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Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Environment and Sc, Science, Environment, Engineering and Technology, Prescribed burning is a tool used in Toohey Forest management systems as a suburban forest fuel reduction burning to mitigate major bushfire risks and has played an important role in the development of plant communities in Australia. Fire influences terrestrial ecosystems and processes, which include vegetation distribution and structure, carbon (C) and nitrogen (N) cycling and climate. The current study examined the effects of prescribed burning (9-14 years after burning) on C and N cycling. We hypothesized that prescribed burning would be able to increase the availability of N, which may benefit regenerating plants shortly after the fire. The prescribed burning would influence C and N pools as well as BNF, water use efficiency, and plant growth of understory acacia species in short time, but its long-term impact might be 0 minimal due to the ecosystem recovery and resilience in the suburban forest ecosystem of southeast Queensland, Australia. Forest litterfall and litter floor recovery would play important roles in the recovery process of soil C and N pools after 9-14 years. Soil C and N pools as well as forest litter floor would gradually be recovery after 9-14 years of prescribed burning in the suburban Toohey Forest ecosystem. Labile soil C and N pools could be affected 9-14 years after prescribed burning in the suburban Toohey Forest ecosystem of subtropical Australia. This study examined the effect of prescribed burning in the short- and medium-term on plant growth and eco-physiological responses of understory acacia species and symbiotic N fixation as well as soil C and N pools in the suburban forest ecosystem of subtropical Australia. This project sought to determine the impacts of repeated prescribed burning on biological nitrogen fixation (BNF) by understorey acacia species, examine the N dynamics and plant N concentrations in Toohey Forest, a suburban forest in subtropical Australia, at different time periods following prescribed burning (9-14 years afte

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Natural Sciences, Science, Environment, Engineering and Technology, Informal agroforestry is a traditional practice in Solomon Islands, mostly intercropping food crops with fruit trees. Agroforestry systems that intercrop food crops with rows of hardwood species for the purposes of timber production have not been practiced. In response to the common problem that growers of valuable hardwood species such as teak (Tectona grandis) are reluctant to thin their trees, the Australian Centre for International Agricultural Research (ACIAR) established project FST/2007/020 to develop novel silvicultural systems to overcome this problem. Flueggea flexuosa (flueggea) is a local hardwood species that is widely utilized for housing and fencing applications. The project team established several agroforestry trials testing the hypothesis that teak and flueggea could be successfully grown together with the local tree being progressively harvested for local use, effectively thinning the plantation and allowing the teak to develop through to harvestable size. The trees could be intercropped with food crops allowing for multiple land use and income generating opportunities whilst the trees grow through to maturity. The model was based on the assumption that trees and crops, when properly managed, complement each other rather than compete in the capture and efficient use of available growth resources. This system is a hybrid of the informal agroforestry traditionally practiced in Solomon Islands and the silvicultural management techniques applied to production forestry. However, teak and flueggea have not been previously grown together under an agroforestry regime and little is known of the species interaction or of the effect of growing different food and cash crops in the interrow. Traditional practices for growing food crops in Solomon Islands begin with forest clearance and burning of debris, a slash and burn system. Mounds are made using man-made hoes or picks to give crops better growing spot away from competing weeds and surface water flow durin

Full Text, Thesis (PhD Doctorate), Doctor of Philosophy (PhD), School of Natural Sciences, Science, Environment, Engineering and Technology, Prescribed burning can play an important role in forest maintenance and management worldwide. Australia is one of the few countries around the world with knowledge and experience in the use of controlled fire for fuel management and ecological purposes. In Australia, prescribed burning, has been used to meet several objectives including protection of forests against wildfires through managing fuel loads, ecosystem maintenance by increasing vegetation, and elimination of pests and diseases. Climate change and the increases in the incidence and severity of wildfire push forest managers to establish prescribed fire regimes with low severity prescribed burning to protect housing and infrastructure from wildfire damage. Prescribed burning has become a more frequent management tool in suburban forests, leading to alteration in the physical, chemical, and biological properties of forest soils. Fire influences ecosystem patterns and processes by affecting vegetation diversity and structure, carbon (C), nitrogen (N) and other nutrients cycles, but these effects are dependent on fire regimes (e.g. frequency and severity). The interval between fires is critical in forest management because the long interval period burns may allow a potentially severe fire hazard to exist, while burning frequently with short interval period may result in loss of soil fertility leading to ecosystem vulnerability.

