Woodlands Of Australia Research Articles

Germinability of seeds stored in capsules on plants of two myrtaceous shrubs: differences among age cohorts and between species

Canopy-stored seed banks are a common trait among members of several plant families in sclerophyllous woodlands of Australia and South Africa, with their fruits usually opening in response to damage or fire. Unknown is whether the degree of dormancy and of germination differs among age cohorts in seeds stored on the mother plant. We examined the extent and speed of germination from two intensely serotinous myrtaceous species, Callistemon glaucus and Calothamnus quadrifidus, for seed held in capsules for up to 9 years. Germination of both species differed significantly among age cohorts (P < 0.0001). However, no consistent increase in germination over a range of temperatures with storage was found, suggesting that no after-ripening occurred and that seeds were non-dormant at maturity. Differences among cohorts may be due to pre-conditioning. Significant (P ≤ 0.0214) differences occurred between the small-seeded Callistemon and the large-seeded Calothamnus. Germination was (1) optimum at ≥20°C for Callistemon but at <20°C for Calothamnus, (2) 9–12 days earlier for Callistemon than for Calothamnus, and (3) higher in light than in darkness for Callistemon but equal in both light conditions for Calothamnus. While germination of the species differed in important features, we would expect synchronous germination of all age cohorts to occur following fire and the onset of regular rainfall.

An automated procedure for estimating the leaf area index (LAI) of woodland ecosystems using digital imagery, MATLAB programming and its application to an examination of the relationship between remotely sensed and field measurements of LAI.

Leaf area index (LAI) is one of the most important variables required for modelling growth and water use of forests. Functional-structural plant models use these models to represent physiological processes in 3-D tree representations. Accuracy of these models depends on accurate estimation of LAI at tree and stand scales for validation purposes. A recent method to estimate LAI from digital images (LAID) uses digital image capture and gap fraction analysis (Macfarlane et al. 2007b) of upward-looking digital photographs to capture canopy LAID (cover photography). After implementing this technique in Australian evergreen Eucalyptus woodland, we have improved the method of image analysis and replaced the time consuming manual technique with an automated procedure using a script written in MATLAB 7.4 (LAIM). Furthermore, we used this method to compare MODIS LAI values with LAID values for a range of woodlands in Australia to obtain LAI at the forest scale. Results showed that the MATLAB script developed was able to successfully automate gap analysis to obtain LAIM. Good relationships were achieved when comparing averaged LAID and LAIM (LAIM = 1.009 - 0.0066 LAID; R2 = 0.90) and at the forest scale, MODIS LAI compared well with LAID (MODIS LAI = 0.9591 LAID - 0.2371; R2 = 0.89). This comparison improved when correcting LAID with the clumping index to obtain effective LAI (MODIS LAI = 1.0296 LAIe + 0.3468; R2 = 0.91). Furthermore, the script developed incorporates a function to connect directly a digital camera, or high resolution webcam, from a laptop to obtain cover photographs and LAI analysis in real time. The later is a novel feature which is not available on commercial LAI analysis softwares for cover photography. This script is available for interested researchers.

Grassland regeneration and reconstruction: the role of grazing animals

Grassland regeneration and reconstruction: the role of grazing animals

Vegetation state change and consequent carbon dynamics in savanna woodlands of Australia in response to grazing, drought and fire: a scenario approach using 113 years of synthetic annual fire and grassland growth

