Academic literature on the topic 'Eucalyptus tetrodonta'

The reproductive phenology-the annual and spatial variation in tree fecundity, ovule development and seedfall-of Eucalyptus miniata Cunn. ex Schauer and E. tetrodonta F. Muell. is described at a tropical savanna site in northern Australia from 1992 to 1994. There was substantial inter-annual variability in fecundity of both species at the individual and the population level. The proportion of ovules which survived did not vary significantly between years. Seed production and seedfall varied substantially between years with large seed yields in 1994 and low seed yields in 1993. Eucalyptus miniata and E. tetrodonta are separated in time (by 2-8 weeks) with respect to peak periods for all key phenology events-budding, flowering and seedfall. Both species are non-serotinous with all seed shed within 8 months of ovule initiation. Peak seedfall occurred up to 1 month before the first wet season rains for E. miniata and coincided with these rains for E. tetrodonta. Post-dispersal conditions for germination and establishment are more likely than seed supply to limit seedling establishment of E. miniata and E. tetrodonta.

Eucalyptus tetrodonta dominated open forests occur across the northern coast of the Northern Territory. They typically have a well developed grass understorey, scattered saplings, numerous woody sprouts (ramets) and a conspicuous absence of seedlings (genets). We compared a typical E. tetrodonta stand on Gunn Point with an atypical stand on Elcho Island; the forest on Elcho Island had less grass cover, greater canopy and litter cover, a deeper organic layer and higher densities of seedlings, woody sprouts and saplings than on Gunn Point. Gunn Point had a greater number of large E. tetrodonta trees that were more widely spaced than trees on Elcho Island. The cause of these differences remains unclear.

Seeds of Maranthes corymbosa Blume and Eucalyptus tetrodonta F.Muell were sown under ambient or CO2 enriched conditions (two replicate tents per treatment) in tropical Australia and allowed to grow, rooted in the ground, for 20 months. For both species, periodic measurements of leaf water potential, stomatal conductance and leaf temperature were made on four replicate leaves on each of four replicate trees within each tent. Measurements were made in November (M. corymbosa) and June (E. tetrodonta). At the same time, atmospheric wet and dry bulb temperatures were recorded and hence leaf-to-air vapour presure difference (LAVPD) calculated. Measurements of pre-dawn leaf water potential were also made on E. tetrodonta. Leaves were also taken to the laboratory, rehydrated to full turgor and pressure-volume analyses undertaken. For M. corymbosa, leaf water potential was lower throughout the day for control leaves compared to leaves growing in CO2 enriched air. Similarly, pre dawn leaf water potential was lower for control E. tetrodonta trees than for trees grown with CO2 enrichment. However, mid-morning and mid-afternoon values of leaf water potential for E. tetrodonta were slightly lower for plants growing in CO2 enriched air compared to control plants. In both species, stomatal conductance was consistently lower for trees grown in CO2 enriched air than for controls. Whole plant hydraulic conductivity of both species was significantly lower for trees grown in CO2 enriched air than for control trees. For both species, maximum turgor and bulk volumetric elastic modulus increased and osmotic potential at zero turgor decreased for trees grown in CO2 enriched air.

The monsoonal areas of northern Australia experience extreme seasonal variations in rainfall, with an annual dry season of 7 months or more. Seasonal changes in leaf water relations were investigated for saplings of two tree species common in northern Australian savannas: Eucalyptus tetrodonta F.Muell, an evergreen, and Terminalia ferdinandiana Excell, which is deciduous. Saplings may experience more severe water stress than mature trees because their root systems are less extensive. This study found a positive correlation between pre-dawn leaf water potential and tree height during the dry season, but not during the wet season, for both E. tetrodonta and T. ferdinandiana trees. Pressure–volume curves were constructed for leaves of E. tetrodonta saplings at 2-monthly intervals throughout the year. Osmotic potential at full turgor decreased from a maximum of −1.33 MPa in February (wet season) to −2.25 MPa in October (late dry season), then increased to an intermediate value of −1.71 MPa in December (early wet season). Leaves of T. ferdinandiana saplings were compared in February (wet season) and April (end of wet season; before leaf senescence). Osmotic potential at full turgor decreased from −1.18 MPa in February to −1.39 MPa in April. The capacity for turgor maintenance was larger for E. tetrodonta than for T. ferdinandiana, with osmotic potential at full turgor and the turgor loss point, relative water content at the turgor loss point and the ratio of turgid weight to dry weight all lower in E. tetrodonta.

