Academic literature on the topic 'Forest ecosystems (Queensland)'

Habitat fragmentation is considered to be one of the greatest threats to biodiversity. Species richness is predicted to decrease with decreasing patch size and increasing isolation, and this has been shown in some ecosystems. However, few studies have specifically investigated the effects of fragmentation on specific vegetation types, or compared different vegetation types within the same region. In this study, we assessed the influence of habitat fragmentation and time since fire on the floristic composition, structure and diversity of three ecosystems with varying fire proneness within the Sunshine Coast region. This study found that the tall-open forest ecosystem (RE 12.9-10.14) had higher overall species richness within fixed sample areas used for this study than did either open forest (RE 12.5.3) or gallery rainforest (RE 12.3.1), because it was composed of species typical of each of these ecosystem types. Open forest species richness was found mostly in the lower stratum, whereas gallery rainforest diversity was found in the upper stratum. Species richness decreased with increasing isolation in the open forest ecosystem where seeds are mostly abiotically dispersed. However, this study did not find strong evidence for reduced species richness within smaller patches in any ecosystem type studied; instead, finding species richness decreased with increasing patch size in the open forest ecosystem. Overall, across ecosystems, time since fire affected vegetation structure, but in fire-prone ecosystems, time since fire was not a determinant of species richness within the sites studied.

Wetlands are one of the most biologically productive ecosystems. Wetland ecosystem services, ranging from provision of food security to climate change mitigation, are enormous, far outweighing those of dryland ecosystems per hectare. However, land use change and water regulation infrastructure have reduced connectivity in many river systems and with floodplain and estuarine wetlands. Mangrove forests are critical communities for carbon uptake and storage, pollution control and detoxification, and regulation of natural hazards. Although the clearing of mangroves in Australia is strictly regulated, Great Barrier Reef catchments have suffered landscape modifications and hydrological alterations that can kill mangroves. We used remote sensing datasets to investigate land cover change and both intra- and inter-annual seasonality in mangrove forests in a large estuarine region of Central Queensland, Australia, which encompasses a national park and Ramsar Wetland, and is adjacent to the Great Barrier Reef World Heritage site. We built a time series using spectral, auxiliary, and phenology variables with Landsat surface reflectance products, accessed in Google Earth Engine. Two land cover classes were generated (mangrove versus non-mangrove) in a Random Forest classification. Mangroves decreased by 1480 hectares (−2.31%) from 2009 to 2019. The overall classification accuracies and Kappa coefficient for 2008–2010 and 2018–2020 land cover maps were 95% and 95%, respectively. Using an NDVI-based time series we examined intra- and inter-annual seasonality with linear and harmonic regression models, and second with TIMESAT metrics of mangrove forests in three sections of our study region. Our findings suggest a relationship between mangrove growth phenology along with precipitation anomalies and severe tropical cyclone occurrence over the time series. The detection of responses to extreme events is important to improve understanding of the connections between climate, extreme weather events, and biodiversity in estuarine and mangrove ecosystems.

This paper investigated the utility of drone-based environmental monitoring to assist with forest inventory in Queensland private native forests (PNF). The research aimed to build capabilities to carry out forest inventory more efficiently without the need to rely on laborious field assessments. The use of drone-derived images and the subsequent application of digital photogrammetry to obtain information about PNFs are underinvestigated in southeast Queensland vegetation types. In this study, we used image processing to separate individual trees and digital photogrammetry to derive a canopy height model (CHM). The study was supported with tree height data collected in the field for one site. The paper addressed the research question “How well do drone-derived point clouds estimate the height of trees in PNF ecosystems?” The study indicated that a drone with a basic RGB camera can estimate tree height with good confidence. The results can potentially be applied across multiple land tenures and similar forest types. This informs the development of drone-based and remote-sensing image-processing methods, which will lead to improved forest inventories, thereby providing forest managers with recent, accurate, and efficient information on forest resources.

The recognition and effective portrayal of floristic heterogeneity is a complex issue for land classification. This study in Toohey Forest, south-east Queensland, examines the effects of mapping scale and environmental variables on a floristically heterogeneous area. Current Version 4.1 regional ecosystem mapping at 1: 1 00 000 scale maps Toohey Forest as a single regional ecosystem unit "12.11.5", described as an "open forest complex with Corymbia citriodora, Eucalyptus siderophloia, E. major on metamorphics ± interbedded volcanics". Plant taxa data from 50, 20 x 20 m sites comprising 247 native vascular plant taxa were collected, along with data for 17 environmental variables and 10 species richness categories. A priori site groupings of 1 :12 500 scale vegetation mapping and a geomorphic classifications of the area were examined using cluster analysis (UPGMA, Bray-Curtis Metric, β = –0.1) and ordination (SSH MDS). Biplots of several variables (shrub species richness, total species richness, per cent rock cover, CEC, carbon and phosphorus) were significantly (P < 0.05) correlated with the ordination axes derived from each of the two strata levels and the total taxa, for both geomorphological and vegetation mapping. Several variables (shrub, vine, woody and introduced species richness, and carbon, nitrogen, phosphorus, pH and CEC) varied significantly (P < 0.05) across both geomorphic categories and 1:12 500 scale vegetation community mapping. The ongoing reduction in regional ecosystem mapping scale, centred on the use of fine-scale geomorphology mapping, is likely to improve the representation of floristic patterns in heterogeneous environments.

