Temperate Eucalypt Forests Research Articles

Fire regimes and environmental gradients shape vertebrate and plant distributions in temperate eucalypt forests

AbstractFire is a global driver of ecosystem structure, function, and change. Problems common to fire scientists and managers worldwide include a limited knowledge of how multiple taxonomic groups within a given ecosystem respond to recurrent fires, and how interactions between fire regimes and environmental gradients influence biodiversity. We tested six hypotheses relating to fire regimes and environmental gradients in forest ecosystems using data on birds (493 sites), mammals (175 sites), and vascular plants (615 sites) systematically collected in dry eucalypt forests in southeastern Australia. We addressed each of these hypotheses by fitting species distribution models which differed in the environmental variables used, the spatial extent of the data, or the type of response data. We found (1) as predicted, fire interacted with environmental gradients and shaped species distributions, but there was substantial variation between species; (2) multiple characteristics of fire regimes influenced the distribution of forest species; (3) common to vertebrates and plants was a strong influence of temperature and rainfall gradients, but contrary to predictions, inter‐fire interval was the most influential component of the fire regime on both taxonomic groups; (4) mixed support for the hypothesis that fire would be a stronger influence on species occurrence at a smaller spatial extent; only for vertebrates did scale have an effect in the direction expected; (5) as predicted, vertebrates closely associated with direct measures of habitat structure were those most strongly influenced by fire regimes; and (6) the modeled fire responses for birds were sensitive to the use of either presence–absence or abundance data. These results underscore the important insights that can be gained by modeling how fire regimes, not just fire events, influence biota in forests. Our work highlights the need for management of fire regimes to be complemented by an understanding of the underlying environmental gradients and key elements of habitat structure that influence resource availability for plants and animals. We have demonstrated that there are general patterns in biotic responses to fire regimes and environmental gradients, but landscape management must continue to carefully consider species, scale, and the quality of biodiversity data to achieve biodiversity conservation in fire‐prone forests.

Evergreen and ever growing – Stem and canopy growth dynamics of a temperate eucalypt forest

Irregular growth rings and long-lived leaves present challenges to quantify stem growth and canopy dynamics of evergreen eucalypt trees, which has impeded understanding of seasonal and inter-year biomass allocation in temperate eucalypt forests. To address this knowledge gap, we examined the sub-annual dynamics of stem and canopy growth by tree canopy class of three co-occurring species over 35months in a temperate eucalypt forest of southeastern Australia. We used dendrometers to monitor basal area increments and daily terrestrial lidar scans to monitor integrated and height-specific canopy dynamics. Associations with concomitant weather data and stand-level carbon fluxes were used to enhance understanding of biomass allocation patterns.Comparisons of growth patterns indicated seasonal asynchronicity of stem and crown growth: the canopy expanded mainly in summer and early autumn, and the stems grew mainly in spring and autumn, but also to a lesser degree in winter. Eucalypts in the dominant crown classes grew all year, with growth allocated to crown expansion and thickening in the summer months, or to stem growth in all other months. Canopy volume was stable during the first part of the study period and subsequently increased by 20%. However, stratum-specific dynamics indicated a distinct seasonality of canopy turnover, characterised by volume gains at the top of the canopy and concurrent volume losses in the middle stratum during summer. Growth patterns, as either canopy expansion or stem increment, were not clearly associated with ecosystem-scale carbon dynamics. In addition, relationships of growth with climatic variables appeared to be associative rather than causative, indicating that allocation dynamics to root growth and nonstructural carbohydrate pools will be essential in explaining ecosystem carbon dynamics in temperate eucalypt forests.

