School of Ecosystem and Forest Sciences - Research Publications

Permanent URI for this collection

Search Results

Now showing 1 - 10 of 12
  • Item
    No Preview Available
    Land use change and the impact on greenhouse gas exchange in north Australian savanna soils
    Grover, SPP ; Livesley, SJ ; Hutley, LB ; Jamali, H ; Fest, B ; Beringer, J ; Butterbach-Bahl, K ; Arndt, SK (COPERNICUS GESELLSCHAFT MBH, 2012-01-01)
    Abstract. Savanna ecosystems are subjected to accelerating land use change as human demand for food and forest products increases. Land use change has been shown to both increase and decrease greenhouse gas fluxes from savannas and considerable uncertainty exists about the non-CO2 fluxes from the soil. We measured methane (CH4), nitrous oxide (N2O) and carbon dioxide (CO2) over a complete wet-dry seasonal cycle at three replicate sites of each of three land uses: savanna, young pasture and old pasture (converted from savanna 5–7 and 25–30 yr ago, respectively) in the Douglas Daly region of Northern Australia. The effect of break of season rains at the end of the dry season was investigated with two irrigation experiments. Land use change from savanna to pasture increased net greenhouse gas fluxes from the soil. Pasture sites were a weaker sink for CH4 than savanna sites and, under wet conditions, old pastures turned from being sinks to a significant source of CH4. Nitrous oxide emissions were generally very low, in the range of 0 to 5 μg N2O-N m−2 h−1, and under dry conditions soil uptake of N2O was apparent. Break of season rains produced a small, short lived pulse of N2O up to 20 μg N2O-N m−2 h−1, most evident in pasture soil. Annual cumulative soil CO2 fluxes increased after clearing, with savanna (14.6 t CO2-C ha−1 yr−1) having the lowest fluxes compared to old pasture (18.5 t CO2-C ha−1 yr−1) and young pasture (20.0 t CO2-C ha−1 yr−1). Clearing savanna increased soil-based greenhouse gas emissions from 53 to ∼ 70 t CO2-equivalents, a 30% increase dominated by an increase in soil CO2 emissions and shift from soil CH4 sink to source. Seasonal variation was clearly driven by soil water content, supporting the emerging view that soil water content is a more important driver of soil gas fluxes than soil temperature in tropical ecosystems where temperature varies little among seasons.
  • Item
    No Preview Available
    Seasonal variation and fire effects on CH4, N2O and CO2 exchange in savanna soils of northern Australia
    Livesley, SJ ; Grover, S ; Hutley, LB ; Jamali, H ; Butterbach-Bahl, K ; Fest, B ; Beringer, J ; Arndt, SK (ELSEVIER, 2011-11-15)
    Tropical savanna ecosystems are a major contributor to global CO2, CH4 and N2O greenhouse gas exchange. Savanna fire events represent large, discrete C emissions but the importance of ongoing soil-atmosphere gas exchange is less well understood. Seasonal rainfall and fire events are likely to impact upon savanna soil microbial processes involved in N2O and CH4 exchange. We measured soil CO2, CH4 and N2O fluxes in savanna woodland (Eucalyptus tetrodonta/Eucalyptus miniata trees above sorghum grass) at Howard Springs, Australia over a 16 month period from October 2007 to January 2009 using manual chambers and a field-based gas chromatograph connected to automated chambers. The effect of fire on soil gas exchange was investigated through two controlled burns and protected unburnt areas. Fire is a frequent natural and management action in these savanna (every 1–2 years). There was no seasonal change and no fire effect upon soil N2O exchange. Soil N2O fluxes were very low, generally between −1.0 and 1.0μg Nm−2h−1, and often below the minimum detection limit. There was an increase in soil NH4+ in the months after the 2008 fire event, but no change in soil NO3−. There was considerable nitrification in the early wet season but minimal nitrification at all other times. Savanna soil was generally a net CH4 sink that equated to between −2.0 and −1.6kg CH4ha−1y−1 with no clear seasonal pattern in response to changing soil moisture conditions. Irrigation in the dry season significantly reduced soil gas diffusion and as a consequence soil CH4 uptake. There were short periods of soil CH4 emission, up to 20μg Cm−2h−1, likely to have been caused by termite activity in, or beneath, automated chambers. Soil CO2 fluxes showed a strong bimodal seasonal pattern, increasing fivefold from the dry into the wet season. Soil moisture showed a weak relationship with soil CH4 fluxes, but a much stronger relationship with soil CO2 fluxes, explaining up to 70% of the variation in unburnt treatments. Australian savanna soils are a small N2O source, and possibly even a sink. Annual soil CH4 flux measurements suggest that the 1.9million km2 of Australian savanna soils may provide a C sink of between −7.7 and −9.4 Tg CO2-e per year. This sink estimate would offset potentially 10% of Australian transport related CO2-e emissions. This CH4 sink estimate does not include concurrent CH4 emissions from termite mounds or ephemeral wetlands in Australian savannas.
