Forests Of South-western Australia Research Articles

Hydrological impact of two intensities of timber harvest and associated silviculture in the jarrah forest in south-western Australia

Summary The hydrological impact of two different intensities of timber harvest and associated silviculture, one standard and the other more intensive, was investigated using a paired-catchment study in jarrah forest in south-western Australia. This study was undertaken during a period when average annual rainfall was below the long-term average and deep groundwater levels were declining. Following treatment, recharge increased and slowed the decline in deep groundwater levels in proportion to the magnitude of the initial reduction in vegetation density. However, neither treatment was sufficiently intense to reverse the continued decline in groundwater levels over the course of the study. Annual stream salinity did not increase in response to either treatment because saline deep groundwater did not rise following the treatments. Annual streamflow did not increase in either catchment for three reasons. Firstly, there was little additional net precipitation to the intermittent shallow perched groundwater system in the streamzone because the area remained untreated. Secondly, there was minimal additional throughflow to the perched groundwater system in the streamzone from upslope areas because the increased net precipitation in hillslope areas following treatment was used in replenishing the progressively increasing soil moisture deficit. Thirdly, because groundwater levels did not rise and hence there was little prospect for an increased discharge of saline groundwater or of an expanded deep groundwater discharge zone. This study has demonstrated that the measures that were implemented to timber harvest and silvicultural methods to reduce the magnitude of the groundwater response and hence the risk of a transient increase in stream salinity are effective. If annual rainfall remains relatively low and deep groundwater levels remain at current levels or decline further, then the risk of an increase in stream salinity from either the standard or the more intensive harvest and silviculture will be low.

Transpiration and hydraulic traits of old and regrowth eucalypt forest in southwestern Australia

We tested the hypothesis that overstorey of eucalypt forest dominated by tall, large diameter trees uses less water than regrowth stands in the high rainfall zone (>1100 mm year −1 ) of the northern jarrah ( Eucalyptus marginata ) forest in southwestern Australia. We measured leaf area, cover, sapwood area and sapwood density at three paired old and regrowth stands. We also measured sapflow velocity at one paired stand (Dwellingup) from June 2007 to October 2008. Old stands had more basal area but less foliage cover, less leaf area and slightly thinner sapwood. The ratio of sapwood area to basal area decreased markedly as tree size increased. Sapwood area of the regrowth forest stands (6.6 ± 0.30 m 2 ha −1 ) was nearly double that of the old stands (3.4 ± 0.17 m 2 ha −1 ), despite larger basal area at the old stands. Leaf area index of the regrowth stands (2.1 ± 0.26) was only one-third larger than that at the old stands (1.5 ± 0.15); hence, the ratio of leaf area to sapwood area was larger in old stands than in regrowth stands (0.45 ± 0.022 m 2 cm −2 versus 0.32 ± 0.045 m 2 cm −2 ). Our results are consistent with theories that trees have evolved to optimize carbon gain rather than maintain stomatal conductance. Neither sapwood density (540–650 kg m −3 ) nor sap velocity differed greatly between regrowth and old stands. At the old forest site, daily transpiration rose from 0.5 mm day −1 in winter to 0.9 mm day −1 in spring–summer, compared to 0.9 mm day −1 and 1.8 mm day −1 at the regrowth site. Annual water use by the overstorey trees was estimated to be ∼230 mm year −1 for the old stand and ∼500 mm year −1 at the regrowth stand, or 20% and 44% of annual rainfall. The overwhelming role of stand sapwood area in determining stand water use, combined with the marked changes in the ratio of sapwood area to basal area with tree age and size, suggest that stand overstorey structure can be managed to alter overstorey water use and catchment water yield. Silviculture to promote old-forest-like attributes may be a viable means of delivering multiple water and conservation benefits.

