Melaleuca densispicata in Currawinya National Park, South-West Queensland: Ecology and preliminary implications for management of a rare plant species

Melaleuca densispicata Byrnes is an uncommon species with a limited distribution, comprising disjunct populations in inland southern Queensland and northern New South Wales, Australia. It is a dense, woody shrub, 2–4 m in height, which exhibits a marked 'clumping' growth habit. It has thick, papery bark and displays many white flowers during spring or early summer. Although it has long been known to exist, M. densispicata was only formally described in 1984, and very little is currently known about its ecology or specific management requirements. There are only seven known subpopulations of the species across its range. A major population at the western limit of its distribution occurs on Currawinya National Park (28°52'S, 144°30'E). Here, it is locally abundant and listed as a noteworthy plant species under the Management Plan (Queensland Parks & Wildlife Service 2001). This study aimed to identify patterns in the distribution of M. densispicata in Currawinya National Park, describe its ecological niche and role, and provide management recommendations for the species within the study area. Recent anecdotal observations of recruitment failure in south-western Queensland (Peter McRae, QPWS, October 2004, pers. comm.; Dick O'Connell, local grazier, July 2005 pers. comm.) caused additional emphasis to be placed on the examination of recruitment and recruitment factors.

Short-term responses of leaf growth rate to water deficit scale up to whole-plant and crop levels: An integrated modelling approach in maize.

Physiological and genetic studies of leaf growth often focus on short-term responses, leaving a gap to whole-plant models that predict biomass accumulation, transpiration and yield at crop scale. To bridge this gap, we developed a model that combines an existing model of leaf 6 expansion in response to short-term environmental variations with a model coordinating the development of all leaves of a plant. The latter was based on: (1) rates of leaf initiation, appearance and end of elongation measured in field experiments; and (2) the hypothesis of an independence of the growth between leaves. The resulting whole-plant leaf model was integrated into the generic crop model APSIM which provided dynamic feedback of environmental conditions to the leaf model and allowed simulation of crop growth at canopy level. The model was tested in 12 field situations with contrasting temperature, evaporative demand and soil water status. In observed and simulated data, high evaporative demand reduced leaf area at the whole-plant level, and short water deficits affected only leaves developing during the stress, either visible or still hidden in the whorl. The model adequately simulated whole-plant profiles of leaf area with a single set of parameters that applied to the same hybrid in all experiments. It was also suitable to predict biomass accumulation and yield of a similar hybrid grown in different conditions. This model extends to field conditions existing knowledge of the environmental controls of leaf elongation, and can be used to simulate how their genetic controls flow through to yield.

Comparative seed and dispersal ecology of three exotic subtropical Asparagus species

The genus Asparagus includes at least six invasive species in Australia. Asparagus aethiopicus and A. africanus are invasive in subtropical Australia, and a third species, A. virgatus is naturalized and demonstrates localized spread in south east Queensland. To better understand how the attributes of these species contribute to their invasiveness, we compared fruit and seed traits, germination, seedling emergence, seed survival, and time-to-maturity. We further investigated dispersal ecology of A. africanus, examining the diet of a local frugivore, the figbird (Sphecotheres viridis) and the effect of gut passage on seedling emergence. Overall, A. aethiopicus was superior in germination and emergence, with the highest mean germination (98.8%) and emergence (94.5%) under optimal conditions and higher emergence (mean of 73.3%) across all treatments. In contrast, A. africanus had the lowest germination under optimal conditions (71.7%) and low mean seedling emergence (49.5%), but had fruits with the highest relative yield (ratio of dry pulp to fruit fresh weight) that were favored by a local frugivore. Figbirds consumed large numbers of A. africanus fruits (~30% of all non-Ficus fruits), and seedling germination was not significantly affected by gut passage compared to unprocessed fruits. Asparagus virgatus germinated poorly under cool, light conditions (1.4%) despite a high optimum mean (95.0%) and had low mean performance across emergence treatments (36.3%). The species also had fruits with a low pulp return for frugivores. For all species, seed survival declined rapidly in the first 12 mo and fell to < 3.2% viability at 36 mo. On the basis of the traits considered, A. virgatus is unlikely to have the invasive potential of its congeners. Uniformly short seed survival times suggest that weed managers do not have to contend with a substantial persistent soil-stored seed bank, but frugivore-mediated dispersal beyond existing infestations will present a considerable management challenge.