Soil methane oxidation in both dry and wet temperate eucalypt forests shows a near-identical relationship with soil air-filled porosity

Abstract. Well-drained, aerated soils are important sinks for atmospheric methane (CH4) via the process of CH4 oxidation by methane-oxidising bacteria (MOB). This terrestrial CH4 sink may contribute towards climate change mitigation, but the impact of changing soil moisture and temperature regimes on CH4 uptake is not well understood in all ecosystems. Soils in temperate forest ecosystems are the greatest terrestrial CH4 sink globally. Under predicted climate change scenarios, temperate eucalypt forests in south-eastern Australia are predicted to experience rapid and extreme changes in rainfall patterns, temperatures and wild fires. To investigate the influence of environmental drivers on seasonal and inter-annual variation of soil–atmosphere CH4 exchange, we measured soil–atmosphere CH4 exchange at high-temporal resolution (< 2 h) in a dry temperate eucalypt forest in Victoria (Wombat State Forest, precipitation 870 mm yr−1) and in a wet temperature eucalypt forest in Tasmania (Warra Long-Term Ecological Research site, 1700 mm yr−1). Both forest soil systems were continuous CH4 sinks of −1.79 kg CH4 ha−1 yr−1 in Victoria and −3.83 kg CH4 ha−1 yr−1 in Tasmania. Soil CH4 uptake showed substantial temporal variation and was strongly controlled by soil moisture at both forest sites. Soil CH4 uptake increased when soil moisture decreased and this relationship explained up to 90 % of the temporal variability. Furthermore, the relationship between soil moisture and soil CH4 flux was near-identical at both forest sites when soil moisture was expressed as soil air-filled porosity (AFP). Soil temperature only had a minor influence on soil CH4 uptake. Soil nitrogen concentrations were generally low and fluctuations in nitrogen availability did not influence soil CH4 uptake at either forest site. Our data suggest that soil MOB activity in the two forests was similar and that differences in soil CH4 exchange between the two forests were related to differences in soil moisture and thereby soil gas diffusivity. The differences between forest sites and the variation in soil CH4 exchange over time could be explained by soil AFP as an indicator of soil moisture status.

Do multiple fires interact to affect vegetation structure in temperate eucalypt forests?

Fire plays an important role in structuring vegetation in fire-prone regions worldwide. Progress has been made towards documenting the effects of individual fire events and fire regimes on vegetation structure; less is known of how different fire history attributes (e.g., time since fire, fire frequency) interact to affect vegetation. Using the temperate eucalypt foothill forests of southeastern Australia as a case study system, we examine two hypotheses about such interactions: (1) post-fire vegetation succession (e.g., time-since-fire effects) is influenced by other fire regime attributes and (2) the severity of the most recent fire overrides the effect of preceding fires on vegetation structure. Empirical data on vegetation structure were collected from 540 sites distributed across central and eastern Victoria, Australia. Linear mixed models were used to examine these hypotheses and determine the relative influence of fire and environmental attributes on vegetation structure. Fire history measures, particularly time since fire, affected several vegetation attributes including ground and canopy strata; others such as low and sub-canopy vegetation were more strongly influenced by environmental characteristics like rainfall. There was little support for the hypothesis that post-fire succession is influenced by fire history attributes other than time since fire; only canopy regeneration was influenced by another variable (fire type, representing severity). Our capacity to detect an overriding effect of the severity of the most recent fire was limited by a consistently weak effect of preceding fires on vegetation structure. Overall, results suggest the primary way that fire affects vegetation structure in foothill forests is via attributes of the most recent fire, both its severity and time since its occurrence; other attributes of fire regimes (e.g., fire interval, frequency) have less influence. The strong effect of environmental drivers, such as rainfall and topography, on many structural features show that foothill forest vegetation is also influenced by factors outside human control. While fire is amenable to human management, results suggest that at broad scales, structural attributes of these forests are relatively resilient to the effects of current fire regimes. Nonetheless, the potential for more frequent severe fires at short intervals, associated with a changing climate and/or fire management, warrant further consideration.

An assessment of ectomycorrhizal fungal communities in Tasmanian temperate high-altitude Eucalyptus delegatensis forest reveals a dominance of the Cortinariaceae.

Fungal diversity of Australian eucalypt forests remains underexplored. We investigated the ectomycorrhizal (EcM) fungal community characteristics of declining temperate eucalypt forests in Tasmania. Within this context, we explored the diversity of EcM fungi of two forest types in the northern highlands in the east and west of the island. We hypothesised that EcM fungal community richness and composition would differ between forest type but that the Cortinariaceae would be the dominant family irrespective of forest type. We proposed that EcM richness would be greater in the wet sclerophyll forest than the dry sclerophyll forest type. Using both sporocarps and EcM fungi from root tips amplified by PCR and sequenced in the rDNA ITS region, 175 EcM operational taxonomic units were identified of which 97 belonged to the Cortinariaceae. The Cortinariaceae were the most diverse family, in both the above and below ground communities. Three distinct fungal assemblages occurred within the wet and dry sclerophyll forest types and two geographic regions that were studied, although this pattern did not remain when only the root tip data were analysed. EcM sporocarp richness was unusually higher than root tip richness and EcM richness did not significantly differ among forest types. The results are discussed in relation to the importance of the Cortinariaceae and the drivers of EcM fungal community composition within these forests.

