Kevin G. Tolhurst

Temperate and boreal forest mega-fires: characteristics and challenges

Mega-fires are often defined according to their size and intensity but are more accurately described by their socioeconomic impacts. Three factors – climate change, fire exclusion, and antecedent disturbance, collectively referred to as the “mega-fire triangle” – likely contribute to todays mega-fires. Some characteristics of mega-fires may emulate historical fire regimes and can therefore sustain healthy fire-prone ecosystems, but other attributes decrease ecosystem resiliency. A good example of a program that seeks to mitigate mega-fires is located in Western Australia, where prescribed burning reduces wildfire intensity while conserving ecosystems. Crown-fire-adapted ecosystems are likely at higher risk of frequent mega-fires as a result of climate change, as compared with other ecosystems once subject to frequent less severe fires. Fire and forest managers should recognize that mega-fires will be a part of future wildland fire regimes and should develop strategies to reduce their undesired impacts.

Effects of bracken (Pteridium esculentum (forst. f.) cockayne) on eucalypt regeneration in west-central Victoria

Abstract An experiment was conducted in mixed species eucalypt forest in west-central Victoria to quantify the effects of shading and burning on the competitiveness of bracken with eucalypt seedlings for light and soil moisture. The effect of bracken competition on the species composition of eucalypt seedling regeneration was also studied. The influence of leachate from bracken founds on germination of eucalypt seedlings was examined in vitro. Bracken competition reduced the number of seedlings surviving at age 10 months by 50%. Bracken competition was predominantly for light which reduced seedling vigour making them more susceptible to drought, frost, insects and fungi. The number of seedlings which established was inversely related to bracken leaf area index. Bracken competition did not differentially affect Eucalyptus obliqua or Eucalyptus radiata. Allelopathy from leachate collected from bracken fronds did not affect germination of seeds. Soil moisture was not a significant factor in the competition, but summer rainfall was exceptionally high during this study. Burning and absence of shading stimulated the production of bracken fronds and these conditions are likely to extend the area of bracken competition.

The Effect of Fireline Intensity on Woody Fuel Consumption in Southern Australian Eucalypt Forest Fires

Summary The relationship between woody fuel consumption and fireline intensity was assessed using data collected at controlled fires and wildfires in south-western Western Australia, central Victoria and south-eastern New South Wales. The combined dataset consisted of fires in a range of dry eucalypt forests. Fire behaviour varied from slow, self-extinguishing prescribed burns to intense, fast—moving fires burning under conditions of extreme fire danger. Fireline intensity ranged from 50 kW m−l to <31000 kW m−1. Woody fuel consumption ranged from 31% to 100%, and generally increased with fire intensity. Percentage consumption was highest for small woody fuels where the diameter was between 0.6 cm and 2.5 cm. Fireline intensity had a statistically significant, positive relationship with the proportion of woody fuel consumed by both controlled fires and wildfires. Two generalised linear models (GLM) describing woody fuel consumption as a function of fireline intensity were developed, one applicable to the prescribed fire environment (with fireline intensities typically < 750 kW m−1) and the other to the full range of fireline intensities. The prescribed burning model produced the best fit and lowest error statistics. The findings of this research have important practical implications for the management of fire to reduce fuel loads, maintain habitat and manage carbon stocks in fire-prone eucalypt forests. The woody fuel consumption models presented may assist the assessment of potential climate change impacts on coarse woody debris in Australian southern eucalypt forests. The results of this research suggest that predicted changes to fire regimes and fire intensity associated with climate change in southern Australia could result in greater woody fuel consumption and carbon release during bushfires and a reduction in woody fuel loads in dry eucalypt forests. Use of low-intensity prescribed fires may provide a practical way of managing woody fuel stocks to achieve particular land management objectives.

