School of Agriculture, Food and Ecosystem Sciences - Research Publications
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ItemBridge to the future: Important lessons from 20 years of ecosystem observations made by the OzFlux network(WILEY, 2022-06)In 2020, the Australian and New Zealand flux research and monitoring network, OzFlux, celebrated its 20th anniversary by reflecting on the lessons learned through two decades of ecosystem studies on global change biology. OzFlux is a network not only for ecosystem researchers, but also for those 'next users' of the knowledge, information and data that such networks provide. Here, we focus on eight lessons across topics of climate change and variability, disturbance and resilience, drought and heat stress and synergies with remote sensing and modelling. In distilling the key lessons learned, we also identify where further research is needed to fill knowledge gaps and improve the utility and relevance of the outputs from OzFlux. Extreme climate variability across Australia and New Zealand (droughts and flooding rains) provides a natural laboratory for a global understanding of ecosystems in this time of accelerating climate change. As evidence of worsening global fire risk emerges, the natural ability of these ecosystems to recover from disturbances, such as fire and cyclones, provides lessons on adaptation and resilience to disturbance. Drought and heatwaves are common occurrences across large parts of the region and can tip an ecosystem's carbon budget from a net CO2 sink to a net CO2 source. Despite such responses to stress, ecosystems at OzFlux sites show their resilience to climate variability by rapidly pivoting back to a strong carbon sink upon the return of favourable conditions. Located in under-represented areas, OzFlux data have the potential for reducing uncertainties in global remote sensing products, and these data provide several opportunities to develop new theories and improve our ecosystem models. The accumulated impacts of these lessons over the last 20 years highlights the value of long-term flux observations for natural and managed systems. A future vision for OzFlux includes ongoing and newly developed synergies with ecophysiologists, ecologists, geologists, remote sensors and modellers.
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ItemConcurrent Measurements of Soil and Ecosystem Respiration in a Mature Eucalypt Woodland: Advantages, Lessons, and Questions(AMER GEOPHYSICAL UNION, 2021-03)Abstract Understanding seasonal and diurnal dynamics of ecosystem respiration (Reco) in forests is challenging, because Reco can only be measured directly during night‐time by eddy‐covariance flux towers. Reco is the sum of soil respiration (Rsoil) and above‐ground respiration (in theory, RAG = Reco − Rsoil). Rsoil can be measured day and night and can provide a check of consistency on Reco, as the difference in magnitude and time dynamic between Reco and Rsoil should be explained by RAG. We assessed the temporal patterns and climatic drivers of Rsoil and Reco in a mature eucalypt woodland, using continuous measurements (only at night for Reco) at half‐hourly resolution over 4 years (2014–2017). Our data showed large seasonal and diurnal (overnight) variation of Reco, while Rsoil had a low diurnal amplitude and their difference (Reco − Rsoil, or RAG) had a low seasonal amplitude. This result implies at first glance that seasonal variation of Reco was mainly influenced by Rsoil while its diurnal variation was mainly influenced by RAG. However, our analysis suggests that the night‐time Reco decline cannot realistically be explained by a decline of RAG. Chamber measurements of autotrophic components at half‐hourly time resolution are needed to quantify how much of the Reco decline overnight is due to declines in leaf or stem respiration, and how much is due to missing storage or advection, which may create a systematic bias in Reco measurements. Our findings emphasize the need for reconciling bottom‐up (via components measured with chambers) and direct estimates of Reco (via eddy‐covariance method).
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ItemThe FLUXNET2015 dataset and the ONEFlux processing pipeline for eddy covariance data (vol 7, 225, 2020)(NATURE RESEARCH, 2021-02-25)A Correction to this paper has been published: https://doi.org/10.1038/s41597-021-00851-9.
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ItemThermal optima of gross primary productivity are closely aligned with mean air temperatures across Australian wooded ecosystems(WILEY, 2021-10)Gross primary productivity (GPP) of wooded ecosystems (forests and savannas) is central to the global carbon cycle, comprising 67%-75% of total global terrestrial GPP. Climate change may alter this flux by increasing the frequency of temperatures beyond the thermal optimum of GPP (Topt ). We examined the relationship between GPP and air temperature (Ta) in 17 wooded ecosystems dominated by a single plant functional type (broadleaf evergreen trees) occurring over a broad climatic gradient encompassing five ecoregions across Australia ranging from tropical in the north to Mediterranean and temperate in the south. We applied a novel boundary-line analysis to eddy covariance flux observations to (a) derive ecosystem GPP-Ta relationships and Topt (including seasonal analyses for five tropical savannas); (b) quantitatively and qualitatively assess GPP-Ta relationships within and among ecoregions; (c) examine the relationship between Topt and mean daytime air temperature (MDTa) across all ecosystems; and (d) examine how down-welling short-wave radiation (Fsd) and vapour pressure deficit (VPD) influence the GPP-Ta relationship. GPP-Ta relationships were convex parabolas with narrow curves in tropical forests, tropical savannas (wet season), and temperate forests, and wider curves in temperate woodlands, Mediterranean woodlands, and tropical savannas (dry season). Ecosystem Topt ranged from 15℃ (temperate forest) to 32℃ (tropical savanna-wet and dry seasons). The shape of GPP-Ta curves was largely determined by daytime Ta range, MDTa, and maximum GPP with the upslope influenced by Fsd and the downslope influenced by VPD. Across all ecosystems, there was a strong positive linear relationship between Topt and MDTa (Adjusted R2 : 0.81; Slope: 1.08) with Topt exceeding MDTa by >1℃ at all but two sites. We conclude that ecosystem GPP has adjusted to local MDTa within Australian broadleaf evergreen forests and that GPP is buffered against small Ta increases in the majority of these ecosystems.