A spatially explicit state and transition model for assessing the interactive effects of grazing, fire and climate on carbon dynamics in Australian savannas is described. The model runs on a yearly time step. It is based on a sequential treatment of events within each year, involving, in order, growth of biomass, consumption of biomass by livestock and burning of the remaining fuel (growth minus consumption). The major drivers are 113 years of annual rainfall data, annual modelled rangeland growth, synthetic fire incidence and timing data, and data describing stocking rates in dry sheep equivalents. Baseline carbon stocks are derived from pre-settlement estimates from the VAST steady-state carbon model. State and transition models for nine vegetation zones define vegetation condition and consequent carbon stock. Change is mediated by key indices of driver variables such as grazing, growth and fire, a series of parameters and default thresholds, and a set of rules. The model is run for three 113-year spin-up cycles to establish a set of initial condition grids that represent a plausible synthetic current state. Sensitivity analyses on selected parameters and index thresholds showed that fire and growth thresholds were most important for woodland zones, and utilisation rates and degradation and recovery periods were most important for grassland zones. The model was used to examine a series of scenarios involving changes to grazing pressure and suppression of fire for different climate sequences. Changes to a few parameters enabled simulation of low and high levels of encroachment of woody weeds, and hence carbon accumulation, in the Astrebla (Mitchell) grasslands; and effective capture of the climate-induced variation in grassland condition, and hence potential for soil carbon loss, within Heteropogon spp.-dominated grasslands in northern Queensland. The scenario results suggest that this simple state and transition model with an annual time step provides a potentially useful and flexible scenario model framework for exploration of vegetation and consequent carbon dynamics of the Australian tropical savanna region.

Effects of habitat complexity on ant assemblages

We investigated responses of ant communities to habitat complexity, with the aim of assessing complexity as a useful surrogate for ant species diversity. We used pitfall traps to sample ants at twenty‐eight sites, fourteen each of low and high habitat complexity, spread over ca 12 km in Sydney sandstone ridge‐top woodland in Australia. Ant species richness was higher in low complexity areas, and negatively associated with ground herb cover, tree canopy cover, soil moisture and leaf litter. Ant community composition was affected by habitat complexity, with morphospecies from the genera Monomorium, Rhytidoponera and Meranoplus being the most significant contributors to compositional differences. Functional group responses to anthropogenic disturbance may be facilitated by local changes in habitat complexity. Habitat complexity, measured as a function of differences in multiple strata in forests, may be of great worth as a surrogate for the diversity of a range of arthropod groups including ants.

Communal nesting in the usually solitary marsupial, Phascogale tapoatafa

AbstractThe marsupial brushtailed phascogale Phascogale tapoatafa is a solitary, hollow‐dependent, arboreal insectivore that occurs at low densities in open forests and woodlands of Australia. Data gathered from nest box surveys (4 years), and from radio‐tracking phascogales to nest sites (3 years) in south‐western Australia confirm solitary nesting after dispersal. However, in the winter of a single year, nest box surveys in one study area showed that 56% of individuals were nest sharing. On a neighbouring site, 81 group nests were also recorded among 18 radio‐collared individuals. In both areas, groups comprised two to four individuals of any age/sex combination. The same phascogales tended to nest together and in a number of different sites. Nest sharing between females was restricted to territory boundaries and continued after the annual die‐off of the males. Nest sharing coincided with prolonged drought conditions and in this year mature phascogales were significantly smaller than normal, i.e. males 25% less in weight, females 12% less. Communal nesting seemed to be a response to thermoregulatory difficulties posed by the three interrelated factors of low body mass, declining temperatures and declining food availability. Nest sharing in this species appeared to be a behavioural indicator of an energetics crisis, there was a population decline during the drought period and a population crash in the following year.

Temperate Eucalypt Woodlands in Australia: Biology, Conservation, Management and Restoration

TEMPERATE Eucalypt Woodlands in Australia provides a comprehensive account of the biology, conservation and management and rehabilitation of one of the most important broad-vegetation types in Australia. The book is divided into four sections, the distribution and status of woodlands, threats, processes and management, regeneration and repair and finally socio-economic issues. Chapters cover a wide range of issues including tree decline, the role of soil fungi, the impacts and opportunities of fuel wood extraction and the attitude of landholders to environmental issues. The characteristics and current status of the temperate woodlands in each state are separately covered in individual chapters. Contributions are included from many different authors and from sources across Australia and for the first time students, researchers or the general public can access information on this fascinating subject. Extensive bibliographies attached to each chapter will enable the reader to pursue topics in greater detail.

The potential of synthetic aperture radar (SAR) for quantifying the biomass of Australia's woodlands.

