Eucalyptus Loxophleba Research Articles

Terpenoidal constituents of Eucalyptus loxophleba ssp. lissophloia

Context: Eucalyptus has been a source of a number of biologically active compounds. The anti-leishmanial activity of terpenoids from Eucalyptus loxophleba (Benth.) ssp. lissophloia (Myrtaceae) has not yet been investigated.Objective: Isolation of the terpenoidal constituents for evaluation of in vitro anti-leishmanial activity against the Leishmania donovani (Dd8 strain) promastigotes.Materials and methods: The chloroform–methanol (8:2) extract of dried leaves of Eucalyptus loxophleba was used to isolate terpenoidal constituents employing solvent partitioning, column chromatography and preparative high performance liquid chromatography and characterized from spectral data. The anti-leishmanial activity of the isolated compounds was tested in vitro using an Alamar blue assay against a culture of L. donovani (Dd8 strain) promastigotes.Results: Two new naturally occurring triterpenes, named loxanic acid and 3-acetyl loxanic acid together with four known ursane triterpenoids and one bis-monoterpene glycoside, cuniloside B isolated from the leaves showed anti-leishmanial activity (IC50 133 to 235 μM) against the promastigotes of the tested strain.Conclusion: The terpenes isolated from the leaves of E. loxophleba showed moderate anti-leishmanial activity.

The Ridgefield Multiple Ecosystem Services Experiment: Can restoration of former agricultural land achieve multiple outcomes?

The ability of restoration approaches to provide valued ecosystem services needs to be assessed. The emerging carbon market provides an incentive to afforest agricultural landscapes and could potentially achieve multiple outcomes. However, planting monocultures for carbon sequestration may preclude effective delivery of other ecosystem services. Here, we describe the rationale behind the Ridgefield Multiple Ecosystem Services Experiment, a long-term investigation into trade-offs that might prevent the simultaneous provision of high levels of multiple services in the agricultural landscape of south-western Australia. We compare a monoculture treatment of a fast growing native species (Eucalyptus loxophleba) with mixtures of 2, 4 or 8 native plant species. We selected species based on different traits that we predict will relate to the provision of different levels of multiple ecosystem services. We ask: Can restoration of multiple ecosystem services be achieved along with carbon sequestration? Nested treatments of nitrogen deposition and weed removal test whether ecosystem service outcomes respond to environmental changes. We show that historical land-use at the site has the potential to affect service delivery via different soil characteristics and survival of planted species. Ridgefield tests the possibility of restoring and managing agricultural landscapes for multiple ecosystem services, providing a much needed experimental investigation of trade-offs among ecosystem functions.

Relationships among soil fertility, native plant diversity and exotic plant abundance inform restoration of forb‐rich eucalypt woodlands

AbstractAim Water and nutrient availability are major limits to productivity in semi‐arid ecosystems; hence, ecological restoration often focuses on conserving or concentrating soil resources. By contrast, nutrient enrichment can promote invasion by exotic annuals, leading to restoration approaches that target reduction of soil nutrients. We aimed to explore potential biodiversity trade‐offs between these approaches by investigating relationships among soil nutrients, exotic annuals and native plant diversity and composition. In particular, we investigated the hypothesis that native plant diversity in semi‐arid to temperate woodlands reflects the productivity–diversity hypothesis, leading to hump‐backed relationships with soil nutrients such that (1) native plant diversity declines with increasing nutrient enrichment and (2) native diversity is limited at the lowest levels of soil fertility.Location Fragmented, long‐ungrazed Eucalyptus loxophleba subsp. loxophleba (York gum)–Acacia acuminata (jam) woodlands in the wheatbelt of South‐Western Australia.Methods We conducted stratified surveys of floristic composition and topsoil nutrient concentrations in 112 woodland patches. We used generalized linear models, structural equation models and ordinations to characterize relationships among soil nutrients, rainfall, exotic annuals and patch‐scale (100 m2) native plant composition and diversity.Results Patch‐scale native plant diversity declined strongly with increasing exotic abundance. This was partly related to elevated soil nutrient concentrations, particularly total nitrogen and available phosphorus. By contrast, there was little evidence for positive correlations between soil nutrients and native diversity, even at very low soil nutrient concentrations.Main conclusions Minimizing weed invasions is crucial for maximizing native plant diversity in E. loxophleba woodlands and could include nutrient‐depleting treatments without substantially compromising the functional capacity of soils to maintain native plant richness and composition. More broadly we emphasize that understanding relationships among ecosystem productivity, plant diversity and exotic invasions in the context of associated theoretical frameworks is fundamental for informing ecological restoration.

