EIGHTH TRIENNIAL CONFERENCE—ADELAIDE

Physical and chemical properties of litter and soil of two adjacent stands of high quality jarrah forest, one unburned since 1937, the other burned periodically during the past 40 years and last burned in Spring 1981, were compared in 1982 and 1983. Sampling of the larger elements of the invertebrate fauna was by litter and soil coring and pitfall-trapping three times during 1983.

Most of the soil properties studied had higher values in the burned stand, suggesting that repeated low intensity fires do not deplete jarrah forest soils of nutrients. Periodic low intensity fires had little impact on the frequency of occurrence or capture of the invertebrate fauna studied.     

Ecology of the pest insect jarrah leaf miner (Lepidoptera) in relation to fire and timber harvesting in jarrah forest in Western Australia

During a period of 7 years we undertook 25 investigations of the ecology of jarrah leafminer Perthida glyphopa Common in relation to fire and logging of jarrah Eucalyptus marginata Donn ex Sm. forest. Prescribed low intensity fires in spring or timber harvesting did not consistently favour jarrah leafminer or disfavour parasitization of its mines. Moderate intensity fire in autumn reduced the density of jarrah leafminer for 18 months.

We integrate these findings with other relevant ecological and historical knowledge and theorize that scarcity of extensive scorching of codominant crowns in jarrah forest from the mid 1950s may have facilitated the spread of the outbreak. We recommend that more extensive autumn burning should be operationally introduced to both test the theory and subdue outbreaks of jarrah leafminer.     

Reinfestation of Eucalyptus marginata ground coppice by jarrah leafminer after scorch by autumn or spring fires

Population densities of jarrah leafminer Perthida glyphopa in adjoining areas of jarrah Eucalyptus marginata forest in southwest Western Australia were monitored before and after autumn and spring fires, then compared to examine the effect of fire season and intensity. Densities of leafminer were reduced in tree canopies and on ground coppice after autumn fire scorched the host canopies. Densities of larval mines on ground coppice increased by the second spring after an autumn fire. Numbers of mines on leaves returned to levels indistinguishable from pre-fire values by the second autumn after fire. Leafminer populations on ground coppice appeared unaffected by a spring fire. Mechanisms that may account for observed differences between the effects of spring and autumn fires are discussed. Managed fires are not considered a practical tool for control of leafminer populations.     

THE FIRST “ALL AUSTRALIAN TIMBER CONGRESS”

The amount of litter deposited in three types of jarrah forest during 1951 varied between 36 and 47 cwt./ac. The litter fall was not evenly distributed throughout the year, but had a definite maximum occurring in January, February, and March.

Data are presented showing the amount of the more common inorganic constituents occurring in the leaf litter, and the amount of nutrients returned to the soil per acre per annum through leaf fall.

The surface soils of the jarrah forest have high organic carbon values but very low total nitrogen values, with consequent high C/N ratios. The cation exchange capacity of the surface soils is largely influenced by the amount of organic matter present.     

Book Review

The effects of three prescribed low intensity fires varying from means of 80 to 209 kWm^?1 within six years on invertebrates in litter/upper soil were assessed. The 8.6 year study was based on 88 934 arthropod specimens, representing 35 ordinal or lower level taxa contained in 3520 pitfall trap samples from a site burnt three times in spring and an unburnt control site within a 30.7 ha area.

The three fires had no discernible effect on total taxa, total non-insects, Araneae (spiders), Acarina (mites), Collembola (springtails), total insects and Formicidae (ants), although activity of the Coleoptera (beetles) decreased significantly after the second and third fires while that of the Diptera (flies) increased over the same period. However, as Coleoptera and Diptera activity on the unburnt control site decreased and increased respectively over the same period, it is uncertain whether the changes in activity were due to the fires or other non fire-related environmental factors. Futhermore, these changes in activity resulted from one or two of the spring fires only, and not all three, further questioning whether the fires were the contributing causal factors.

Three prescribed low-intensity fires in spring appear therefore, not to impact adversely on the activity of major forest litter arthropod groups, although the situation of the Coleoptera and Diptera is less clear due to similar activity on the unburnt control site in both cases. This therefore suggests that any fuel reduction burning in spring be conducted at intervals of not less than three years in order to minimize any impact on litter arthropods. Where a period of drought has occurred, burning should be delayed until the drought period has ended.     