Dynamics of plant populations in Heteropogon contortus(black speargrass) pastures on a granite landscape in southern Queensland. 1. Dynamics of H. contortus populations

The dynamics of Heteropogon contortus (black speargrass) populations were measured in a subset of treatments contained within an extensive grazing study conducted between 1990 and 1996 in H. contortus pasture in southern Queensland. This subset included 2 landscape positions and 3 stocking rates in both native pasture and legume-oversown native pasture. Severe drought conditions throughout much of the study necessitated ongoing adjustments to the original stocking rates and, as a result, drought was the major influence on the dynamics of H. contortus populations. Plant density and basal area in the silver-leaved ironbark landscape were consistently higher than those in the narrow-leaved ironbark landscape. There was limited evidence of any impact by either light or moderate stocking rate but there was evidence of an impact at the heaviest stocking rate. There was minimal impact of legume oversowing. Relatively large fluctuations in plant density occurred during this study resulting from the death of existing plants, due mainly to drought, and seedling recruitment. Similarly, there were relatively large fluctuations in basal area caused mainly by changes in plant size. Rates for turnover of plant numbers were relatively high whereas plant turnover rates of basal areas were relatively low. Regular seedling recruitment appeared necessary to ensure the persistence of this species. Despite the high turnover, populations were maintained at reasonable levels indicating the overall resilience of H. contortus.

The original native pasture ecosystems of the eastern and western Darling Downs - Can they be restored?

The original pasture ecosystems of southern inland Queensland ranged from treeless grasslands on cracking clays through grassy woodlands of varying density on a great range of soil types to those competing at the dynamic edges of forests and scrubs. Fire, both wild and aboriginal-managed, was a major factor, along with rainfall extremes, in shaping the pastures and tree:grass balance. Seedling recruitment was driven by rainfall extremes, availability of germinable seed and growing space, with seed availability and space being linked to the timing and intensity of recent fires and rain. The impact of insects, diseases, severe wind and hailstorms on recruitment should not be underestimated. The more fertile soils had denser grass growth, greater fire frequency and thinner tree cover than infertile soils, except where trees were so dense that grass growth was almost eliminated. The pastures were dominated by perennial tussock grasses of mid-height but included a wide array of minor herbaceous species whose abundance was linked to soil type and recent seasonal conditions. Many were strongly perennial with Asteraceae, Fabaceae, Malvaceae, Cyperaceae and Goodeniaceae most common in an environment, which can experience effective rainfall at any time of year. The former grassland communities that are now productive farming lands are not easily returned to their original composition. However, conservation of remnant examples of original pasture types is very achievable provided tree density is controlled, prescribed burning and grazing are used and rigorous control of invasive, exotic species is undertaken. This should be done with a clear understanding that significant short-and medium-term fluctuations in botanical composition are normal.

Reproductive ecology of invasive Ochna serrulata (Ochnaceae) in south-eastern Queensland

We investigated aspects of the reproductive ecology of Ochna serrulata (Hochst.) Walp., an invasive plant in eastern Australia. O. serrulata drupes were similar in size to fleshy fruits of other local invasive plants, but showed some distinct differences in quality, with a very high pulp lipid content (32.8% of dry weight), and little sugar and water. Seeds were dispersed by figbirds, Sphecotheres viridis Vieillot, a locally abundant frugivore, and comprised between 10 and 50% of all non-Ficus spp. fruit consumed during October and November. The rate of removal of O. serrulata drupes was greater in bushland than suburban habitats, indicating that control in bushland habitats should be a priority, but also that suburban habitats are likely to act as significant seed sources for reinvasion of bushland. Germination occurred under all seed-processing treatments (with and without pulp, and figbird gut passage), suggesting that although frugivores are important for dispersal, they are not essential for germination. Recruitment of buried and surface-sown seed differed between greenhouse and field experiments, with minimal recruitment of surface-sown seed in the field. Seed persistence was low, particularly under field conditions, with 0.75% seed viability after 6 months and 0% at 12 months. This provides an opportunity to target control efforts in south-eastern Queensland in spring before fruit set, when there is predicted to be few viable seeds in the soil.