Simple models for predicting dead fuel moisture in eucalyptus forests

Fire behaviour prediction requires models of dead fuel moisture that are both accurate and suitable for use for operational applications. The paper investigates two methods of developing a simple operational fine fuel moisture model from a more complex process-based model. The first simple model is a table of fuel moisture predictions for values of air temperature, relative humidity, wind speed and solar radiation. The second model reduces the original model to a single differential equation, which may be used on low-powered computers. The simple models are tested against the output of the original model and against observations from two case studies in dry eucalyptus forest in south-western Australia. The single differential equation model was capable of reproducing the prediction of the process-based model at all times of the day, with mean error (ME) in predictions of –0.1% and mean absolute error (MAE) of 0.6%. The table model performed less well, with ME = –0.7% and MAE = 1.1% at 1500 hours, and ME = –1.2% and MAE = 3.0% at other times of the day.

Architectural plasticity in young Eucalyptus marginata on restored bauxite mines and adjacent natural forest in south-western Australia

The aboveground architecture of Eucalyptus marginata (Jarrah) was investigated in chronosequences of young trees (2.5, 5 and 10 m height) growing in a seasonally dry climate in a natural forest environment with intact soils, and on adjacent restored bauxite mine sites on soils with highly modified A and B horizons above an intact C horizon. Compared to forest trees, trees on restored sites were much younger and faster growing, with straighter, more clearly defined main stems and deeper, narrower crowns containing a greater number of branches that were longer, thinner and more vertically angled. Trees on restored sites also had a higher fraction of biomass in leaves than forest trees, as indicated by 20-25% thicker leaves, 30-70% greater leaf area, 10-30% greater leaf area to sapwood area ratios and 5-30% lesser branch Huber values. Differences in crown architecture and biomass distribution were consistent with putatively greater soil-water, nutrient and light availability on restored sites. Our results demonstrate that under the same climatic conditions, E. marginata displays a high degree of plasticity of aboveground architecture in response to the net effects of resource availability and soil environment. These differences in architecture are likely to have functional consequences in relation to tree hydraulics and growth that, on larger scales, is likely to affect the water and carbon balances of restored forest ecosystems. This study highlights substrate as a significant determinant of tree architecture in water-limited environments. It further suggests that the architecture of young trees on restored sites may need to change again if they are to survive likely longer-term changes in resource availability.

Effect of time since burn on soil seedbanks in the jarrah forest of Western Australia

Bauxite is mined in the jarrah (Eucalyptus marginata Sm.) forest of south-western Australia and 700–800 ha each year are rehabilitated by mining companies. As well as broadcasting seeds and planting, the mine restoration relies heavily on the natural soil seedbank as a means of reinstating plant diversity after mining. The natural soil seedbank is a large but highly variable resource, both spatially and temporally. In the present study, we used 32 sites paired across burn boundaries to determine changes in soil seedbanks due to time since burn. At each site, we took one hundred 100-cm2 soil samples down to 5-cm depth and recorded germinable seeds. The mean total seedbank over all sites was 472 seeds m–2 (90–1210 seeds m–2). Five months after a spring burn, there was a significant decrease in the seedbank of legumes, compared with unburnt sites, probably due to germination in spring immediately after burning. Non-legumes (mostly non-heat-responsive species) did not show this decrease. One year after burning, there was a significant reduction in the total seedbank, presumably due to germination of most species in the winter following the burn. Legumes and non-legumes both showed this decrease. There was a recovery of the soil seedbank by 3 years after burning. This recovery was associated with higher densities of species from the families Apiaceae, Rhamnaceae (Trymalium ledifolium Fenzl), Stylidiaceae, Rutaceae, Centrolepidaceae and Sterculiaceae (Lasiopetalum floribundum Benth.). These families represent annuals, herbaceous species and small perennial shrubs. The recovery was likely due to vigorous flowering, and seed set by seedlings and sometimes resprouts following the burn. Once recovered, the soil seedbank stayed reasonably consistent up to 22 years after burning. Soils stripped 1 year after burning may contribute less plant density and diversity to rehabilitated areas. There is no evidence that the soil seedbank significantly decreases in the longer term with increasing time since burning up to 22 years. The community composition of the soil seedbank was strongly affected by geographical location, with sites closer to each other having similar composition. Only sites 1-year-since burn showed changes in the community composition due to burning.