Distribution and status of the red-tailed phascogale (Phascogale calura)

The red-tailed phascogale once extended widely across semiarid and arid Australia, but is now entirely confined to the southern wheatbelt of Western Australia, occupying less than 1% of its former range. Here it occurs in a portion of the Avon Wheatbelt, Jarrah Forest, Mallee, and Esperance Plains biogeographical regions. The species persists only in areas that have been extensively cleared for agriculture and where the remaining bushland is highly fragmented. It does not appear to extend into unfragmented habitat in either the Jarrah Forest to the west or Mallee region to the east. It occurs primarily in woodland habitat with old-growth hollow-producing eucalypts, primarily wandoo (Eucalyptus wandoo) or York Gum (E. loxophleba), but records from the periphery of its current range appear to come from a broader range of habitats, including shrublands and various mosaics of woodland, shrubland, and scrub-heath. Key factors limiting persistence are likely to be fragmentation of habitat that is likely to greatly increase the risks associated with dispersal, a shortage of suitable nesting hollows in many vegetation associations, and predation by feral and domestic cats and by foxes. These factors, particularly fragmentation and lack of suitable nesting hollows, suggest that the species’ long-term persistence in areas beyond the wandoo belt is far from assured.

Chemical composition of essential oils of two cultivated Eucalyptus species from the central Iran

The chemical composition of essential oils of leaves of two cultivated species,Eucalyptus loxophleba Benth. and Eucalyptus leocoxylon F. Muell. in the central of Iran were obtained by hydrodistillation and analyzed by gas chromatography, using flame ionization and mass spectrometric detection. A total of thirty nine compounds representing 98.0% of total oil have been identified in the oil of E. loxophleba. 1,8-cineole (39.4%), methyl amyl acetate (19.8%), aromadendrene (10.0%), viridiflorol (6.0%) andα-pinene (5.4%) were the major constituents in the volatile oil of E. loxophleba oil. Forty three components were identified in the E. leocoxylon oil where 1,8-cineole (59.1%), cryptone (15.1%), α-pinene (9.9%), α-terpineol (5.1%) and globulol (5.0%) are considered as the main components. The amount of 1,8-cineole as the main component was higher in the oil of E. leocoxylon. Key words: Eucalyptus loxophleba, Eucalyptus leocoxylon, Myrtaceae, essential oil, 1,8-cineole

Chemical composition of essential oil and in vitro antioxidant activities of the essential oil and methanol extracts of Eucalyptus loxophleba

This study was designed to examine the chemical composition of the essential oil and the antioxidant activity of the essential oil and methanol extracts of Eucalyptus loxophleba Benth. subsp. The chemical composition of the essential oil of the leaves of E. loxophleba was analysed by GC and GC/MS. The main constituents of the oil were found to be 1,8-cineole (39.4%), methyl amyl acetate (19.8%) and aromadendrene (10%). Antioxidant activities of the samples were determined by two different test systems namely DPPH and β-carotene/linoleic acid. In the DPPH system, the highest radical-scavenging activity was shown by the polar subfraction of the methanol extract (15.2 ± 1.7 µg mL−1). Also, in the second case, the inhibition capacity (%) of the polar subfraction (94.1 ± 1.3) was found to be stronger. In addition, the amounts of total phenol components in the polar subfraction (273.0 ± 2.6 µg mg−1) and nonpolar subfraction (146.3 ± 2.5 µg mg−1) were determined.

