Soil temperatures during bushfires in semi-arid,mallee shrublands

Abstract Soil temperatures were measured during 11 experimental fires in semi-arid mallee shrublands in central NSW. Sensors were placed at depths from 1–10 cm beneath the soil surface in three fuel types; litter beneath Eucalyptus shrubs, live hummocks of the grass Triodia irritans and litter beneath shrubs of Acacia species. Weights of these fuels per unit area were determined. Maximum soil temperature and its duration were related to fuel type and depth. Mean weights of Eucalyptus and Triodia fuels were similar (0.35 kg m^?2), while there was less Acacia fuel (0.1 kg m^?2). Highest maximum temperatures were registered under Eucalyptus litter (e.g. 140°C at 2 cm). Maximum temperatures under Triodia and Acacia litter were similar (e.g. 60–70°C at 2 cm). Durations were examined in two temperature classes (60–120 and > 120°C) chosen to represent threshold for stimulation of germination and mortality, respectively, of soil-stored seeds. Temperatures between 60 and 120°C were recorded only between 0–2 cm soil depth for Acacia and Triodia (one exception at 4 cm). No temperatures >120°C were recorded for these fuel types. Temperatures between 60 and 120°C were recorded to 5 cm depth under Eucalyptus fuels while putative lethal temperatures for seeds occurred occasionally at 0–2 cm depth. The results indicated greatest potential for stimulation of germination and death of buried seeds under Eucalyptus fuels, although the level of variability of temperature was highest under Eucalyptus fuels. Despite similar fuel loads, differences between temperatures under Eucalyptus and Triodia fuels reflected the influence of the depth of the fuel bed, with Triodia hummocks constituting a deep fuel bed and Eucalyptus litter a shallow fuel bed.     

Aboriginal fire management in south-eastern Australia: aims and frequency

Aim To examine the purpose of burning by Aborigines of south‐eastern Australia. Location South‐eastern Australia. Methods A survey of the ethnography and ecology relating to Aboriginal fire. Results Ecologists have only recently acknowledged the past history of Aboriginal burning. Its purpose was to maximise plant and animal food resources. Main Conclusions The seasonal timing and frequency of Aboriginal burning is embedded in various ecosystems.     

Vegetation succession after fire in sclerophyll woodland communities in south-eastern Australia

The dynamics of vegetation regeneration after burning were examined in three dry sclerophyll communities near Canberra, in south-eastern Australia. Changes in seedling and regrowth populations were followed in permanent quadrats during the first two years after burning, compared with both the preburn vegetation and population changes over the same period in adjacent, unburnt plots. All species represented either by living plants in the tree and shrub strata and/or by seed in the soil and litter prior to burning regenerated during the first year after the fire treatments. No new species invaded the areas after burning. Species varied in their regenerative strategy and recovered after the fires either by germination of seed residual in the soil and ash or released from trees after burning, by regrowth from surviving vegetative organs, or by a combination of germination and regrowth. Both seedling input and the vegetative recovery of populations were higher during the first than second year after burning. The vegetative multiplication and seed gertnination of many species were stimulated by fire. It was concluded that the regeneration of the communities studied, as well as the post-fire recovery of numerous different communities reported in the literature, closely resembled an initial floristic composition model. It is considered that the process of vegetation redevelopment after a disturbance (i.e. secondary succession) will be influenced greatly by the species composition at the time of disturbance, and by the type of disturbing agent. A single model would not be expected to adequately describe secondary succession following disturbance by agents imposing different stress conditions on a community.     

