Climate Of South-western Australia Research Articles

Approaches to scheduling water allocations to kikuyugrass grown on a water repellent soil in a drying-climate

Water allocation is a principal planning method for managing water supplies to agricultural and horticultural land in drying climates. Regulatory bodies often establish the water allocation amount, but its distribution during the irrigation season is left to the land manager’s discretion. We evaluated approaches to best manage water allocations to a warm-season turfgrass [Pennisetum clandestinum (Holst. Ex Chiov)] grown on a free-draining sand prone to surface (0–25 mm) soil water repellence in a Mediterranean climate in south-western Australia under ‘deficit irrigation’, in a two-year field study. The three factorial experiment consisted of three levels for each treatment applied to plots (10 m2) of kikuyugrass: water allocation (5000, 6250 or 7500 kL ha−1 yr−1), irrigation schedule, and soil wetting agent rate (nil, recommended ‘label’ rate, double recommended ‘label’ rate), and was replicated three times. The irrigation schedules were based on historical net evaporation at the site, and then refined monthly using in-season net evaporation data or measurements of soil water content. Kikuyugrass growth and color was adequate when irrigated using the current regional water allocation (7500 kL ha−1 yr−1) under a low wear situation and to a lesser extent when the water allocation was lowered to 6250 kL ha−1 yr−1. Application of a soil wetting agent diminished water repellence and improved kikuyugrass color for 7500 or 6250 kL ha−1 yr−1 water allocations. Distributing a water allocation based on historical monthly net evaporation rates was a simple and effective scheduling approach to maintaining a warm-season turfgrass.

Adaptation and acclimation both influence photosynthetic and respiratory temperature responses in Corymbia calophylla.

Short-term acclimation and long-term adaptation represent two ways in which forest trees can respond to changes in temperature. Yet, the relative contribution of thermal acclimation and adaptation to tree physiological responses to temperature remains poorly understood. Here, we grew two cool-origin and two warm-origin populations of a widespread broad-leaved evergreen tree species (Corymbia calophylla (Lindl.) K.D.Hill & L.A.S.Johnson) from a Mediterranean climate in southwestern Australia under two growth temperatures representative of the cool- and warm-edge of the species distribution. The populations selected from each thermal environment represented both high and low precipitation sites. We measured the short-term temperature response of leaf photosynthesis (A) and dark respiration (R), and attributed observed variation to acclimation, adaptation or the combination of both. We observed limited variation in the temperature optimum (Topt) of A between temperature treatments or among populations, suggesting little plasticity or genetic differentiation in the Topt of A. Yet, other aspects of the temperature response of A and R were dependent upon population and growth temperature. Under cooler growth temperatures, the population from the coolest, wettest environment had the lowest A (at 25 °C) among all four populations, but exhibited the highest A (at 25 °C) under warmer growth temperatures. Populations varied in R (at 20 °C) and the temperature sensitivity of R (i.e., Q10 or activation energy) under cool, but not warm growth temperatures. However, populations showed similar yet lower R (at 20 °C) and no differences in the temperature sensitivity of R under warmer growth temperatures. We conclude that C. calophylla populations from contrasting climates vary in physiological acclimation to temperature, which might influence how this ecologically important tree species and the forests of southwestern Australia respond to climate change.

Soil-water dynamics in a pasture-cropping system

Pasture cropping is a farming system in which annual crops are sown into established perennial pastures. It may provide environmental benefits such as increased groundcover and reduced deep drainage, while allowing traditional crop production in the Mediterranean-style climate of south-western Australia. In this research, we investigated deep drainage and the temporal patterns of water use by a subtropical perennial grass, annual crops, and a pasture-cropping system over a 4-year period. Both the pasture and pasture-cropped treatments reduced deep drainage significantly, by ~50 mm compared with the crop treatment. Competition between the pasture and crop components altered patterns of average daily water use, the pasture-cropped treatment having the highest water use for July, August and September. Consequently, water-use efficiency for grain production was lower in the pasture-cropped plots. This was offset by pasture production, so that over a full 12-month period, water-use efficiency for biomass production was generally greater for the pasture-cropped plots than for either the pasture or crop monocultures. Pasture cropping may be a viable way of generating sustainable economic returns from both crop and pasture production on sandy soils of south-western Australia.