The diet of the yellow-bellied glider (Petaurus australis) was examined at a site in north Queensland by extensive observation of individuals from 10 glider groups. The diet was assessed in four seasons over 12 months by collating large numbers of qualitative feeding observations and by analysis of faeces. Data were also collected on flowering and bark shedding in the forest. Sap feeding accounted for more than 80% of the feeding observations throughout the year. Nectar and pollen of eucalypts (Eucalyptus spp.) and banksias (Banksia spp.) accounted for much of the remainder of the diet although arthropods and honeydew were present in spring and summer. Faecal analysis was based on much smaller sample sizes but confirmed the qualitative result obtained from direct observations. It also revealed the presence of a wide variety of pollen types. Many of these could be attributed to incidental ingestion but at least six rain forest genera were moderately common in faeces, which is consistent with observations of brief and infrequent visits by gliders to these trees. Examination of eucalypt, banksia and other pollen types showed that 60-70% of pollen was devoid of cell contents, supporting earlier suggestions that gliders obtained protein from pollen digestion, but at this site also from harvesting arthropods. This study confirms the dependence of the yellow-bellied glider in north Queensland on the sap of the red stringybark (Eucalyptus resinifera) and that conservation of the yellow-bellied glider is intimately associated with the management of this tree species. The use of various species for nectar and pollen suggests that the yellow-bellied glider may be an important pollinator in these forests. Moreover, sap from the wounds created by gliders is used by a range of other animal species. These observations suggest that the yellow-bellied glider is likely to be a keystone species in the open-forest ecosystems of north Queensland and that it deserves special emphasis in management.

The aim of this study was to develop a method that will use satellite imagery to identify areas of high forest growth and productivity, as a primary input in prioritising revegetation sites for carbon sequestration. Using the Moderate Resolution Imaging Spectroradiometer (MODIS) satellite data, this study analysed the annual net primary production (NPP) values (gC/m²) of images acquired from 2000 to 2013, covering the Condamine Catchment in southeast Queensland, Australia. With the analysis of annual rainfall data during the same period, three transitions of "normal to dry" years were identified to represent the future climate scenario considered in this study. The difference in the corresponding NPP values for each year was calculated, and subsequently averaged to the get the "<i>Mean of Annual NPP Difference</i>" (MAND) map. This layer identified the areas with increased net primary production despite the drought condition in those years. Combined with key thematic maps (i.e. regional ecosystems, land use, and tree canopy cover), the priority areas were mapped. The results have shown that there are over 42 regional ecosystem (RE) types in the study area that exhibited positive vegetation growth and productivity despite the decrease in annual rainfall. However, seven (7) of these RE types represents the majority (79 %) of the total high productivity area. A total of 10,736 ha were mapped as priority revegetation areas. This study demonstrated the use of MODIS-NPP imagery to map vegetation with high carbon sequestration rates necessary in prioritising revegetation sites.

Abstract Speedy and reliable measurements of soil soluble nitrogen (N) are critical for estimating N fluxes in forest ecosystems. The high temperature catalytic oxidation (HTCO) method was assessed and compared with persulfate oxidation (PO) to measure total soluble N in water, hot water, 2 m KCl, and 0.5 m K2SO4 extracts of 24 forest soils collected from south-east Queensland. All salt extracts were diluted 5-fold before measurement by the HTCO method to minimise the effects of salt precipitation on the surface of the Pt/Al2O3 catalysts that may impair oxidation efficiency. Drifts of sensitivity of signals in diluted KCl (0.4 m), K2SO4 (0.1 m), and water matrixes by the HTCO method were minor, with <2% in KCl matrix and <3% in K2SO4 and water matrices. Nitrogen recoveries from most standard N-containing compounds (5 mg/L) analysed by the HTCO method in all the matrices tested were >94%. The values of total soluble N in all extracts of soils obtained by both the PO and the HTCO methods were highly correlated. However, the HTCO method generally gave greater values than the PO method, particularly with high concentrations of N. We consider the HTCO method to be a simple, automated, rapid, quantitative, and reliable method for determining total soluble N in both water extracts and diluted salt extracts of forest soils.

Physical changes and flows of energy at the interface between two contrasting ecosystems affect the distribution of species across the ecotone. The maintenance and stability of the, often abrupt, transition between Australian rainforest and non-rainforests is often attributed to fire. We use pre-germination treatments of smoke and heat on soil seed bank samples to determine plant distributions across the edge between subtropical rainforest and an adjacent eucalypt-dominated wet sclerophyll forest. Soil seed bank collections at 15 m within the eucalypt forest had both significantly higher density and diversity of seedlings than those at 30 m, at the edge itself or at any site within the rainforest. This response was most apparent when a pre-germination smoke treatment was applied. We suggest that smoke is an important germination trigger for species regenerating at this interface. Our results confirm the importance of fire in determining and maintaining the nature of this ecotone.

Forest health is described and perceived in different ways by the general public, land owners, managers, politicians, and scientists, depending on their values and objectives. Native tree pathogens and diseases are often associated with negative impacts even though damage is limited or not widespread. Too often, the concepts of tree health and forest health are used interchangeably and are not related to scale. Similar to fire, occurrences of disease outbreaks focus on the negative effects. However, native pathogens often exist in equilibrium with natural forest communities so their critical ecological roles are not easily discernible. Examined holistically, native fungi and diseases, dead and dying trees, and the many complex ecological interactions among them provide valuable benefits that ultimately contribute to sustainable, healthy forest ecosystems.