Production of pyrogenic carbon during planned fires in forests of East Gippsland, Victoria

Management strategies such as planned burning for fuel reduction can help mitigate the effects of wildfires. The amount of biomass consumed is of interest to fire managers as reduction of fuel loads is imperative to reducing the risk and extent of a wildfire event. Biomass regeneration is also of importance for ecosystem recovery and resilience. Pyrogenic carbon (PyC), a product of combustion during both planned and unplanned fires, plays a key role in global carbon stores and balances. A three-year study of planned burning practices examined fires in Lowland temperate Eucalypt forest of south eastern Australia. We collected data on overstorey, understorey, coarse woody debris, fine litter, PyC and soil across nine sites to determine biomass consumption, PyC production and changes in ecosystem carbon during planned burning. Lowland forest showed significant recovery of combustible biomass (fine litter and understorey) one year after planned fire. Across our sites, PyC was produced at a rate of approximately 5% of the biomass consumed. The PyC produced is destined to become part of soil and litter carbon and contributes to long-term carbon storage. Planned burning had a short-term (<1year) impact on forest carbon balance, and on reduction risk of wildfire and associated losses of biomass carbon, but no long-term impact, through deposition of PyC and recovery of biomass.

Too much, too soon? A review of the effects of increasing wildfire frequency on tree mortality and regeneration in temperate eucalypt forests

In temperate Australia, wildfires are predicted to be more frequent and severe under climate change. This could lead to marked changes in tree mortality and regeneration in the region’s predominant eucalypt forests, which have been burned repeatedly by extensive wildfires in the period 2003–14. Recent studies have applied alternative stable state models to select ‘fire sensitive’ forest types, but comparable models have not been rigorously examined in relation to the more extensive ‘fire tolerant’ forests in the region. We review the effects of increasing wildfire frequency on tree mortality and regeneration in temperate forests of Victoria, south-eastern Australia, based on the functional traits of the dominant eucalypts: those that are typically killed by wildfire to regenerate from seed (‘obligate seeders’) and those that mostly survive to resprout (‘resprouters’). In Victoria, over 4.3 million ha of eucalypt forest has been burned by wildfire in the last decade (2003–14), roughly equivalent to the cumulative area burned in the previous 50 years (1952–2002; 4.4 million ha). This increased wildfire activity has occurred regardless of several advancements in fire management, and has resulted in over 350 000 ha of eucalypt forest being burned twice or more by wildfire at short (≤11 year) intervals. Historical and recent evidence indicates that recurrent wildfires threaten the persistence of the ‘fire sensitive’ obligate seeder eucalypt forests, which can facilitate a shift to non-forest states if successive fires occur within the trees’ primary juvenile period (1–20 years). Our review also highlights potential for structural and state changes in the ‘fire tolerant’ resprouter forests, particularly if recurrent severe wildfires kill seedlings and increase tree mortality. We present conceptual models of state changes in temperate eucalypt forests with increasing wildfire frequency, and highlight knowledge gaps relating to the development and persistence of alternative states driven by changes in fire regimes.

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).

