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In 2020, the Australian and New Zealand flux research and monitoring network, OzFlux, celebrated its 20 th 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 CO 2 sink to a net CO 2 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., (© 2022 The Authors. Global Change Biology published by John Wiley & Sons Ltd.)

High water tables (WT) stabilise peatland carbon (C) through regulation of biogeochemical processes. The impact of peatland WT on ecosystem function, including C exchange, alters over time, and the factors that cause some peatlands to display resilience and others to undergo degradation are poorly understood. Here we use CO 2 flux measurements, measured by eddy covariance, to compare ecosystem function between two raised bogs; one drainage-affected, with a deep and fluctuating water table and the other near-natural, with a shallow and stable water table. The drainage-affected bog was found to be a moderate sink for CO 2 (69 g C m -2  yr -1 ), which was 134 g C m -2  yr -1 less than the near-natural bog (203 g C m -2  yr -1 ). Greater ecosystem productivity has allowed the drainage-impacted bog to act as a CO 2 sink despite higher ecosystem respiration; most likely due to an increase in photosynthetic capacity caused by expansion of ericaceous shrub cover. The tolerance of the vegetation community, particularly the main peat former Empodisma robustum (Restionaceae), to low and fluctuating WT appears to have been key in allowing the site to remain a sink. Despite the current resilience of the ecosystem CO 2 sink, we found gross primary production to be limited under both high and low water tables, even in a year with typical rainfall. This is best explained by the limited physiological ability of ericaceous shrubs to tolerate a fluctuating WT. As such we hypothesise that if the WT continues to drop and become even more unstable, then without further vegetation change, a reduction in gross primary production is likely which may in turn cause the site to become a source for CO 2 ., (Copyright © 2018 Elsevier B.V. All rights reserved.)

It is commonly assumed that agricultural peatlands are net sources of CO 2 to the atmosphere because of lowered water tables and intensive land management altering the balance of plant productivity and respiration. Yet actual farm-scale fluxes of CO 2 have been infrequently quantified. We measured net ecosystem exchange of CO 2 (NEE) using a permanent and a mobile eddy covariance tower installed over dairy farms with year-round rotational grazing on deep peats in New Zealand. The permanent tower was in place for one year and the mobile tower was deployed for periods of 3–4 weeks at three other farms on peat between spring and autumn. At all sites, grazing cycles caused large variations in pasture biomass and consequent daytime NEE and we accounted for these variations using an index of photosynthesising biomass (phytomass index, Lohila et al., 2004 ) automatically derived from daily CO 2 flux measurements. We estimated annual CO 2 loss of 190 gC m −2 yr −1 for the permanent site, which is in broad agreement with other agricultural peatland studies. Including other farm-scale exports of C, overall net ecosystem carbon loss estimated for the permanent site was 294 gC m −2 yr −1 . Accounting for changes in phytomass index, daytime NEE was similar for permanent-mobile site farm pairings, except when there were very large differences in water table depths between farms in autumn. In contrast, night-time respiration losses were almost identical between farms even when water tables were markedly different, suggesting that spatial differences in NEE in these agricultural peatlands are caused by reduced photosynthesis in dry periods, due to plant water stress, rather than increased respiration. Comparisons between permanent and mobile towers appeared a useful approach for determining spatial variability of CO 2 fluxes from peat soils. Taken together, our results suggested that the CO 2 losses measured at the permanent site were representative of CO 2 losses for farmed peats in the Waikato region when the water table was within ∼0.5 m of the surface. Where water tables were deeper net CO 2 losses would be expected to be greater due to reduced pasture photosynthesis and production. Maintaining higher water tables might achieve dual benefits of increasing pasture productivity and reducing CO 2 losses. [ABSTRACT FROM AUTHOR]

Highlights: [•] We measured net CO2 exchange (NEE) in a remnant raised peat bog for two years. [•] Mean annual NEE was −234gCm−2 yr−1 indicating substantial CO2 sink strength. [•] Year-round growing conditions accounted for large component CO2 fluxes and NEE. [•] Summertime light response of NEE was similar to northern hemisphere peatlands. [•] Small differences in cool season NEE accounted for differences in annual NEE. [Copyright &y& Elsevier]