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

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 species of the Coleoptera within litter of native forest.

A high level of stability in activity was evident among coleopteran populations over the 4-year study period when fire was absent. The same was observed at the two sites burnt in autumn (fire intensity = 176 kW m^?1). Both fires had no effect on family or species richness. However, the spring fire (256 kW m^?1) at one study site temporarily boosted activity of the ‘major’ family Staphylinidae after early autumn of the second post-fire year, and induced a short burst in activity of species Thalycrodes pulchrum (Nitidulidae) during the first post-fire winter, and among Leiodidae during the first postfire spring. At both spring-burnt sites, the pool of the 19 less commonly trapped ‘minor’ families incurred an immediate post-fire upsurge lasting until early summer 1986. As these positive responses at the spring-burnt sites were associated with a 4.41 ha^?1 lower fine fuel load (humus, litter, twigs of < 6mm diameter) during the first post-fire year compared with the autumn-burnt sites, it is possible that they reflect enhanced trapping efficiency and not increased population levels. Until this question is resolved, it appears preferable to apply any necessary one-off prescribed fire for reducing fuel loads on the forest floor during autumn rather than spring to minimise possible short-term impacts on surface-active Coleoptera.     

Problems of regeneration of the mature Eucalyptus regnans F. Muell, (The Big Ash) forest,in the absence of fire at Wallaby Creek,Victoria, Australia

This paper is based on observations on the regeneration of a mature E. regnans forest begun in 1949 and extending over the next 50 years. Any regeneration of E. regnans in the unburnt, mature forest is confronted by a phalanx of obstacles. The formation of large gaps which synchronously involve the overstorey, shrub understorey and fern stratum are an essential prerequisite for establishment, although success may not be assured unless the seedbed has been favourably prepared by mechanical disturbance or fire. In this study, regeneration, which was initiated experimentally by a heavy sowing of seed, scarification of soil, addition of nitrogenous fertilizer, creation of moderately good light conditions and the removal of competition by seedlings of understorey species in the first season, failed completely after 10–11 years even though understorey species which germinated from the soil seed bank continued to thrive.

Processes of seed germination and seedling development are explored in terms of seed harvesting by ants, insect attack, heating and desiccation of the soil surface, mammal browsing, light intensity and dimorphic leaf orientation, mycorrhizal associations, root competition, allelopathic factors, leaf spot fungi and chewing and gall-forming insects. In the tall forest lateral light is considered critical for continued vigour of advanced seedlings with pendulous foliage. Thus, gaps which permit satisfactory development of young seedlings are inadequate for saplings, especially if they are in competition with vigorous regeneration of understorey species. Under light-limiting conditions, survival is severely jeopardized by any factor affecting leaf area or leaf function. It is concluded that while E. regnans appears to be physiologically tolerant of moderate shade it lacks the wider ecological tolerance to it.

Without fire, the regeneration of E. regnans will almost certainly fail in the mature forest unless accompanied by exceptional circumstances. Group tree falls are needed to create regeneration but only on sites incompletely covered by dense ground fern. Synchronous gaps may be needed to disperse herbivore activity in the critical early years. Crown fire eliminates most of the difficulties encountered by E. regnans regeneration by causing mass seedfall, creating a suitable seed bed and by temporarily changing the microclimate, soil moisture regime, soil nutrient status, microbial populations and ant foraging activity. Regeneration may occur in groups following surface fires if large canopy gaps have been produced. In the unlikely event of a very long period without fire, succession to a form of rainforest is likely to occur, although the species may not be eliminated entirely from the area due to the possibility of chance establishment.     

Extreme wildfire behaviour in 3-year-old fuels in a Western Australian mixed Eucalyptus forest

This paper describes the behaviour of an intense wildfire which burnt through three-year-old fuels in open forest of jarrah (Eucalyptus marginata), marri (E. calophylla) and karri (E. diversicolor) near Manjimup, W.A. The fire occurred during very dry fuel conditions which resulted from record high air temperatures (maximum 43.5°C) following a rainless period of twenty eight days. Fire danger at the time was Extreme, with a peak McArthur Forest Fire Danger Index of 65. The fire crowned extensively in mixed-aged jarrah/marri stands, and it is proposed that crown fire initiation was facilitated by the substantial component of sapling and pole-sized regrowth which provided a vertically continuous fuel structure. Concentrated spotting occurred up to 2km downwind of the fire, and an isolated spot fire developed 8km away. During an initial run under north-westerly winds the fire travelled 2.2km with an average forward rate of spread of 1300m/h, which is somewhat faster than predicted by either the Western Australian Forest Fire Behaviour Tables or the McArthur Forest Fire Danger Meter. The relatively low fuel loads in the area appear to have assisted in the rapid containment of the fire once burning conditions moderated.     