Evaluating long-term effects of prescribed fire regimes on carbon stocks in a temperate eucalypt forest

Prescribed fires are a common management practice in the temperate forests of Australia, but effects on total forest carbon (C) of long-term prescribed fire regimes, involving multiple repeat fires, remain under-examined. This study quantified C stocks in multiple pools after 27years of a long-term prescribed fire experiment in a mixed-species eucalypt forest in south-eastern Australia. The experimental design included five replications of each of five treatments – a long-unburnt Control, plus a factorial combination of two fire frequencies (c. 3-yearly ‘High’, c. 10-yearly ‘Low’), and two fire seasons (Spring, Autumn) – encompassing up to 7 low-intensity repeat fires over the 27years.Overall, total C stocks (the sum of all pools: Above-ground biomass, Dead wood, Litter, and Soil) were significantly greater in Control than Fire treatments. Mean total C stock differences (Control minus Fire) were 36Mgha−1, and increased with both fire frequency (46Mgha−1, Control versus High frequency treatments) and fires in autumn rather than spring (42Mgha−1, Control versus Autumn treatments). Mean differences had wide 95% confidence intervals (e.g. 4–67MgCha−1, Control versus Fire), indicating considerable uncertainty about the magnitude of effects of prescribed fire regimes on total C in these native forests. Weighted averaging of linear multiple regression models was used to identify the most important variables for explaining proportional C stock differences ((Control–Fire)/Control), and involved consideration of 85 explanatory variables including measures of fire intensity, fire severity, fuel, pre- and post-fire rainfall, fire weather, and topography. The best regression model explained 80% of variation in total C stock differences between Control and Fire treatments. Consistently important explanatory variables were those representing or associated with fire intensity (flame angle, wind speed, Forest Fire Danger Index), and number of prescribed fires. Measures of fuel load, pre- and post-fire rainfall, and, in particular, fire severity, were less important explanatory variables. The study provides indications of management options for minimising C stock decreases associated with prescribed fire regimes in temperate eucalypt forests; notably, wide fire intervals (closer to 10 than 3years), and utilising strategies to minimise mean fire intensity, including burning in moist (spring) rather than dry (autumn) conditions.

A warmer world will reduce tree growth in evergreen broadleaf forests: evidence from Australian temperate and subtropical eucalypt forests

AbstractAimsUnderstanding how tree growth is influenced by climate is vital for predicting how forests will respond to climate change, yet there have been few studies of tree growth spanning macroclimatic gradients. The aim of this study is to correlate growth of a single lineage of broadleaf evergreen trees with continental‐scale variability in climate.LocationAustralia's temperate mesic eucalypt forests, spanning latitudes from 23 to 43° S and longitudes from 115 to 153° E.MethodsWe compiled and analysed a dataset containing around half a million measurements of growth in eucalypt tree diameter, collected from 2409 permanent forestry plots. These plots spanned a range of 558–2105 mm mean annual precipitation and 6–22 °C mean annual temperature. Generalized additive models were used to study the relationship between growth in tree diameter and several temperature and water availability variables.ResultsTree growth increased with precipitation, but with a diminishing response above a mean annual precipitation of 1400 mm. There was a peaked response to temperature, with maximum growth occurring at a mean annual temperature of 11 °C and maximum temperature of the warmest month of 25–27 °C. Lower temperatures directly constrain growth. High temperatures primarily reduced growth by reducing water availability, but they also appeared to exert a direct negative effect. Our best model, which included maximum temperature of the warmest month and the ratio of precipitation to evaporation, explained 28% of the deviance.Main conclusionsThe productivity of Australia's temperate eucalypt forests could decline substantially as the climate warms, given that 87% of these forests currently experience a mean annual temperature above 11 °C, where the highest growth rates were observed. This will reduce carbon sequestration and slow recovery after catastrophic disturbances such as wildfire.

Can precipitation influence landscape controls on wildfire severity? A case study within temperate eucalypt forests of south-eastern Australia

The environmental, economic and social impacts of wildfires depend on spatial patterns of fire severity. An understanding as to how drivers of fire severity vary across broad vegetation communities exists. However, examination of variation within communities in response to gradients of moisture has received little attention so far. This study examined whether relationships between environmental variables (i.e. fire weather, topography and fuel age) and fire severity were modified by increasing mean annual precipitation. Understorey fires were more likely to occur in young fuels (i.e. &lt;5 years since fire) in drier sites, although this effect diminished as precipitation increased. The probability of occurrence of understorey fires under non-extreme weather and on steep slopes was reduced in wetter areas. Relationships between crown fire and weather, topography and fuel age were largely unaltered by the precipitation gradient, with only a marginally significant interaction occurring between weather and mean annual precipitation. Greater fine fuel accumulation associated with increased precipitation presumably reduced fuel limitations imposed by environmental factors (i.e. fire weather, slope, fuel age), altering their relative control on the probability of understorey fire. The probability of crown fires is predominantly driven by fire weather and is consequently less sensitive to precipitation gradients. Consideration of precipitation gradients will be necessary when identifying controls of fire severity and devising effective fire management strategies.