The potential of Synthetic Aperture Radar (SAR) for estimating the above ground and component biomass of woodlands in Australia is demonstrated using two case studies. Case Study 1 (In,june; central Queensland) shows that JERS-1 SAR L HH data can be related more to the trunk than the leaf and branch biomass of woodlands. A strong relationship between L HH and above ground biomass is obtained when low biomass pasture sites are included. Case Study I1 (Talwood, southern Queensland) determines that L and P band data can be related both to trunk and branch biomass, due to the similarity in the orientation and size of these scattering elements, and also to total above ground biomass. Saturation of the C. L and P band data occurred at approximately 20-30 Mglha; 60-80 Mglha and 80-100 Mglha. These preliminary results indicate that data from SAR are useful for quantifying changes in carbon stocks resulting from land use change in Australia's woodlands and for applications in rangeland assessment and management. Key words: remote sensing, biomass, woodlands

Ecology and physiology of establishment of eucalypt seedlings from seed: A review

Summary This paper provides a comprehensive review of the ecological and physiological factors affecting the establishment of eucalypts from seed, with particular reference to native forests and woodlands in Australia. Water, temperature, light in some cases, seed harvesting, pathogens, allelopathy, overstorey density and seedbed all have the potential to affect germination and emergence of eucalypts, but probably the most generally important factors are seed harvesting, water and seedbed condition. Mortality of eucalypt seedlings has been attributed to water deficits, high soil-surface temperatures, pathogenic fungi, low light intensity, frost, freezing temperatures, snow, fire, grazing and high seedling density. Mortality is usually greater beneath an overstorey and on undisturbed seedbeds, and may be reduced by application of fertilisers. Probably the most widespread causes of mortality are water deficits, especially in the drier areas, pathogens and the unsuitable conditions of an undisturbed seedbed....

Maternal Strategies of Phascogale-Tapoatafa (Marsupialia, Dasyuridae) .1. Breeding Seasonality and Maternal Investment

Phascogale tapoatafa, an arboreal carnivorous marsupial, is the largest mammal in which an obligate yearly die-off of all males occurs. The species is one of the most widespread of Australian marsupials, being found in tropical, subtropical and temperate forests and woodlands of Australia. Its breeding season varies little throughout this range, with most births occurring in July. In three Victorian populations, 2-year-old females typically gave birth earlier than first-year females, births were spread on average over 15 days, and, in some years, occurred two weeks earlier than average. Modal litter size equalled the number of teats (8), but litters of 1-6 young comprised 29% of the sample (n = 45), and litter size averaged 6.6 young. The sex ratio of litters produced by second-year females was significantly male-biased (0.62); that of first-year females was 0.48. When juveniles first released the teats (c. 48 days of age), they weighed about 4 g. Weight gain by captive juveniles was more rapid than that of wild conspecifics prior to weaning, but skeletal growth rate and morphological development were similar. Total lactational investment by P. tapoatafa is much greater than expected for a dasyurid of its size (wild litters at weaning average 313% of maternal weight; captive litters average 370%). The high mortality of wild adult females during lactation may reflect this energetic drain.

Eucalypt-Feeding Insects Bite off More Than They Can Chew: Sabotage of Induced Defences?

