ALBERT

Description: Abstract The influence of different drivers on changes in North American and European boreal forests biomass burning (BB) during the Holocene was investigated based on the following hypotheses: land use was important only in the southernmost regions, while elsewhere climate was the main driver modulated by changes in fuel type. BB was reconstructed by means of 88 sedimentary charcoal records divided into six different site clusters. A statistical approach was used to explore the relative contribution of (a) pollen‐based mean July/summer temperature and mean annual precipitation reconstructions, (b) an independent model‐based scenario of past land use (LU), and (c) pollen‐based reconstructions of plant functional types (PFTs) on BB. Our hypotheses were tested with: (a) a west‐east northern boreal sector with changing climatic conditions and a homogeneous vegetation, and (b) a north‐south European boreal sector characterized by gradual variation in both climate and vegetation composition. The processes driving BB in boreal forests varied from one region to another during the Holocene. However, general trends in boreal biomass burning were primarily controlled by changes in climate (mean annual precipitation in Alaska, northern Quebec, and northern Fennoscandia, and mean July/summer temperature in central Canada and central Fennoscandia) and, secondarily, by fuel composition (BB positively correlated with the presence of boreal needleleaf evergreen trees in Alaska and in central and southern Fennoscandia). Land use played only a marginal role. A modification towards less flammable tree species (by promoting deciduous stands over fire‐prone conifers) could contribute to reduce circumboreal wildfire risk in future warmer periods.

Description: The road to net‐zero is fraught with geopolitical dangers that threaten to de‐rail progress and create new sources of conflict and inequity (“Windfarm sunset” by brian.abeling is licensed under CC BY‐NC‐ND 2.0.). Abstract This opinion article offers insights into the geopolitics of the ongoing global energy transition. In doing so, it draws heavily on a workshop in Berlin in late 2018, and a subsequent paper in the journal Nature. Four scenarios are presented. First, the “Big Green Deal” offers a positive story of the future, under the assumption that there will be a multilateral approach to tackling climate change. Second, “Dirty Nationalism” explores the fallout of nations choosing to turn inward and pursue a short‐term, protectionist, and self‐interested agenda. Third, “Technology Breakthrough” illustrates how a technological leap forward could lead to a great power rivalry and distinct regional energy blocs. Finally, “Muddling On” investigates the outcome of an energy transition that reflect business as usual. By comparing and contrasting the different scenarios, the article highlights the potential winners and losers of the different scenarios, and the geopolitical consequences. It also sketches the implications for policy, theory, and scenario thinking more broadly. This article is categorized under: Integrated Assessment of Climate Change 〉 Integrated Scenario Development The Carbon Economy and Climate Mitigation 〉 Future of Global Energy

Description: The National Ecological Observatory Network (NEON) intends to monitor mosquito populations across its broad geographical range of sites because of their prevalence in food webs, sensitivity to abiotic factors, and relevance for human health. We describe the design of mosquito population sampling in the context of NEON's long-term continental scale monitoring program, emphasizing the sampling design schedule, priorities, and collection methods. Freely available NEON data and associated field and laboratory samples, will increase our understanding of how mosquito abundance, demography, diversity, and phenology are responding to land use and climate change.

Description: North Atlantic late-Pleistocene climate (60,000 to 11,650 years ago) was characterized by abrupt and extreme millennial-duration oscillations known as Dansgaard-Oeschger (D-O) events. However, during the Last Glacial Maximum (LGM) 23,000 to 19,000 calendar years ago (23 to 19 ka), no D-O events are observed in the Greenland ice cores. Our new analysis of the Greenland δ 18 O record reveals a switch in the stability of the climate system around 30 ka, suggesting that a critical threshold was passed. Climate-system modelling suggests low axial obliquity at this time caused vastly expanded sea ice in the Labrador Sea, shifting Northern Hemisphere westerly winds south and reducing the strength of Meridional Overturning Circulation. The results suggest these feedbacks tipped the climate system into full glacial conditions, leading to maximum continental ice growth during the LGM.