The ecology of the rufous treecreeper in the jarrah forest of south-western Australia and implications for its conservation and management

Rufous treecreepers (Climacteris rufa) are common in southern jarrah forests of Western Australia, but nothing has been recorded of their ecology in the region. I investigated the foraging and nesting ecology of the species in the southern jarrah forests from January 1994 to April 1996. Rufous treecreepers foraged exclusively on two eucalypt species, jarrah and marri, and foraged on trees that were significantly larger and taller than random. Foraging on the ground, logs and fallen trees was relatively infrequent. Nest hollows were also located exclusively in jarrah and marri trees that were significantly larger and taller than random. The important foraging and nesting resources for the species in the southern jarrah forest appear to be large mature and overmature eucalypts. Anthropogenic impacts in the region, primarily logging, should aim to retain these resources in affected areas to improve the survival prospects of the species. When compared with studies in wandoo woodlands, the results of the present study indicate that the conservation of ground-layer habitat is likely to be of less importance in the jarrah forest. These habitat differences indicate that site-specific information is critical if the management and conservation of individual species is to be effective.

Average body length of arboreal and aerial beetle (Coleoptera) assemblages from remnant and plantation Eucalyptus forests in southwestern Australia

We examined body length differences between the beetle fauna of Eucalyptus plantation forests and remnant Eucalyptus forest in the same region using aerial and arboreal sampling. Mean body length of plantation-using species was greater than for remnant forest species, and the same pattern was apparent in the mean of all individuals collected regardless of species. This pattern was true for both Malaise-trap-collected beetles (aerial) and canopy-collected (arboreal) beetles. The tendency for plantation-restricted species to have longer bodies is significant even if clade is treated as a random factor in the analysis. Greater body length among plantation-using species is consistent with a few other studies that have found body size of insect species in early successional environments is typically greater than in late successional environments. Some studies suggest that larger species are better dispersers, which can rapidly colonise early successional habitats. In this study, however, there was little relationship between body length and the number of sites occupied; suggesting dispersal was not a major determinant of community membership. Two different patterns in this study support the hypothesis that body size differences are linked to trophic structure of the communities. First, the body length shift comparing remnant users to plantation users was greater among phytophages than for predators or saprophages. Second, saprophages were typically smaller than phytophages, and constituted a larger fraction of the remnant forest using fauna, driving down the mean body length in the saprophage-rich remnant forest community.

Invertebrate prey of the bark-foraging insectivore Phascogale tapoatafa: distribution of biomass amongst alternative foraging substrates within south-western Australian woodlands

The bark of trees is an important foraging substrate for a range of vertebrate insectivores. This study aimed to investigate the distribution of food resources available to the bark-foraging insectivore Phascogale tapoatafa, and to compare prey biomass on bark versus the litter layer. We conducted nocturnal sampling for arthropods on tree trunks and litter in a forest in south-western Australia. The bark fauna biomass was dominated by spiders, with cockroaches, beetles and ants also well represented. In contrast, the litter was dominated by orthopterans. Invertebrate biomass was much greater in the litter layer than on tree trunks. Prey items in bark were more plentiful in Melaleuca swamps than in the surrounding dry sclerophyll woodland. Within swamps, trees with the highest invertebrate densities had thin trunks or loose bark, whilst in woodland it was trees with thick bark. Water availability may increase the prey resource used by bark-foraging insectivores.