Hydraulic traits and water use of Eucalyptus on restored versus natural sites in a seasonally dry forest in southwestern Australia

Eucalyptus is a globally important genus for reforestation but eucalypt growth in non-native environments has uncertain ecohydrological consequences. This study investigated the hydraulic structure and function of juvenile (2.5–10m height) Eucalyptus marginata on restored mine sites and forest sites in a seasonally dry climate in southwestern Australia. We measured sap flow, leaf area, sapwood area, leaf water potential, stomatal conductance and weather variables and applied a simple model of plant water use to examine hydraulic traits across chronosequences of trees (using height as an index of age) in each environment. Younger trees on restored sites grew three times faster and used four times more water per unit leaf area (0.53kgm−2day−1) than forest trees, consistent with greater light, water and nutrient availability on restored sites. To maintain hydraulic homeostasis, trees on restored sites reduced leaf area/sapwood area ratio by 25%, increased sapwood permeability by 20%, and reduced stomatal conductance and transpiration by 50% to counterbalance fourfold increases in height and leaf area. In contrast, forest trees reduced leaf area/sapwood area ratio by 33% but increased sapwood permeability by 100% and stomatal conductance and transpiration by 50% in response to increased water availability, in addition to increased height and leaf area. A linear relationship between leaf area and water use for forest trees was indicative of hydrological equilibrium, whereas a curvilinear relationship for trees on restored sites suggested transition from high to lower water availability. Young eucalypts are likely to develop traits that are hydraulically compatible with their climate and substrate, but they may also adjust their architecture and physiology over time in response to changes in water availability. Trees in reforested landscapes with modified soils and initially abundant soil moisture may develop hydraulic architectures that are more efficient than found in native forests, which may pose risks if they can only access a fixed volume of soil. The long-term sustainability of such systems is likely to depend on trees eventually developing appropriate hydraulic architectures to cope with regimes of water availability more akin to native forests, especially in drought-prone environments.

Response of intensively grazed ryegrass dairy pastures to fertiliser phosphorus and potassium

Intensively grazed, rain-fed dairy pastures on the predominantly sandy soils in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise >90% ryegrass (annual ryegrass, Lolium rigidum Gaud. and Italian ryegrass, L. multiflorum Lam.). To maximise pasture use for milk production, the pastures are rotationally grazed by starting grazing when ryegrass plants have 3 leaves per tiller, and fertiliser nitrogen (N) and sulfur (S), in the ratio of 3–4 N and 1S, need to be applied after each grazing for profitable pasture dry matter (DM) production. In addition, farmers usually also apply low levels of phosphorus (P) and potassium (K) fertiliser to these pastures after each grazing, despite Colwell soil test P usually being well above critical values for pasture production, and fertilizer K being only required for clover in the traditional clover (Trifolium subterraneum L.) ryegrass pastures of the region. In field experiments undertaken May 2006–June 2010 on intensively grazed ryegrass dairy pastures in the region, no significant ryegrass DM responses to applied fertiliser P or K were obtained, regardless of level or method of P or K application. When no P was applied, soil test P declined gradually, by between 4.4 and 7.1 mg/kg per year, and remained above the critical value for the soils at 2 sites, but declined below the critical value for soil at a third site. Critical soil test P is located near the maximum yield plateau in the flat part of the relationship between yield and soil test P, particularly when, as appropriate for dairy production, the critical value is for 95% of the maximum pasture DM yield. Consequently, when no P is applied and soil test P decreases, significant pasture DM yield decreases will only occur when soil test P approaches the steeper part of the relationship, which can take some time. In addition, as occurs on farms, faeces deposited by cows while grazing supplied P to pasture even when no fertiliser P was applied. Soil K testing proved unreliable for indicating the need for fertiliser K applications to pasture in the next growing season because many soil samples collected within and between urine patches contained elevated levels of K deposited by cows while grazing. We conclude fertiliser P should only be applied to intensively grazed ryegrass dairy pastures when soil testing indicates it is required. Further research is required to assess if plant K testing is an alternative, but urine patches may also pose a problem for plant testing.