Savanna communities dominate the wet–dry tropical regions of the world and are an important community type in monsoonal northern Australia. As such they have a significant impact on the water and carbon balance of this region. Above the 1200-mm isohyet, savanna’s are dominated by Eucalyptus miniata–E. tetrodonta open forests. We have described in detail the composition and structure as well as seasonal patterns of leaf area index and above-ground biomass in the E. miniata–E. tetrodonta open forests of the Gunn Point region near Darwin in the Northern Territory of Australia. In all, 29 tree species from four phenological guilds were recorded in these forests. Stand structure suggests that the forests were still recovering from the impacts of cyclone Tracy and subsequent frequent fires. Eucalyptus miniata and E. tetrodonta were significant contributors to overstorey leaf area index and standing biomass (>70%), and both leaf area index and biomass were strongly correlated to basal area. Leaf area index was at a maximum (about 1.0) at the end of the wet season and declined over the dry season by about 30–40%. There were proportionally greater changes in the understorey reflecting the greater contribution of deciduous and semi-deciduous species in this strata. Standing biomass was about 55 t ha –1 . Detailed descriptions of leaf area index and biomass are important inputs into the development of a water and carbon balance for the savanna’s of northern Australia.

The biomass of component parts of individuals of three dominant canopy tree species in the northern savannas of Australia was determined from field populations in World Heritage Kakadu National Park. Forty individual trees of Eucalyptus tetrodonta F. Muell., E. miniata Cunn. ex Schauer and E. papuana F.Muell., representing a range in size from 4 to 50 cm diameter at breast height (DBH), were felled for dry biomass of leaves, branches, woody stems and bark. Forty-seven other trees of E. tetrodonta and E. miniata were excavated for belowground biomass, by using trenching methods. The average proportion of aboveground biomass in foliage was 3–5%, to branches 20–32%, and trunk wood 77–59%, with little change over the size of a tree. Water content of foliage decreased with size of tree in all species, indicating an increasing xeromorphy as the trees age. Gross morphology of roots was bimorphic, with 70% of biomass at <20-cm soil depth, and large roots running horizontally on top of the shallow (0.3–1.4 m) ferricrete layer. There was no evidence of roots having access to water below this layer. Patterns of heights, percentage biomass allocation, percentage water content, and bark thickness of the three species were consistent with the rank order of their distributions across a topographic gradient, reflecting relative capacities to withstand drought, belowground competition and fire. By using tree diameter as the independent variable (x in cm DBH), allometric relationships were calculated to provide a method for calculating growth and productivity by using non-destructive repeat measures of sizes of trees. The total aboveground biomass (y in kg) of individual trees is y = 0.2068x2.3191 for E. tetrodonta, y = 0.1527x2.390 for E. miniata and y = 0.0356x2.8567 for E. papuana. Total belowground biomass per tree for E. tetrodonta is y = 31.150e0.0601x and for E. miniata, y = 28.753e0.0644x. As a tree grows, the aboveground biomass increases as a power function and belowground biomass as an exponential function of DBH, producing a decreasing proportion of total biomass below ground, e.g. the root/shoot ratio of E. tetrodonta is 0.50 for trees <10 cm DBH, 0.40 for trees 20 cm DBH, and 0.25 for trees 40–55 cm DBH. The overall proportion of total biomass below ground in Kakadu is well below 50%, contrary to the commonly accepted notion that the majority of biomass in savannas is below ground.