The abundance of a threatened arboreal marsupial in relation to anthropogenic disturbances at local and landscape scales in Mediterranean-type forests in south-western Australia

This study investigated associations between the relative abundance of the threatened ngwayir (western ringtail possum, Pseudocheirus occidentalis) and anthropogenic disturbances at local and landscape scales within the publicly-managed jarrah ( Eucalyptus marginata) forests of south-western Australia. Logging, fire, fox ( Vulpes vulpes) control and forest fragmentation were investigated in relation to the relative abundance of ngwayir at 90 sites within an area of 285,000 ha east of Manjimup; the location of the last remaining substantial population of ngwayir in jarrah forest. Overall, ngwayir abundance was greatest in areas with limited anthropogenic disturbance. At the local-scale, ngwayir abundance was negatively associated with greater fire intensity. At the landscape-scale, it was positively associated with fox control and negatively associated with forest fragmentation and distance from non-remnant vegetation (i.e., agriculture and tree plantations). Abundance was also greatest in predominantly unlogged landscapes and in forests that had been regrowing for an average of 40 years since the landscape was most recently logged, in other words, where logging was historically least intense. Interactions between fox control efforts and forest fragmentation were also important. This study emphasises the importance of conducting research at appropriate spatial scales and to account for the synergistic effects of the causes of decline. An adaptive management approach to the mitigation of the agents of decline is recommended. Indirect evidence indicates that high value habitat for ngwayir has in all likelihood been selectively cleared for agriculture, owing to its fertile and productive nature. Habitat loss is, therefore, also likely to be a major cause of the modern decline of the species. While many jarrah forest areas that support remaining high abundances of the ngwayir have been incorporated into reserves, conservation of ngwayir habitat and populations outside reserves also will be essential for the recovery and long-term viability of the species.

Impact of N and P fertilizer application on nutrient cycling in jarrah (Eucalyptus marginata) forests of south western Australia

Jarrah (Eucalyptus marginata Donn ex Smith) forest grows on poor soils with low stores of plant-available nutrients. We evaluated the impact of fertilizers on nutrient cycling in soil under Jarrah forest using a field study with three rates of P (0, 50, 200 kg P ha−1) and three rates of N (0, 100, 200 kg N ha−1) in a full factorial design. Litterfall was significantly increased by N application (30% relative to controls) in the first 2 years after treatment and by P application in the second year. The amounts of N, P, K, Ca and Mg in litterfall were also increased significantly by both N and P fertilizer. Although fertilizer treatments did not affect the total amount of litter accumulated on the forest floor over 4–5 years after application, there were large treatment differences in the amounts of N and P stored in the forest floor. Microbial respiration in litter was significantly greater (19%) on P-treated plots relative to controls, but this increase did not translate into increased decomposition rates as measured in long-term (5-year) mesh-bag studies. The results indicate that factors other than nutrition are mainly responsible for controlling the rate of decomposition in this ecosystem. Application of P, in particular, resulted in substantial accumulation of P in forest floor litter over 5 years. This accumulation was partly a result of the deposition of P in litterfall, but was also probably a result of translocation of P from the mineral soil. During the 5-year decomposition study, there was no net release of P from leaf litter and, at the highest rate of P application, the amounts of P stored in forest floor litter were more than four-fold greater than in fresh litter. Regular fire, a common phenomenon in these ecosystems, may be an important P-mobilizing agent for enhancing plant P uptake in these forests.

Long-term trends in native mammal capture rates in a jarrah forest in south-western Australia

Summary The south-western Australian forests and woodlands are important refugia for many species of native mammals that were once widespread across the continent. In the late 1960s, the Perup jarrah forest was identified as being particularly rich in native mammals. Following light selection logging in the 1960s and early 1970s, the forest was primarily managed for the conservation of fauna in recognition of its outstanding conservation value. Detailed fauna studies commenced in 1974 following a preliminary survey and trapping in 1971. Mammal trapping has continued in the Perup forest for twenty-six years, making that forest the site of one of the longest mammal monitoring studies in Australia. Long-term trends in the capture rates of four species, Bettongia penicillata (woylie), Dasyurus geoffroii (chuditch), Isoodon obesulus (quenda) and Trichosurus vulpecula (common brushtail possum), reveal that capture rates, which could be interpreted as mammal abundance, coincide with the level of effort to control the introduced fox (Vulpes vulpes). In the absence of fox control during the early 1970s capture rates of native mammals were less than 12% (i.e. fewer than 12% of traps set caught an animal overnight). In the northern part of Perup forest the woylie was presumed extinct as none was trapped or observed. Between 1977 and 1998, with ongoing fox control, capture rates increased to more than 70%. The woylie showed the greatest increase in capture rate and was the most widespread and commonly caught animal. The capture rates of the other species also increased, but more than 80% of mammals captured were woylies. The high abundance of woylies in recent times has compromised the monitoring protocol, with virtually all traps set catching or being tampered with by woylies, rendering them unavailable to other less-abundant species. A new monitoring protocol is suggested to accommodate the high population density of native mammals.