Quantitative Analysis of Euglobals in Eucalyptus loxophleba Leaves by qNMR¶

A simple, rapid, accurate and selective 1H NMR spectroscopic method to detect and quantify euglobals in the leaves of Eucalyptus loxophleba ssp. lissophloia has been developed. The method allows for the estimation of total concentration of diformylphloroglucinol-monoterpene adducts, as well as the quantitation of sabinene- and alpha/beta-phellandrene-adducts, separately. The method was validated for accuracy, precision and linearity using as reference standards 2-ethyl phenol and mixtures of jensenone, a monomeric formylated phloroglucinol, and 2-ethyl phenol.

Formylated phloroglucinols from Eucalyptus loxophleba foliage

Two new naturally occurring formylated phloroglucinol compounds (FPCs), a dimer, loxophlebal B (10) and a cyclized FPC, loxophlebene (8) together with eight other formylated phloroglucinols (1–7 and 9) were isolated from the chloroform-methanol (8:2) extract of the leaves of Eucalyptus loxophleba ssp. lissophloia. The structures of new compounds were established by comprehensive spectral analysis and by comparison of their NMR data with those of related compounds in the literature. All the isolated compounds were evaluated for anti-leishmanial activity against promastigotes of Leishmania donovani.

Resource heterogeneity and persistence of exotic annuals in long-ungrazed Mediterranean-climate woodlands

Processes that promote weed invasion are often well-demonstrated, but mechanisms that facilitate ecological resistance to weed invasion in non-invaded communities, or promote weed persistence in invaded communities, are poorly understood. Yet it is these processes that must be addressed to achieve sustainable ecological restoration. We surveyed soil heterogeneity in 25 long-ungrazed, unfertilized York gum (Eucalyptus loxophleba Benth. subsp. loxophleba)—jam (Acacia acuminata Benth.) woodlands of the Western Australian wheatbelt to investigate differences in soil characteristics between patches locally-invaded or non-invaded by widespread exotic annuals. Based on studies in other ecosystems, we hypothesized that (1) weed persistence is associated with elevated soil resource levels, and (2) of these soil resources, phosphorus is the key contributor to weed persistence in Western Australian woodlands, that typically occur on phosphorus-impoverished soils. Our first hypothesis was partly supported, with soil nutrients associated with up to 40% of the variation in cover of exotic annuals. In particular, low concentrations of total nitrogen, nitrate and available phosphorus are likely to contribute to resistance to invasion in many non-invaded woodland patches, especially in gaps between trees. However, other non-invaded patches had comparable nutrient concentrations to invaded patches, suggesting this resistance may be weak at more productive sites or that patches have not reached a stable equilibrium. Inconsistent with our second hypothesis, exotic annuals were as strongly correlated with elevated total nitrogen and associated variables as they were with available phosphorus, probably reflecting a history of grazing without fertilization. We conclude that effectiveness of ‘bottom-up’ approaches to weed control is likely to differ among ecosystems according to interactions with disturbance history and attributes of the non-invaded community, even where the weed species or functional types are the same.