Rapid estimation of the moisture content of dead Pinus pinaster needle litter in the field

Knowing fuel moisture content is important for predicting the behaviour of forest fires. This paper presents a method for quickly and inexpensively estimating the moisture content of pine (Pinus pinaster) needle litter. A simple mechanical device is used in the field to measure the angle at which freshly cast needles fracture, which is strongly related to their moisture content. This technique has potential for application to other forest litter types.     

Linking a decade of forest decline in the south-west of Western Australia to bioclimatic change

The south-west of Western Australia has experienced severe and prolonged drought over the last three decades. This has coincided with forest declines and more recently (following the summer of 2010–2011) sudden stand mortality in the Northern jarrah forest. Over the same period the Southern jarrah and Southern karri forests remained unaffected. The bioclimatic linkage between these localised climatic events and forest responses is key to developing a predictive capability that permits timely interventionist management strategies. We looked at the temporal dynamics of three accessible bioclimatic parameters (monthly mean diurnal temperature range, monthly mean precipitation and an aridity index derived from evaporation data) that were spatially registered with forested areas known to have been affected by this shift towards dryer and hotter conditions. Changes in forest condition were determined by accessing the vegetation fractional-cover data set, freely available from the high temporal resolution satellite MODIS. This data set provided estimates of three vegetation-related indices, namely photosynthetic vegetation, non-photosynthetic vegetation and bare soil cover. Both the climatic variables and the vegetative response variables were spatially co-registered over each of the three selected forest areas and a time series analysis undertaken for each variable. From the observed trends, we identify a set of threshold values for each bioclimatic metric and the approximate time lag associated with observed notable deterioration in the vegetation cover metrics.     

Forestcheck: the response of vascular flora to silviculture in jarrah (Eucalyptus marginata) forest

Forest understorey vascular plants were monitored across a sequence of time since treatment to assess the effects of silviculture (timber harvesting and regeneration systems) in jarrah (Eucalyptus marginata) forest in south-west Western Australia. Species richness, abundance and structure were assessed at 48 sites in four jarrah forest ecosystems. Monitoring grids in reference forest, which was either uncut or had not been harvested for at least 40 y, were compared to grids in forest that had undergone shelterwood/selective cut and gap release silvicultural treatments. A total of 446 plant species was recorded of which 68, 22 and 35 species were recorded on only one grid within the reference, shelterwood/selective cut and gap release treatments respectively. Silvicultural treatments had no significant long-term effect on mean species richness and abundance of understorey plants, but had a distinct influence on plant community composition. Reference forest had more species of small and medium shrubs compared with silvicultural treatments. Xanthorrhoea preisii (a grass tree) was significantly less common in silvicultural treatments compared with reference forest and Allocasuarina fraseriana (a small to medium tree) and Kennedia coccinea (a vine) were more common on harvested grids. The mean number of plant species per grid was not significantly different between treatments or forest ecosystems. There was, however, strong regional variation in plant community composition, especially in the Jarrah Blackwood Plateau and Jarrah South forest ecosystems and which probably reflects the influence of climatic and edaphic factors on jarrah forest species composition. Dominance-diversity curves for each treatment showed that ranking of species with high abundance was similar in all treatments, but varied between treatments for species with very low abundances. There was no significant relationship between species richness and time since last fire because field assessments were carried out at least 3–13 y after disturbance, by which time species assemblages had stabilised.     

REVIEWS

Over a wide range of conditions fine fuel re-accumulation after fire in eucalypt forests is well described by equations of the form X_t = X_ss (l-e^?kt)

where X_t is the weight (t ha^?1) of litter accumulated at time t(yr), X_ss is the weight of accumulated litter under steady-state conditions, and k is a decomposition rate constant (yr^?1). Decomposition constants ranged from 0.11 to 0.31 yr^?1, and steady- state litter accumulations varied between 11.1 and 29.4 t ha^?1.