Soil microorganisms play important roles in maintaining soil quality and ecosystem health. Development of effective methods for studying the composition, diversity, and behavior of microorganisms in soil habitats is essential for a broader understanding of soil quality. Forest management strategies and practices are of vital significance for sustainable forest production. How the different forest management measures will influence soil microbial communities is a widespread concern of forest industry and scientific communities. Only a small proportion (~0.1%) of the bacteria from natural habitats can be cultured on laboratory growth media. Direct extraction of whole-community DNA from soil, followed by polymerase chain reaction (PCR) and other analysis circumvents the problems of the culture-dependent methods and may shed light on a broader range of microbial communities in the soil. DNA-based molecular methods rely on high quality soil microbial DNA as template, and thus extraction of good quality DNA from soil samples has been a challenge because of the complex and heterogeneous nature of the soil matrix. The objectives of this research were to establish a set of DNA-based molecular methods and to apply them to investigate forest soil microbial composition and diversity. Soil samples were collected from different forest ecosystems, i.e., the natural forest (YNF) and the first rotation (~ 50 years) (Y1R) and the second rotation (~ 1 year) (Y2R) of hoop pine plantations at Yarraman, and from different forest residue management practices (the experiments had established 6.4 years before the samples were collected) at Gympie, two long-term experimental sites of the Queensland Department of Primary Industry-Forestry in subtropical Queensland, Australia. Some DNA-based molecular techniques, including DNA extraction and purification, PCR amplification, DNA screening, cloning, sequencing and phylogenetic analyses, were explored using Yarraman soil samples, which were high in organic matter, clay and iron oxide contents. A set of methods was assembled based on the recommendations of the method development experiments and applied to the investigations of the microbial composition and diversity of the Yarraman and Gympie soil samples. Four soil DNA extraction methods, including the Zhou method (Zhou et al., 1996), the Holben method (Holben, 1994), the UltraClean (Mo Bio) and FastDNA (Bio 101) soil DNA extraction kits, were explored. It was necessary to modify these methods for Yarraman soil. I designed and introduced a pre-lysis buffer washing step, to partially remove soil humic substances and promote soil dispersion. This modification greatly improved the quality of the extracted DNA, decreasing co-extracted humic substances by 31% and increasing DNA yield by 24%. The improved Holben method was recommended for fungal community studies, and the improved Zhou method for bacterial community studies. The extracted DNA was good in quality, with a consistent size of ~20 kb and a yield of 48-87 g g-1 soil, and could be successfully used for 16S (Zhou method) and 18S (Holben method) rDNA amplifications. For less difficult environmental samples, UltraClean kits could be a good option, because they are simple and fast and the extracted DNA are also of good quality. Screening of the DNA PCR products using TGGE, Heteroduplex-TGGE and SSCP was also explored. These methods were not so effective for the screening of the soil DNA PCR products, owing to the difficulty in interpretation of the results. Cloning was a necessary step to obtain a single sequence at species level in soil microbial community studies. The screening of the clone library by TGGE, Heteroduplex-TGGE and SSCP could only separate the clones into several major bands, although SSCP gave better separation. Sequencing of selected clones directly from the clone library obtained ultimate results of microbial taxonomic composition and diversity through well-established sequence analysis software packages and the databases. It was recommended that, in this project with the target of microbial community composition and diversity, soil DNA PCR products were directly cloned to construct clone libraries and a sample of clones were sequenced to achieve an estimate of the taxonomic composition of the soil. Fungal communities of the Yarraman soil samples under the natural forest (YNF) and the hoop pine plantations (YHP) were investigated using 18S rDNA based cloning and sequencing approaches. Twenty-eight clone sequences were obtained and analysed. Three fungal orders, i.e., Zygomycota, Ascomycota and Basidiomycota were detected from the YNF and YHP samples. By contrast, culture-based analyses of fungi in the literature were mostly Ascomycetes. YNF appeared to have more Ascomycota but less Zygomycota than YHP, and within the Zygomycota order, YHP had more unidentified species than YNF. Bacterial communities of Yarraman soil samples of YNF, Y1R and Y2R were investigated using 16S rDNA-based cloning and sequencing approaches. 305 16S rDNA clone sequences were analysed and showed an overall bacterial community composition of Unclassified bacteria (34.4%), Proteobacteria (22.0%), Verrucomicrobia (15.7%), Acidobacteria (10.2%), Chloroflexi (6.9%), Gemmatimonadetes (5.6%), and Actinobacteria (5.2%). There was a significant difference among YNF, Y1R and Y2R in the taxonomic group composition. YNF had a greater proportion of Acidobacteria (18.0%), Verrucomicrobia (23.0%) and Chloroflexi (9.0%) than Y1R and Y2R (corresponding to 6.3%, 12.1% and 5.9%, respectively), while Y1R and Y2R had a higher percentage of the Unclassified group (38.5% for Y1R and 46.5% for Y2R) than YNF (18.0%). For the Proteobacteria group, YNF had more Alpha-subdivision but Y1R and Y2R had more Delta-subdivision. From YNF to Y1R to Y2R, the clone sequence variable site ratios, 5% and 10% OTU numbers and Shannon's diversity index H' values tended to decrease, indicating the soil bacterial diversity decreased from the natural forest to the first and the second rotation hoop pine plantations. The large amount of unclassified clone sequences could imply a novel group of bacteria in the soil, particularly in the hoop pine soil samples. Alternatively they may result from artefacts during the PCR process. Bacterial communities of the Gympie soil under different residue management practices, i.e., residue (litter plus logging residue) removed (G0R), residue retained (G1R), and residue doubled (G2R), were also investigated using the 16S rDNA-based cloning and sequencing approaches. Acidobacteria (37.6%) and Proteobacteria (35.6%, including Alpha-subdivision of 29.9% and Gamma-subdivision of 5.7%) were dominant components of the communities, followed by Actinobacteria (14.7%), Verrucomicrobia (7.3%) and Unclassified bacteria. There was no significant difference among G0R, G1R and G2R in the bacterial community compositions and diversity. These findings provided an in-depth vision of the soil microbial communities under different forest management practices. Their combination with other soil analysis results, such as physical and chemical properties, and forest production data, could provide an improved understanding of sustainable forest management strategies.