Leaf fossils of Banksia (Proteaceae) from New Zealand: An Australian abroad

Fossils can shed new light on plant biogeography and phylogeny. Pinnately lobed leaves from the Oligo-Miocene Newvale lignite mine, South Island, New Zealand are the first extra-Australian leaf fossils of the charismatic genus Banksia (Proteaceae), and they are assigned to a new species, B. novae-zelandiae. Comparison with extant taxa shows that the fossils are best regarded as an extinct stem relative of Banksia because their available features are either plesiomorphic for the genus (notably, the stomata are superficially placed, not sunken in balloon-like pits as in many extant species) or lack evidence of synapomorphies that would enable them to be placed in the crown group. Banksia novae-zelandiae does, however, exhibit two cuticular features that are unique or highly derived for Banksia. These are rugulate subsidiary cell ornamentation and the presence of complex papillae that extensively cover the abaxial leaf surface. The fossils add to the widespread records of the pinnately lobed leaf form in Banksia in Australia beginning in the late Paleocene. This form is now limited to species confined to sclerophyllous heathlands of Mediterranean climate in southwestern Australia. Banksia novae-zelandiae could be part of a lineage that had a long history in New Zealand, perhaps dating to the early Paleogene.

Quantifying pasture dry matter responses to applications of potassium fertiliser for an intensively grazed, rain-fed dairy pasture in south-western Australia with or without adequate nitrogen fertiliser

Rain-fed dairy pastures on sandy soils common in the high rainfall (>800 mm annual average) Mediterranean-type climate of south-western Australia comprise the annual species subterranean clover (Trifolium subterraneum L.) and annual and Italian ryegrass (Lolium rigidum Gaud. and L. multiflorum Lam.). In wet years, clover becomes potassium (K) deficient and shows large dry matter (DM) responses to applied fertiliser K due to leaching of K in soil by rainfall. In contrast, ryegrass rarely shows DM responses to applied K. Many dairy pastures in the region are now intensively grazed to maximise pasture use for milk production, and nitrogen (N) fertiliser is applied after each grazing. It is not known if frequent applications of fertiliser N to these pastures changes pasture DM responses to applied K. Therefore, a long-term (2002–07) field experiment was undertaken on an intensively grazed dairy pasture in the region to quantify pasture DM responses to applied fertiliser K with or without applications of adequate fertiliser N (141–200 kg N/ha per year). Soil samples (top 10 cm of soil) were collected from each plot of the experiment each February to measure soil test K by the standard Colwell sodium bicarbonate procedure used for both K and phosphorus soil testing in the region. When no N was applied, pasture comprised ~70% (dry weight basis) clover and 25% ryegrass, compared with ~70% ryegrass and 25% clover when adequate N was applied. Significant linear responses of pasture DM to applied K occurred in 3 of the 6 years of the experiment only when no N was applied and clover dominated the pasture. The largest response varied from ~1.7 to 2.0 t/ha DM consumed by dairy cows at all grazings in each year, giving a K response efficiency of between 8 and 10 kg DM/ha per kg K/ha applied. Significant pasture DM responses to applied N occurred at all grazings in each year, with ~2–3 t/ha extra DM consumed by dairy cows at all grazings in each year being produced when a total of 141–200 kg N/ha was applied per year, giving an N response efficiency of ~7–19 kg DM/ha per kg N/ha applied. Soil test K values were very variable, attributed to varying proportions of soil samples per plot collected between and within cow urine patches, containing much K, arbitrarily deposited on experimental plots during grazing. Soil test K values were not significantly affected by the rates of K applied per year. A re-evaluation of results from the major soil K test study conducted for pastures in the region confirm that ryegrass rarely showed DM responses to applied K, and that for clover, soil K testing poorly predicted the likelihood of K deficiency in the next growing season.