Determinants of the economic viability of mallee eucalypts as a short rotation coppice crop integrated into farming systems of Western Australia

Mallee eucalypts are being developed as a short rotation coppice crop for integration into agricultural systems in the south‐west of Western Australia. These have potential for biomass production for bioenergy, eucalyptus oil and generating carbon credits and to help control the extensive occurrence of dryland salinity. Some 12,000 ha of mallee planting has been undertaken since 1994, mostly in the form of wide‐spaced, narrow belts within the annual agricultural system. Production and market data were used to estimate levelized costs (LC) of mallee biomass production under different harvest regimes across 11 sites from 2006 to 2012. We found LC ranged from AUD40 to AUD257 fresh Mg^?1. LC was most strongly determined by mallee production, followed by the crop/pasture rotation decisions of the landholder. Mallee harvest regime had minor impact on LC. Crop and pasture yield loss due to competition from the mallee belts accounted for 38% of costs, harvesting biomass was 32%, opportunity cost of the land occupied by the mallee belts was 16% while establishment and maintenance costs accounted for 14% of the costs. When income from carbon sequestered in mallee root biomass was included, the LC dropped by an average of 11% at the current Australian price of AUD15 Mg^?1 CO₂ equivalent (CO₂e). The income from carbon sequestered in root biomass alone is unlikely to make mallee agroforestry economically viable. Hence, income from harvested biomass in the form of feedstocks for industry or carbon credits is necessary to make mallee agroforestry commercially attractive. LC for unharvested mallee belts ranged from AUD33 to AUD237 Mg^?1. Where above‐ and below‐ground biomass is converted to CO₂e at AUD15 Mg^?1, the LC drops to AUD11–AUD64, with three of 11 sites likely to be profitable. These three sites were characterized by high biomass production with low agricultural gross margins.     

Ant diversity in relation to time since fire in a mallee landscape of South-Eastern Australia

Fire is a dominant process shaping the Australian landscape and in many regions the frequency and severity of wildfires are predicted to increase under climate change. The primary impact of fire on fauna is typically indirect through habitat change. In particular, in mesic forests different animal species are favoured at different times since fire as habitat complexity increases with vegetation recovery. However, this will not necessarily be the case in habitats with low complexity such as many of those occurring in arid and semi-arid regions. Here, we investigate the relationship between fire history and ant diversity and composition in semi-arid mallee of south-eastern Australia. We surveyed ants at 11 sites in the Little Desert National Park and nearby private land that last burnt 0.5, 6 or 40 years ago. We found no relationship between time since fire and either ant diversity or composition, and this can be explained by a lack of relationship between time since fire and vegetation cover. Our findings contrast with those for mallee bird species, which show clear successional patterns following fire, but are likely to be typical of ground-foraging fauna that lack specialized habitat requirements.     

Influence of fire severity on the regeneration,recruitment and distribution of eucalypts in the Cotter River Catchment,Australian Capital Territory

Abstract Plant responses to fire are variable between and within species and are influenced by numerous factors including fire severity. This study investigated the effects of fire severity on the regeneration and recruitment of forest eucalypts in the Cotter River Catchment, Australian Capital Territory (ACT). This study also examined the potential for the obligate seeder Eucalyptus delegatensis R.T. Baker (Myrtaceae) to expand into adjacent stands dominated by the facultative resprouter Eucalyptus fastigata H. Deane & Maiden (Myrtaceae) by seed shed and seedling establishment beyond the pre‐fire boundary. Sites were located in areas of either higher or lower fire severity, and transects were placed across the boundary of stands of E. delegatensis and E. fastigata. Species distributions, tree survival and seedling densities and heights were recorded, and the location of each boundary was determined as the region of maximum change in species composition along the transects. Eucalyptus delegatensis was the only eucalypt killed by higher severity fire. However, E. delegatensis seedling density was greater at higher severity sites than lower severity sites. Eucalyptus fastigata seedling density was low across all sites, with other eucalypts producing few, if any, seedlings. There was no evidence that E. delegatensis had increased its range into downslope stands dominated by E. fastigata. Patterns of vegetative recovery and seedling recruitment may be related to a number of factors, including differences in allocation patterns between seeders and sprouters, and the effects of overstory and understory competition. It is unclear what processes impede E. delegatensis seedling establishment beyond the stand boundary, but may involve an inability of E. delegatensis to shed seed sufficiently far downslope; unsuitable conditions for germination beyond the boundary; or, competition from a retained or resprouting overstory, despite the potential for increased dispersal distance soon after fire.     