Habitat requirements of the endangered red-tailed phascogale, Phascogale calura

Context The red-tailed phascogale once occurred widely across semiarid and arid Australia, but is now confined to the southern wheatbelt of Western Australia. Its apparently extensive former range suggests a broad habitat tolerance, yet it is now reported primarily from remnant vegetation within farmland containing wandoo Eucalyptus wandoo and rock sheoak Allocasuarina huegeliana associations. Aims To establish the habitat requirements of phascogales with a view to understanding their current and likely future distribution and status. Methods We established presence or absence of phascogales at a number of sites within their current range, primarily by trapping, and then compared habitat attributes between the two classes of sites to establish those of apparent significance to species persistence. Key results Phascogales are widespread in suitable upland (wandoo–rock sheoak) and lowland habitat (riverine fringing vegetation of swamp sheoak Casuarina obesa, York gum E. loxophleba and wandoo). They occupy areas of remnant vegetation of varying sizes from very small to very large, many on private agricultural land. Large connected areas, such as riverine corridors and clusters of upland remnants appear important to their long-term persistence. Sites isolated by increasing distance from another occupied site tended to be unoccupied. Habitats occupied by phascogales typically had a greater canopy density and greater abundance of hollows than unoccupied sites. The presence of plants of the genus Gastrolobium, often cited as a key factor in the persistence of phascogales, did not appear to influence the presence or absence of phascogales. Conclusions Red-tailed phascogales currently occupy a broader range of habitats than identified in the literature and the role of some key aspects of habitat in protecting them from further decline may have been overstated. The presence of suitable hollows for nesting and shelter and a dense mid-storey canopy, perhaps to protect from predation by owls, are key features of suitable phascogale habitat. Implications Suitable habitat for phascogales appears widespread in the surveyed portion of the remaining range of the species, but is under threat over the longer term. Increasing salinity in lowland areas (which transforms woodland to samphire with a consequent long-term loss of nesting hollows), lack of fire in upland areas to maintain dense stands of rock sheoak and the increasing loss of corridors of vegetation along roadsides due to the widening of roads by local councils are all contributing to loss of habitat and habitat connectivity.

After the fence: vegetation and topsoil condition in grazed, fenced and benchmark eucalypt woodlands of fragmented agricultural landscapes

Emerging ecological theory predicts that vegetation changes caused by introduction of livestock grazing may be irreversible after livestock are removed, especially in regions such as Australia that have a short evolutionary exposure to ungulate grazing. Despite this, fencing to exclude livestock grazing is the major tool used to restore vegetation in Australian agricultural landscapes. To characterise site-scale benefits and limitations of livestock exclusion for enhancing biodiversity in forb-rich York gum (Eucalyptus loxophleba Benth. subsp. loxophleba)–jam (Acacia acuminata Benth.) woodlands, we compared 29 fenced woodlands with 29 adjacent grazed woodlands and 11 little-grazed ‘benchmark’ woodlands in the Western Australian wheatbelt. We explored the following two hypotheses: (1) fencing to exclude livestock facilitates recovery of grazed woodlands towards benchmark conditions, and (2) without additional interventions after fencing, complete recovery of grazed woodlands to benchmark conditions is constrained by ecological or other limits. Our first hypothesis was supported for vegetation parameters, with fenced woodlands being more similar to benchmark woodlands in tree recruitment, exotic plant cover, native plant cover, native plant richness and plant species composition than were grazed woodlands. Further, exotic cover decreased and frequency of jam increased with time-since-fencing (2–22 years). However, we found no evidence that fencing led to decline in topsoil nutrient concentrations towards concentrations at benchmark sites. Our second hypothesis was also supported, with higher topsoil nutrient concentrations and exotic plant cover, and lower native plant richness in fenced than in benchmark woodlands, and different plant species composition between fenced and benchmark woodlands. Regression analyses suggested that recovery of native species richness is constrained by exotic species that persist after fencing, which in turn are more persistent at higher topsoil nutrient concentrations. We conclude that fencing to exclude livestock grazing can be valuable for biodiversity conservation. However, consistent with ecological theory, additional interventions are likely to be necessary to achieve some conservation goals or to promote recovery at nutrient-enriched sites.

Antibacterial sideroxylonals and loxophlebal A from Eucalyptus loxophleba foliage

Loxophlebal A, a new antibacterial formylated phloroglucinol was isolated from the mother liquor obtained after separation of sideroxylonals from the chloroform–methanol extract of leaves of Eucalyptus loxophleba ssp lissophloia. The structure of loxophlebal A was determined to be 3-desformyl sideroxylonal A by spectroscopic methods including 1D- and 2D-NMR. The stereochemistry of loxophlebal A was determined by chemical correlation with sideroxylonal A. This article also reports an efficient, simple and economic method for large scale isolation of sideroxylonals in a purity of > 90% from the leaves of Eucalyptus loxophleba ssp lissophloia.

