Julian Ash

Influence of seed size and seedling ecological attributes on shade-tolerance of rain-forest tree species in northern Queensland

Growth, leaf anatomy and stomatal responses were examined in seedlings of 12 rainforest tree species in northern Queensland. Plants were kept in a shade house for a period of 15 months at 37%, 10% and 2.5% photosynthetically active radiation (PAR), roughly corresponding to light environments in large gaps, small gaps, and forest understorey, respectively. The species were chosen to represent a wide array of taxa, ecological, and morphological characteristics, and were assigned regeneration niche (RN) index values based on observations of life history and spatial distribution of their seedlings and saplings in various forest microsites. Growth, biomass allocation patterns, leaf anatomy and stomatal responses varied appreciably among species, as well as in response to shading (...)

Factors affecting survival of tree seedlings in North Queensland rainforests

SummarySeedlings of six species of rainforest trees with widely constrasting ecology and seed morphology were transplanted at 3 weeks of age into tree-fall gaps and the shaded understoreys at two rainforest sites (Curtain Fig and Lamins Hill) on the Atherton Tableland, North Queensland, Australia. In each forest habitat, half of the transplanted seedlings were protected from vertebrates by means of wire cages, and survival was monitored over 16 months. The main objective was to estimate the extent to which independent variables (forest, habitat, protection from vertebrates, and species) contribute to explaining survival differences among the seedlings. Significant differences existed in the mortality among species, whether caged or uncaged. Seedlings unprotected from vertebrates suffered greater mortality (i.e. averaged over all species and forests, mortality > 75%), compared to the caged seedlings (mortality < 40%). Seedling of most species survived better in forest gaps, though the effects varied significantly among the six species. Survival of caged seedlings in Curtain Fig was significantly greater than in Lamins Hill, a pattern attributed to the partial deciduousness of the Curtain Fig forest. Because only few of the uncaged seedlings survived to 16 months, we focussed on the caged seedlings to examine the role of light at the forest habitats on survival. Relationship between seedling mortality and increasing light availability vary significantly among the six species. However across species, seedling mortality decreased linearly as photosynthetically active radiation (PAR) rose from 0.48 to 2.0%, after which an asymptote was reached and further increase in light (up to 8% PAR) did not influence survival significantly. Overall, temporal, species and the various environmental variables and their interactions explained about 60% of the variations in the seedling mortality data, with protection and species differences making the greatest contributions.

Growth of tree seedlings in tropical rain forests of North Queensland, Australia

The effects of forest habitat, canopy light condition, vertebrate herbivory and species mean seed size on growth of tree seedlings were evaluated for six widely different species of North Queensland tropical rain forests. Two forest localities differing in size and rainfall intensity were used for the trial. In each forest, seedlings were transplanted three weeks after germination into small to medium-sized canopy gaps and into the forest interiors, with half protected by cages and the other half unprotected. Growth measurements were made over a period of 16 months. All growth parameters examined differed significantly between the six species. At the end of the study period, for most species, forest site and protection from vertebrates did not affect seedling biomass (...)

Effects of phosphorus and nitrogen on growth of pasture plants and VAM fungi in SE Australian soils with contrasting fertiliser histories (conventional and biodynamic)

The soil biological community has been reported to differ between conventional and alternative (organic and biodynamic) farming systems. However, few studies have investigated whether this results in substantial differences in the biological pathways controlling major ecosystem processes, such as plant nutrient uptake. This paper describes a glasshouse experiment conducted using a red-brown earth (Natrixeralf) soil sampled from three conventional and three biodynamic irrigated dairy pastures located in the Goulburn River Valley, Victoria, Australia. The biodynamic soils had not had organic or inorganic fertilisers applied for, on average, 17 years, while the conventional soils had received regular inputs of fertilisers containing soluble phosphorus (P) and nitrogen (N). The experiment examined whether the contrasting fertiliser histories had resulted in different pathways of plant nutrient uptake through assessing the response of white clover (Trifolium repens L.), perennial rye grass (Lolium perenne L.) and the indigenous vesicular-arbuscular mycorrhizal (VAM) fungi to addition of four levels of soluble P and N. The response to added P and N did not differ between the conventional and biodynamic soils, although, plants in the biodynamic soils had a slower growth rate and a higher level of colonisation by VAM fungi due to lower initial soil P and N concentrations. Overall, there was no indication that the biodynamic and conventional soils had developed substantially different processes to enhance plant nutrient uptake or that the indigenous VAM fungi differed in their tolerance to applications of soluble nutrients.