Spatial indicators of fire risk in the arid and semi-arid zone of Australia

Fire plays a role in determining the shape of the earth's ecosystems, impacts socio-economic issues, and influences our climate. In arid and semi-arid Australia (70% of the continent), individual fires frequently exceed 1 million ha, and have collectively burnt up to 9% of the total area in a single year, associated with antecedent periods of above average rainfall which boost the fuel load. People affected by these fires – Federal and State governments, pastoralists, Aboriginal communities, larger towns, conservation park managers and tourist operators – all have different outlooks and priorities about these phenomena. Little objective information about the fire regime and its drivers has been available for this vast area with its very low population density. A predictive understanding of the spatial and temporal pattern of risk of large uncontrollable fires is needed to promote pro-active management.We present a conceptual framework which serves both to summarise existing knowledge and to reduce the complexity for a quantitative statistical analysis. This conceptual framework contains four main groups of independent variables; biomass, curing, ignition source, and fire weather. For these groups of variables we identified direct data sources or spatial surrogates. To quantify different aspects of the fire regime, interpretation of NOAA-AVHRR satellite imagery was employed, which identifies both fire hotspots (FHS) and fire affected area (FAA). For temporal variables, we present a surface displaying relationships for different combinations of lag/phase. This highlights different patterns for each region, and the most appropriate timeframes to use in modelling.Results of exploratory regression analysis in arid and semi-arid Australia show that the strongest influence is exerted by biomass or fuel load. As this is highly dependent on antecedent rainfall, we can anticipate a strong effect of climate change on the fire regime. The strongest combinations of relationships may be used as spatial indicators in the development of long-lead fire risk models for these areas. This can help improve the timing of pro-active strategies to manage fire, and in the allocation of sparse funds and resources. Our analysis has highlighted regional patterns of fire across different land tenures. Heightened awareness of these patterns may encourage a more cooperative and coordinated approach to fire management amongst stakeholders.     

Neoformation of clay in lateral root catchments of mallee eucalypts: a chemical perspective

Background and Aims

A previous paper (Annals of Botany 103: 673–685) described formation of clayey pavements in lateral root catchments of eucalypts colonizing a recently formed sand dune in south-west Western Australia. Here chemical and morphological aspects of their formation at the site are studied.

Methods

Chemical and physical examinations of soil cores through pavements and sand under adjacent heath assessed build-up of salts, clay and pH changes in or below pavements. Relationships of root morphology to clay deposition were examined and deposits subjected to scanning electron microscopy and energy-dispersive X-ray analysis. Xylem transport of mineral elements in eucalypt and non-eucalypt species was studied by analysis of xylem (tracheal) sap from lateral roots.

Key Results

The columns of which pavements are composed develop exclusively on lower-tier lateral roots. Such sites show intimate associations of fine roots, fungal filaments, microbiota and clay deposits rich in Si, Al and Fe. Time scales for construction of pavements by eucalypts were assessed. Cores through columns of pavemented profiles showed gross elevations of bulk density, Al, Fe and Si in columns and related increases in pH, Mg and Ca status in lower profiles. A cutting through the dune exhibited pronounced alkalinity (pH 7–10) under mallee woodland versus acidity (pH 5–6·5) under proteaceous heath. Xylem sap analyses showed unusually high concentrations of Al, Fe, Mg and Si in dry-season samples from column-bearing roots.