Soil microorganisms play important roles in maintaining soil quality and ecosystem health. Development of effective methods for studying the composition, diversity, and behavior of microorganisms in soil habitats is essential for a broader understanding of soil quality. Forest management strategies and practices are of vital significance for sustainable forest production. How the different forest management measures will influence soil microbial communities is a widespread concern of forest industry and scientific communities. Only a small proportion (~0.1%) of the bacteria from natural habitats can be cultured on laboratory growth media. Direct extraction of whole-community DNA from soil, followed by polymerase chain reaction (PCR) and other analysis circumvents the problems of the culture-dependent methods and may shed light on a broader range of microbial communities in the soil. DNA-based molecular methods rely on high quality soil microbial DNA as template, and thus extraction of good quality DNA from soil samples has been a challenge because of the complex and heterogeneous nature of the soil matrix. The objectives of this research were to establish a set of DNA-based molecular methods and to apply them to investigate forest soil microbial composition and diversity. Soil samples were collected from different forest ecosystems, i.e., the natural forest (YNF) and the first rotation (~ 50 years) (Y1R) and the second rotation (~ 1 year) (Y2R) of hoop pine plantations at Yarraman, and from different forest residue management practices (the experiments had established 6.4 years before the samples were collected) at Gympie, two long-term experimental sites of the Queensland Department of Primary Industry-Forestry in subtropical Queensland, Australia. Some DNA-based molecular techniques, including DNA extraction and purification, PCR amplification, DNA screening, cloning, sequencing and phylogenetic analyses, were explored using Yarraman soil samples, which were high in organic matter, clay and iron oxide contents. A set of methods was assembled based on the recommendations of the method development experiments and applied to the investigations of the microbial composition and diversity of the Yarraman and Gympie soil samples. Four soil DNA extraction methods, including the Zhou method (Zhou et al., 1996), the Holben method (Holben, 1994), the UltraClean (Mo Bio) and FastDNA (Bio 101) soil DNA extraction kits, were explored. It was necessary to modify these methods for Yarraman soil. I designed and introduced a pre-lysis buffer washing step, to partially remove soil humic substances and promote soil dispersion. This modification greatly improved the quality of the extracted DNA, decreasing co-extracted humic substances by 31% and increasing DNA yield by 24%. The improved Holben method was recommended for fungal community studies, and the improved Zhou method for bacterial community studies. The extracted DNA was good in quality, with a consistent size of ~20 kb and a yield of 48-87 g g-1 soil, and could be successfully used for 16S (Zhou method) and 18S (Holben method) rDNA amplifications. For less difficult environmental samples, UltraClean kits could be a good option, because they are simple and fast and the extracted DNA are also of good quality. Screening of the DNA PCR products using TGGE, Heteroduplex-TGGE and SSCP was also explored. These methods were not so effective for the screening of the soil DNA PCR products, owing to the difficulty in interpretation of the results. Cloning was a necessary step to obtain a single sequence at species level in soil microbial community studies. The screening of the clone library by TGGE, Heteroduplex-TGGE and SSCP could only separate the clones into several major bands, although SSCP gave better separation. Sequencing of selected clones directly from the clone library obtained ultimate results of microbial taxonomic composition and diversity through well-established sequence analysis software packages and the databases. It was recommended that, in this project with the target of microbial community composition and diversity, soil DNA PCR products were directly cloned to construct clone libraries and a sample of clones were sequenced to achieve an estimate of the taxonomic composition of the soil. Fungal communities of the Yarraman soil samples under the natural forest (YNF) and the hoop pine plantations (YHP) were investigated using 18S rDNA based cloning and sequencing approaches. Twenty-eight clone sequences were obtained and analysed. Three fungal orders, i.e., Zygomycota, Ascomycota and Basidiomycota were detected from the YNF and YHP samples. By contrast, culture-based analyses of fungi in the literature were mostly Ascomycetes. YNF appeared to have more Ascomycota but less Zygomycota than YHP, and within the Zygomycota order, YHP had more unidentified species than YNF. Bacterial communities of Yarraman soil samples of YNF, Y1R and Y2R were investigated using 16S rDNA-based cloning and sequencing approaches. 305 16S rDNA clone sequences were analysed and showed an overall bacterial community composition of Unclassified bacteria (34.4%), Proteobacteria (22.0%), Verrucomicrobia (15.7%), Acidobacteria (10.2%), Chloroflexi (6.9%), Gemmatimonadetes (5.6%), and Actinobacteria (5.2%). There was a significant difference among YNF, Y1R and Y2R in the taxonomic group composition. YNF had a greater proportion of Acidobacteria (18.0%), Verrucomicrobia (23.0%) and Chloroflexi (9.0%) than Y1R and Y2R (corresponding to 6.3%, 12.1% and 5.9%, respectively), while Y1R and Y2R had a higher percentage of the Unclassified group (38.5% for Y1R and 46.5% for Y2R) than YNF (18.0%). For the Proteobacteria group, YNF had more Alpha-subdivision but Y1R and Y2R had more Delta-subdivision. From YNF to Y1R to Y2R, the clone sequence variable site ratios, 5% and 10% OTU numbers and Shannon's diversity index H' values tended to decrease, indicating the soil bacterial diversity decreased from the natural forest to the first and the second rotation hoop pine plantations. The large amount of unclassified clone sequences could imply a novel group of bacteria in the soil, particularly in the hoop pine soil samples. Alternatively they may result from artefacts during the PCR process. Bacterial communities of the Gympie soil under different residue management practices, i.e., residue (litter plus logging residue) removed (G0R), residue retained (G1R), and residue doubled (G2R), were also investigated using the 16S rDNA-based cloning and sequencing approaches. Acidobacteria (37.6%) and Proteobacteria (35.6%, including Alpha-subdivision of 29.9% and Gamma-subdivision of 5.7%) were dominant components of the communities, followed by Actinobacteria (14.7%), Verrucomicrobia (7.3%) and Unclassified bacteria. There was no significant difference among G0R, G1R and G2R in the bacterial community compositions and diversity. These findings provided an in-depth vision of the soil microbial communities under different forest management practices. Their combination with other soil analysis results, such as physical and chemical properties, and forest production data, could provide an improved understanding of sustainable forest management strategies.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Australian School of Environmental Studies
