Jb Marsden-Smedley

Estimating fuel response time and predicting fuel moisture content from field data

We develop a method for estimating equilibrium moisture content (EMC) and fuel moisture response time, using data collected for Eucalyptus twig litter. The method is based on the governing differential equation for the diffusion of water vapour from the fuel, and on a semi-physical formulation for EMC (Nelson 1984), based on the change in Gibbs free energy, which estimates the EMC as a function of fuel temperature and humidity. We then test the model on data collected in Western Australian mallee shrubland and in Tasmanian buttongrass moorland. This method is more generally applicable than those described by Viney and Catchpole (1991) and Viney (1992). The estimates of EMC and response time are in broad agreement with laboratory-based estimates for similar fuels (Anderson 1990a ; Nelson 1984). The model can be used to predict fuel moisture content by a book-keeping method. The predictions agree wellwith the observations for all three of our data sets.

The relative importance of fine-scale fuel mosaics on reducing fire risk in south-west Tasmania, Australia

In many landscapes, an important fire management objective is to reduce the negative impacts from unplanned fires on people, property and ecological values. In Australia, there exists an inherent assumption that high spatial variability in fire ages and hence fuel loads will have negative effects on both the incidence and spread of subsequent fires, and will enhance ecological values. A recent study using the process-based computer simulation model FIRESCAPE-SWTAS predicted several relationships between prescribed burn treatment levels and spatial patterning and management objectives in south-west Tasmania, Australia. The present study extended this investigation to additionally explore the effects of prescribed burning treatment unit size on unplanned fire incidence and area burned both in the general landscape and specifically in fire-intolerant vegetation. Simulation results suggest that treatment level had the greatest influence on modifying fire effects, whereas treatment unit size had the least effect. The model predicted that all three parameters interacted to determine the mean annual area burnt by unplanned fires. In fire-intolerant vegetation, treatment unit size did not influence the incidence of unplanned fires and the area burnt by unplanned fires in these communities. Where significant differences were evident, fire risk was reduced by higher treatment levels, deterministic spatial patterns of burning units, and smaller burning unit sizes.

A generic, empirical-based model for predicting rate of fire spread in shrublands

A shrubland fire behaviour dataset was assembled using data from experimental studies in Australia, New Zealand, Europe and South Africa. The dataset covers a wide range of heathlands and shrubland species associations and vegetation structures. Three models for rate of spread are developed using 2-m wind speed, a wind reduction factor, elevated dead fuel moisture content and either vegetation height (with or without live fuel moisture content) or bulk density. The models are tested against independent data from prescribed fires and wildfires and found to predict fire spread rate within acceptable limits (mean absolute errors varying between 3.5 and 9.1 m min–1). A simple model to predict dead fuel moisture content is evaluated, and an ignition line length correction is proposed. Although the model can be expected to provide robust predictions of rate of spread in a broad range of shrublands, the effects of slope steepness and variation in fuel quantity and composition are yet to be quantified. The model does not predict threshold conditions for continuous fire spread, and future work should focus on identifying fuel and weather factors that control transitions in fire behaviour.

In Vitro Germination of Eucalyptus Pollen: Response to Variation in Boric Acid and Sucrose

The effect of boric acid (0-450 ppm) and sucrose (0-40%) on pollen germination and pollen tube growth in Eucalyptus globulus, E. morrisbyi, E. ovata and E. tirnigera was examined in vitro. Over the con- centrations tested, sucrose had by far the largest effect upon both pollen germination and tube lengths. The optimum sucrose concentration for pollen germination (30%) and pollen tube growth (20%) differed markedly with very little ( E. ovata > E. morrisbyi = E. urnigera. Pollen germination and tube growth of all four species on a medium comprising 20% sucrose and 200 ppm boric acid would not differ significantly from the observed maximum response of each species and this could suffice as a generalised medium. However, if only percentage germination is to be assessed 30% sucrose would be preferable. It is argued that subtle interspecific differences in optimal in vitro con- ditions for pollen germination and pollen tube growth are likely to reflect differences in pollen physiology which in vivo may have important implications for the success of hybridisation where pollen competition occurs.

