Search

Ecosystems managed with contrasting fire regimes provide insight into the responses of vegetation and soil. Heathland, woodland and forest ecosystems along a gradient of resource availability were burnt over four decades in approximately 3- or 5-year intervals or were unburnt for 45–47 years (heathland, woodland), or experienced infrequent wildfires (forest: 14 years since the last fire). We hypothesized that, relative to unburnt or infrequent fires, frequent burning would favour herbaceous species over woody species and resprouting over obligate seeder species, and reduce understorey vegetation height, and topsoil carbon and nitrogen content. Our hypothesis was partially supported in that herbaceous plant density was higher in frequently burnt vegetation; however, woody plant density was also higher in frequently burnt areas relative to unburnt/infrequently burnt areas, across all ecosystems. In heathland, omission of frequent fire resulted in the dominance of fern Gleichenia dicarpa and subsequent competitive exclusion of understorey species and lower species diversity. As hypothesized, frequent burning in woodland and forest increased the density of facultative resprouters and significantly reduced soil organic carbon levels relative to unburnt sites. Our findings confirm that regular burning conserves understorey diversity and maintains an understorey of lower statured herbaceous plants, although demonstrates the potential trade-off of frequent burning with lower topsoil carbon levels in the woodland and forest. Some ecosystem specific responses to varied fire frequencies were observed, reflecting differences in species composition and fire response traits between ecosystems. Overall, unburnt vegetation resulted in the dominance of some species over others and the different vegetation types were able to withstand relatively high-frequency fire without the loss of biodiversity, mainly due to high environmental productivity and short juvenile periods.

Historically, Queensland’s private native forests have supplied between 40 and 70% of the hardwood resource to the state’s primary processors. Hardwood timber production from state-owned native forests and plantations in Queensland has decreased substantially in recent decades, increasing the hardwood timber industry’s reliance on private native forests. However, timber production opportunities from these forests are poorly understood. This study assessed the future wood supply capacity from private native forests in southern Queensland assuming alternative levels of landowner interest in management for timber production and willingness to invest in silvicultural treatment. Commercial and harvestable private native forests in southern Queensland were classified into six forest types and their spatial distributions were assessed. Potential growth rates for each forest type were estimated based on available literature and expert opinion, and their ability to supply logs to industry with and without silvicultural treatments was projected. Commercial and harvestable private native forests were found to cover an area of approximately 1.9 M ha in southern Queensland, of which spotted gum (693,000 ha) and ironbark (641,500 ha) forest types are most common. The private native forest estate is distributed over 17,665 landholdings (LotPlans), with 17% of these accounting for 66% of the commercial and harvestable resource. Most private native forests have not been actively managed for timber production and are in poor condition. Nevertheless, they presently have the potential to supply between about 150,000 and 250,000 m3 of logs to industry per annum. Silvicultural treatments were found to have the potential to increase the mean annual increment of these forests by a factor of between two and four, indicating substantial opportunities to increase harvestable log volumes in the medium and long-term. Private native forests in southern Queensland could potentially more than comp

This work investigated the link between exceptionally bright and variable debris disks, often called extreme debris disks, and energetic collisions between planetary embryos - giant impacts. The primary method of investigation was a simulation pipeline which modelled the evolution of the disk created by dust material ejected by a giant impact. This pipeline included an $N$-body code which simulated the dynamical evolution of the dust, a semi-analytical Poynting-Robertson (P-R) model which approximated the effect of P-R drag on the mass distribution of the disk, and a radiative transfer package to reproduce the infrared emission of the dust in the disk. Eighty four collision scenarios were run, covering a broad parameter space. The collision parameters included the eccentricity of the centre of mass of the two colliders, the position of the collision along this orbit, and the orientation of the collision with respect to the same orbit. A detailed analysis of the patterns in disk morphology and infrared emission was performed to determine how observability changed in different cases. Eccentric disks were found to inherit the eccentric properties of their centre of mass progenitor orbit. The orientation of the collision with the respect to this orbit helped to determine how closely the disk resembled the centre of mass orbit. Some orientations resulted in disks more tightly concentrated around the original orbit while others were more distributed. Additionally, increased eccentricity created more distinct variability in disk emission owing to changes in dust temperature, but also suppressed the formation of certain short-term variations dependent on collision position. Observed short-term variability is consistent with the variability seen in some of the simulations, lending support for the hypothesis that giant impacts are the source of extreme debris disks. Poynting-Robertson drag was found to have a minimal effect on the disk over timescales of around twenty orb