Are traits measured on pot grown plants representative of those in natural communities

Abstract Question: The quantification of functional traits in natural communities can be difficult (e.g. root traits, RGR). Can functional traits measured on pot grown plants be reliably applied to natural communities? Alternatively, can below-ground plant traits be predicted from above-ground traits? Location: Southeastern Australia. Methods: We compared 17 shoot, root and whole-plant morphological traits measured on 14 plant species in a native grassland community to those measured under two different pot conditions: unfertilised and fertilised. Results: The majority of trait values for pot grown plants differed to plants in the field, however, species ranking remained consistent for most leaf traits between the field and the two pot growing conditions. In contrast, species ranking was not consistent for most whole plant traits when comparing field plants to fertilised pot grown plants, providing a caution against the tendency to grow plants in controlled conditions at ‘optimal’ (high) resource levels. Moderate to strong correlations were found between below-ground and above-ground plant traits, including between root dry matter content and leaf dry matter content, and between specific root area and specific leaf area. Conclusions: The utility of pot grown plants to quantify traits for field plants is highly dependent on the selection of the growing conditions in the controlled environment. The consistency we observed between above-ground and below-ground trait strategies suggests that below-ground traits may be predictable based on above-ground traits, reducing the need to quantify root traits on cultured plants. Nomenclature: Harden (1996); Linder (1997).

Herbicides, weeds and endangered species: management of bitou bush (Chrysanthemoides monilifera ssp. rotundata) with glyphosate and impacts on the endangered shrub, Pimelea spicata

Environmental weed invasion threatens the biodiversity of native species. Unfortunately, managing these weeds may also affect biodiversity adversely. A recent example occurred when glyphosate, a herbicide used to control the highly invasive weed, bitou bush (Chrysanthemoides monilifera ssp. rotundata), accidentally drifted over a small population of an endangered shrub, Pimelea spicata. Following concerns that the affected population would not recover and, thereby, cause the local extinction of P. spicata, we conducted a series of glasshouse and field experiments to explore the impacts of glyphosate on this endangered species. Seedlings and young plants of P. spicata, in which the tap root was undeveloped, were killed by a single application of glyphosate. Older plants with a well developed tap root also died back initially, but about 50% of individuals re-sprouted. This re-growth was associated with a significant decrease in tap root diameter, implying that further disturbance, including repeated treatment with glyphosate, would kill plants by impairing their potential for recovery. Unlike some sclerophyllous native shrubs, the tolerance of P. spicata to glyphosate was limited, even when its growth was slowed artificially by limiting water availability. Winter applications of glyphosate to manage infestations of bitou bush will impact adversely on populations of P. spicata and may also affect the other rare and endangered species whose survival is threatened by this species, even though some natives are unaffected by the herbicide. Protecting native biodiversity from bitou bush will involve sustainable weed management that minimises impacts on non-target native species.

Estimating rainforest biomass stocks and carbon loss from deforestation and degradation in Papua New Guinea 1972-2002: Best estimates, uncertainties and research needs.