Fire modelling in Tasmanian buttongrass moorlands. IV. Sustaining versus non-sustaining fires

Buttongrass moorlands are widespread in western Tasmania. In these moorlands, the ability to conduct burning without having to rely on hard fuel boundaries (e.g. vegetation which is too wet to burn, water courses, mineral earth breaks and/or roads) would be a major advantage to land managers. Such burning relies on fires self-extinguishing and is normally referred to as unbounded burning. The aim of this project was to model the probability of fires extinguishing using the data from 156 buttongrass moorland fires. The variables used were wind speed, dead fuel moisture and site productivity. The model, derived from a combination of logistic regression and classification tree modelling, predicts that fires will self-extinguish over a wide range of conditions in low productivity moorlands but, in medium productivity moorlands, the conditions within which fires will self-extinguish will be much more restrictive. As a result, the technique of unbounded burning should be widely applicable in low productivity moorlands, but will be of marginal utility in medium productivity moorlands.

Fire modelling in Tasmanian buttongrass moorlands. III. Dead fuel moisture

An experimental program was carried out in Tasmanian buttongrass moorlands to develop fire behaviour prediction models for improving fire management. This paper describes the results of the fuel moisture modelling section of this project. A range of previously developed fuel moisture prediction models are examined and three empirical dead fuel moisture prediction models are developed. McArthur’s grassland fuel moisture model gave equally good predictions as a linear regression model using humidity and dew-point temperature. The regression model was preferred as a prediction model as it is inherently more robust. A prediction model based on hazard sticks was found to have strong seasonal effects which need further investigation before hazard sticks can be used operationally.

The early effects of fire and grazing on bryophytes and lichens in tussock grassland and hummock sedgeland in north-eastern Tasmania

Little is known of the interactive effects of fire and grazing on cryptogam species and assemblages. These effects were observed for bryophyte and lichen species in Tasmanian tussock grassland and hummock sedgeland several months after experimental burning and fencing. A factorial design was used on 40 randomly located and treated pairs of 1m1m quadrats in each of the vegetation types. In total, 24 cryptogam taxa were found, with grassland having a greater taxon richness, as well as higher total cryptogam cover and a different species composition, to the hummock sedgeland. There was greater cryptogam cover in the burned quadrats than the unburned quadrats in the grassland. However, only bryophytes had different species composition between burned and unburned quadrats. There was a small but significant difference in richness in hummock sedgeland, with burned being richer than unburned. Three species were more abundant in the burned than in the unburned treatments in the grassland, whereas no species responded to treatment in the sedgeland and no species responded to grazing. The fact that no species or assemblage of species was significantly reduced in cover by the burns testifies to a high degree of cryptogam resilience to this disturbance. The total lack of negative grazing effects suggests cryptogams are not a major source of sustenance for the local vertebrate herbivores. These conclusions differ from those made elsewhere in the world.

Explaining the distribution, structure and species composition of snow-patch vegetation in Tasmania, Australia

The term ‘snow patch’ indicates an area in an alpine zone with distinct vegetation because snow persists there longer than in the surrounding areas. Snow patches are a well known rare and threatened ecosystem on mainland Australia, but little is known of their distribution and vegetation in Tasmania. We describe, and determine the environmental relationships of, snow patches and their vegetation in Tasmania. There are 119 snow patches in Tasmania, covering 86 ha in toto, 43 of which have some fjaeldmark vegetation and the rest of which have a complete vegetation cover. Snow patches are confined to the taller, more continental mountains where they occur on north-east- to east-facing slopes, with the surrounding alpine vegetation usually being free of persistent snow. Their considerable floristic and structural variability relates to substrate and climate. Within Tasmania, several species are largely restricted to snow patches. The high degree of Tasmanian endemism in the snow-patch vegetation makes it distinct from the snow-patch vegetation of mainland Australia. The Tasmanian snow patches are also distinct in their environmental conditions. In Tasmania, snow does not usually persist over the winter outside the 119 snow patches. There are five floristic communities in these patches, all being distinct from those in mainland Australian snow patches. The Tasmanian snow patches merit listing as a threatened ecosystem on the basis of their distinctiveness and restricted extent.