Conclusions

Deposition of Al–Fe–Si-rich clay is pivotal to pavement construction by eucalypts and leads to profound chemical and physical changes in relevant soil profiles. Microbial associates of roots are likely to be involved in clay genesis, with parent eucalypts supplying the required key mineral elements and carbon sources. Acquisition of the Al and Fe incorporated into clay derives principally from hydraulic uplift from ground water via deeply penetrating tap roots.Key words: Niche construction, eucalypts, root morphology, xylem transport, hydraulic lift, element mining, soil formation, biomineralization, soil pans, duplex soils     

Defining grassland fire events and the response of perennial plants to annual fire in temperate grasslands of south-eastern Australia

Many species-rich Themeda triandra grasslands in south-eastern Australia have been burnt annually in summer as a land management practice for decades. The characteristics of annual fires (maximum surface temperatures, maximum soil temperature changes at 10 mm depth, Byram fire intensity and duration of surface heating) were compared to fires that occur less frequently (2, 4 or 7-year inter-fire interval). The impacts of annual summer fires on seed survival, perennial plant dynamics and flowering were also documented at two sites over two years.Annual grassland fires differ principally from other grassland fire types in their duration of surface temperatures above 100°C (i.e., <1 min versus >2–3 min in grasslands burnt at 4–7-year intervals). This was correlated to fuel load, but not rate of spread or Byram fire intensity. Maximum surface temperatures were variable within annual fire events (98–458°C ) and did not differ significantly from those observed in other grassland fires. All sites experienced temperatures above 350°C but no site had its soil temperature increase at 10 mm depth by >10°C during fire. Byram fire intensity was lower in annually burnt sites, but positively correlated with rate of spread moreso than fuel load.Many perennial species (34–55%) and most perennial individuals (70–83%) avoid the annual summer fire event by being dormant at the time of burning. All perennial species regenerated rapidly by vegetative means after fire and seedlings were absent or rare for most species. As a result, turnover of species at the small-scale was low.Annual burning permits high perennial species richness (mean 18 species/0.25 m²) and high numbers of individual perennial plants (range 189–1036 plants/0.25 m²) to co-exist at the small-scale. Seasonal plant density maxima peaked in spring, 6–8 months after fire, and the number of plants in a species' population each year following fire depended on their seasonal response more than their direct fire response. The direction and magnitude of population change from one year to the next was species and site specific and did not correlate with life form or a plant's ability for vegetative spread. All perennial species have a short secondary juvenile period (i.e., 6–11 months) but relatively few individual plants flower in any one year. Seed that has made its way into the soil is completely protected from the direct effects of fire and hence, occasional post-fire seedling recruitment may be possible for all species.Maintaining annual burning in grasslands as a management regime is unlikely to lead to a decline in richness and plant density in the short-term. Rather, delayed burning (i.e., >3 year intervals), and the impact that this may have on interval dependent processes such as above-ground competition, are predicted to have more substantial long-term effects on the small-scale dynamic of this community.     

Modelling the response of eucalypts to fire,Brindabella Ranges,ACT

Abstract A new algorithm for the responses of Eucalyptus species to fire was developed to be used in BRIND, an existing forest gap simulation model. After a fire, trees may be: (i) killed outright; (ii) have their above-ground parts killed but resprout from basal lignotubers; or (iii) continue to grow from undamaged and epicormic above-ground buds. Data collected after a fire in the Gudgenby region, Brindabella Ranges, southern Australian Capital Territory, indicate that tree size and vigour can be used to predict the response of individual trees. There was not enough information about fire intensity to estimate its effect on the response of trees. The new algorithm was tested using data from a 1982 fire in Bushrangers Creek, Brindabella Ranges. The predicted probabilities of stem death were similar to the field data.     

Impact of fire on leaf nutrients,arthropod fauna and herbivory of native and exotic eucalypts in Kings Park,Perth, Western Australia