  • Item
    No Preview Available
    The relationships between termite mound CH4/CO2 emissions and internal concentration ratios are species specific
    Jamali, H ; Livesley, SJ ; Hutley, LB ; Fest, B ; Arndt, SK (COPERNICUS GESELLSCHAFT MBH, 2013-01-01)
    Abstract. We investigated the relative importance of CH4 and CO2 fluxes from soil and termite mounds at four different sites in the tropical savannas of northern Australia near Darwin and assessed different methods to indirectly predict CH4 fluxes based on CO2 fluxes and internal gas concentrations. The annual flux from termite mounds and surrounding soil was dominated by CO2 with large variations among sites. On a carbon dioxide equivalent (CO2-e) basis, annual CH4 flux estimates from termite mounds were 5- to 46-fold smaller than the concurrent annual CO2 flux estimates. Differences between annual soil CO2 and soil CH4 (CO2-e) fluxes were even greater, soil CO2 fluxes being almost three orders of magnitude greater than soil CH4 (CO2-e) fluxes at site. The contribution of CH4 and CO2 emissions from termite mounds to the total CH4 and CO2 emissions from termite mounds and soil in CO2-e was less than 1%. There were significant relationships between mound CH4 flux and mound CO2 flux, enabling the prediction of CH4 flux from measured CO2 flux; however, these relationships were clearly termite species specific. We also observed significant relationships between mound flux and gas concentration inside mound, for both CH4 and CO2, and for all termite species, thereby enabling the prediction of flux from measured mound internal gas concentration. However, these relationships were also termite species specific. Using the relationship between mound internal gas concentration and flux from one species to predict mound fluxes from other termite species (as has been done in the past) would result in errors of more than 5-fold for mound CH4 flux and 3-fold for mound CO2 flux. This study highlights that CO2 fluxes from termite mounds are generally more than one order of magnitude greater than CH4 fluxes. There are species-specific relationships between CH4 and CO2 fluxes from a mound, and between the inside mound concentration of a gas and the mound flux emission of the same gas, but these relationships vary greatly among termite species. Thus, there is no generic relationship that will allow for the accurate prediction of CH4 fluxes from termite mounds of all species, but given the data limitations, the above methods may still be used with caution.
  • Item
    No Preview Available
    Soil Methane Uptake Increases under Continuous Throughfall Reduction in a Temperate Evergreen, Broadleaved Eucalypt Forest
    Fest, B ; Hinko-Najera, N ; von Fischer, JC ; Livesley, SJ ; Arndt, SK (SPRINGER, 2017-03-01)
    Soils in temperate forests ecosystems are the greatest terrestrial CHâ sink globally. Global and regional circulation models predict decreased average rainfall, increased extreme rainfall events and increased temperatures for many temperate ecosystems. However, most studies of soil CHâ uptake have only considered extended periods of drought rather than an overall decrease in rainfall amount. We measured soil CHâ uptake from March 2010 to March 2012 after installing passive rainfall reduction systems to intercept approximately 40% of throughfall in a temperate broadleaf evergreen eucalypt forest in south-eastern Australia. Throughfall reduction caused an average reduction of 15.1 ± 6.4% (SE) in soil volumetric water content, a reduction of 19.8 ± 6.9% in soil water-filled pore space (%WFPS) and a 20.1 ± 6.8% increase in soil air-filled porosity. In response to these changes, soil CHâ uptake increased by 54.7 ± 19.3%. The increase in soil CHâ uptake could be explained by increased diffusivity in drier soils, whilst the activity of methanotrophs remained relatively unchanged. It is likely that soil CHâ uptake will increase if rainfall reduces in temperate broadleaf evergreen forests of Australia as a consequence of climate change.