Outcrossing between an agroforestry plantation and remnant native populations of Eucalyptus loxophleba

Gene dispersal among populations of a species is an important force influencing their genetic structure. Dispersal may also occur between taxa that would normally be isolated when nonendemic, domesticated or transgenic species are planted within the natural range of interfertile taxa. Such a mosaic of populations is typical of many agricultural landscapes, and investigations are needed to assess the risks of genetic contamination of the endemic populations but a combination of approaches may be necessary because of the limitations of research in this landscape. This study used microsatellite markers and a range of analyses (mating system, paternity exclusion, Bayesian assignment) to examine gene dispersal between remnants of the endemic Eucalyptus loxophleba ssp. supralaevis and a plantation of a nonendemic subspecies. Our results indicate that remnant populations are connected by significant dispersal to pollen sources up to 1.94 km away including the plantation. The combined analyses showed that the pollen pool and outcrossing rates of individuals within remnants varied significantly probably because of asynchronous flowering and that the likelihood of paternity was not correlated with spatial proximity. More than half of all progeny had male parents from outside their stand with the largest proportions estimated to come from the plantation by exclusion (42.4%) or Bayesian analyses (18.8-76%). Fragmentation may not be associated with decreased gene dispersal between populations of tree species, natural or planted, so that the distances required to buffer endemic trees in fragmented rural landscapes are likely to be large.

Seedling response to phosphate addition and inoculation with arbuscular mycorrhizas and the implications for old-field restoration in Western Australia

We predicted that P-fertiliser residues will limit the establishment of native plant species and their mycorrhizas to old-fields in the wheat-growing region (i.e. the wheatbelt) of Western Australia. To test this prediction, we assessed the growth and P uptake of seedlings of three native plant species to phosphate addition and inoculation with arbuscular mycorrhizas (AM) in a pot study. The native plant species were Acacia acuminata Benth. (Mimosaceae), Eucalyptus loxophleba Benth. subsp. loxophleba (Myrtaceae) and Hakea preissii Meisn. (Proteaceae); and each pot contained one seedling. P was added to field soil to mimic pre-agricultural (P0), old-field (P1) and 10 times old-field (P10) soils. AM inoculant, which was a mix of Scutellospora calospora (Nicolson and Gerdemann) Walker and Sanders, Glomus intraradices Schenck and Smith and Glomus mosseae (Nicolson and Gerdemann) Gerdemann and Trappe, was added to half of the pots. After 12 weeks, the biomass and P uptake of the mycorrhizal A. acuminata were greater than those of the non-mycorrhizal plants across all P treatments. Plant biomass decreased significantly with increasing P addition, yet this species was apparently unable to suppress its mycorrhizal colonisation at high P despite this reduction in growth. In contrast, mycorrhizal and non-mycorrhizal E. loxophleba subsp. loxophleba were of a similar biomass after 12 weeks; maximum biomass was attained at intermediate (old-field) levels of P. P uptake increased with increasing P supply, beyond that required to attain maximum biomass. AM did not form on H. preissii. P uptake increased with increasing P supply for this species also. Overall, it is the apparent inability of these species to down-regulate P uptake rather than a lack of mycorrhizal symbiosis that will constrain their establishment on wheatbelt old-fields.

"Paradise" and "Cloverdowns": following natural systems

Two properties, "Paradise" and "Cloverdowns", are farmed by the Melvin family near Dowerin in the central wheatbelt of Western Australia (see Fig. 1, Hobbs 2003). The annual average rainfall is 350 mm and, before Europeans settled the area, it was well vegetated with perennial vegetation. The sandplain soils were dominated by mallees Eucalyptus spp., Kwongan or heath (predominantly Myrtaceae, Proteaceae and Leguminosae), and patches of York Gum E. loxophleba woodland. The heavier soils such as the brown sandy loams and red brown loams were clothed in woodland of Salmon Gum E. salmonophloia and York gum. The gravelly sands were covered by Tamma scrub which was dominated by sheoak Allocasuarina spp.