Significant Nitrogen by Sulfur Interactions Occurred for Canola Grain Production and Oil Concentration in Grain on Sandy Soils in the Mediterranean-Type Climate of Southwestern Australia

ABSTRACT The nitrogen (N) by sulfur (S) interaction for canola (Brassica napus L.) grain production and oil concentration in grain has been quantified in temperate climates, but it is not known if these results also apply to sandy soils common in the Mediterranean-type climate of southwestern Australia where canola is now a major crop. Seventeen field experiments were undertaken with canola in the region during 1994 to 2005 in which 4 rates of both N (0–138 kg N/ha) and S (0–34 kg S/ha) were applied. Significant grain yield responses to applied N occurred in all experiments and the responses increased as more S was applied. Grain yield responses to applied S only occurred when N was applied and tended to increase as more N was applied. When no S was applied the two largest rates of N applied, 69 and 138 kg N/ha, induced S deficiency reducing grain yields. The oil concentration in grain tended to decrease as more N was applied and increased as more S was applied, particularly when the two largest rates of N were applied. Consequently significant N × S interactions were obtained in all experiments for grain production and in 15 experiments for oil concentration in grain.

Effect of site, harvesting stage, and genotype on environmental staining in faba bean (Vicia faba L.)

Seed discoloration due to environmental staining in faba bean leads to poor quality and reduced market price. Environmental staining in faba bean is characterised by a dark brown, grey, or black discoloration of the seed coat at harvest. Its cause is unknown, but it does not appear to be caused by a pathogen. Environmental conditions during pod and seed formation and at maturity are thought to have a large effect on the degree of environmental staining. To test the hypothesis that seeds formed under stressful conditions will have a higher degree of staining, faba bean seeds were harvested at 2 different stages of maturity from trials located in a range of environmental conditions under a Mediterranean-type climate of south-western Australia over 2 seasons. Four faba bean varieties were studied (Fiord, Fiesta, Ascot, and Cairo). The majority of seeds had good colour but across the trials, 3–25% were stained up to an unacceptable level and this varied with location and variety. Seeds formed later in plant development (located on the upper nodes of the plant) had more staining than seeds formed earlier (located on the lower nodes). Seeds formed on small and weak plants had more staining than seeds formed on normal sized healthy plants. Fiord showed a greater amount of staining than Ascot, Fiesta, and Cairo when grown in the mild, southern environments. Early harvesting (at physiological maturity) did not reduce environmental seed staining compared with harvesting at full maturity. Chemical analysis of seed testa and cotyledons revealed that total phenolic contents of the testa and cotyledons increased with staining. An increase in Zn and Na and a decrease in K concentration in the testa were also associated with increased staining levels.

Responses of intensively grazed dairy pastures to applications of fertiliser nitrogen in south-western Australia

For the first time, we quantified pasture dry matter (DM) responses to applied fertiliser nitrogen (N) for intensively grazed, rain-fed, dairy pastures on sandy soils common in the Mediterranean-type climate of south-western Australia. The pastures are composed of subterranean clover (Trifolium subterraneum L.) and annual and Italian ryegrass (Lolium rigidum Gaud. and L. multiflorum Lam.). Six rates of N, as urea (46% N), were applied to 15 m by 15 m plots four times during 2002 and after each of the first 5–7 grazings in 2003 and 2004, throughout the typical April–October growing season. Total rates of N applied in the first year of the experiments were 0, 60, 120, 160, 200 and 320 kg N/ha, which were adjusted in subsequent years as detailed in the ‘Materials and methods’ section of this paper. The pastures in the experiments were rotationally grazed, by starting grazing when ryegrass plants had 2–3 leaves per tiller. The amount of pasture DM on each plot was measured before and after each grazing and was then used to estimate the amount of pasture DM consumed by the cows at each grazing for different times during the growing season. Linear increases (responses) of pasture DM to applied N occurred throughout the whole growing season when a total of up to 320 kg N/ha was applied in each year. No maximum yield plateaus were defined. Across all three experiments and years, on average in each year, a total of ~5 t/ha consumed DM was produced when no N was applied and ~7.5 t/ha was produced when a total of 200 kg N/ha was applied, giving ~2.5 t/ha increase in DM consumed and an N response efficiency of ~12.5 kg DM N/kg applied. As more fertiliser N was applied, the proportion of ryegrass in the pasture consistently increased, whereas clover content decreased. Concentrations of nitrate-N in the DM consistently increased as more N was applied, whereas concentrations of total N, and, therefore, concentration of crude protein in the DM, either increased or were unaffected by applied N. Application of N had no effect on concentrations of other mineral elements in DM and on dry matter digestibility and metabolisable energy of the DM. The results were generally consistent with findings of previous pasture N studies for perennial and annual temperate and subtropical pastures. We have shown that when pasture use for milk production has been maximised in the region, it is profitable to apply fertiliser N to grow extra DM consumed by dairy cows; conversely, it is a waste of money to apply N to undergrazed pastures to produce more unused DM.