In many types of eucalypt forest, litter re-accumulates to dangerous (from a fire control point of view) weights in 3–6 years, thus severely limiting the period during which prescribed burning provides protection from wildfire. The rapid rate of litter re-accumulation is mostly due to a marked decrease in the total amount of litter decomposing (relative to rates of litter input), rather than to any fire-induced reduction in the rate of decomposition. The implications of these findings for fire management in eucalypt forests are briefly discussed.

More quantitative information on the relationships between fuel mass (and other fuel characteristics) and fire behaviour under high to very high fire danger conditions is required to enable better evaluation of the effectiveness of low intensity prescribed burning for fire control. The ecological impacts of prescribed burning regimes, which also need to be considered when devising burning programs, are briefly discussed.     

Bushfire Disasters in Australia, 1945–1975

Conflagrations occur whenever there is a favourable combination of fuel, weather and ignition source and may be disastrous when human resources are affected; the role of these factors in past conflagrations is discussed. Some of the most severe fire seasons and the major fires between 1945 and 1975 are discussed briefly with reference to the areas burnt and the losses of life and property.

While past disaster fires have been quite variable a common characteristic is that the period when the fire exhibits violent behaviour and when most damage occurs is relatively short (generally less than 8 hours) although these periods can recur in close succession.

The frequency of large fires has been used to delineate fire-hazardous areas; the frequency ranges from once every 3 years in coastal districts of New South Wales and eastern Victoria to less than once every 30 years in central Australia. Likely changes in the patterns of large fire frequency and in the nature and intensity of disaster fires are discussed. Forest fires are likely to decrease in frequency and intensity but rural fires may become more destructive in the future.     

Evaluating MODIS active fire products in subtropical Yucatán forest

The Yucatán Peninsula has experienced increasingly frequent wildfire activity associated with drought and forest clearing during the last two decades. Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data provide timely, although not invariably, consistent estimates of fire dynamics for reasons that are not fully explicated. This research evaluates the accuracy of the MODIS active fire products (MOD14/MYD14) using field inventory reports for the 2011 fire season. Results show that 23% of fires in forest were detected by MODIS Terra and Aqua and that a higher detection rate (70%) occurs in pasture and milpa/secondary forest. Analysis of detection omission reveals that the 310-K MODIS 4-μm threshold is higher than the temperature of the majority of forest fires. This article recommends the use of a lower detection threshold at 305 K for densely forested locations and use of forest versus non-forest masks to improve forest fire detection in subtropics.     

Effect of Prescribed Burning in a Forest on Wood Characteristics of Jarrah

Wood specimens have been examined which were collected from three positions along the merchantable bole of jarrah (Eucalyptus marginata Sm.) trees growing in Western Australia. These trees had been subjected to a series of two experimental fires at either of two intensities in either spring or autumn. The more intense fire caused crown and trunk damage and resulted in kino vein formation. If such burning took place in autumn, loss of radial growth resulted. The less intense fire treatment did not result in external damage. Minor disturbances to the density profiles in the first year after the fire were the only observed effects on characteristics of the wood.     

Forestcheck: the response of birds to silviculture in jarrah (Eucalyptus marginata) forest

In the five-year period from 2001 to 2006, 48 monitoring grids comprising the FORESTCHECK initiative were established in open eucalypt (jarrah, Eucalyptus marginata) forest in south-west Western Australia. Since 1985, revised silvicultural objectives have necessitated detailed monitoring of responses by bird species and assemblages to silvicultural treatments (timber harvesting and associated burning). Few marked changes in the avifauna were detected. Species accumulated (in terms of numbers of grids) at similar rates in gap release, shelterwood/selective cut, and reference (either never harvested or harvested more than 40 years previously) forests. In terms of individuals, species accumulated faster in the gap release forests. The number of species represented as singletons was greatest on the never harvested (8), coupe buffer (7) and gap release (6) grids. Dominance-diversity curves also showed only minor differences between silvicultural treatments. Neither nMDS nor CAP ordinations showed any clear separation between the treatments. There was little evidence of any substantial effect of silvicultural treatments on avian community structure or on individual bird species. Community structure was, however, significantly associated with forest ecosystem/year of sampling. The basal area of live trees was not correlated with bird species richness or abundance on each grid. These results are consistent with previous studies, which indicate that most bird species in jarrah forest have a high threshold level of tolerance to disturbance. It is likely that the rapid regeneration of dominant tree species after harvesting and associated fire, the patchiness of treatments at the landscape scale, the high degree of connectivity of harvested and burnt forests with forests not recently harvested or burnt, and the retention of habitat trees in the most heavily—harvested (gap release) forests all conduce to dampen local-scale impacts and conserve the avifauna in relation to the home range and normal movements of its constituent bird species.     