The long-term ability of phosphite to control Phytophthora cinnamomi in two native plant communities of Western Australia

This study examined the ability of foliar applications of the fungicide phosphite to contain colonisation of Phytophthora cinnamomi in a range of plant species growing in natural plant communities in the northern sandplain and jarrah (Eucalyptus marginata) forest of south-western Australia. Wound inoculation of plant stems with P. cinnamomi was used to determine the efficacy of phosphite over time after application. Colonisation by P. cinnamomi was reduced for 5–24 months after phosphite was applied, depending on the concentration of phosphite used, plant species treated and the time of phosphite application. Plant species within and between plant communities varied considerably in their ability to take up and retain phosphite in inoculated stems and in the in planta concentrations of phosphite required to contain P. cinnamomi. As spray application rates of phosphite increased from 5 to 20 g L–1, stem tissue concentrations increased, as did the ability of a plant species to contain P. cinnamomi. However, at application rates of phosphite above 5 g L–1 phytotoxicity symptoms were obvious in most species, with some plants being killed. So, despite 10 and 20 g L–1 of phosphite being more effective and persistent in controlling P. cinnamomi, these rates are not recommended for application to the plant species studied. The results of this study indicate that foliar application of phosphite has considerable potential in reducing the impact of P. cinnamomi in native plant communities in the short-term. However, in order to maintain adequate control, phosphite should be sprayed every 6–12 months, depending on the species and/or plant community.

Plant species affect acid phosphatase, ergosterol and microbial P in a Jarrah ( Eucalyptus marginata Donn ex Sm.) forest in south-western Australia

Dry sclerophyll forest dominated by Jarrah ( Eucalyptus marginata Donn ex Sm.) covers about 1.6 Mha of south-western Australia and is, relative to other eucalypt forests, low in many nutrients, especially N and P. If fire is excluded from these forests, Banksia grandis Willd. (Proteaceae) often grows in dense thickets as the dominant understorey. Jarrah has an extensive surface (0–20 cm) system of fine lateral roots with ectomycorrhizal associations, while B. grandis produces a mat of cluster (proteoid) roots (0–20 cm) in the late winter and early spring. We measured seasonal changes in acid phosphatase activity and concentrations of ergosterol, microbial P and other P fractions (NaOH-extractable inorganic and organic P, Bray inorganic P) in soil from a forest where B. grandis was either present (Jarrah+Banksia) or absent (Jarrah). Acid phosphatase activity was between 30 and 40 μmol p-NP g −1 h −1 in the moist winter and spring, but declined to less than 10 μmol p-NP g −1 h −1 during the dry summer. Microbial P varied from less than 10 μg g −1 in the late summer to more than 50 μg g −1 during the wetter times of the year. Ergosterol also increased about four-fold as soil moisture content increased ( P≤0.05). Acid phosphatase was significantly and positively related to both ergosterol and microbial P in both Jarrah+Banksia and Jarrah soils, but the intercepts and slopes of the regressions varied seasonally and were not significantly different ( P≤0.05) between species composition. About 50% of the variation in phosphatase activity in Jarrah soils was explained by variation in fungal biomass (ergosterol), regardless of season, while in Jarrah+Banksia soils, 74% was explained by fungal biomass when soils were dry, decreasing to less than 10% as soil moisture increased. Linear regression models showed that ergosterol and microbial P are good predictors of acid phosphatase activity in soil, but their relative importance is dependent on plant species composition and season. We propose that the relative importance of fungal biomass as a determinant of phosphatase activity in the soil decreases as the seasonal flush of cluster roots dominate in the Jarrah+Banksia soils, while in Jarrah soils the phosphatase flush is primarily due to increased activity of the fungal biomass. Seasonal and spatial heterogeneity in microbial P, ergosterol and in the source of acid phosphatase in the soil are therefore a consequence of plant species composition and root type and will influence nutrient availability at the ecosystem scale.