  • Item
    Thumbnail Image
    Soil methane oxidation in both dry and wet temperate eucalypt forests shows a near-identical relationship with soil air-filled porosity
    Fest, BJ ; Hinko-Najera, N ; Wardlaw, T ; Griffith, DWT ; Livesley, SJ ; Arndt, SK (Copernicus Publications, 2017-01-27)
    Well-drained, aerated soils are important sinks for atmospheric methane (CH4) via the process of CH4 oxidation by methane-oxidising bacteria (MOB). This terrestrial CH4 sink may contribute towards climate change mitigation, but the impact of changing soil moisture and temperature regimes on CH4 uptake is not well understood in all ecosystems. Soils in temperate forest ecosystems are the greatest terrestrial CH4 sink globally. Under predicted climate change scenarios, temperate eucalypt forests in south-eastern Australia are predicted to experience rapid and extreme changes in rainfall patterns, temperatures and wild fires. To investigate the influence of environmental drivers on seasonal and inter-annual variation of soil–atmosphere CH4 exchange, we measured soil–atmosphere CH4 exchange at high-temporal resolution (<  2 h) in a dry temperate eucalypt forest in Victoria (Wombat State Forest, precipitation 870 mm yr−1) and in a wet temperature eucalypt forest in Tasmania (Warra Long-Term Ecological Research site, 1700 mm yr−1). Both forest soil systems were continuous CH4 sinks of −1.79 kg CH4 ha−1 yr−1 in Victoria and −3.83 kg CH4 ha−1 yr−1 in Tasmania. Soil CH4 uptake showed substantial temporal variation and was strongly controlled by soil moisture at both forest sites. Soil CH4 uptake increased when soil moisture decreased and this relationship explained up to 90 % of the temporal variability. Furthermore, the relationship between soil moisture and soil CH4 flux was near-identical at both forest sites when soil moisture was expressed as soil air-filled porosity (AFP). Soil temperature only had a minor influence on soil CH4 uptake. Soil nitrogen concentrations were generally low and fluctuations in nitrogen availability did not influence soil CH4 uptake at either forest site. Our data suggest that soil MOB activity in the two forests was similar and that differences in soil CH4 exchange between the two forests were related to differences in soil moisture and thereby soil gas diffusivity. The differences between forest sites and the variation in soil CH4 exchange over time could be explained by soil AFP as an indicator of soil moisture status.
  • Item
    Thumbnail Image
    Fire in Australian savannas: from leaf to landscape
    Beringer, J ; Hutley, LB ; Abramson, D ; Arndt, SK ; Briggs, P ; Bristow, M ; Canadell, JG ; Cernusak, LA ; Eamus, D ; Edwards, AC ; Evans, BJ ; Fest, B ; Goergen, K ; Grover, SP ; Hacker, J ; Haverd, V ; Kanniah, K ; Livesley, SJ ; Lynch, A ; Maier, S ; Moore, C ; Raupach, M ; Russell-Smith, J ; Scheiter, S ; Tapper, NJ ; Uotila, P (WILEY, 2015-01-01)
    Savanna ecosystems comprise 22% of the global terrestrial surface and 25% of Australia (almost 1.9 million km2) and provide significant ecosystem services through carbon and water cycles and the maintenance of biodiversity. The current structure, composition and distribution of Australian savannas have coevolved with fire, yet remain driven by the dynamic constraints of their bioclimatic niche. Fire in Australian savannas influences both the biophysical and biogeochemical processes at multiple scales from leaf to landscape. Here, we present the latest emission estimates from Australian savanna biomass burning and their contribution to global greenhouse gas budgets. We then review our understanding of the impacts of fire on ecosystem function and local surface water and heat balances, which in turn influence regional climate. We show how savanna fires are coupled to the global climate through the carbon cycle and fire regimes. We present new research that climate change is likely to alter the structure and function of savannas through shifts in moisture availability and increases in atmospheric carbon dioxide, in turn altering fire regimes with further feedbacks to climate. We explore opportunities to reduce net greenhouse gas emissions from savanna ecosystems through changes in savanna fire management.
