Focus on changing fire regimes: interactions with climate, ecosystems, and society

Fire is a complex Earth system phenomenon that fundamentally affects vegetation distributions, biogeochemical cycling, climate, and human society across most of Earth’s land surface. Fire regimes are currently changing due to multiple interacting global change drivers, most notably climate change, land use, and direct human influences via ignition and suppression. It is therefore critical to better understand the drivers, patterns, and impacts of these changing fire regimes now and continuing into the future. Our review contributes to this focus issue by synthesizing results from 27 studies covering a broad range of topics. Studies are categorized into (i) Understanding contemporary fire patterns, drivers, and effects; (ii) Human influences on fire regimes; (iii) Changes in historical fire regimes; (iv) Future projections; (v) Novel techniques; and (vi) Reviews. We conclude with a discussion on progress made, major remaining research challenges, and recommended directions

US fires became larger, more frequent, and more widespread in the 2000s

Recent fires have fueled concerns that regional and global warming trends are leading to more extreme burning. We found compelling evidence that average fire events in regions of the United States are up to four times the size, triple the frequency, and more widespread in the 2000s than in the previous two decades. Moreover, the most extreme fires are also larger, more common, and more likely to co-occur with other extreme fires. This documented shift in burning patterns across most of the country aligns with the palpable change in fire dynamics noted by the media, public, and fire-fighting officials. &nbsp;</p

Recent droughts in the United States are among the fastest-developing of the last seven decades

Drought has traditionally been characterized as a slow process that requires seasons or even years to fully develop. Recent fast-evolving drying events, however, have challenged our forecasting and response capabilities. A fundamental question emerges: are droughts setting in more quickly? We address this question by evaluating drought intensification rates for the contiguous United States and find that median drought onset rates did not change significantly in 1951&ndash;2021. Conversely, development of fast onset droughts (i.e., the 95th percentile of the drought intensification rates per drought region in a given month of the time series) has been speeding up in recent years across most of the country. As a result, intensification rates of the quickest-onset droughts in 2011&ndash;2021 are among the fastest of the last seven decades. &nbsp;</p

Transparency in supply chains and the lived experiences of workers and their families in the garment sectors of Bangladesh and Myanmar

This article explores the issue of transparency in supply chains for garment sector workers in two countries (Bangladesh and Myanmar). Drawing upon over 100 qualitative fieldwork interviews with workers and stakeholders, the article details the lived experiences of workers and their families. Their stories unveil the impact of factory operating practices and culture in a ‘gendered workplace’ on individuals and communities. Worker narratives are analysed to reflect upon the bearing of enhanced requirements on business stemming from the ‘Transparency in Supply Chains’ clause of the UK Modern Slavery Act 2015. The article presents evidence regarding the impacts of work in the garment sector in Myanmar and Bangladesh on the lives of workers, their children, and family life. The findings offer insights into the reality of the gendered workplace in supply chains for products manufactured in countries that are then exported to UK and worldwide markets. The discussion reflects on the value and appropriateness of transparency as a tool to address exploitation faced by workers in these sectors

Leafcutter Ant Nests Inhibit Low-Intensity Fire Spread in the Understory of Transitional Forests at the Amazon's Forest-Savanna Boundary

Leaf-cutter ants (Atta spp.) remove leaf litter and woody debris—potential fuels—in and around their nests and foraging trails. We conducted single and three annual experimental fires to determine the effects of this leaf-cutter ant activity on the behavior of low-intensity, slow-moving fires. In a transitional forest, where the southern Amazon forest meets the Brazilian savanna, we tested whether leaf-cutter ant nests and trails (i) inhibit fire spread due to a lack of fuels, and (ii), thereby, reduce the total burned area during these experimental low-intensity fires, particularly at forest edges where leaf-cutter ant abundance was higher. Fine-medium fuel mass increased with an increase in distance from ant nest, and the mean area of bare soil was greater on nests than on the forest floor. Between 60 to 90 percent of the unburned area was within 30 m of ant nests, and burned area significantly increased with increasing distance to ant nests. In addition, the number of ant nests declined with increasing distance from the forest edge, and, with exception of the first experimental fire, burned area also increased with increasing distance from the edge. The present study provides new insight to fire ecology in Amazon environments

Cheatgrass (Bromus tectorum) distribution in the intermountain Western United States and its relationship to fire frequency, seasonality, and ignitions

