hindered bythe need for increased understanding ofpeatland processes to enable a sustainablebalance of conservation of a small resourcewith localised utilisation. Themanagement focus in Australasia has largelybeen on ensuring ecologically sustainable Sphagnum moss harvesting, withlimited peat mining. We have found thatgeneral recovery of Sphagnum after moss harvesting canbe enhanced by harvesting larger peatlands,and by leaving one-third of the acrotelm toregenerate. The largest upland peat swampin mainland Australia, Wingecarribee Swamp,suffered a major collapse in 1998 followingpeat mining. Environmental and managementconsequences of this collapse have majorramifications for rehabilitation options. Sphagnum peatlands in Australasia arelikely to be adversely affected bydrainage, burning, grazing, trampling,global warming and peat mining.

Aspects of the ecology of two species of Passiflora (P. mollissima (Kunth) L Bailey and P. pinnatistipula Cav.) 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...

Seasonal frost hardiness of Nothofagus solandri seedlings from two altitudinally diverse sites in Canterbury, New Zealand

Abstract Seasonal variation in frost hardiness was evaluated in beech (Nothofagus solandri) seedlings from sites in North Canterbury at 460 m near the lower altitude limit, and at 1100 m near timberline. Both 1-. 2-year old seedlings were lifted on five occasions through the year and exposed to a range of controlled frosts. Visual frost damage was measured four weeks later as the percentage of foliage damaged, and frost hardiness determined as that temperature causing an average of 50% foliage damage. Low-altitude seedlings achieved a maximum midwinter frost hardiness of-4.5°C and about-l°C in summer whereas the high-altitude seedlings were respectively hardy to -11.5. -3.5°C. From a conditioning experiment, and in keeping with the differences in seasonal variation in frost hardiness high-altitude seedlings apparently have an inherently greater capacity to develop frost hardiness than low-altitude seedlings. Consideration of temperatures at timberline indicated that frost hardiness of seedlings would be r...

Sphagnum peatlands of Australasia: An assessment of harvesting sustainability

Sphagnum peatlands make up only a small fraction of the Gondwanic landscape when compared to Laurasian deposits. However, they are a distinctive and unusual habitat. This paper describes the biogeography of Sphagnum species and the distribution of Sphagnum peatlands in Australasia. Methods used and problems encountered in estimating Sphagnum growth rates are outlined. Growth rates for Sphagnum species are presented and factors affecting growth rates are suggested. The sustainability of Sphagnum harvesting is influenced by altitude, shade, watertable level and reseeding. The general decline in both growth rates and the recovery of the moss ecosystem after harvesting increases with altitude. This has ramifications for harvesting, management and conservation. As there is variability in recovery after moss harvesting, we outline methods that may assist recovery of harvested sites. The adequacacy of reservation of Sphagnum peatlands is addressed. This is pertinent as the conservation of Sphagnum peatlands is likely to be affected by drainage, burning, grazing, trampling, moss harvesting and peat mining.

Intraspecific Relationships among Wood Density, Leaf Structural Traits and Environment in Four Co-Occurring Species of Nothofagus in New Zealand

Plant functional traits capture important variation in plant strategy and function. Recent literature has revealed that within-species variation in traits is greater than previously supposed. However, we still have a poor understanding of how intraspecific variation is coordinated among different traits, and how it is driven by environment. We quantified intraspecific variation in wood density and five leaf traits underpinning the leaf economics spectrum (leaf dry matter content, leaf mass per unit area, size, thickness and density) within and among four widespread Nothofagus tree species in southern New Zealand. We tested whether intraspecific relationships between wood density and leaf traits followed widely reported interspecific relationships, and whether variation in these traits was coordinated through shared responses to environmental factors. Sample sites varied widely in environmental variables, including soil fertility (25–900 mg kg–1 total P), precipitation (668–4875 mm yr–1), temperature (5.2–12.4 °C mean annual temperature) and latitude (41–46 °S). Leaf traits were strongly correlated with one another within species, but not with wood density. There was some evidence for a positive relationship between wood density and leaf tissue density and dry matter content, but no evidence that leaf mass or leaf size were correlated with wood density; this highlights that leaf mass per unit area cannot be used as a surrogate for component leaf traits such as tissue density. Trait variation was predicted by environmental factors, but not consistently among different traits; e.g., only leaf thickness and leaf density responded to the same environmental cues as wood density. We conclude that although intraspecific variation in wood density and leaf traits is strongly driven by environmental factors, these responses are not strongly coordinated among functional traits even across co-occurring, closely-related plant species.

Multiple factors determine the rate of increase of an invading non-native tree in New Zealand

We reconstructed the invasion of a non-native tree (hawthorn, Crataegus monogyna) into fire-induced grassland in montane South Island, New Zealand. Using the relationship between height and age to reconstruct the rate of increase of the population, we identified three distinct invasion phases. We hypothesised that these related to the abundance of woody vegetation and therefore of non-native blackbirds (Turdus merula), the primary disperser of hawthorn in this environment. From the 1930s to 1959, increase was relatively slow, with hawthorn spread probably constrained due to browsing of seedlings by European rabbits (Oryctolagus cuniculus) and the low abundance of a native N-fixing shrub (matagouri, Discaria toumatou) providing few perches and nesting sites for blackbirds and safe sites for hawthorn establishment. Subsequently, from 1959 to 1976, hawthorn showed greater than six fold acceleration in its rate of population increase, resulting largely from intensive rabbit control, less frequent fires, and aerial topdressing of phosphate fertilizer promoting the growth of matagouri scrub. In addition, maturing hawthorn trees provided additional food and nesting sites for blackbirds. Hawthorn population increase slowed again from 1976, possibly because most suitable habitat in the immediate vicinity of the population neared saturation. From this case study we have constructed a general hypothesis for the factors determining the rate of invasion of matagouri—grassland habitats by bird-dispersed non-native woody plants in montane New Zealand.