A fire driven shift from forest to non-forest: evidence for alternative stable states?

We test the validity of applying the alternative stable state paradigm to account for the landscape-scale forest/non-forest mosaic that prevails in temperate Tasmania, Australia. This test is based on fine-scale pollen, spore, and charcoal analyses of sediments located within a small patch of non-forest vegetation surrounded by temperate forest. Following nearly 500 years of forest dominance at the site, a catastrophic fire drove an irreversible shift from a forested Cyperaceae-Sphagnum wetland to a non-forested Restionaceae wetland at ca. 7000 calibrated (cal) yr BP. Persistence of the non-forest/Restionaceae vegetation state over 7000 years, despite long fire-free intervals, implies that fire was not essential for the maintenance of the non-forest state. We propose that reduced interception and transpiration of the non-forest state resulted in local waterlogging, presenting an eco-hydrological barrier to forest reestablishment over the succeeding 7000 years. We further contend that the rhizomatous nature of the non-forest species presented a reinforcing eco-physical barrier to forest development. Our results satisfy a number of criteria for consideration as an example of a switch between alternative stable states, including different origin and maintenance pathways, and they provide insights into the role of threshold dynamics and hysteresis in forest-non-forest transitions

ENSO Controls Interannual Fire Activity in Southeast Australia

El Niño–Southern Oscillation (ENSO) is the main mode controlling the variability in the ocean-atmosphere system in the South Pacific. While the ENSO influence on rainfall regimes in the South Pacific is well documented, its role in driving spatiotemporal trends in fire activity in this region has not been rigorously investigated. This is particularly the case for the highly flammable and densely populated southeast Australian sector, where ENSO is a major control over climatic variability. Here we conduct the first region-wide analysis of how ENSO controls fire activity in southeast Australia. We identify a significant relationship between ENSO and both fire frequency and area burnt. Critically, wavelet analyses reveal that despite substantial temporal variability in the ENSO system, ENSO exerts a persistent and significant influence on southeast Australian fire activity. Our analysis has direct application for developing robust predictive capacity for the increasingly important efforts at fire management

The Southern Annular Mode determines inter-annual and centennial-scale fire activity in temperate southwest Tasmania, Australia

Southern Annular Mode (SAM) is the primary mode of atmospheric variability in the Southern Hemisphere. While it is well established that the current anthropogenic‐driven trend in SAM is responsible for decreased rainfall in southern Australia, its role in driving fire regimes in this region has not been explored. We examined the connection between fire activity and SAM in southwest Tasmania, which lies in the latitudinal band of strongest correlation between SAM and rainfall in the Southern Hemisphere. We reveal that fire activity during a fire season is significantly correlated with the phase of SAM in the preceding year using superposed epoch analysis. We then synthesized new 14 charcoal records from southwest Tasmania spanning the last 1000 years, revealing a tight coupling between fire activity and SAM at centennial timescales, observing a multicentury increase in fire activity over the last 500 years and a spike in fire activity in the 21st century in response to natural and anthropogenic SAM trends

Aquatic ecosystem response to climate, fire, and the demise of montane rainforest, Tasmania, Australia

The 2019/2020 southeast Australian fires ravaged the environment and threatened endemic vegetation groups, including the Tasmanian montane rainforest. This endemic biome, dominated by Athrotaxis species and Nothofagus gunnii, is declining due to increased aridity and fire frequency (years between fire events). Little is known about the impacts of fire and the montane rainforest decline on aquatic ecosystems in the region, yet aquatic ecosystems are strongly reliant on the terrestrial environment for nutrients and humic acids to support their ecosystem health. Here we evaluate the impacts of repeat fires and decline in montane rainforest species on the aquatic ecosystem of Lake Osborne, Tasmania, Australia, during the past 6500 years using a palaeoecological approach. Newly obtained data including organic carbon (δ13C) and nitrogen (δ15N) isotope composition, visible reflectance spectroscopy (R650–700 as a measure of chlorophyll a and derivatives), and diatom remains are compared with previously published charcoal, pollen, micro-X-Ray fluorescence, magnetic susceptibility, and organic carbon and nitrogen elemental data. Results suggest repeat fire occurrence from 6300 to 4200 years ago caused a decline in montane rainforest, increased erosion, and high aquatic productivity, pH, and conductivity (as indicated by diatoms Epithemia species, Fragilaria type species, Karayevia clevei, and Tabellaria flocculosa). Recovery of montane rainforest due to low fire activity from 4200 to 3000 years ago caused an anomalous assemblage of diatoms dominated by Aulacoseira species along with a less productive aquatic environment (inferred from low δ13C and δ15N, R650–700, and percent macrophytes and algal remains), higher lake level and clearer waters at Lake Osborne. A fire event 2500 years ago caused the removal of montane rainforest and a shift to Eucalyptus dominance within the catchment, leading to an increase in aquatic productivity, and a shift toward benthic diatom taxa dominant in clearer waters-characteristic of eastern Tasmanian sites. The aquatic environment at Lake Osborne for the past 6500 years has responded to increased fire frequency, declines in the montane rainforest and climate change. Fire disturbance removes montane rainforest, burns the underlying soils resulting in erosion of terrigenous material and increases aquatic productivity with communities that favour higher conductivity and low light conditions. With projected increases in fire frequency and loss of rainforest, freshwater ecosystems are vulnerable to changes in physical characteristics, productivity, species assemblages, and ecological resilience