What drives plant biodiversity in the clay floodplain grasslands of NSW?

An assessment of the relative influences of management and environment on the composition of floodplain grasslands of north-western New South Wales was made using a regional vegetation survey sampling a range of land tenures (e. g. private property, travelling stock routes and nature reserves). A total of 364 taxa belonging to 55 different plant families was recorded. Partitioning of variance with redundancy analysis determined that environmental variables accounted for a greater proportion (61.3%) of the explained variance in species composition than disturbance-related variables (37.6%). Soil type (and fertility), sampling time and rainfall had a strong influence on species composition and there were also east-west variations in composition across the region. Of the disturbance-related variables, cultivation, stocking rate and flooding frequency were all influential. Total, native, forb, shrub and subshrub richness were positively correlated with increasing time since cultivation. Flood frequency was positively correlated with graminoid species richness and was negatively correlated with total and forb species richness. Site species richness was also influenced by environmental variables (e. g. soil type and rainfall). Despite the resilience of these grasslands, some forms of severe disturbance (e. g. several years of cultivation) can result in removal of some dominant perennial grasses (e. g. Astrebla spp.) and an increase in disturbance specialists. A simple heuristic transitional model is proposed that has conceptual thresholds for plant biodiversity status. This knowledge representation may be used to assist in the management of these grasslands by defining four broad levels of community richness and the drivers that change this status.

Optimal eradication: when to stop looking for an invasive plant

The notion of being sure that you have completely eradicated an invasive species is fanciful because of imperfect detection and persistent seed banks. Eradication is commonly declared either on an ad hoc basis, on notions of seed bank longevity, or on setting arbitrary thresholds of 1% or 5% confidence that the species is not present. Rather than declaring eradication at some arbitrary level of confidence, we take an economic approach in which we stop looking when the expected costs outweigh the expected benefits. We develop theory that determines the number of years of absent surveys required to minimize the net expected cost. Given detection of a species is imperfect, the optimal stopping time is a trade-off between the cost of continued surveying and the cost of escape and damage if eradication is declared too soon. A simple rule of thumb compares well to the exact optimal solution using stochastic dynamic programming. Application of the approach to the eradication programme of Helenium amarum reveals that the actual stopping time was a precautionary one given the ranges for each parameter.

Domestication for Conservation of an Endangered Species: The Case of the Wollemi Pine

A small population of tall slender conifers was discovered in 1994 in a deep rainforest canyon of the Wollemi National Park, New SouthWales, Australia. The living trees closely resembled fossils that were more than 65 million years old, and this ‘living fossil’ was recognised as a third extant genus in the Araucariaceae (Araucaria, Agathis and now Wollemia). The species was named the Wollemi pine (W. nobilis). Extensive searches uncovered very few populations, with the total number of adult trees being less than 100. Ex situ collections were quickly established in Sydney as part of the Wollemi Pine Recovery Plan. The majority of the ex situ population was later transferred to our custom-built facility in Queensland for commercial multiplication. Domestication has relied very heavily on the species’ amenability to vegetative propagation because seed collection from the natural populations is dangerous, expensive, and undesirable for conservation reasons. Early propagation success was poor, with only about 25% of cuttings producing roots. However, small increases in propagation success have a very large impact on a domestication program because plant production can be modelled on an exponential curve where each rooted cutting develops into a mother plant that, in turn, provides more rooted cuttings. An extensive research program elevated rooting percentages to greater than 80% and also provided in vitro methods for plant multiplication. These successes have enabled international release of the Wollemi pine as a new and attractive species for ornamental horticulture.