Leaf Mechanical Properties in Sclerophyll Woodland and Shrubland on Contrasting Soils

Sclerophylly is a common feature of vegetation on infertile soils, and its adaptive significance has been linked to nutrient-use efficiency by protection of leaves to maximise carbon gain. However, there has been little investigation of how the leaf mechanical properties that contribute to the phenomenon of sclerophylly vary along nutrient gradients. In this paper, we investigate how leaf mechanical properties vary among plants on three contrasting soil types (grey sand, laterite soil, and soil overlying dolerite) in a Mediterranean climate in southwestern Australia. Most species were sclerophyllous, but there was 5-fold variation in leaf mass per unit area (LMA) and 17- to 473-fold variation in mechanical properties among species. Species growing on laterite and/or sand (low-nutrient soils) had higher punch strength, work (a measure of toughness) to punch, specific (per unit leaf thickness) work to punch, work to shear, specific work to shear, and flexural stiffness (EIW) than those on dolerite soils (higher in nutrients). There were few differences in mean values of leaf mechanical properties between the two low-nutrient soils, possibly because the lower concentration of nutrients in the sand is balanced by the greater soil volume than the laterite soil (higher concentration of nutrients, but shallower). There were also few differences in leaf properties between plants of the same species growing on contrasting soil types. There was some variation among sclerophyllous species in their mechanical characteristics, but overall, EIW provided the strongest contribution to sclerophylly, explaining up to 81% of the variation in LMA. There was no evidence of differences among soil types in the relationships of mechanical properties with LMA, and therefore, no evidence of variation in the mechanical constitution of sclerophylly among soil types.

A process-based model of nitrogen cycling in forest plantations: Part II. Simulating growth and nitrogen mineralisation of Eucalyptus globulus plantations in south-western Australia

We applied a new version of the G’DAY ecosystem model to short-rotation plantations of Eucalyptus globulus growing under a Mediterranean climate in south-western Australia. The new version, that includes modified submodels for biomass production, water balance, litter and soil organic matter (SOM) decomposition, and soil inorganic N balance, was parameterised and applied to three experimental eucalypt sites (Mumballup, Darkan and Northcliffe) of contrasting productivity. With a common base set of parameter values, the model was able to correctly reproduce observed time series of soil water content, canopy leaf area index and stemwood data at the three sites. The model's ability to simulate soil N supply under forest plantations was tested by simulating N mineralisation at each of the three sites over the duration of the experiment (10 years). Simulated annual net N mineralisation in the litter and top 20 cm soil layer ranged from 50 to 170 kg N ha −1 across the sites as a result of differences in rates of litter production, SOM and litter decomposition, and microbial N immobilisation and (re-)mineralisation. Simulations of annual soil N mineralisation were similar to measured rates over a 3-year period, except for an overestimation in 1 year at Mumballup and 2 years at Darkan. Model results indicated the importance of fine root production and turnover for N supply. As plantations age, supply of N to trees increasingly originates from litter decomposition, while the contribution from decomposition of SOM decreases. Although major soil feedbacks associated with litter production, decomposition and N availability are adequately integrated into G’DAY, further work is required in some aspects of the model, including the utility of the C-allocation submodel over a wide range of site conditions and silvicultural treatments.