Changes in a remnant of salmon gum Eucalyptus salmonophloia and York gum E. loxophleba woodland, 1978 to 1997. Implications for woodland conservation in the wheat–sheep regions of Australia

The condition of salmon gums Eucalyptus salmonophloia with large hollows in them in a 15-ha patch of remnant salmon gum-York gum E. loxophleba woodland in the northern wheatbelt of Western Australia was examined in 1978. The patch was an important breeding area for six species of cockatoo, including two endangered species. The patch was revisited in 1981 when the condition of all 682 salmon gums and York gums in the patch was examined and each was measured and photographed. A further visit was made in 1997 when the condition of the surviving trees was examined and each was again measured and photographed. The condition of the trees at each visit was classified as “good”, “staghorn”, “broken top”, “dead” or “fallen.” Over the period of the study there was a serious decline in the condition of the trees, with few large trees in the “good” category by 1997. The decline was particularly marked between 1978 and 1981 after a period of well-below average annual rainfall. Using data based on the rate of decline over the period 1978–1997, predictions were made of the fate of the trees in the patch. By 2125 only 46 (11% of the 1981 total) salmon gums were predicted to be alive with only one in the “good” category. Only 16 (17%) York gums were predicted to be alive by 2125, with only one in the “good” category. There was no evidence of any regeneration of woodland trees since 1929 when the patch was isolated by clearing for agriculture, and domestic livestock allowed to graze the patch. This deterioration of the dominant trees in the patch is symptomatic of remnant native vegetation over vast areas of Australia's extensively cleared wheat–sheep regions. The future of woodland patches like the one studied is bleak, as is the future of animals dependent on them for food, breeding sites and shelter. Active management, including fencing to exclude domestic livestock and measures to encourage regeneration of native plant communities, is necessary to counter the present regime of benign neglect that characterises most of Australia's management of native vegetation in agricultural landscapes.

Genetic differentiation between mallee and tree forms in the Eucalyptus loxophleba complex.

The Eucalyptus loxophleba complex comprises two tree taxa (E. loxophleba ssp. loxophleba and ssp. supralaevis), two mallee taxa (E. loxophleba ssp. lissophloia and ssp. gratiae), and three rare mallee species, of which one, E. blaxellii, is included in this study. The genetic diversity and phylogenetic relationships between the taxa, particularly in relation to habit, were assessed using anonymous nuclear RFLP loci. The level of diversity in the taxa was high and similar to that detected in other eucalypt species. The populations showed low differentiation at both the subspecies and the species levels. Phylogenetic relationships showed some genetic separation between the tree and mallee habit but no separation of the two taxa within the tree habit or within the mallee habit. The genetic analysis does not support the recognition of E. gratiae as a separate species. The geographically restricted E. blaxellii showed similar levels of diversity to populations of the other widespread taxa of E. loxophleba.

Establishment and growth of sandalwood (Santalum spicatum) in south-western Australia: the influence of host species