Plant chemical defences that are induced by insect attack have evolved in a wide variety of species, including deciduous and coniferous trees (Rhoades 1979). The forests and woodlands of Australia are dominated by the genus Eucalyptus, which comprises several hundred species of evergreen trees. As yet, there is no evidence that induced defences occur in eucalypts. However, here we report that several species of eucalypt-feeding insects chew off and discard partially-eaten leaves, and we propose the hypothesis that these insects are sabotaging the transmission of induced defences to neighbouring leaves. We have observed larvae from four families of Lepidoptera and one family of Hymenoptera chewing off partially-eaten eucalypt leaves on which they have been feeding. It has been observed on Eucalyptus melliodora, E. viminalis, E. leucoxylon and E. pauciflora. The behaviour of all insect species involved is remarkably similar and is described in some detail for Anthela varia (Anthelidae) on E. leucoxylon (Fig. 1). After feeding on a leaf for up to an hour or more, the larva moves on to the stem and starts chewing around the petiole at the base of the leaf (Fig. 1A). Chewing results in characteristic girdling of the petiole (Fig. 1B), and continues until the leaf falls from the plant (Fig. 1C). The insect then chews on the petiole stump for a few more minutes (Fig. 1D). The complete behavioural sequence (A-D) is very deliberate and may take 10 min or more. If the insect is disturbed, as in Fig. 1B, it will quickly resume chewing, rather than abandon the task. We have also seen the cup moth Doratifera quadriguttata (Limacodidae) (Fig. 2) and two other species in the same family removing partially-eaten leaves. Additionally, it has been noted in two unidentified species of Geometridae and one species of Lasiocampidae. We have also observed partially-eaten eucalypt leaves being cut off by two species of sawfly, Perga affinis and Perga sp. (Fig. 3). Sawfly larvae often feed gregariously, and when a group moves from a leaf, the last larva to depart performs the petiole-chewing. On many occasions we have seen two or more larvae of P. affinis co-operate in chewing off a leaf on which they and other larvae had been feeding. There are only a few records in the literature of insects, all lepidopteran larvae, chewing off partiallyeaten leaves (Scriber 1975, Heinrich and Collins 1983). Damaged leaves may act as searching cues for birds (Heinrich and Collins 1983) and parasitoids (Faeth 1987), however three pieces of evidence lead us to argue that removal of feeding evidence is not the primary function of the behaviour we have observed on eucalypts. Firstly, obligate leaf-removal would be expected if natural enemies using leaf damage as a searching cue had provided the effective selective pressure for this behaviour. However, petiole-chewing behaviour is not obligate in most of the species we have observed. For instance, D. quadriguttata larvae often move from a partially-eaten leaf without chewing it off, suggesting that leaf removal occurs as a facultative response to an immediate stimulus. Induced defences can be mobilized very rapidly (Carroll and Hoffman 1980), however the strength of the response is likely to vary between occasions. Such variation may determine whether an insect

Ecological Traits of the Eucalyptus L'hérit Subgenera Monocalyptus and Symphyomyrtus

The genus Eucalyptus L'Hérit. dominates most of the forests and woodlands of Australia. Many stands consist of intimate mixtures of species from different subgenera. The ecological traits of the two largest subgenera, Symphyomyrtus and Monocalyptus, are reviewed. Consistent differences in herbivore and parasite damage to leaves; in water relations; in tolerance to waterlogging, flooding, salinity and frost; in nutrient usage; in response to Phytophthora cinnamorni; and in early growth patterns are described. These can be summarised as differences in leaf chemistry; in root morphology, chemistry and activity; and in early growth rates. It is suggested that the differences in the ecological traits, and especially in the early growth rate, may help explain the coexistence of closely related species of similar habits in eucalypt communities.

Report on discussion of paper by P. J. H. Sharpe.

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Effect of Neighbouring Trees on Eucalypt Growth in a Semi-Arid Woodland in Australia

(1) The effects of neighbouring trees on the growth of Eucalyptus populnea in a native semi-arid woodland in Queensland, Australia, were investigated using three different measures of interference: (i) nearest-neighbour distance (NN); (ii) Weiner's neighbourhood interference (W); (iii) a competitive-interference measure (CI) which included the size of the influenced individual. (2) The relationship between relative girth increment and the interference measures was obscured by the range of tree sizes and it was necessary to treat the data in three separate size classes. (3) The performance of the three different measures of interference in acting as predictors of relative girth increment varied across the size classes. All three measures gave a usable result for the large size class (>60 cm gbh), both W and CI performed well for the small size class (0-30 cm gbh), but only CI gave a stable result for the middle size class (30-60 cm gbh). (4) Use of a vector in the model for plant influences allowed the generation of an influence surface, which was then used to derive CI values. This surface could also be used to calculate values for relative-recruitment potential at any point within the system. (5) The competitive-interference model used leaf area as a measure of plant size which is related to resource demand. This measure reflects important functional variables such as water uptake, litter input, root volume and shading, and can be applied to different growth forms. It should then be possible to generate influence surfaces which combine trees, shrubs and grasses and to investigate interactions between these different growth forms.