Edges and gaps in mature karri forest, south-western Australia: logging effects on bird species abundance and diversity.

The impact of logging operations on bird species abundance and diversity was studied over an eight-year period using a variable-circular plot bird survey procedure and a Before–After–Control–Impact (BACI) design in karri ( Eucalyptus diversicolor) forest in south-western Australia. The magnitude and spatial extent of impact was assessed from sample points in five bands parallel to the edge between clearfelled areas and mature forest (unburnt-forest, burnt-forest, forest-edge, gap-edge and gap). A total of 24 748 birds of 53 species were detected within 30 m of the observer during the study. Bird species abundance, and diversity, were similar in the five bands prior to treatment, and observed differences could be attributed to spatial patterns of flowering in the overstorey. Following logging, 19 of the 40 species that were detected more than five times showed changes in relative abundance (including both, increases and decreases) in one or more bands. Gaps showed the greatest number of significant changes (15) and these were typically of the greatest magnitude over the four years studied post-treatment. Gap-edges showed fewer changes (six), while both, the burnt-forest (three) and forest-edge (nil) bands showed few changes in relative abundance. Both, the number of species detected (for a given sampling effort), and species diversity declined in gap and gap-edge bands following logging. Nevertheless, variation in bird counts between successive seasons and years necessitates considerable replication before changes can be reliably assigned to disturbance impacts. In addition, the long period before maturation of the overstorey suggests that the local impact of logging and burning is likely to extend well beyond the life of experimental studies. Our results support the implementation of a well-dispersed system of retained mature forest along road, river and stream zones within the regeneration mosaic.

The effects of fire on a population of Red-winged Fairy-wrens Malurus elegans in Karri forest in southwestern Australia

In April 1994, an intense fire burnt part of Smith's Brook Nature Reserve near Manjimup, Western Australia where we had studied an individually marked population of the Red-winged Fairy-wren Malurus elegans in Karri Eucalyptus diversicolor forest since 1980. We estimated the population size in a 25 ha area at the start of the breeding season each year 1980?95, including two years post-fire. In the 32 territories present in 1993, the entire area of 26 was almost completely burnt to a height of 10 m, with few remaining unburnt patches. The mean population size for the 13 years 1981?93 was 119 birds in a mean of 29 groups. In November 1993, 126 birds were present in 32 groups. In November 1994, following the April fire, there were 114 birds in 31 groups, but nesting substrate was very scarce, breeding was delayed, and only 0.18 yearling males per group were produced, compared with 0.52 for the years 1981?93. By November 1995, the population had fallen to 73 birds in 23 groups with nine territories vacant. The time necessary for the population to recover to its prefire level was estimated from long-term demographic data to be at least 10 years, longer than the present cycle of 7?9 years for prescribed burns in the southern (Karri) State Forests of Western Australia.

Site index and dominant height growth curves for regrowth karri ( Eucalyptus diversicolor F. Muell.) in south-western Australia

Site index and dominant height growth curves are derived for intensively managed karri regrowth forests in south-western Australia. An algebraic difference approach was used to formulate nine height/age models, which were parametrised using stem analysis and validated using increment plot data. An anamorphic Weibull-based formulation was the most accurate in estimating future stand height. Parameters of the candidate and final model forms were invariant across existing landform, soil, climatic and vegetation classifications.

Stimulation of Germination of Acacia pulchella: Laboratory Basis for Forest Management Options

(a) The leguminous shrub Acacia pulchella is a valued understorey species of jarrah (Eucalyptus marginata)forests in south-western Australia. It regenerates from buried seeds mainly after fire, which breaks seed dormancy.