Catastrophic Bushfires, Indigenous Fire Knowledge and Reframing Science in Southeast Australia.

The catastrophic 2019/2020 Black Summer bushfires were the worst fire season in the recorded history of Southeast Australia. These bushfires were one of several recent global conflagrations across landscapes that are homelands of Indigenous peoples, homelands that were invaded and colonised by European nations over recent centuries. The subsequent suppression and cessation of Indigenous landscape management has had profound social and environmental impacts. The Black Summer bushfires have brought Indigenous cultural burning practices to the forefront as a potential management tool for mitigating climate-driven catastrophic bushfires in Australia. Here, we highlight new research that clearly demonstrates that Indigenous fire management in Southeast Australia produced radically different landscapes and fire regimes than what is presently considered “natural”. We highlight some barriers to the return of Indigenous fire management to Southeast Australian landscapes. We argue that to adequately address the potential for Indigenous fire management to inform policy and practice in managing Southeast Australian forest landscapes, scientific approaches must be decolonized and shift from post-hoc engagement with Indigenous people and perspectives to one of collaboration between Indigenous communities and scientists

Silencing alanine transaminase 2 in diabetic liver attenuates hyperglycemia by reducing gluconeogenesis from amino acids

Hepatic gluconeogenesis from amino acids contributes significantly to diabetic hyperglycemia, but the molecular mechanisms involved are incompletely understood. Alanine transaminases (ALT1 and ALT2) catalyze the interconversion of alanine and pyruvate, which is required for gluconeogenesis from alanine. We find that ALT2 is overexpressed in the liver of diet-induced obese and db/db mice and that the expression of the gene encoding ALT2 (GPT2) is downregulated following bariatric surgery in people with obesity. The increased hepatic expression of Gpt2 in db/db liver is mediated by activating transcription factor 4, an endoplasmic reticulum stress-activated transcription factor. Hepatocyte-specific knockout of Gpt2 attenuates incorporation o

Disruption of cultural burning promotes shrub encroachment and unprecedented wildfires

Recent catastrophic fires in Australia and North America have raised broad-scale questions about how the cessation of Indigenous burning practices has impacted fuel accumulation and structure. For sustainable coexistence with fire, a better understanding of the ancient nexus between humans and flammable landscapes is needed. We used novel palaeoecological modeling and charcoal compilations to reassess evidence for changes in land cover and fire activity, focusing on southeast Australia before and after British colonization. Here, we provide what we believe is the first quantitative evidence that the region’s forests and woodlands contained fewer shrubs and more grass before colonization. Changes in vegetation, fuel structures, and connectivity followed different trajectories in different vegetation types. The pattern is best explained by the disruption of Indigenous vegetation management caused by European settlement. Combined with climate-change impacts on fire weather and drought, the widespread absence of Indigenous fire management practices likely preconditioned fire-prone regions for wildfires of unprecedented extent

Dynamics of Saturn's South Polar Vortex

The camera onboard the Cassini spacecraft has allowed us to observe many of Saturn's cloud features. We present observations of Saturn's south polar vortex (SPV) showing that it shares some properties with terrestrial hurricanes: cyclonic circulation, warm central region (the eye) surrounded by a ring of high clouds (the eye wall), and convective clouds outside the eye. The polar location and the absence of an ocean are major differences. It also shares properties with the polar vortices on Venus, such as polar location, cyclonic circulation, warm center, and long lifetime, but the Venus vortices have cold collars and are not associated with convective clouds. The SPV's combination of properties is unique among vortices in the solar system