Eucalyptus spp. is a dominant tree genus in Australia and most Eucalyptus spp. are canopy dominant species. In Australian natural forests, Eucalyptus spp. commonly are associated with understorey legumes which play a crucial role for ecological restoration owing to their nitrogen (N) fixing ability for replenishing the soil N lost after frequent prescribed burning. This study aimed to explore to what extent physiological responses of these species differ 7 and 12 years after last fire. Two most common understorey Acacia spp., Acacia leiocalyx and A. disparrima, as well as one non-leguminous Eucalyptus resinifera, were studied due to their dominance in the forest. Both A. leiocalyx and A. disparrima showed higher carbon (C) assimilation capacity, maximum photosynthetic capacity, and moderate foliar C/N ratio compared with E. resinifera. A. leiocalyx showed various advantages compared to A. disparrima such as higher photosynthetic capacity, adaptation to wider light range and higher foliar total N (TNmass). A. leiocalyx also relied on N2-fixing ability for longer time compared to A. disparrima. The results suggested that the two Acacia spp. were more beneficial to C and N cycles for the post burning ecosystem than the non-N2-fixing species E. resinifera. A. leiocalyx had greater contribution to complementing soil N cycle long after burning compared to A. disparrima.

Purpose This study investigated how nitrogen (N) nutrition and key physiological processes varied under changed water and nitrogen competition resulting from different weed control and fertilisation treatments in a 2-year-old F1 hybrid (Pinus elliottii Engelm var. elliottii × P. caribaea var. hondurensis Barr. ex Golf.) plantation on a grey podzolic soil type, in Southeast Queensland. Materials and methods The study integrated a range of measures including growth variables (diameter at ground level (DGL), diameter at breast height (DBH) and height (H)), foliar variables (including foliar N concentration, foliar δ13C and δ15N) and physiological variables (including photosynthesis (An), stomatal conductance (gs), transpiration (E), intrinsic water use efficiency (WUEi) (A/gs) and xylem pressure potential (ΨXPP)) to better understand the mechanisms influencing growth under different weed control and fertilisation treatments. Five levels of weed control were applied: standard (routine), luxury, intermediate, mechanical and nil weed control, all with routine fertilisation plus an additional treatment, routine weed control and luxury fertilisation. Relative weed cover was assessed at 0.8, 1.1 and 1.6 years after plantation establishment to monitor the effectiveness of weed control treatments. Soil investigation included soil ammonium (NH4 +-N), nitrate (NO3 −-N), potentially mineralizable N (PMN), gravimetric soil moisture content (MC), hot water extractable organic carbon (HWETC), hot water extractable total N (HWETN), total C, total N, stable C isotope composition (δ13C), stable N isotope composition (δ15N), total P and extractable K. Results and discussion There were significant relationships between foliar N concentrations and relative weed cover and between tree growth and foliar N concentration or foliar δ15N, but initial site preparation practices also increased soil N transformations in the planting rows reducing the observable effects of weed control on foliar δ1

Purpose We investigated the effects of weed control and fertilization at early establishment on foliar stable carbon (δ13C) and nitrogen (N) isotope (δ15N) compositions, foliar N concentration, tree growth and biomass, relative weed cover and other physiological traits in a 2-year old F1 hybrid (Pinus elliottii var. elliottii (Engelm) × Pinus caribaea var. hondurensis (Barr. ex Golf.)) plantation grown on a yellow earth in southeast Queensland of subtropical Australia. Materials and methods Treatments included routine weed control, luxury weed control, intermediate weed control, mechanical weed control, nil weed control, and routine and luxury fertilization in a randomised complete block design. Initial soil nutrition and soil fertility parameters included (hot water extractable organic carbon (C) and total nitrogen (N), total C and N, C/N ratio, labile N pools (nitrate (NO3 −) and ammonium (NH4 +)), extractable potassium (K+)), soil δ15N and δ13C. Relative weed cover, foliar N concentrations, tree growth rate and physiological parameters including photosynthesis, stomatal conductance, photosynthetic nitrogen use efficiency, foliar δ15N and foliar δ13C were also measured at early establishment. Results and discussion Foliar N concentration at 1.25 years was significantly different amongst the weed control treatments and was negatively correlated to the relative weed cover at 1.1 years. Foliar N concentration was also positively correlated to foliar δ15N and foliar δ13C, tree height, height growth rates and tree biomass. Foliar δ15N was negatively correlated to the relative weed cover at 0.8 and 1.1 years. The physiological measurements indicated that luxury fertilization and increasing weed competition on these soils decreased leaf xylem pressure potential (Ψxpp) when compared to the other treatments. Conclusions These results indicate how increasing N resources and weed competition have implications for tree N and water use at establishment in F1 hybrid plantations