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Moth assemblages have been widely used to examine patterns of beta-diversity in forest ecosystems. This thesis aims to expand and test the generality of results obtained as part of the IBISCA-Queensland Project (Investigating Biodiversity of Soil and Canopy Arthropods-Qld) which examined patterns of diversity in a large sub-set of night-flying moths along an altitudinal gradient in subtropical rainforest. The permanent IBISCA-Qld transect, located in Lamington National Park (NP), in south-east Queensland, Australia, spans altitudes from 300 to 1100 meters above sea level (m a.s.l.) within continuous rainforest. Along this transect, moth assemblages showed strong altitudinal stratification. A number of species were restricted to the Nothofagus moorei dominated cloud forest around 1100m a.s.l., and may be the most threatened by climatic change. The IBISCA-Qld Project produced a set of moth species that could be included within a predictor set of taxa that may be useful for future monitoring of the impact of global warming on forest biodiversity. The IBISCA-Qld study was predicated on the idea that a range of adjacent climates along a single altitudinal gradient can be taken as a surrogate for larger scale climatic changes which occur along latitudinal gradients. This thesis expands on the IBISCA-Qld Project by establishing a latitudinal network of analogous altitudinal transects, in Australia and south-west China (tropical, subtropical and sub-alpine temperate forests), allowing inter-continental comparisons on the generality of altitudinal patterns of diversity.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
Griffith School of Environment
Science, Environment, Engineering and Technology
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The nitrogen (N) cycle is one of the key biogeochemical processes in terrestrial ecosystem which is interlinked with some important soil N transformations, notably soil N mineralization, nitrification and denitrification through both biotic and abiotic mechanisms. Global climate change and soil management practices have disrupted the soil N cycling processes. Soil types, plant species and vegetation diversity and management practices are also associated with changing N cycling processes. Prescribed burnings are applied periodically for fuel reduction to reduce the risk of wildfires. Nevertheless, high frequency burning may limit N availability, and make soil more N and water limited. Biochar is a carbon-rich product produced from organic materials using pyrolysis process and has the potential to modify soil N transformations and N retentions by improving soil-plant water relationships and N availability. In the soil-plant system, biochar can recover and retain N by controlling efficient inorganic N use as well as by recycling the N in a balanced manner which determines the flow, direction and availability of soil N and directly influences N use efficiency by plants and controls the productivity of terrestrial ecosystem. However, the effects of biochar on soil N processes are determined by biochar characteristics and soil properties. Biochar pyrolysis temperatures directly influence biochar properties, for example, the surface area and porosity of biochar increase with increasing pyrolysis temperature, leading to enhanced soil N retention and improve water holding capacity (WHC). Additionally, biochar application rate is another factor to consider because large amounts of applied biochar can impact the N cycle by altering soil pH, enhancing N immobilization, leading to changes in N availability. However, the quantitative information about the relationships between biochar pyrolysis temperature and the mechanisms regulating soil N cycling processes as well as biochar application rates and the mechanisms determining whether and how biochar application rates would affect soil N cycling processes have not been well studied especially under field conditions. Therefore, my thesis aimed to examine how biochar application would enhance soil N transformations and N retention by improving soil-plant water relationships and N availability in the N cycling processes in the forest soils of southeast Queensland, Australia. Briefly, in Chapter 2, I assessed how pyrolysis temperature would affect biochar properties and subsequently soil N transformations through a short term laboratory incubation study at two moisture levels. In Chapter 3, I examined how pyrolysis temperature dependent biochar would influence soil labile C and N pools and microbial biomass under the same experimental condition of Chapter 2. To evaluate the interactions between soil N transformations and soil- plant-biochar systems under field conditions, in Chapter 4, I investigated the soil-plant-biochar relationships by examining how biochar and understorey Acacia species would affect the biological N fixation (BNF) and water use efficiency (WUE) of understorey Acacia species as well as soil C and N pools 15 months after biochar application post fire (nearly 3 years after controlled prescribe burning) in suburban native forest of subtropical Australia. Finally, in Chapter 5, I set up a laboratory incubation study to assess the effects of biochar application rates and understorey Acacia species (Acacia leiocalyx and Acacia disparrima) on soil N pools and transformations post fire soil following a 5-day laboratory incubation at two moisture levels (i.e. 60% and 90% WHC). In Chapter 2, I set up a laboratory incubation for 5-days with pine wood (Pinus radiata) biochar at a rate of 5% (w/w) which was produced under six pyrolysis temperatures (e.g. 500, 600, 650, 45 700, 750 and 850°C). I used 15N natural abundance (δ15N) of inorganic N (NH4+-N and NO3--N) to assess the potential of biochar materials in facilitating forest soil N transformations at two soil moisture levels of 50% and 65% WHC. This study revealed that pyrolysis temperature had significant effects on biochar total N and δ15N. Cumulative nitrification and N mineralization were significantly lower in the biochar amended soils than those of the control soil, with significantly lower δ15N of NH4+-N and δ15N of NO3--N in the biochar amended soil. In this 51 study, nitrification was the key driver of soil N mineralization. Additionally, cumulative nitrification and N mineralization responded non-linearly to the increase in pyrolysis temperature. In this