Description: Abstract Most assessments of the effectiveness of river restoration are done at small spatial scales (〈10 km) over short time frames (less than three years), potentially failing to capture large‐scale mechanisms such as completion of life‐history processes, changes to system productivity, or time lags of ecosystem responses. To test the hypothesis that populations of two species of large‐bodied, piscivorous, native fishes would increase in response to large‐scale structural habitat restoration (reintroduction of 4,450 pieces of coarse woody habitat into a 110‐km reach of the Murray River, southeastern Australia), we collected annual catch, effort, length, and tagging data over seven years for Murray cod (Maccullochella peelii) and golden perch (Macquaria ambigua) in a restored “intervention” reach and three neighboring “control” reaches. We supplemented mark–recapture data with telemetry and angler phone‐in data to assess the potentially confounding influences of movement among sampled populations, heterogeneous detection rates, and population vital rates. We applied a Bayesian hierarchical model to estimate changes in population parameters including immigration, emigration, and mortality rates. For Murray cod, we observed a threefold increase in abundance in the population within the intervention reach, while populations declined or fluctuated within the control reaches. Golden perch densities also increased twofold in the intervention reach. Our results indicate that restoring habitat heterogeneity by adding coarse woody habitats can increase the abundance of fish at a population scale in a large, lowland river. Successful restoration of poor‐quality “sink” habitats for target species relies on connectivity with high‐quality “source” habitats. We recommend that the analysis of restoration success across appropriately large spatial and temporal scales can help identify mechanisms and success rates of other restoration strategies such as restoring fish passage or delivering water for environmental outcomes.

Description: Abstract To bolster freshwater supplies, water managers are increasingly interested in recharging groundwater using stormwater and recycled water. However, such multi‐supply groundwater recharge projects are hindered by the lack of planning tools to evaluate system design costs and trade‐offs. This study presents modeling advancements that provide enhanced insights into multi‐supply spreading basin systems (i.e., spreading basins that accommodate both advanced treated recycled water and dynamically available stormwater), a form of managed aquifer recharge. The model identifies system designs that optimize infrastructure life cycle cost and total groundwater recharge. To illustrate the model's application under realistic conditions, we present a case study of Los Angeles, California. In this case study, we find competition between stormwater and recycled water for spreading basin use is relatively minor. Moreover, compared to systems based on existing conservative assumptions, our methods identify optimal dynamic system designs that are 5–20% more cost‐effective, primarily resulting from higher water recycling facility utilization. Overall, this approach, which considers the dynamic nature of stormwater availability and variable recycled water production, can inform water planners of the cost, water volume, and energy trade‐offs associated with different multi‐supply spreading basin system designs, including varying levels of centralization.

Description: Stochastic simulation models requiring many input parameters are widely used to inform the management of ecological systems. The interpretation of complex models is aided by global sensitivity analysis, using simulations for distinct parameter sets sampled from multidimensional space. Ecologists typically analyze such output using an “emulator”; that is, a statistical model used to approximate the relationship between parameter inputs and simulation outputs and to derive sensitivity measures. However, it is typical for ad hoc decisions to be made regarding: (1) trading off the number of parameter samples against the number of simulation iterations run per sample, (2) determining whether parameter sampling is sufficient, and (3) selecting an appropriate emulator. To evaluate these choices, we coupled different sensitivity-analysis designs and emulators for a stochastic, 20-parameter model that simulated the re-introduction of a threatened species subject to predation and disease, and then validated the emulators against new output generated from the simulation model. Our results lead to the following sensitivity analysis-protocol for stochastic ecological models. (1) Run a single simulation iteration per parameter sample generated, even if the focal response is a probabilistic outcome, while sampling extensively across the parameter space. In contrast to designs that invested in many model iterations (tens to thousands) per parameter sample, this approach allowed emulators to capture the input-output relationship of the simulation model more accurately and also to produce sensitivity measures that were robust to variation inherent in the parameter-sampling stage. (2) Confirm that parameter sampling is sufficient, by emulating subsamples of the sensitivity-analysis output. As the subsample size is increased, the cross-validatory performance of the emulator and sensitivity measures derived from it should exhibit asymptotic behavior. This approach can also be used to compare candidate emulators and select an appropriate interaction depth. (3) If required, conduct further simulations for additional parameter samples, and then report sensitivity measures and illustrate key response curves using the selected emulator. This protocol will generate robust sensitivity measures and facilitate the interpretation of complex ecological models, while minimizing simulation effort.

Description: An essential ecosystem service is the dilution effect of biodiversity on disease severity, yet we do not fully understand how this relationship might change with continued climate warming and ecosystem degradation. We designed removal experiments in natural assemblages of Tibetan alpine meadow vegetation by manipulating plot-level plant diversity to investigate the relationship between different plant biodiversity indices and foliar fungal pathogen infection, and how artificial fertilization and warming affect this relationship. Although pathogen group diversity increases with host species richness, disease severity decreases as host diversity rises (dilution effect). The dilution effect of phylogenetic diversity on disease held across different levels of host species richness (and equal abundances), meaning that the effect arises mainly in association with enhanced diversity itself rather than from shifting abundances. However, the dilution effect was weakened by fertilization. Among indices, phylogenetic diversity was the most parsimonious predictor of infection severity. Experimental warming and fertilization shifted the most supported predictor to species richness. Compared to planting experiments where artificial communities are constructed from scratch, our removal experiment in natural communities more realistically demonstrate that increasing perturbation adjusts natural community resistance to disease severity. This article is protected by copyright. All rights reserved.