Demography of three perennial grasses in a central Queensland eucalypt woodland.

The population dynamics of the palatable, perennial grasses Bothriochloa ewartiana (Domin) C.E.Hubb. (desert Mitchell grass), Chrysopogon fallax S.T.Blake (golden beard grass) and Heteropogon contortus (L.) P.Beauv. ex Roem. & Schult. (black speargrass), were studied in an extensive grazing study conducted in a eucalypt woodland within the Aristida-Bothriochloa pasture community in central Queensland between 1994 and 2000. Treatments were three grazing pressures based on light, medium and heavy utilisation of forage available at the end of summer and two timber treatments (trees intact and trees killed). Seasonal rainfall throughout this study was generally favourable for plant growth with no severe drought periods. Grazing pressure had a greater overall impact on plant dynamics than timber treatment, which had minimal impact. Grazing pressure had a large impact on H. contortus dynamics, an intermediate impact on B. ewartiana and no impact on C. fallax. Fluctuations in plant density of both B. ewartiana and C. fallax were small because both species were long lived with low levels of seedling recruitment and plant death, whereas fluctuations in H. contortus density were relatively high because of its relatively short life span and higher levels of both recruitment and death. Heavy grazing pressure increased the recruitment of B. ewartiana and H. contortus in some years but had no impact on that of C. fallax. Heavy grazing pressure reduced the survival of the original plants of both B. ewartiana and H.contortus but not of C. fallax. For H. contortus, the size of the original plants was larger where trees were killed than where trees were left intact and plants of the 1995 seedling cohort were larger in 1998 at heavy compared with those at light and medium grazing pressure. Grazing had a minor negative impact on the soil seed bank of H. contortus. Populations of all three species remained stable throughout this study, although the favourable seasonal rainfall experienced and the short duration of this study relative to the life span of these species may have masked longer term, deleterious impacts of heavy grazing pressure.

Seed persistence of the invasive aquatic plant, Gymnocoronis spilanthoides (Asteraceae)

Seed persistence of Gymnocoronis spilanthoides (D.Don) DC.; Asteraceae (Senegal tea), a serious weed of freshwater habitats, was examined in relation to burial status and different soil moisture regimes over a 3-year period. Seeds were found to be highly persistent, especially when buried. At the end of the experiment, 42.0%, 27.3% and 61.4% of buried seeds were viable following maintenance at field capacity, water logged and fluctuating (cycles of 1 week at field capacity followed by 3 weeks’ drying down) soil moisture conditions, respectively. Comparable viability values for surface-situated seeds were ~3% over all soil moisture regimes. Predicted times to1% viability are 16.2 years for buried seed and 3.8 years for surface-situated seed. Persistence was attributed primarily to the absence of light, a near-obligate requirement for germination in this species, although secondary dormancy was induced in some seeds. Previous work has demonstrated low fecundity in field populations of G. spilanthoides, which suggests that soil seed banks may not be particularly large. However, high levels of seed persistence, combined with ostensibly effective dispersal mechanisms, indicate that this weed may prove a difficult target for regional or state-wide eradication.

Emergence and seed persistence of Echinochloa colona, Urochloa panicoides and Hibiscus trionum in the sub-tropical environment of north-eastern Australia.

Better understanding of seed-bank dynamics of Echinochloa colona, Urochloa panicoides and Hibiscus trionum, major crop weeds in sub-tropical Australia, was needed to improve weed control. Emergence patterns and seed persistence were investigated, with viable seeds sown at different depths in large in-ground pots. Seedlings of all species emerged between October and March when mean soil temperatures were 21-23C. However, E. colona emerged as a series of flushes predominantly in the first year, with most seedlings emerging from 0-2 cm. Urochloa panicoides emerged mostly as a single large flush in the first two years, with most seedlings emerging from 5 cm. Hibiscus trionum emerged as a series of flushes over three seasons, initially with majority from 5 cm and then 0-2 cm in the later seasons. Longevity of the grass seed was short, with <5% remaining after burial at 0-2 cm for 24 months. In contrast, 38% of H. trionum seeds remained viable after the same period. Persistence of all species increased significantly with burial depth. These data highlight that management strategies need to be tailored for each species, particularly relating to the need for monitoring, application times for control tactics, impact of tillage, and time needed to reduce the seed-bank to low numbers.