Nutrient accumulation in and release from the litter layer of karri ( Eucalyptus diversicolor) forests of southwestern Australia

Dry weight and nutrient content of the litter layer of pole-stand karri forest growing in southwestern Australia were related to period of accumulation by the function X t =X SS (1 − e − kt )+ X 0e − kt where X t is the amount of dry weight or nutrients present in the forest floor at time t, X SS is the amount present under equilibrium conditions, X 0 is the amount present at t=0, and k is a constant. This relation explained 90% of the variation in litter dry weight and from 65% to 91% of the variation in amounts of nutrients accumulating in the forest floor. Rate of dry weight and nutrient accumulation was initially rapid, reaching 50% of the equilibrium values, X SS, in 2.4 to 5.5 years. Almost half of the litter dry weight and two-thirds of the N, P and S were stored in the fine (< 1-cm) fraction of litter 9 years after fire. Rates of release of dry weight and nutrients from the forest floor were estimated from annual inputs in litterfall and annual increments in the amounts stored in the forest floor. The mobile elements Na and K were released rapidly from the litter layer, Ca and Mg were released at approximately the same rate as litter dry-weight and N, P and S initially accumulated were then slowly released from the forest floor. The effects of periodic prescribed burning on cycling of nutrients in forest litter are discussed. Nitrogen and P are the elements most affected by current burning practices. More research is needed to quantify the effects of recurrent fires in karri forest on P nutrition. Budgets based on data currently available on rates of N accession in rainfall and through symbiotic and non-symbiotic N 2-fixation suggest that, with current burning frequencies, volatilization of N from the litter layer and understorey vegetation during fire may exceed cumulative accretion of N to the ecosystem during inter-fire periods. More precise estimates of N inputs and outputs are needed to confirm this.

Changes in an Assemblage of Small Birds in the Understorey of Dry Sclerophyll Forest in Southwestern Australia After Fire

Changes in the numbers and types of small birds caught in mist-nets in the understorey of dry sclerophyll forest in south-western Australia were recorded for three years after a low intensity fire. There were few changes in the species composition of the assemblage but abundances of the 6-8 most numerous and relatively sedentary species were approximately halved. Many marked individuals (22%) were recaptured up to three years after the fire. After the fire, the number of prey taxa recorded from the faeces of birds caught fell from twelve to six, and the birds ate proportionately more ants and fewer beetles. Ants eaten after the fire were smaller than those eaten before it.

Seasonal variation in C 2H 2 reduction (N 2-fixation) in the litter layer of eucalypt forests of South-Western Australia

Seasonal variation in C 2H 2 reduction by forest litter was determined at four sites in jarrah ( Eucalyptus marginata Donn ex Sm.) and karri ( E. diversicolor F. Muell.) forests in south-western Australia. Rates of C 2H 2 reduction and microbial activity (CO 2 respiration) were measured every 4 weeks for 14 months on 10 intact litter mats at each site. Mean monthly rates of C 2H 2 reduction ranged from 0 to 24 nmol C 2H 2 g −1 litter day −1 in jarrah forest and from 0 to 56 nmol C 2H 2 g −1 litter day −1 in karri forest. Seasonal variation in rates of both C 2H 2 reduction and CO 2 respiration was related to variations in moisture content and temperature of the litter. C 2H 2 reduction and CO 2 respiration were highest during the cool, moist winter and decreased to zero during the warm dry summer. Functions relating C 2H 2 reduction to temperature and moisture content were derived from laboratory incubations of leaf litter under controlled conditions. These were used to develop models of the seasonal variation in N 2 ase activity based on field measurements of C 2H 2 reduction, litter moisture content and temperature. The models demonstrate that moisture content of litter is the factor contributing most to seasonal variation in N 2ase activity in jarrah and karri forests. Approximate amounts of N 2 fixed annually in the litter layer were 38 and 49 mg Nm −2 yr −1 in jarrah forest and 149 and 257 mg Nm −2yr −1 in karri forest. These are within the range of values reported for other forest ecosystems.