study, an optimum pyrolysis temperature range of 600-700°C was identified for improving soil nitrification and N mineralization under the laboratory incubation conditions whereas the greater cumulative nitrification and N mineralization were found at the 65% WHC compared with those at 50% WHC. In Chapter 3, I measured water extractable organic C (WEOC) and total N (WETN), hot water extractable organic C (HWEOC) and total N (HWETN), microbial biomass C (MBC) and N (MBN) as well as mineral N (NH4+-N, NO3--N) to understand the key mechanisms and identify the main indicators of soil quality which can determine soil labile C and N pools through a 5- day laboratory study using different pyrolysis temperature dependent biochar (500-850°C) at two moisture levels of 50% and 65% WHC. This study showed that WETN was significantly lower in the biochar amended soils compared with those of the control soil. WETN was the most sensitive indicators for determining the changes in soil labile C and N pools and had a significant positive correlation with soil MBN, suggesting that microbial biomass would be able to use water extractable N as energy sources for metabolism purposes. Biochar application significantly reduced soil NO3--N and increased N retention in Yarraman soil by enhancing N immobilization due to increased C input from biochar. The 65% WHC had generally greater soil labile C and N pools compared with those of the 50% WHC. In Chapter 4, I used the soil and foliar samples from a suburban forest where pine wood biochar (600°C) was applied at the rate of 0, 5 and 10 t ha-1, 20 months after prescribed burning. I collected the samples months after biochar application. I used N and C isotope compositions (δ15N and δ13C) to assess the BNF and WUE of two understorey Acacia species (A. leiocalyx and A. disparrima). I also examined soil C and N pools and their stable isotope compositions (δ15N and δ13C). This study revealed that biochar did not affect the BNF and WUE 15 months after biochar application. However, BNF varied significantly between the Acacia species and were significantly greater for A. leiocalyx compared with those of A. disparrima; suggesting that understorey A. leiocalyx was more effective in improving N recovery after prescribed burning via BNF as reflected in more N availability in the soil compared with that of A. disparrima in the suburban native forest of subtropical Australia. Soil NH4+-N was significantly lower in the biochar amended soils compared with that of the control soil due to the surface adsorption and N immobilization. The significant positive relationship between soil δ15N (10-83 20 cm) and foliar δ15N highlights that the mechanisms influencing soil δ15N also influence plant δ15N through N uptake. In Chapter 5, I collected soil from a depth of 0-5 cm from biochar treated forest soil 15 months after biochar application and conducted a 5-day laboratory incubation study. I used δ15N approaches to assess and measure the soil N pools and N transformations. Biochar application at the rate of 10 t ha-1 had lower soil NH4+-N and lower cumulative ammonification in the soil which would help improve N availability by reducing mineral N losses. Day 5 NH4+-N was significantly greater at 90% WHC compared with that of 60% WHC whereas Day 5 δ15N of NH4+-N showed an opposite result, indicating a negative liner relationship between NH4+-N and δ15N of NH4+-N . These results demonstrated that at the greater soil moisture level of 90% WHC, N availability in the form of NH4+-N was greater due to greater N mineralization of organic N with lower δ15N, leading to lower δ15N of NH4+-N. Hence, δ15N of organic and inorganic N in the forest soil could be a useful tool for distinguishing the contributions of different processes such as BNF from soil N transformations as well as N loss mechanisms in the soil N cycle.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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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 after prescribed burning). The study examined how prescribed burning could alter the soil biological, physical and chemical properties, particularly N cycling and availability, soil C pools and dynamics as well as soil microbial composition, under specific fire regimes that are followed in a native forest ecosystem of southeast Queensland, Australia. However, the study explored also short-term responses of biochar amendment in typical Toohey Forest on BNF, water use efficiency, soil mineral N pools as well as tree growth of Acacia leiocalyx and Acacia disparimma 1, 2, 3, 6 and 9 months after three rates of biochar application (0, 5 and 10 t per ha) following about 12 months of prescribed burning at Site 7. The studies were undertaken within Toohey Forest which is located 10 km south of the Brisbane, in South-East Queensland, Australia (27°30′S, 135°E). This forest has been subjected to fuel reduction prescribed burning over the last 30 years. The fuel reduction prescribed burning is usually done on a cycle of 7-10 year, depending on seasonal conditions and fuel loads. The studies were conducted at five sites within Toohey Forest. The first site, S7-B4 (B4- means 4 years after prescribed burning) was last burnt in August 2017. Site 4-B6 (B6-means 6 years after prescribed burning) was last burnt in May 2014. Site 1-B9 (9 years after prescribed burning) “27°32'26.79 S” & “153°02'39.81E”, was last burned in August 2011. Site 2-B12 (12 years after prescribed burning) “27°32'34.02S” & “153°03'09.06E”, was last burnt in April 2008. Finally, Site 3-B14 (14 years after prescribed burning) “27°32'28.61S”& “153°02'50.60E”, was last burnt in May 2006. The main aims of this study were to assess the long-term impacts of prescribed burning on BNF, water use efficiency (WUE), and plant rowth of understory acacia species as well as soil C and N pools in the Toohey Forest ecosystem. The objectives of this PhD project, addressed in each of Chapters 3, 4 , 5, and 6 were: (1) to examine the long-term effect of prescribed burning on biological nitrogen fixation (BNF) and water use efficiency as well as tree growth of understory acacia species in a native forest ecosystem of subtropical Australia, as revealed by 15N natural abundance method during the growing season (summer) and non-growing season (winter) (Chapter 3); (2) to evaluate the contribution of BNF by the understory acacia species to ecosystem N availability and cycling processes as well as ecosystem recovery in the Toohey Forest Ecosystem of subtropical Australia, in the context of fuel reduction prescribed burning and climate change (Chapter 3); (3) to examine whether biochar addition could reduce N loss and improve biological, physical and chemical properties of surface soils (Chapter 4); (4) to examine the short-term effect of biochar addition on BNF, WUE and tree growth of understory acacia