The vegetation of Kings Park, near the centre of Perth, Western Australia, once had an overstorey of Eucalyptus marginata (jarrah) or Eucalyptus gomphocephala (tuart), and many trees still remain in the bushland parts of the Park. Avenues and roadsides have been planted with eastern Australian species, including Eucalyptus cladocalyx (sugar gum) and Eucalyptus botryoides (southern mahogany), both of which have become invasive. The present study examined the effect of a recent burn on the level of herbivory on these native and exotic eucalypts. Leaf damage, shoot extension and number of new leaves were measured on tagged shoots of saplings of each tree species in unburnt and burnt areas over an 8‐month period. Leaf macronutrient levels were quantified and the number of arthropods on saplings was measured at the end of the recording period by chemical knockdown. Leaf macronutrients were mostly higher in all four species in the burnt area, and this was associated with generally higher numbers of canopy arthropods and greater levels of leaf damage. It is suggested that the pulse of soil nutrients after the fire resulted in more nutrient‐rich foliage, which in turn was more palatable to arthropods. The resulting high levels of herbivory possibly led to reduced shoot extension of E. gomphocephala, E. botryoides and, to a lesser extent, E. cladocalyx. This acts as a negative feedback mechanism that lessens the tendency for lush, post‐fire regrowth to outcompete other species of plants. There was no consistent difference in the levels of the various types of leaf damage or of arthropods on the native and the exotic eucalypts, suggesting that freedom from herbivory is not contributing to the invasiveness of the two exotic species.     

Species diversity and temporal distribution of ants in the semi-arid mallee region of northwestern Victoria

The ant communities of two adjacent sites bearing markedly different vegetation (heath and mallee) were studied using quadrat counts and pitfall traps in semi-arid northwestern Victoria. The ants were extremely abundant and rich in species (86 species from 27 genera were recorded from two 50 m × 25 m plots within 25 m of each other) and were dominated by species ofMonomorium and Iridomyrmex. Pronounced site differences in species composition were found, with 73% of the most abundant species showing a strong site preference. The ants exhibited marked seasonality: activity was highest in summer and lowest in winter and this was accompanied by a high turnover of species in time, resulting in pronounced seasonal differences in species composition. Most foraging was nocturnal during summer but was almost exclusively diurnal during winter, and individual species displayed distinctive patterns of diet foraging activity. Although the overall temporal distribution of the communities were apparently controlled by temperature, interspecific competition may also be an important factor influencing the seasonal and diel distributions of individual species, resulting in their high degree of temporal separation. The overall consequence is that although the study area contains many abundant species with similar ecological requirements, few of these are active in the same place at the same time.     

Immediate effects of Ore on ants in the semi-arid mallee region of north-western Victoria

The immediate effects of a high intensity wildfire on the ant communities of a heath and a mallee site in semi-arid north-western Victoria are reported. Following fire the number of species trapped on the ground doubled (to ca. 80 each site), total ant abundance decreased by half (due to the demise of previously dominant species), surface activity of reproductive castes increased, and dramatic changes in species relative abundance (including shifts toward greater equitability) occurred. These changes are interpreted in terms of fire-induced simplification of the habitat and release from competition with dominant species. The results appear to illustrate the importance of interspecific competition in structuring foraging activity in mallee ant communities. Observations are also reported on seed-harvesting by ants, including changes in harvester ant abundance, germination from within-nest seed storage, and the first record of Heteroponera removing seeds.     

Plant species richness in the mallee region of Western Australia

Sixteen sites (area 1000 m²) within the mallee region of southern Western Australia were sampled for vascular plant species richness. Species richness ranged from 17 species per 1000m² in a Halosarcia syncarpa salt-complex site and a Eucalyptus occidentalis tree mallee site, up to 48 species per 1000 m² in a Eucalyptus angulosa-Eucalyptus tetragona shrub mallee site. Woodland, woodland/mallee and mallee sites consisted mainly of perennial species while shrubland sites and salt-complex sites had a higher percentage of ephemeral species. Sites with the highest species richness occurred on soils with the lowest nutrient content. Sites with lowest species numbers were those with severe habitat conditions or where better nutrient conditions may have provided the dominants with a competitive advantage to suppress associated species.     