The importance of ectomycorrhizas in Eucalyptus tetrodonta F.Muell. and E. miniata Cunn. ex Schauer dominated forests and woodland communities in the monsoonal tropics of northern Australia was assessed. Ectomycorrhizas colonised between 24 and 54% of final order lateral roots in soil cores collected at 16 native forest sites. Only a minority of the plant species present formed ectomycorrhizas (mainly eucalypts and acacias) but these species contributed more than 75% of the basal area. More than 70 species of putative ectomycorrhizal fungi were collected, with three hypogeous taxa (Nothocastoreum, Hysterangium and an undescribed Boletaceae) most frequently encountered. Glasshouse inoculation experiments confirmed that a diverse range of fungi was capable of forming ectomycorrhizas with E. tetrodonta and E. miniata seedlings, and that the growth of both species could be substantially increased by inoculation with specific fungi. The fungi most effective in increasing seedling growth were generally those which most extensively colonised the seedling roots. A second component of this study investigated the requirements for ectomycorrhizal fungi in native forest rehabilitation following mining. Ectomycorrhizal infectivity was low in disturbed soils and mine spoil materials, with the intensity of disturbance and the presence of regrowth vegetation key determinants of the level of infectivity. Inoculation of seedlings of E. miniata with spores of ectomycorrhizal fungi increased both growth and leaf phosphorus concentrations by between two- and three-fold at 7 months after planting out on a waste rock dump devoid of native ectomycorrhizal propagules. The application of these findings to minesite rehabilitation in the region, and the feasibility of using spores for broad-scale inoculation, are discussed.

Abstract:Six rhizotrons in an Eucalyptus tetrodonta savanna revealed seasonal changes in the abundance of fine roots (≤ 5 mm diameter). Fine roots were almost completely absent from the upper 1 m of soil during the dry season, but proliferated after the onset of wet-season rains. At peak abundance of 3.9 kg m−2 soil surface, fine roots were distributed relatively uniformly throughout 1 m depth, in contrast with many tropical savannas and tropical dry forests in which fine roots are most abundant near the soil surface. After 98% of cumulative annual rainfall had been received, fine roots began to disappear rapidly, such that 76 d later, less than 5.8% of peak abundance remained. The scarcity of fine roots in the upper 1 m of soil early in the dry season suggests that evergreen trees may be able to extract water from below 1 m throughout the dry season. Persistent deep roots together with abundant fine roots in the upper 1 m of soil during the wet season constitute a ‘dual’ root system. Deep roots might buffer atmospheric CO2 against increase by sequestering carbon at depth in the soil.

Rehabilitation is seen as a key strategy for minimising biodiversity losses. Although most rehabilitation strategies aim to provide habitat for fauna, they usually focus entirely on establishing vegetation. Successful vegetation establishment, however, does not necessarily provide habitat to the same species that are threatened by habitat loss. Improved understanding of faunal response to rehabilitation is required if rehabilitation techniques are to be refined and deliver the hoped for biodiversity outcomes. This study aimed to assess to what extent post-mining rehabilitation on the Weipa bauxite plateau has restored the bird habitat values of the pre-mining native forest. Bird assemblages, vegetation, and landscape functionality were compared between: (1) Eucalyptus tetrodonta open forest reference sites representative of the pre-mining native forest; (2) two reference land units of Eucalyptus tetrodonta tall woodland that have previously been nominated as ecologically appropriate analogues for the post-mining landscapes; and (3) a chronosequence of post-mining rehabilitation sites up to 23 years old. Bird species richness and mean bird abundance increased with rehabilitation age. Bird species composition also changed and became more similar to native forest bird assemblages with increasing age. Significant differences remained, however, in mean bird abundance and composition of the bird assemblages between the oldest age class of mine rehabilitation and reference native forest land units. The mean bird species shortfall index in the oldest age class of mine rehabilitation was 63%, compared to a mean species shortfall index of 27% for pre-mining native forest sites. There were also significant differences in vegetation composition and structure between reference native forest land units and post-mining rehabilitation sites. Most importantly, the framework plant species that dominate the native vegetation community occurred at much lower densities in mine rehabilitation than in reference land units. Site detection rates of birds were strongly related to vegetation composition and structure. It is concluded that mining and post-mining rehabilitation on the Weipa bauxite plateau has so far resulted in habitat conversion rather than habitat restoration. It therefore contributes to the causes of biodiversity decline. Post-mining rehabilitation created new habitat for 18 bird species not sourced from the pre-mining native forest. It also provided partial habitat for many of the generalist native forest bird species recorded, although their presence in the landscape remained dependent on access to native forest. However, rehabilitation did not provide the habitat resources that are required by habitat specialists and foraging specialists. This study found that the native forest bird species most sensitive to habitat loss, and most in need of habitat restoration, may be the last to return to rehabilitation if they return at all. The findings of this study have implications for rehabilitation practices, biodiversity conservation on the Weipa bauxite plateau, as well as broader implications for policies that rely on the assumption that rehabilitation can offset biodiversity losses.
ANU Graduate School Scholarship. Rio Tinto Aluminium Weipa