Temperate eucalypt forest decline is linked to altered ectomycorrhizal communities mediated by soil chemistry

Eucalypt forest decline has a complex aetiology often linked to altered soil chemistry caused by environmental disturbances. Forest decline has also been linked to alterations in ectomycorrhizal (ECM) fungal communities, which are imperative for nutrient transfer and affect ecosystem productivity and health. Our aim was to determine the influence of soil chemistry on ECM fungal communities and tree health in declining temperate eucalypt forests. We hypothesise that forests with changed soil chemistry, in particular altered nitrogen cycling associated with forest decline, supports unique ECM fungal communities. ECM communities from twelve Eucalyptus delegatensis forest plots were characterised by DNA sequencing of root tip and sporocarp samples. Tree health and nutrient concentrations from soil and foliage samples were quantified for each plot. Multivariate and regression analyses and t-tests were used to determine ECM fungal community differences between forest health classes, and identify which soil variables were important for defining these communities. Elevated available soil nitrogen and soil acidity were associated with severely declining forest. Soil pH, nitrate and organic carbon significantly explained the majority of variation in ECM fungal community composition and structure, which differed between moderately and severely declining forest. Russulaceae species richness was greatest in acidic soils (severely declining forest) while Cortinariaceae species richness was greatest in soils with lower concentrations of soil nitrate (moderately declining forest). Total ECM fungal richness was inversely related to available soil phosphorus and soil nitrate. Thus, altered soil chemistry associated with eucalypt forest decline mediates changes in the ECM fungal community. Forest management must consider the role of disturbance in maintaining suitable soil conditions for symbiotic fungi which are important for maintaining healthy eucalypt forest and restoring declining forest ecosystems.

Can gullies preserve complex forest structure in frequently burnt landscapes?

Structurally complex forest provides important habitat for a diverse array of vertebrate fauna. Frequent fire can simplify forest structure, though topographic mitigation of fire effects could potentially preserve structurally more complex habitat within certain topographic locations of fire prone landscapes. Our study assessed whether the effects of fire frequency on forest structure (tree hollows, log volume, vegetation complexity) varied with topographic position. The effect of wildfire severity and intensive logging were also examined. Frequent fire reduced vegetation cover on ridges, but not in gullies. The risk of collapse (i.e. presence of fire scars) increased for large trees on frequently burnt ridges, but remained suppressed in gullies. Crown fire reduced hollow presence in dead trees (i.e. snags), but increased hollow presence in trees with a healthy crown. The volume of extensively decomposed logs was three times greater in gullies than ridges, but was unaffected by fire frequency. Intensive logging reduced the number of hollow bearing trees and increased the volume of extensively decomposed logs, though future declines in log volume are predicted due to bottlenecks in log input. Our results suggest that gullies may play a critical role in preserving structurally complex stands within frequently burnt temperate eucalypt forests. Protecting gullies from land clearing and intensive logging is likely to be an important step in maintaining key habitat features and associated fauna in these landscapes.

Modelling the potential for prescribed burning to mitigate carbon emissions from wildfires in fire-prone forests of Australia

Prescribed fire can potentially reduce carbon emissions from unplanned fires. This potential will differ among ecosystems owing to inherent differences in the efficacy of prescribed burning in reducing unplanned fire activity (or ‘leverage’, i.e. the reduction in area of unplanned fire per unit area of prescribed fire). In temperate eucalypt forests, prescribed burning leverage is relatively low and potential for mitigation of carbon emissions from unplanned fires via prescribed fire is potentially limited. Simulations of fire regimes accounting for non-linear patterns of fuel dynamics for three fuel types characteristic of eucalypt forests in south-eastern Australia supported this prediction. Estimated mean annual fuel consumption increased with diminishing leverage and increasing rate of prescribed burning, even though average fire intensity (prescribed and unplanned fires combined) decreased. The results indicated that use of prescribed burning in these temperate forests is unlikely to yield a net reduction in carbon emissions. Future increases in burning rates under climate change may increase emissions and reduce carbon sequestration. A more detailed understanding of the efficacy of prescribed burning and dynamics of combustible biomass pools is required to clarify the potential for mitigation of carbon emissions in temperate eucalypt forests and other ecosystems.