TIMBER IN AUSTRALIA IN WARTIME

Fire history since 1850 was reconstructed by analysing tall wet eucalypt forest stands in the Warra long-term ecological research (LTER) site in southern Tasmania. Major fires occurred in 1898, 1906, 1914 and 1934. Fifty-seven percent of the forest has remained unburnt since 1850. Sixty percent of the forest burnt since 1850 occurs as mixed age stands, while 40 percent is pure regrowth. Ring counts of stumps of three veteran eucalypt trees indicated that the mature and oldgrowth forests of the Warra site represent a number of pre-1850 fires. One extant oldgrowth eucalypt stand was estimated to be over 450 years old. The common occurrence of multi-aged wet eucalypt stands has silvicultural implications where a management objective is to emulate pre-existing stand structures. While the fire history reported here is limited mainly to the period since 1850, it provides a good basis for understanding the current stand structures of the tall wet eucalypt forests of the Warra site. Such an understanding is essential to interpret results from current and planned ecological studies associated with the LTER program at Warra.     

Response of bird populations in jarrah and yarri forest in Western Australia following removal of half the canopy of the jarrah forest

Counts of birds present in jarrah (Eucalyptus marginata) forest on ridges and in yarri (E. patens) forest along streams were made during spring in three consecutive years, 1981–83. Thirty-eight species were recorded in set transects during the study. Six species were restricted to yarri, nine occurred only in jarrah, and eleven tended to be more abundant in yarri. The number of birds of all species was greater in the yarri forest.

Early in 1983, part of the jarrah forest was thinned, reducing canopy cover by about one-half, including removal of all Banksia grandis. The bird community showed few immediate changes. Two species were recorded as significantly more frequent after treatment and no species was recorded as significantly less frequent after treatment. The number of bird species present was similar in unlogged and logged jarrah forest. Two species became significantly more abundant in the yarri forest after the jarrah forest was logged. These findings suggest that most bird species in the jarrah forest may be adaptable to gross disturbance of the forest.     

SO2 enhanced desorption from basic aluminum sulfate desulphurization–regeneration solution by falling-film evaporation

To find the optimal structure of the converging–diverging tube and develop a high-efficiency falling-film evaporator, the heat and mass transfer performances of falling-film evaporation with converging–diverging tubes of different dimensions were studied. The optimal converging–diverging tube was used in falling-film evaporation desorption of the basic aluminum sulfate desulphurization–regeneration solution, and different influential factors on the desorption effect were analyzed. It was found that converging–diverging tubes with large falling-film flow rate performed well in the heat and mass transfer of falling-film evaporation, and their rib height largely affected the heat and mass transfer performances. At the same rib height and rib pitch, the longer the converging segment of the converging–diverging tube was, the better the heat transfer performance was. The evaporation heat transfer coefficient and evaporation mass transfer rate in the optimal converging–diverging tube were 1.6 and 1.38 times larger than the smooth tube, respectively. The optimal converging–diverging tube was used in falling-film evaporation desorption of basic aluminum sulfate desulphurization–regeneration solution, at a perimeter flow rate of 0.114–0.222 kg m⁻¹ s⁻¹, the desorption efficiency inside the tube was up to 94.2%, which was 10.3–10.5% higher than that of the smooth tube. At the inlet sulfur concentration of 0.02–0.1 kmol m⁻³, the desorption efficiency was up to 94.1%, which was 12.0–16.3% larger than that of the smooth tube. At the heating temperature of 371.15–386.15 K, the desorption efficiency was up to 93.4%, which was 6.7–11.5% larger than that of the smooth tube. Smaller falling-film flow rate, higher sulfur concentration, or higher heating temperature was more constructive to SO₂ desorption. Correlations were obtained to predict the mass transfer coefficient and SO₂ desorption efficiency. This study develops a new type of falling-film evaporator for SO₂ desorption from basic aluminum sulfate desulphurization–regeneration solution and provides a basis for process design and industrial application.

The heat and mass transfer performances of falling-film evaporation with converging–diverging tubes of different dimensions were studied.