  • Item
    Thumbnail Image
    Reduced throughfall decreases autotrophic respiration, but not heterotrophic respiration in a dry temperate broadleaved evergreen forest
    Hinko-Najera, N ; Fest, B ; Livesley, SJ ; Arndt, SK (ELSEVIER, 2015-01-15)
    Climate change may have major implications on soil respiration dynamics and the carbon sink strength of forest soils. To assess the effect of climate change on soil respiration (RS), it is crucial to understand individual responses of autotrophic (RA) and heterotrophic (RH) components. We investigated the effect of continuously (20 months) reduced throughfall (TFR, −40%) and the influence of seasonal changes in soil temperature and moisture on RS, RA and RH, partitioned by root exclusion, in a dry temperate broadleaved evergreen eucalypt forest in south-eastern Australia. TFR decreased mean RS from 4.7±0.1 (Control) to 3.8±0.1 (TFR) μmolCO2m−2s−1 (−19%). TFR indicated a strong decrease in RA from 2.5±0.1 (Control) to 1.5±0.1 (TFR) μmolCO2m−2s−1 (−40%), but had no effect on RH. The mean relative contribution of RH to RS was 47% in the Control and increased to 61% under TFR. RS was the result of distinct seasonal patterns and dependencies of RH and RA on environmental variables. Soil temperature was a good predictor of RH (Control: R2=0.72, TFR: R2=0.75), but not of RA. In contrast, RH was not limited by soil moisture, while RA was partly influenced by soil moisture (Control: R2=0.29, TFR: R2=0.56). The lack of response of RH to changes in soil moisture (seasonal and under TFR) was likely influenced by the high rainfall conditions such that soil moisture did not decrease to a point where it limited soil microbial decomposition processes. Our results show that TFR implied the strongest effect on RA and that changes in soil temperature and moisture alone do not sufficiently explain seasonal changes in RA and RS. This indicates that biotic factors, such as plant internal carbon allocation, may exert a stronger influence on RA and hence, RS. In short-term a reduction in rainfall will lead to a decrease of soil respiration in dry temperate broadleaved evergreen eucalypt forests. The magnitude of this decrease and its persistence under extended drought will be greatly influenced by seasonal and inter-annual climate variability and potential changes in plant carbon allocation.
  • Item
    No Preview Available
    Vulnerability of native savanna trees and exotic Khaya senegalensis to seasonal drought
    Arndt, SK ; Sanders, GJ ; Bristow, M ; Hutley, LB ; Beringer, J ; Livesley, SJ ; Goldstein, G (OXFORD UNIV PRESS, 2015-07-01)
    Seasonally dry ecosystems present a challenge to plants to maintain water relations. While native vegetation in seasonally dry ecosystems have evolved specific adaptations to the long dry season, there are risks to introduced exotic species. African mahogany, Khaya senegalensis Desr. (A. Juss.), is an exotic plantation species that has been introduced widely in Asia and northern Australia, but it is unknown if it has the physiological or phenotypic plasticity to cope with the strongly seasonal patterns of water availability in the tropical savanna climate of northern Australia. We investigated the gas exchange and water relations traits and adjustments to seasonal drought in K. senegalensis and native eucalypts (Eucalyptus tetrodonta F. Muell. and Corymbia latifolia F. Muell.) in a savanna ecosystem in northern Australia. The native eucalypts did not exhibit any signs of drought stress after 3 months of no rainfall and probably had access to deeper soil moisture late into the dry season. Leaf water potential, stomatal conductance, transpiration and photosynthesis all remained high in the dry season but osmotic adjustment was not observed. Overstorey leaf area index (LAI) was 0.6 in the native eucalypt savanna and did not change between wet and dry seasons. In contrast, the K. senegalensis plantation in the wet season was characterized by a high water potential, high stomatal conductance and transpiration and a high LAI of 2.4. In the dry season, K. senegalensis experienced mild drought stress with a predawn water potential -0.6 MPa. Overstorey LAI was halved, and stomatal conductance and transpiration drastically reduced, while minimum leaf water potentials did not change (-2 MPa) and no osmotic adjustment occurred. Khaya senegalensis exhibited an isohydric behaviour and also had a lower hydraulic vulnerability to cavitation in leaves, with a P50 of -2.3 MPa. The native eucalypts had twice the maximum leaf hydraulic conductance but a much higher P50 of -1.5 MPa. Khaya senegalensis has evolved in a wet-dry tropical climate in West Africa (600-800 mm) and appears to be well suited to the seasonal savanna climate of northern Australia. The species exhibited a large phenotypic plasticity through leaf area adjustments and conservative isohydric behaviour in the 6 months dry season while operating well above its critical hydraulic threshold.