The 10 Australian ecosystems most vulnerable to tipping points

We identify the 10 major terrestrial and marine ecosystems in Australia most vulnerable to tipping points, in which modest environmental changes can cause disproportionately large changes in ecosystem properties. To accomplish this we independently surveyed the coauthors of this paper to produce a list of candidate ecosystems, and then refined this list during a 2-day workshop. The list includes (1) elevationally restricted mountain ecosystems, (2) tropical savannas, (3) coastal floodplains and wetlands, (4) coral reefs, (5) drier rainforests, (6) wetlands and floodplains in the Murray-Darling Basin, (7) the Mediterranean ecosystems of southwestern Australia, (8) offshore islands, (9) temperate eucalypt forests, and (10) salt marshes and mangroves. Some of these ecosystems are vulnerable to widespread phase-changes that could fundamentally alter ecosystem properties such as habitat structure, species composition, fire regimes, or carbon storage. Others appear susceptible to major changes across only part of their geographic range, whereas yet others are susceptible to a large-scale decline of key biotic components, such as small mammals or stream-dwelling amphibians. For each ecosystem we consider the intrinsic features and external drivers that render it susceptible to tipping points, and identify subtypes of the ecosystem that we deem to be especially vulnerable.

The contribution of mistletoes to nutrient returns: Evidence for a critical role in nutrient cycling

AbstractBoth nutrient cycling and nutrient relationships between mistletoe and host have been widely studied; yet it is unclear whether high nutrient concentrations commonly found in mistletoes affect rates of nutrient cycling. To address this question, we assessed 13 elements in the leaf litter of a temperate eucalypt forest in southern New South Wales, comparing concentrations from trees (Eucalyptus blakelyi, E. dwyeri, and E. dealbata) with and without the hemiparasitic mistletoe Amyema miquelii. Results were in accord with previous research on fresh leaves showing that concentrations of many elements were higher in the mistletoe than the host. This was not the case for all elements; most notably for N, where concentrations were significantly lower in the mistletoe. However, the return of all elements increased with mistletoe infection because of the combined effect of enrichment in mistletoe tissues and high rates of mistletoe litterfall. Annual returns of N and P in leaf litter increased by a factor of 1.65 and 3 respectively, with the greatest increase being for K by a factor of 43 in spring. These increased element returns were not significantly influenced by any changes in host leaf litter quality, as mistletoe infection was not found to affect host element concentrations. Mistletoe infection also altered the spatial and temporal distribution of element returns because of the patchy occurrence of mistletoes and extended period of mistletoe litterfall compared with the host. These findings provide a mechanistic explanation for the role of mistletoes as a keystone resource and, together with comparable results from root‐parasitic plants in boreal tundra and cool‐temperate grasslands, suggest that enhancing nutrient return rates may be a generalized property of parasitic plants.

Sediment aggregation and water quality in wildfire-affected river basins

Off-site transfer of nutrient-rich burnt soil has implications for downstream water quality. Coarsening of effective particle size (EPS) distributions in burnt material via aggregation of fines into composite particles modifies post-fire sediment and nutrient transport dynamics. Experiments were undertaken to establish temperature controls on wildfire-enhanced soil aggregation. Burnt and unburnt soil from a temperate eucalypt forest were analysed for EPS and settling velocity using a LISST-ST (Laser In Situ Scatter and Transmissometry with Settling Tube) particle size analyser. Next, samples were burnt (250–550°C) before further analysis with the LISST-ST. Settling velocities of naturally burnt soil aggregates were greater than unburnt aggregates of the same EPS. Experimental burning indicated that dense water-stable aggregates form at relatively low temperatures (250°C) probably due to distillation and carbonisation, through pyrolysis, of organic volatiles in surface litter. Under these conditions, the EPS distribution of burnt surface soil coarsens with up to 50% of the &lt;63-μm fraction becoming aggregated. A positive relationship between ‘plant-available’ phosphorus and burn temperature was observed. Given that a large proportion of soil particulate phosphorus is associated with the &lt;63-μm fraction, fire-related aggregation processes have potentially important implications for post-fire fine sediment and nutrient transport and storage dynamics.