Immediate and longer-term effects of fire on seed predation by ants in sclerophyllous vegetation in south-eastern Australia

Following a prescribed spring fire at a woodland site with heathy understorey in south-eastern Australia, the following features changed markedly: the composition of the ant fauna taken in pitfall traps; the abundance of seed-eating species; seedfall from woody-fruited Eucalyptus obliqua and Casuarina pusilla; and rates of seed predation by ants. Broadly adapted species of Monomorium and Rhytidoponera, uncommonly recorded before the fire, became the most abundant ants caught. Seed removal from baits dropped by almost half during the week after fire, despite an increased catch of seed-eating Rhytidoponera tasmaniensis. This coincided with a massive fire-induced release of seeds stored inside woody fruits, suggesting that predator satiation occurred. The fall of Casuarina seeds and Eucalyptus chaff returned to pre-fire (low) levels 1 week after the fire, but a substantial proportion of Eucalyptus seeds fell after several weeks. By this time rates of seed removal were increasing rapidly as the abundance of seed-eating R. tasmaniensis continued to increase. Weekly removal from baits reached 100% 7 weeks after the fire, which was much higher than any level recorded before it. Results from a nearby heathland site, burned by an earlier fire, indicated that unusually high rates of seed removal, paralleling increases in abundance of R. tasmaniensis, can persist for at least 2 years following fire. These results have potentially important implications for post-fire recruitment.     

Productivity and water relations of burnt and long-unburnt semi-arid shrubland in Western Australia

This study provides a comparison between vegetation of relatively recent and long-unburnt shrubland in terms of structural and functional groups, annual net primary productivity and water relations. Adjacent areas of vegetation long-unburnt or burnt 5 years previously were compared within a remnant block of Acacia–Allocasuarina–Melaleuca arid shrubland at Kalannie, south west Western Australia. Species were classified according to growth and life form, fire response, phenology and rooting morphology and densities, mean plant above-ground dry weights and shoot:root dry mass ratios of each assessed. Species compositions, seedling densities and absence of recruitment in the long-unburnt area suggested marked dependence on fire in maintenance of biodiversity. Comparisons of above-ground standing dry biomass and annual net primary productivity of total (above-ground plus below-ground) dry matter showed the 4.09 kg m^–2 biomass of long-unburnt vegetation to be increasing at 0.52 kg m^–2 year^–1 versus 0.45 and 0.18 kg m^–2 year^–1 for vegetation of the burnt area. Water relations of soils indicated consistently wetter profiles in burnt than long-unburnt areas and no deep drainage during the year of study. Lower water stress of key species in burnt than long-unburnt areas were indicated by less negative pre-dawn water potentials and higher stomatal conductance during the year of study and more negative carbon-isotope composition (¹³C) in wood laid down over the past 5 years. Budgets for water use were estimated for both sites and compared with annual net primary productivities. Data suggested much greater transpiration loss per unit dry matter gain by the rapidly growing plants at the burnt site (437 ml H₂O g^–1 DM) than by the plants of the long-unburnt community (92 ml H₂O g^–1 DM). Results are discussed in relation to composition and functioning of other Western Australian ecosystems. It is clear that time since fire affects productivity and water-use of vegetation of semi-arid shrublands and is therefore an important consideration for management and protection of remnant vegetation.     

Reproduction, age and growth of Sillago maculata in south-eastern Australia

Sillago maculata is endemic to the east coast of Australia where it is harvested by recreational and commercial fishers; however, little is known of the important aspects of its biology and ecology to assist with fisheries management planning. This situation is redressed here by investigating aspects of the reproduction, age and growth of estuarine populations of S. maculata in south-eastern Australia. Gonadosomatic index (GSI) values indicated peak spawning occurred between September and February and that the estimated mean fork length at maturity (L₅₀) was 14.6 cm for males and 15.2 cm for females. Females displayed an asynchronous pattern of oocyte development, with individuals probably spawning multiple times in a spawning season. A validated aging protocol using thin sectioned otoliths was used to estimate the age of fish. The maximum ages for males and females were 9.5 and 12.0 years, respectively. Growth differed between sexes, with males ( L ∞ = 24.04, K  = 0.70, t ₀ = −0.09) attaining a smaller maximum length than females ( L ∞ = 25.01, K  = 0.72, t ₀ = −0.04). The age composition of gill-net and beach-seine samples mainly consisted of individuals aged 2–4 years, and there was evidence of variable recruitment. Management implications are also discussed.