Cheatgrass (Bromus tectorum) is an invasive grass pervasive across the Intermountain Western US and linked to major increases in fire frequency. Despite widespread ecological impacts associated with cheatgrass, we lack a spatially extensive model of cheatgrass invasion in the Intermountain West. Here, we leverage satellite phenology predictors and thousands of field surveys of cheatgrass abundance to create regional models of cheatgrass distribution and percent cover. We compare cheatgrass presence to fire probability, fire seasonality and ignition source. Regional models of percent cover had low predictive power (34% of variance explained), but distribution models based on a threshold of 15% cover to differentiate high abundance from low abundance had an overall accuracy of 74%. Cheatgrass achieves ≥ 15% cover over 210,000 km2 (31%) of the Intermountain West. These lands were twice as likely to burn as those with low abundance, and four times more likely to burn multiple times between 2000 and 2015. Fire probability increased rapidly at low cheatgrass cover (1–5%) but remained similar at higher cover, suggesting that even small amounts of cheatgrass in an ecosystem can increase fire risk. Abundant cheatgrass was also associated with a 10 days earlier fire seasonality and interacted strongly with anthropogenic ignitions. Fire in cheatgrass was particularly associated with human activity, suggesting that increased awareness of fire danger in invaded areas could reduce risk. This study suggests that cheatgrass is much more spatially extensive and abundant than previously documented and that invasion greatly increases fire frequency, even at low percent cover

A Synthesis of the Effects of Cheatgrass Invasion on US Great Basin Carbon Storage

Non-native, invasive Bromus tectorum (cheatgrass) is pervasive in sagebrush ecosystems in the Great Basin ecoregion of the western United States, competing with native plants and promoting more frequent fires. As a result, cheatgrass invasion likely alters carbon (C) storage in the region. Many studies have measured C pools in one or more common vegetation types: native sagebrush, invaded sagebrush and cheatgrass-dominated (often burned) sites, but these results have yet to be synthesized. We performed a literature review to identify studies assessing the consequences of invasion on C storage in above-ground biomass (AGB), below-ground biomass (BGB), litter, organic soil and total soil. We identified 41 articles containing 386 unique studies and estimated C storage across pools and vegetation types. We used linear mixed models to identify the main predictors of C storage. We found consistent declines in biomass C with invasion: AGB C was 55% lower in cheatgrass (40 ± 4 g C/m2) than native sagebrush (89 ± 27 g C/m2) and BGB C was 62% lower in cheatgrass (90 ± 17 g C/m2) than native sagebrush (238 ± 60 g C/m2). In contrast, litter C was \u3e4× higher in cheatgrass (154 ± 12 g C/m2) than native sagebrush (32 ± 12 g C/m2). Soil organic C (SOC) in the top 10 cm was significantly higher in cheatgrass than in native or invaded sagebrush. SOC below 20 cm was significantly related to the time since most recent fire and losses were observed in deep SOC in cheatgrass \u3e5 years after a fire. There were no significant changes in total soil C across vegetation types. Synthesis and applications. Cheatgrass invasion decreases biodiversity and rangeland productivity and alters fire regimes. Our findings indicate cheatgrass invasion also results in persistent biomass carbon (C) losses that occur with sagebrush replacement. We estimate that conversion from native sagebrush to cheatgrass leads to a net reduction of C storage in biomass and litter of 76 g C/m2, or 16 Tg C across the Great Basin without management practices like native sagebrush restoration or cheatgrass removal

Insights from wildfire science: A resource for fire policy discussions

Record blazes swept across parts of the US in 2015, burning more than 10 million acres. The four biggest fire seasons since 1960 have all occurred in the last 10 years, leading to fears of a ‘new normal’ for wildfire. Fire fighters and forest managers are overwhelmed, and it is clear that the policy and management approaches of the past will not suffice under this new era of western wildfires. In recent decades, state and federal policymakers, tribes, and others are confronting longer fire seasons (Jolly et al. 2015), more large fires (Dennison et al. 2014), a tripling of homes burned, and a doubling of firefighter deaths (Rasker 2015). Federal agencies now spend $2 to$3 billion annually fighting fires (and in the case of the US Forest Service, over 50% of their budget), and the total cost to society may be up to 30 times more than the direct cost of firefighting. If we want to contain these costs and reduce risks to communities, economies, and natural systems, we can draw on the best available science when designing fire management strategies, as called for in the recent federal report on Wildland Fire Science and Technology. Here, we highlight key science insights that can contribute to the public discourse on wildfire policy and associated management of forests, woodlands, and shrublands. This information is fundamental to decisions that will promote resilient communities and landscapes facing more fire in the future