  • Item
    Thumbnail Image
    Storage management influences greenhouse gas emissions from biosolids
    Majumder, R ; Livesley, SJ ; Gregory, D ; Arndt, SK (ACADEMIC PRESS LTD- ELSEVIER SCIENCE LTD, 2015-03-15)
    Biosolids produced by wastewater treatment plants are often stored in stockpiles and can be a significant source of greenhouse gases (GHG). Growing trees in shallow stockpiled biosolids may remove nutrients, keep the biosolids drier and offset GHG emissions through C sequestration. We directly measured methane (CH4), carbon dioxide (CO2) and nitrous oxide (N2O) flux from a large biosolid stockpile and two shallow stockpiles, one planted with Salix reichardtii (willow) trees, from December 2009 to January 2011. All stockpiles emitted large annual amounts of GHG ranging from 38 kg CO2-e Mg(-1) dry biosolid for the large stockpile, to 65 kg CO2-e Mg(-1) for the unplanted shallow stockpile, probably due to the greater surface area to volume ratio. GHG emissions were dominated by N2O and CO2 whilst CH4 emissions were negligible (<2%) from the large stockpile and the shallow stockpiles were actually a CH4 sink. Annual willow tree growth was 12 Mg dry biomass ha(-1), but this only offset 8% of the GHG emissions from the shallow planted stockpile. Our data highlight that biosolid stockpiles are significant sources for GHG emissions but alternate management options such as shallow stockpiles or planting for biomass production will not lead to GHG emission reductions.
  • Item
    No Preview Available
    Changes in soil moisture drive soil methane uptake along a fire regeneration chronosequence in a eucalypt forest landscape
    Fest, B ; Wardlaw, T ; Livesley, SJ ; Duff, TJ ; Arndt, SK (WILEY-BLACKWELL, 2015-11-01)
    Disturbance associated with severe wildfires (WF) and WF simulating harvest operations can potentially alter soil methane (CH4 ) oxidation in well-aerated forest soils due to the effect on soil properties linked to diffusivity, methanotrophic activity or changes in methanotrophic bacterial community structure. However, changes in soil CH4 flux related to such disturbances are still rarely studied even though WF frequency is predicted to increase as a consequence of global climate change. We measured in-situ soil-atmosphere CH4 exchange along a wet sclerophyll eucalypt forest regeneration chronosequence in Tasmania, Australia, where the time since the last severe fire or harvesting disturbance ranged from 9 to >200 years. On all sampling occasions, mean CH4 uptake increased from most recently disturbed sites (9 year) to sites at stand 'maturity' (44 and 76 years). In stands >76 years since disturbance, we observed a decrease in soil CH4 uptake. A similar age dependency of potential CH4 oxidation for three soil layers (0.0-0.05, 0.05-0.10, 0.10-0.15 m) could be observed on incubated soils under controlled laboratory conditions. The differences in soil CH4 uptake between forest stands of different age were predominantly driven by differences in soil moisture status, which affected the diffusion of atmospheric CH4 into the soil. The observed soil moisture pattern was likely driven by changes in interception or evapotranspiration with forest age, which have been well described for similar eucalypt forest systems in south-eastern Australia. Our results imply that there is a large amount of variability in CH4 uptake at a landscape scale that can be attributed to stand age and soil moisture differences. An increase in severe WF frequency in response to climate change could potentially increase overall forest soil CH4 sinks.