Predicting nitrogen supply in plantation eucalypt forests

Nitrogen mineralization was measured experimentally and predicted by simulation modelling in three plantations of Eucalyptus globulus in south-western Australia where annual rainfall ranged from 600 to 1500 mm. Nitrogen mineralization was measured in the field each 4 weeks for 3 yr (2 sites) and 2.8 yr (1 site) using the in situ coring technique. Potentially available N was estimated at each sampling time using anaerobic incubations in the laboratory. In the field, soil temperature was logged each hour and soil moisture was estimated gravimetrically each month at the start and end of each field exposure period. The relationship of N mineralization to environmental variables was determined through aerobic incubations of soil samples in the laboratory at 6 temperatures (4 to 42°C) and 10 soil moistures (air dry to 10 kPa soil moisture tension). A generalized model using an exponential function to describe temperature response and a logistic function to describe moisture response was fitted to the laboratory N mineralization incubation data. This function was used as a basis for predicting N mineralization in the field from measured soil moisture and temperature. Model output was scaled by tuning the simulated and observed N mineralization rates over the experimental period at each site. Finally, independent scale factors were derived by regressing the tuned scale factors against soil chemical (anaerobic N) and physical characteristics (soil moisture content at 25 kPa moisture tension) and these were used in model simulations to predict N mineralization. There was a marked seasonal pattern in monthly rates of mineralization related to the seasonally dry climate in south-western Australia. Rates were highest during late winter and spring when microbial activity was not limited by soil moisture deficits and soil temperatures were rising, and lowest in summer when the surface soils dried to below wilting point. Model simulations generally reflected the observed pattern of mineralization and mean annual rates of N mineralization at each sites were predicted within about plus or minus 20%

Application of the process-based model BIOMASS to Eucalyptus globulus ssp. globulus plantations on ex-farmland in south western Australia : II. Stemwood production and seasonal growth

In south western Australia 31 Eucalyptus globulus plantations were surveyed. The plantations had been established on previously farmed land and were from 2 to 10 years old. They were growing on differing soils and were located on a climatic gradient with mean annual rainfall ranging from 600 to 1450 mm. Statistical analysis showed that 89% of the variation in mean DBHOB and 85% of the variation in mean tree height were accounted for by multiple regression against the age of the plantation and mean annual rainfall. Plantation age, mean annual rainfall and stocking rate together accounted for 77% of the variation in mean annual increment of stemwood production. Five of the plantations were selected for more detailed studies ranging in age from 2 to 6 years in 1990 and with mean annual rainfall ranging from 590 to 1450 mm. At these plantations mean annual stemwood production from planting to 1993 varied from 5.1 to 25.9 t ha −1. Factors affecting growth were studied by applying the BIOMASS model. Measured seasonal patterns of growth were compared with simulated patterns of growth modelled using BIOMASS. The model allows for differences in weather conditions, soil water contents, leaf area index, tree size, canopy architecture and stocking rates. The climate in south western Australia is classified as Mediterranean with cool wet winters and hot dry summers. Therefore, the capacity of the soils to store water was expected to be crucial for survival and growth over summer. At two of the plantations storage of water in the soil was limited by its depth. Measured growth rates at these plantations were slower during summer than in winter. The seasonal pattern of growth simulated using BIOMASS was growth slowed in summer due to the decrease in availability of soil water and low relative humidity (high atmospheric vapour pressure deficits). Measurements of DBHOB appear to show slow growth from October to June, whereas simulations suggest that slow growth would be expected only from January to June. However, this difference may be an artefact due to dehydration and consequent stem shrinkage in early summer (October to January). A third plantation had a slightly saline watertable at 3 to 4 m depths and the other two plantations were on soils where soil water is available at depth. For these three plantations closest agreement between the measured and simulated seasonal patterns of growth was obtained by assuming that the availability of soil water was not limiting. Net C assimilation simulated using BIOMASS was allocated to growth of aboveground tree components estimated from measurements of increases in DBHOB and tree heights. Coefficients for allocation to foliage varied among plantations from 0.10 to 0.12, allocation to stems from 0.23 to 0.60 and allocation to branches from 0.05 to 0.12. Allocation to the below-ground component was estimated by difference to range from 0.18 to 0.60. Although the variation in allocation coefficients was large, similar values have been reported in other studies. Possible reasons for the variation among plantations are discussed.