Reduction of carbon emissions from tropical deforestation and forest degradation is being considered a cost-effective way of mitigating the impacts of global warming. If such reductions are to be implemented, accurate and repeatable measurements of forest cover change and biomass will be required. In Papua New Guinea (PNG), which has one of the worlds largest remaining areas of tropical forest, we used the best available data to estimate rainforest carbon stocks, and emissions from deforestation and degradation. We collated all available PNG field measurements which could be used to estimate carbon stocks in logged and unlogged forest. We extrapolated these plot-level estimates across the forested landscape using high-resolution forest mapping. We found the best estimate of forest carbon stocks contained in logged and unlogged forest in 2002 to be 4770 Mt (+/-13%). Our best estimate of gross forest carbon released through deforestation and degradation between 1972 and 2002 was 1178 Mt (+/-18%). By applying a long-term forest change model, we estimated that the carbon loss resulting from deforestation and degradation in 2001 was 53 Mt (+/-18%), rising from 24 Mt (+/-15%) in 1972. Forty-one percent of 2001 emissions resulted from logging, rising from 21% in 1972. Reducing emissions from logging is therefore a priority for PNG. The large uncertainty in our estimates of carbon stocks and fluxes is primarily due to the dearth of field measurements in both logged and unlogged forest, and the lack of PNG logging damage studies. Research priorities for PNG to increase the accuracy of forest carbon stock assessments are the collection of field measurements in unlogged forest and more spatially explicit logging damage studies.

Regional and local patterns in the spatial distribution of the flower-infecting smut fungus Sporisorium amphilophis in natural populations of its host Bothriochloa macra

Regional variation in the incidence of the systemic floral-smut fungus Sparisorium amphilophis (Syd.) Langdon & Fullerton an the perennial grass Bothriochloa macra (Steud.) S. T. Blake was investigated through three surveys over a 12 yr period (1981-93). In all three surveys a marked north-south trend in percentage of infection was detected with a greater proportion of plants in northerly populations being infected than in populations located to the south. The incidence of disease in populations was negatively correlated with the frequency of days with temperatures <0°C in winter. Detailed exploration of local variation in a subset of five populations showed that the incidence of S. amphilophis was density-dependent and was greater in the edge areas of host populations than in the less disturbed core areas. Smut prevented seed production and negatively affected different aspects of the morphology of the plants, such as the height and basal diameter. Infection also significantly increased the number of inflorescences per plant. These field results were complemented by glasshouse-based competition experiments which indicated that, despite causing reductions in size, S. amphilophis only affected the competitive ability of infected plants grown under sub-optimal conditions. The results of this study indicate that an interplay between physical and biotic aspects of the environment determines regional and local levels of disease.

Combined effects of two arthropod herbivores and water stress on growth of Hypericum species

The interaction between physiological stress and arthropod herbivory was studied using two perennial species of Hypericum. Seedlings of H. perforatum, a herb introduced to Australia and weedy in places, and H. gramineum, an indigenous species, were subjected to water stress and/or herbivory by a mite, Aculus hyperici and an aphid, Aphis chloris. Both arthropods have recently been released in Australia for biological control of H. perforatum. Individually, stresses reduced measures of plant growth. Combinations of the three stresses decreased plant growth by slightly more than the product of their separate effects, suggesting that there is a weak positive interaction exacerbating the damage caused by each stress. Seedlings of the target weed and the ‘non-target’ indigenous species were equally affected by the arthropods. The implications for weed biological control are discussed.

Scale insects consistently affect roots more than shoots: the impact of infestation size on growth of eucalypt seedlings

1 Different infestation levels of the phloem-feeding scale insect, Eriococcus coriaceus Maskell (Hemiptera: Eriococcidae), consistently reduced root growth more than shoot growth in seedlings of Eucalyptus blakelyi Maiden (Myrtaceae). 2 Low levels of scale insect infestation significantly decreased root and lignotuber biomass but not shoot biomass. High levels of infestation, however, adversely affected all plant parts. Root and lignotuber biomass declined linearly, while the responses of stem and leaf biomass were nonlinear, with respect to increasing total insect load. 3 Plant responses to scale insect infestations may be explained by considering sapsucking insects as additional sinks that compete against plant sinks and both redirect and drain resources from the plant. 4 Scale insect populations exhibited strong density dependent effects, suggesting they were severely depleting resources within their hosts. Extensive shoot death at high levels of infestation may have contributed to insect population decline by causing scale insects to die prematurely or by reducing the availability of suitable feeding sites.