Patterns of seed bank and size asymmetry of plant growth across varying sites in the invasive Lantana camara L. (Verbenaceae)

Lantana camara L. (Verbenaceae) is a weed of great significance in Australia and worldwide, but little is known about connections among components of its life history. We document over a 3-year period, the links between L. camara seed-bank dynamics and its above-ground growth, including size asymmetry in four land-use types (a farm, a hoop pine plantation and two open eucalypt forests) invaded by the weed near Brisbane, Queensland Australia. Seed-bank populations varied appreciably across sites and in response to rainfall and control measures, and they were higher (~1,000 seeds/m2) when annual rainfall was 15-30 % below the long-term yearly average. Fire reduced seed-bank populations but not the proportion germinating (6-8 %). Nearly a quarter of fresh seeds remain germinable after 3 years of soil burial. For small seedlings (<10 cm high), the expected trade-offs in two life-history traits-survival and growth-did not apply; rather the observed positive association between these two traits, coupled with a persistent seed-bank population could contribute to the invasiveness of the plant. Relationships between absolute growth rate and initial plant size (crown volume) were positively linear, suggesting that most populations are still at varying stages of the exponential phase of the sigmoid growth; this trend also suggests that at most sites and despite increasing stand density and limiting environmental resources of light and soil moisture, lantana growth is inversely size asymmetric. From the observed changes in measures of plant size inequality, asymmetric competition appeared limited in all the infestations surveyed. © 2013 Crown Copyright as represented by: Department of Agriculture, Fisheries and Forestry, Australia.

The short-term effects of a routine poisoning campaign on the movements and detectability of a social top-predator

Top-predators can be important components of resilient ecosystems, but they are still controlled in many places to mitigate a variety of economic, environmental and/or social impacts. Lethal control is often achieved through the broad-scale application of poisoned baits. Understanding the direct and indirect effects of such lethal control on subsequent movements and behaviour of survivors is an important pre-requisite for interpreting the efficacy and ecological outcomes of top-predator control. In this study, we use GPS tracking collars to investigate the fine-scale and short-term movements of dingoes (Canis lupus dingo and other wild dogs) in response to a routine poison-baiting program as an example of how a common, social top-predator can respond (behaviourally) to moderate levels of population reduction. We found no consistent control-induced differences in home range size or location, daily distance travelled, speed of travel, temporal activity patterns or road/trail usage for the seven surviving dingoes we monitored immediately before and after a typical lethal control event. These data suggest that the spatial behaviour of surviving dingoes was not altered in ways likely to affect their detectability, and if control-induced changes in dingoes' ecological function did occur, these may not be related to altered spatial behaviour or movement patterns.

Precise determination of aquatic plant wet mass using a salad spinner

The reliable assessment of macrophyte biomass is fundamental for ecological research and management of freshwater ecosystems. While dry mass is routinely used to determine aquatic plant biomass, wet (fresh) mass can be more practical. We tested the accuracy and precision of wet mass measurements by using a salad spinner to remove surface water from four macrophyte species differing in growth form and architectural complexity. The salad spinner aided in making precise and accurate wet mass with less than 3% error. There was also little difference between operators, with a user bias estimated to be below 5%. To achieve this level of precision, only 10–20 turns of the salad spinner are needed. Therefore, wet mass of a sample can be determined in less than 1 min. We demonstrated that a salad spinner is a rapid and economical technique to enable precise and accurate macrophyte wet mass measurements and is particularly suitable for experimental work. The method will also be useful for fieldwork in situations when sample sizes are not overly large.