Water use of plum trees ( Prunus salicina) trained to four canopy arrangements

Water supply is a limiting factor in the production of stone fruit in the Mediterranean climate of South Western Australia. Fruit growers are adopting intensive orchard systems and are using a variety of canopy training methods. To establish whether the training system was likely to have a strong influence on water use, we studied the soil water balance and plant water status of 6-year-old plum trees (cultivars ‘Laroda’ and ‘Santa Rosa’) trained to Lincoln, Vase, Palmette and Tatura trellis systems, and growing on a loamy sand. When trickle irrigated at 110% class A pan evaporation rate, the Tatura trellis used more water than the other systems, but the differences were small, being 9–12% between training systems. Trees with a high crop load used slightly more water than those with a low crop load. There were no significant differences between the two cultivars in their water use. When irrigated after harvest at 40% of A pan, the Vase system used more water than the other systems, but again differences were small (∼ 18%). When water was withheld for a week in a period of high evaporative demand (7.3 mm day −1), the Tatura and Palmette systems used more water than the Lincoln trees. This was associated with their ability to extract water from deeper layers in the soil. When well watered, the trees used 75–99% of the intercepted net radiation for evaporation of water. As differences in canopy water use were not large, but yield differences were considerable (34 t ha −1 for the Vase cf. 62 t ha −1 for the Tatura trellis), the efficiency of water use will be greatest on those canopies giving the greatest yield.

Recruitment and Mortality in Populations of Banksia grandis Willd. In Western Australian Forest

This paper examines seed release and seed dispersal; recruitment in relation to fire and logging; mortality of seedlings in relation to their age; and the dynamics of one population from November 1979 to March 1983. Dehiscence of follicles is caused by wetting and drying of the infructescence, so that most seeds fall to the ground during autumn in the Mediterranean climate of south-western Australia. Seeds are wind- dispersed, settling downward from the parent tree: 90% of seed falls within the first year. There is large variation in annual recruitment of seedlings, reflecting large annual differences in the number of infructescences produced. Fires of various intensities or logging do not enhance recruitment. Seedling mortality is greatest during the first summer after germination; this may be related to the rudimentary development of the lignotuber. A population of 1890 individually marked plants was studied for 3.5 years. Over twice as many deaths took place in summer and autumn as in winter and spring, and 90% of deaths were of plants less than 20 cm tall. At the conclusion of the study, total population size, through recruitment of three cohorts of seedlings, had increased by 7%. This indicates how important control of reproduction would be in achieving long-term reduction in the abundance of B. grandis, which harbours the pathogenic fungus Phytophthora cinnamomi.

Studies in Australian amphibia II..Taxonomy, ecology and evolution of the genus Heleioporus Gray (Anura : Leptodactylidae)

The status of the five existing species of the genus Heleioporus Gray, H. albopunctatus Gray, H. australiacus (Shaw), H. eyrei (Gray), H. inornatus Lee & Main, and H. psammophilus Lee & Main are confirmed on the basis of morphological and behavioural criteria and the results of interpopulation in vitro crosses. The Western Australian population, formerly included under H. australiacus, is raised to species status on the basis of consistent differences in morphology and mating call. Each species is redescribed, and descriptions of the larvae and juveniles are included. The results of in vitro crosses support the recognition of two species groups, a bassian group comprising H. australiacus, the H. australiacus-like frog, and H. inornatus, and an eyrean group comprising H. albopunctatus, H. eyrei, and H. psammophilus. The breeding biology of all of the western species appears closely tied to the Mediterranean climate of south-western Australia. All species breed in April and May. Rain sufficient to moisten the soil, and declining temperatures are the two most obvious environmental factors influencing the timing of breeding. Breeding sites include ephemeral ponds and water courses, and the edges of coastal lakes. Breeding occurs before these are covered by water, in winter. Males call from burrows, and copulation, oviposition, and embryonic development all occur at the bottom of these burrows. Where they occur together, the burrows of H. albopunctatus, H. eyrei, and H. psammophilus are found scattered through the centre of a swamp and those of H. inornatus, around the periphery. The eggs are laid in froth, and development to hatching takes between 1 and 3 weeks. Hatching may be delayed by withholding the eggs from water. The period between the onset of calling and hatching of the embryos roughly corresponds to the period between the onset of winter rain and the flooding of larval sites. The larvae of H. albopunctatus, H. eyrei, and H, psammophilus are found in ponds, those of H. inornatus in collapsed, flooded breeding burrows, and those of H. australiacus and the H. australiacus-like frog in creeks.