Repeated prescribed fires decrease stocks and change attributes of coarse woody debris in a temperate eucalypt forest

Previous studies have found negligible effects of single prescribed fires on coarse woody debris (CWD), but the cumulative effects of repeated low-intensity prescribed fires are unknown. This represents a knowledge gap for environmental management because repeated prescribed fires are a key tool for mitigating wildfire risk, and because CWD is recognized as critical to forest biodiversity and functioning. We examined the effects of repeated low-intensity prescribed fires on the attributes and stocks of (fallen) CWD in a mixed-species eucalypt forest of temperate Australia. Prescribed fire treatments were a factorial combination of two seasons (Autumn, Spring) and two frequencies (three yearly High, 10 yearly Low), were replicated over five study areas, and involved two to seven low-intensity fires over 27 years. Charring due to prescribed fires variously changed carbon and nitrogen concentrations and C to N ratios of CWD pieces depending on decay class, but did not affect mean wood density. CWD biomass and C and N stocks were significantly less in Fire than Control treatments. Decreases in total CWD C stocks of -8 Mg/ha in Fire treatments were not balanced by minor increases in pyrogenic (char) C (-0.3 Mg/ha). Effects of prescribed fire frequency and season included significantly less C and N stocks in rotten CWD in High than Low frequency treatments, and in the largest CWD pieces in Autumn than Spring treatments. Our study demonstrates that repeated low-intensity prescribed fires have the potential to significantly decrease CWD stocks, in pieces of all sizes and particularly decayed pieces, and to change CWD chemical attributes. CWD is at best a minor stock of pyrogenic C under such fire regimes. These findings suggest a potential trade-off in the management of temperate eucalypt forests between sustained reduction of wildfire risk, and the consequences of decreased CWD C stocks, and of changes in CWD as a habitat and biogeochemical substrate. Nonetheless, negative impacts on CWD of repeated low-intensity prescribed fires could be lessened by fire intervals of 10 rather than three years (to decrease losses of decayed CWD), and fires in moist rather than dry conditions (to conserve large CWD).

Roots of Australian alpine plant species contain high levels of stored carbohydrates independent of post-fire regeneration strategy

The relationships between root morphology, level of stored non-structural carbohydrates and post-fire regeneration strategy were investigated in 37 Australian alpine plant species: 6 reseeders, 14 resprouters and 17 capable of both reseeding and resprouting. High concentrations of stored carbohydrate (up to 61.8% DW) were a feature of most species, with more than half of the 37 species containing non-structural carbohydrate concentrations of more than 10%. Fructan was the major reserve polysaccharide in 32 of the 37 species, with particularly high concentrations in the Asteraceae (up to 43.1%). Herbaceous species stored higher concentrations of carbohydrates and had fleshier roots than did shrub species, but swollen underground storage organs were found in only one species (Microseris scapigera sensu Willis1, Asteraceae). There was no significant relationship between post-fire regeneration strategy and either root morphology or level of carbohydrate storage, contrasting with results from drier, Mediterranean environments. Root storage of high levels of carbohydrate, and especially fructan, in Australian alpine species could therefore result from an adaptation to the alpine environment, such as a need for annual regeneration of leaf tissue in alpine conditions.

Effects of two short rotation prescribed fires in spring on surface-active arthropods and earthworms in dry sclerophyll eucalypt forest of west-central Victoria

Summary The effects of two prescribed low intensity fires (from 137 to 209 kWm−1) within three years on invertebrates in litter/upper soil were assessed in dry sclerophyll eucalypt forest near Daylesford in west-central Victoria. The 5.9 year study was based on 65 210 arthropod specimens representing 34 ordinal or lower level taxa contained in 2 300 pitfall trap samples, and on in situ counts of earthworms (Annelida) in 2 120 litter/upper soil samples, from a twice burnt site and an unburnt “control” site within a 31.3 ha area. The two fires had no discernible effect on total arthropods, total non-insects, total insects and total arthropod decomposers, though activity of total predators increased significantly after the second fire due largely to the Dermaptera (earwigs). A reduction in activity, up to one year, was recorded after each fire for the commonly trapped Collembola (springtails). Earthworm populations also declined substantially, but recovered to “control” levels within three years of each fire...