Summary This study examined the performance of sandalwood (Santalum spicatum) parasitising two N2-fixing woody hosts (Acacia acuminata and Allocasuarina huegeliana) and a non N2-fixing host (Eucalyptus loxophleba subsp. loxophleba) on farmland at Kwobrup, Western Australia. The host seedlings were planted in 1991, and the S. spicatum were direct seeded at host age five years. Survival and growth of the S. spicatum were assessed at age three years. S. spicatum survival was significantly higher when planted next to A. acuminata (86 %) than A. huegeliana (29 %), and all seedlings next to E. loxophleba subsp. loxophleba died within two years of establishment. Mean height and stem diameter of S. spicatum parasitizing A. acuminata were significantly greater than those parasitising A. huegeliana. The initial presence of S. spicatum did not reduce host survival or growth. The foliar N and K concentrations, and the K:Ca ratio were significantly higher in S. spicatum parasitising A. acuminata than A. huegeliana. However, the S. spicatum attached to A. huegeliana had significantly higher concentrations of foliar P, Ca and Mg. The leaf and stem water potentials (Ψleaf' Ψstem) of S. spicatum trees were the same or significantly lower than their paired hosts, at pre-dawn and midday, in February-March 1999, the stem water potentials of the S. spicatum: A. acuminata pairing were significantly lower than the S. spicatum: A. huegeliana pairing.

Seed/cotyledon size and nutrient content play a major role in early performance of species on nutrient‐poor soils

summaryWe examined the importance of seed size in the early establishment of seedlings of four cotyledonous species restricted to nutrient‐impoverished soils in south‐western Australia. Experimentally removing cotyledons from seedlings increased mortality and reduced root‐penetration, growth rate and final weight of plants after 12 wk, in proportion to seed size. The impact of removal of the cotyledons was least in the smallest‐seeded, Eucalyptus loxophleba Benth., grown in the more fertile of two soils, and greatest in the largest‐seeded, Hakea psilorrhyncha R. M. Barker, whose growth was otherwise unaffected by soil type. In the smallest‐seeded species, cotyledon content of most mineral nutrients increased over time, especially in the more fertile soil, while chlorophyll content showed some decrease by the end of the experiment. In the other species, most nutrients (especially N, P, K and Cu in the less fertile soil) were translocated from the cotyledons to the growing plant, and chlorophyll content declined markedly. The translocated N, P, K, Mg and Cu in these species made up a substantial part of the total plant content by 12 wk after germination, while total Ca and Fe tended to increase in the cotyledons via substantial soil uptake. The results indicate, contrary to reports for some other species, that the cotyledons have an important nutritional function in the early establishment of seedlings in these species. The results also show that, in the larger‐seeded species, young seedlings rely to a greater extent on nutrient support from the cotyledons than from the soil. We propose that large seeds might be an adaptation for enhancing establishment in nutrient‐poor soils.

Alkalinity Tolerance of Woody Species Used in Bauxite Waste Rehabilitation, Western Australia

AbstractGlasshouse trials, using trickle irrigation and increasing levels of NaOH‐induced alkalinity, identified species that could be expected to tolerate the high‐pH conditions of bauxite processing waste residue sites. Of 29 taxa tested, the most tolerant were Casuarina obesa, Melaleuca lanceolata, M. armillaris, M. nesophila, Eucalyptus loxophleba, E. halophila, E. platypus, Tamarix aphylla, and a particular clone of E. camaldulensis; E. spathulata, E. tetragona, E. preissiana, E. gomphocephala, E. diptera, and E. occidentalis proved to be relatively sensitive to severe alkaline conditions. Tolerance appeared to relate to an ability to maintain root membrane function, nutrient uptake balance, and ultimately root tissue structure while under increasing levels of alkalinity stress. Species normally inhabiting alkaline soils tended to have increased growth rates in nutrient irrigation conditions between pH 8 and 10 compared with control plants irrigated with nutrient solutions of pH values near 7.4. However, once the irrigation solutions reached pH 12 and the buffering capacity of the soil appeared to be exceeded, the condition of susceptible plants rapidly declined and death followed. Sensitive plants initially showed symptoms related to nutrient deficiency, followed by wilting and death as the root systems failed. Field trial conditions in the bauxite residue impoundments at Kwinana, Western Australia, include soils with pH values as high as 11.00. In general, the relative survival and growth of seedlings after eight months were predicted by the response under glasshouse trial conditions. Appropriately designed stress trials can be important ecological techniques in choosing species most capable of surviving difficult environmental conditions in the rehabilitation of damaged landscapes.