species in the Toohey Forest of southeast Queensland, Australia (Chapter 4); (5) to quantify the recovery of forest litter floor and total C, total N, C and N isotope composition (δ13C and δ15N) in the 0-5, 5-10, and 10-20 cm soil at Site 1 (S1, 9 years after burning), Site 2 (S2, 12 years after burning) and Site 3 (S3, 14 years after burning) in the suburban Toohey Forest ecosystem of subtropical Australia (Chapter 5); (6) to examine the role of forest litter floor in the nutrient cycling and forest litter floor recovery in the soil C and N pools and their dynamics in the periods of 9-14 years after prescribed burning in the suburban Toohey Forest ecosystem (Chapter 5); (7) to quantify the effect of prescribed burning on soil labile C and N pools 9-14 years after prescribed burning in the Toohey Forest ecosystems of subtropical Australia (Chapter 6); and (8) to examine the ability of soil labile C and N pools at the three burned sites to recover 9-14 years after the prescribed burning in the Toohey Forest ecosystems (Chapter 6). In Chapter 3 (Study 1), there were no significant differences in foliar total C and δ13C between Acacia leiocalyx and Acacia disparimma at all the four sites after long term prescribed burning (6-14 years after burning). However, our result showed that foliar total N concentrations of A. leiocalyx was higher at sites of S1, S2, S3, and S4 than those of A. disparimma after 6-14 years of prescribed burning. There were significant differences in foliar δ15N between Acacia leiocalyx and Acacia disparimma at Site 1 (9 years after prescribed burning), and Site 3 (14 years after prescribed burning), while there were no significant differences in foliar δ15N between Acacia leiocalyx and Acacia disparimma at Site 2 (12 years after prescribed burning), and Site 4 (6 years after prescribed burning). However, our result showed that δ15N values of A. leiocalyx were significantly higher for August 2019 (winter-dry season) at sites of S1-B9 and S3- B14 after 9-14 years of prescribed burning respectively than those of A. disparimma in May 2019 (autumn) and August 2019 (winter) after 9 and 14 years of prescribed burning. Overall, at Site 4 (6 years after burning), BNF rates were in the range of 65-85% for Acacia leiocalyx and Acacia disparimma, while the corresponding BNF values were 40-55% at Site 1 (after 9 years of prescribed burning), 58-73% at Site 2 (after 12 years of prescribed burning), and 48-62% at Site 3 (after 14 years of prescribed burning). However, BNF of Acacia leiocalyx did not differ from that of Acacia disparimma at any of the study sites (S1, S2, S3, and S4). Meanwhile, we assessed the WUE of two acacia species growing at suburban Toohey Forest sites subjected to prescribed burns. We found that 6-14 years after prescribed burning, A. disparimma had higher WUE than that of A. leiocalyx for sites of S2, S3, and S4, but not at S1. In general, this study demonstrates that A. disparimma for all sites S1, S2, S3, and S4 had relatively higher WUE than A. leiocalyx in winter season sampling of August 2019. In Chapter 4 (Study 2), the study explored short-term responses of biochar amendment in typical Toohey Forest on BNF, water use efficiency, soil mineral N pools as well as tree growth of Acacia leiocalyx and Acacia disparimma 1, 2, 3, 6 and 9 months after three rates of biochar application (0, 5 and 10 t per ha) following about 12 months of prescribed burning at Site 7. There were significant differences in foliar total C and total N as well as foliar δ15N, δ13C and tree growth (tree height and diameter at ground level) of both Acacia leiocalyx and Acacia disparimma among the biochar application rates in the Toohey Forest, southeast Queensland, Australia, with the highest values in the biochar application at 5 t per ha compared with those of the control and the biochar rate at 10 t per ha, in the first 6 months. The present study indicated that the biochar treatment of 10 t ha-1 improved foliar total N, BNF, and δ15N of understory acacia species for all sampling months, but not at month 2 (July 2019). However, our study showed that the biochar applied at 5 t ha-1 contributed to increases in total C, δ13C and WUE, but did not differ from those of the 10t ha-1 in the Toohey Forest ecosystem of subtropical Australia. Foliar total N concentrations of A. leiocalyx was higher in the autumn of March 2020 after 9 months of biochar application, also that foliar total N concentrations were significantly higher (P < 0.05) in the treatment of biochar applied at 10 t ha-1 in the autumn of March 2020 compared with those of the 5t ha-1 and control. This study demonstrated that A. disparimma had relative higher BNF in the winter sampling than those of A. leiocalyx, and also the current study showed that BNF was increased after two months of biochar applied at 5 t ha- 1, which did not differ than those of biochar applied at 10 t ha-1. The BNF ranged from 42.2 % to 80.7 % for A. leiocalyx and from 62.4 % to 93.4 % for A. disparimma for all foliar samples before and after biochar application during the autumn and winter of April and July 2019. There were positive relationships among δ13C, δ15N and TN “R2= 36.6% and R2= 13.3%”, P < 0.05 at month 0 and 6 for autumn and spring of April and November 2019 respectively, but there was no significant difference at month 9 for autumn of March 2020. Meanwhile, there were positive relationships among δ13C, δ15N and TN “R2=15.2%, R2= 22.8% and R2= 19.9%”, P < 0.05) at 1-2 months after biochar applied for winter of June and July 2019. There were no significant differences in plant growth for both tree height and diameter at ground level between of A. leiocalyx and A. disparimma at S7-B3. However, there were significant higher in plant growth for both tree height and diameter at ground level among biochar treatments at S7-B3 in the Toohey Forest. We conclude that different biochar application rates led to different effects on BNF and WUE due to the high variation in biochar properties, highlighting the role of BNF in improving plant WUE and subsequently tree growth after biochar was applied in the suburban Toohey Forest. In Chapter 5 (Study 3), this study aimed to determine the long term (9-14 years) impact of prescribed burning on the dynamics of litter floor quantity and quality, and soil C and N pools as well as their dynamics in the Toohey Forest Ecosystems. The S1-B9 (9 years after prescribed burning), S2-B12 (12 years after prescribed burning), and S3-B14 (14 years after prescribed burning), were sampled for litter floors and 0-20 cm soil profile in August 2019. Soil samples were collected at 0-5, 5-10 and 10-20 cm depths from each of the four plots at each of the three sites (S1, S2, and S3) for total C, total N, δ13C and δ15N 9-14 years following the prescribed burning to examine the long term impact of prescribed burning on soil C and N pools (total C, total N, δ13C and δ15N) and their dynamics. The litter floor samples were also collected from each plot of the three sites (S1, S2, and S3) for total C, total N, δ13C and δ15N 9-14 years after prescribed burning, which would be expected to be burnt in the next 1-2 years. The soil total C, total N, δ13C and δ15N at the 0-5, 5-10 and 10-20 cm soil depths at Site 1 after 9 years following the last prescribed burning were also compared with those of the corresponding properties shortly before the last prescribed burning in August 2011. Similarly, litter floor total C, total N, δ13C and δ15N as well as total C and N content at Site 1 after 9 years of prescribed burning would be compared with those of the corresponding properties in the Forest litter floor at Site 1 shortly before prescribed burning in August 2011 to quantify the recovery of C and N pools in the top 20 cm soil and litter floor 9 years after prescribed burning. Overall, after 9 years of prescribed burning at Site 1, soil total C and total N concentration at 0-5, 5-10 and 10-20 cm soil have recovered and indeed been higher than those of the corresponding soil depths shortly before the burning. Similarly, litter floor total C and N contents have also recovered after 9 years of the mild prescribed burning at Site 1, but the C:N ratio in the forest litter floor 9 years later is about 94, which is significantly higher than that of 68 sampled about 9 years ago, shortly before the prescribed burning. This highlights that the surface soil total C and total N concentrations have recovered and indeed been higher than those of the corresponding soil samples collected shortly before the prescribed burning about 9 years after prescribed burning. Similarly, the forest floor total C and N contents have also recovered about 9 years after prescribed burning at Site 1, but the C:N ratio of the forest litter floor 9 years later (96) is significantly higher than that of 68, highlighting that the forest litter floor would be more N limiting, with much less N losses or released into the soil via litter decomposition since litter floor δ15N is much less 9 years after prescribed burning at Site 1 than that collected shortly before prescribed burning, while forest litter floor δ13C is significantly higher 9 years later than that shortly before prescribed burning, suggesting that the vegetation / forest WUE would be higher, partly due to increasing water limitation under climate change and partly due to the suburban N deposition / N fertilization during the past 9 years. Soil total C and total N at Sites 2 and 3 have also been significantly higher 9 years later than those of soil samples collected about 9 years ago. Both soil δ13C and δ15N at Sites 1, 2 and 3 (9, 12 and 14 years after prescribed burning) have also been significantly lower 9 years later than those of soil samples collected 9 years ago, highlighting increasing N limitation and decreasing N availability as well as significant N deposition in the suburban forest ecosystems. In Chapter 6 (Study 4), this study aimed to examine the availability of soil labile C and N pools such as hot water extractable organic C (HWEOC) and hot water extractable total N (HWETN), water soluble organic C (WSOC) and water soluble total N (WSTN), as well as microbial biomass C (MBC) and microbial biomass N (MBN) at the three burned sites to recover 9-14 years after prescribed burning; and to quantify the long term effect of prescribed burning on soil labile C and N pools 9-14 years after the prescribed burning in the Toohey Forest ecosystems of subtropical Australia. The S1-B9 (9 years after prescribed burning), S2-B12 (12 years after prescribed burning), and S3-B14 (14 years after prescribed burning), were sampled for 0-20 cm soil profile in August 2019. Soil samples were collected at 0-5, 5-10 and 10-20 cm depths from each of the four plots at each of the three sites (S1, S2, and S3) for determining the soil labile C and N pools. Labile C and N pools such as HWEOC, HWETN, WSOC, WSTN, MBC and MBN are commonly used as sensitive indicators of soil quality and fertility and soil organic matter stability. The repeated measures analysis revealed that labile C and N pools were recovered after 9-14 years of prescribed burning for HWEOC and HWETN, but in regard to the time since fire for 9-14 years, the present study indicated that WSOC and WSTN were decreased for all soil depth highlighting that both WSOC and WSTN were not yet recovered. Meanwhile, the results have also been indicated that fire had significantly increased MBC for both depths of 5-10 and 10-20 cm at sites of S2 and S3 after 12-14 years of prescribed burning compared with those of samples collected in August 2019. The current study also indicated that MBN was significantly decreased after 9-14 years of prescribed burning for all soil depths. In conclusion, all soil labile C and N pools were recovered 9-14 years after prescribed burning, except for WSOC and WSTN which were not recovered for S1 9 years after prescribed burning. At S1-B9, while the biomass of the litter floor was recovered, the C:N ratio of 96 was much higher than that of 68 for litter floor about 9 years ago before the last prescribed burning. This would limit the decomposition of litter floor, which would be closely linked to the soil WSOC and WSTN that were not recovered either. The lower soil δ15N and higher δ13C in the litter floor highlights that both water and N are becoming increasingly limiting due the climate change and prescribed burning. Overall, our study concluded that soil total C and total N were fully recovered after 9-14 years of prescribed burning, as well as litter floor leaf and twigs total C and total N were fully recovered 12-14 years after prescribed burning in the suburban Toohey forest ecosystem of subtropical Australia. Litter floor leaf and twigs total C and total N were not fully recovered 9 years after the prescribed burning at S1, compared with those of corresponding samples collected shortly before the last burn in June 2011. Litter floor leaf and twigs δ13C 9, 12 and 14 years after prescribed burning at sites of S1, S2 and S3 were significantly higher compared with those of corresponding samples collected shortly before, 3 and 5 years after the prescribed burning. Meanwhile, soil HWEOC and HWETN were recovered after 9-14 years of prescribed burning. MBN of 0-5 and 5-10 cm soil at S1 did not recover even 9 years after the prescribed burning. However, WEOC and WETN did not recover even 9 years after prescribed burning at S1. Similar trends of WEOC and WETN were also noted for sites of S2 and S3 12-14 years after prescribed burning in Toohey Forest ecosystem of subtropical Australia.
Thesis (PhD Doctorate)
Doctor of Philosophy (PhD)
School of Environment and Sc
Science, Environment, Engineering and Technology
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