Operational wildfire suppression modelling: a review evaluating development, state of the art and future directions

Wildfires are an inherent part of the landscape in many parts of the world; however, they often impose substantial economic burdens on human populations where they occur, both in terms of impacts and of management costs. As wildfires burn towards human assets, a universal response has been to deploy fire suppression resources (crews, vehicles and aircraft) to extinguish them, and limit their spread or impacts. The determination of the appropriate levels of investment, resource allocation and suppression tactics is a challenge for managers. As suppression expenses account for a substantial proportion of the cost of fires, and escaped fires account for a large portion of impacts, fire suppression models have been developed to better inform decision-makers. We undertake a review of the literature pertaining to the development of operational models that emulate fire suppression as part of decision support systems. We provide a summary of the development of modelling approaches, discuss strengths and limitations and provide perspectives on the direction of future research.

Effects of the fire retardant Phos-Chek on vegetation in eastern Australian heathlands

The effects of the fire retardant Phos-Chek D75R on species composition, survival and growth of eastern Australian heathland vegetation are described. Two sites in Victoria were selected, Victoria Valley in the Grampian Ranges and Marlo in East Gippsland. Both areas supported heathland vegetation that was long, unburnt and relatively undisturbed. Plots were subjected to single applications of increasing concentrations of retardant (0.5, 1.0 and 1.5 L fire retardant m−2) or no additional fire retardant (‘Control’ and ‘Water only’ treatments). A single application of Phos-Chek did not appear to significantly change species composition or projected foliage cover of the major life forms of native heathland vegetation. However, it did cause whole plant and shoot death of key species Allocasuarina paludosa, Banksia marginata, Leptospermum continentale and L. myrsinoides, and was observed to affect other species. The fertilising effect of the fire retardant generally increased shoot growth of the key species but did not significantly increase the overall height of these species. The application of fire retardant enhanced weed invasion, particularly when supplied at higher concentrations. A number of research recommendations are made from this preliminary investigation.

Effects of fire, post-fire defoliation, drought and season on regrowth and carbohydrate reserves of alpine snowgrass Poa fawcettiae (Poaceae)

Following defoliation, grasses regenerate foliage from basal buds. We used a combination of field, glasshouse and growth-room experiments to investigate the role of carbohydrate reserves in regrowth of Poa fawcettiae Vickery following fire or mock grazing, and the effect on reserve dynamics of post-fire defoliation, drought and seasonal factors. Fructan reserves of burnt plants were depleted during foliage regeneration, and remained below those of unburnt plants for up to 10 months in the field, and for up to 3 months in the glasshouse. Plants were resilient to occasional mechanical clipping of foliage, but experienced significant depletion in fructan reserves and high tiller mortality when clipped at frequent intervals. Cold treatment led to fructan concentrations almost double those in plants growing at a warm temperature, explaining peak autumn levels in field plants, whereas a short drought treatment doubled the concentration of ethanol-soluble carbohydrates. Taken together, these data show how the dynamics of carbohydrate reserves, and specifically tiller-base fructan reserves, explain the vegetative regeneration capacity of P. fawcettiae.

Coleoptera in litter of dry sclerophyll eucalypt forest and the effects of low-intensity prescribed fire on their activity and composition in west-central Victoria

Summary Surface-active Coleoptera (beetles) were monitored in dry sclerophyll mixed eucalypt forest of west-central Victoria near Daylesford, and the effects of a one-off low-intensity prescribed fire applied during spring (15 October 1985) or autumn (25 March 1987) were assessed on families and species between 19 March 1985 and 28 February 1989. The study was based on 27 550 adult specimens, ranging in length from 0.5 mm to 22.0 mm and representing 30 families and 109 species, of which 78 species (71.6%) are undescribed. The most commonly trapped ‘major’ families were the Staphylinidae (predominantly predators), followed by the Nitidulidae and Leiodidae (both decomposers/fungus feeders). The specimens were contained in 3 140 pitfall trap samples taken from two sites burnt in spring, two sites burnt in autumn and one ‘control’ site, all adjacent to each other within an 80.5 ha study area. This is the first Australian study that has examined in detail the effects of prescribed fire on both families and spe...