Physiology Complements Population Structure of Two Endemic Log-Dwelling Beetles

Given rapid, global land modification and the likelihood of major global climate changes, it is becoming increasingly important to understand the physiological limits and capabilities of species to allow more accurate prediction of species' distributions under different scenarios of climate and landscape management. We studied whether the different habitat requirements of two species of tenebrionid beetles in temperate eucalypt forest could explain their patterns of dispersal and gene flow by applying flow-through respirometry to analysis of their physiological responses to different, ecologically relevant temperatures. Both Adelium calosomoides and Apasis puncticeps showed sensitivity to increasing temperatures (in terms of water loss), but Ap. puncticeps lost more water per unit of CO2 produced than did Ad. calosomoides. Recovery time from chill coma was also significantly longer for Ap. puncticeps than Ad. calosomoides. This supported prior qualitative assessment that Ap. puncticeps is more of a habitat specialist than Ad. calosomoides, at least concerning the critical factor of moisture requirements, and is consistent with stronger population genetic patterning and inferred low mobility of Ap. puncticeps. Despite its relatively lower mobility as deduced from population genetic structure, Ap. puncticeps walked four times faster than Ad. calosomoides in a laboratory assay, indicating that, for these species, mobility and gene flow are influenced more by physiological limitations than by speed.

Systematics of the Australasian endemic wasp genus Syngaster Brullé (Hymenoptera: Braconidae: Doryctinae)

The braconid genus Syngaster Brullé is revised and nine species are recognized, six of which are new: S. lepidus Brullé, S. quadricolor (Cameron), S. variegatus (Szépligeti), S. crypticus sp. nov., S. hirtus sp. nov., S. neoguineensis sp. nov., S. polychromus sp. nov., S. stevensi sp. nov., and S. tricolor sp. nov. Host data are only available for S. lepidus which is a parasitoid of cerambycid larvae, notably Phoracantha spp. associated with temperate, subtropical and Mediterranean eucalypt forests in eastern and southern Australia. Other than S. lepidus, S. polychromus is the only other species known from Australia (south‐east Queensland), the remaining seven species all being restricted to mainland New Guinea. Preliminary phylogenetic analysis indicates the genus comprises two species groups with S. lepidus and S. quadricolor forming a polytomy with these. The two Australian species (S. lepidus and S. polychromus) are not monophyletic, nor are the two species that lack an occipital carina (S. tricolor and S. cryptus). Present address: M. Iqbal, Department of Environment & Heritage, Canberra, Australia

Correlation of burning and grazing indicators with composition of woody understorey flora of dells in a temperate eucalypt forest

Abstract Areas of warm temperate eucalypt forests of northern NSW escarpment, previously managed for cattle production, have recently been transferred into the conservation reserve system. The forests were seasonally grazed by cattle and were burnt frequently to promote green pick for stock feed. The hypothesis that disturbances associated with previous management had led to a simplification of the forest understorey, particularly a depletion in the density and species richness of shrubs was investigated. A disturbance history of the study area was constructed by compiling fire history records and using surrogate measures for recent and historical grazing. Shrub species composition was sampled in randomly located quadrats in dells within the forest, with a set of environmental and spatial covariables. Variation in shrub composition was partitioned among three sources (disturbance, environment and space) using a stepwise canonical correspondence analysis. Grazing and burning disturbance explained substantially more variation in vegetation than the environmental and spatial variables combined. Between 15 and 45% of total variation in adult shrub composition was attributable to the disturbance indicators. Similar results were obtained for composition of juvenile shrubs. Species richness and population densities of woody species were lower where disturbance was more intensive. It is concluded that historical grazing and burning practices had a substantial impact on the woody understoreys of the north‐east escarpment forests. The species that were adversely affected spanned a range of life‐history functional types. Estimates of the magnitude of grazing and burning impacts were limited by the lack of spatially explicit disturbance history data over the full period of pastoral exploitation and the unavailability of suitable ungrazed‘controls’for sampling.