Global rise in forest fire emissions linked to climate change in the extratropics

High-resolution inventory of polycyclic aromatic hydrocarbon emissions from wildfires in China

Polycyclic aromatic hydrocarbons (PAH) are a class of global environmental pollutants, to which wildfire emissions are important contributors. However, research estimating wildfire PAH emissions in China remains limited, particularly regarding historical trends and spatial distribution. This study employs a bottom-up approach to analyze the temporal variations in PAH emissions from wildfires across China from 2001 to 2023, integrating satellite data, emission factors, and aboveground biomass data for forests, shrubs, and grasslands. The results show that wildfires in China emitted a total of 4080 tons of PAHs from 2001 to 2023, averaging about 177.5 tons annually. Forest fires contributed the largest wildfire PAH emissions from 2001 to 2023 at 75.0 %, followed by grass fires (17.6 %) and shrub fires (7.4 %). The PAH emissions from forest and grassland fires exhibited a downward trend, with a decline of 4.5 and 0.9 tons per year from 2001 to 2023, whereas the emissions from shrub fires did not exhibit obvious change. Furthermore, seasonal variations in PAH emissions were predominantly observed in February, March, and April, collectively accounting for approximately two-thirds of total emissions, primarily attributed to the dry weather conditions and the accumulation of combustible materials in spring. Geographically, high PAH emissions from wildfires were mainly concentrated in the northern and northeastern regions of China, contributing 55.8 % of the total emissions. In addition, the normalized difference vegetation index (NDVI) and soil moisture are primary influencing factors of wildfire PAH emissions, which are mainly given that soil moisture is conducive to vegetation growth and these two factors increased the frequency of wildfires. This study highlights the temporal and spatial variations in PAH emissions from wildfires in China, and the environmental and health impacts of wildfire PAH should be investigated in the future.

Protected areas as hotspots of wildfire activity in fire-prone Temperate and Mediterranean biomes

The European Union has recently passed the Nature Restoration Law which, among others, seeks to increase the cover of forest reserves protected for biodiversity and, globally, the Kunming-Montreal Global Biodiversity Framework similarly seeks to expand protected areas. Here we test whether a trade-off exists between protected areas expansion and fire activity, leading to a higher exposure to fire for the population in protected areas, because they often harbor more biomass and occur in remote areas. We analyzed forest fires affecting 14,892,174 ha, and intersecting 10,999 protected areas, across fire-prone European Temperate and Mediterranean forest biomes, and in similar ecosystems within California, Chile and Australia. Protected areas were being disproportionally affected by fire within most Temperate biomes, and fire severity was 20 % higher within protected areas also in Mediterranean biomes. Population in the periphery of forest areas was up to 16 times more likely to be exposed to large wildfires when their environment was within, or near, protected areas. Differences in manageable factors such as fuel loads and road density were primary drivers of the divergence in burned area across protection status, with abiotic factors playing also significant roles. The importance of fuel loads indicates that current plans for expanding strictly protected areas, where no human intervention is allowed, may be particularly problematic from a fire perspective. Wildfire prevention and mitigation must be central goals in the development of conservation/restoration programs to diminish population exposure and fire severity.

Carbon Emissions From Fires in Eastern Siberian Larch Forests

Siberian boreal forests have experienced increases in fire extent and intensity in recent years, which may threaten their role as carbon (C) sinks. Larch forests (Larix spp.) cover approximately 2.6 million km2 across Siberia, yet little is known about the magnitude and drivers of carbon combustion in these ecosystems. To address the paucity of field-based estimates of fuel load and consumption in Siberian larch forests, we sampled 41 burned plots, one to two years after fire, in Cajander larch (Larix cajanderi) forests in the Republic of Sakha (Yakutia), Russia. We estimated pre-fire carbon stocks and combustion with the objective of identifying the main drivers of carbon emissions. Pre-fire aboveground (trees and woody debris) and belowground carbon stocks at our study plots were 3.12 ± 1.26 kg C m-2 (mean ± standard deviation) and 3.50 ± 0.93 kg C m-2. We found that combustion averaged 3.20 ± 0.75 kg C m-2, of which 78% (2.49 ± 0.56 kg C m-2) stemmed from organic soil layers. These results suggest that severe fires in Cajander larch forests can result in combustion rates comparable to those observed in North American boreal forests and exceeding those previously reported for other forest types and burning conditions in Siberia. Carbon combustion was driven by both fire weather conditions and landscape variables, with pre-fire organic soil depth being the strongest predictor across our plots. Our study highlights the need to better account for Siberian larch forest fires and their impact on the carbon balance, especially given the expected climate-induced increase in fire extent and severity in this region.

Increasing severity of large-scale fires prolongs recovery time of forests globally since 2001

Ongoing and sharply increased global forest fires, especially extreme large-scale fires (LFs) with their greater destructiveness, have significantly altered forest structures and functions. However, long-term variations in the severity of LFs and corresponding effects on the natural post-LF recovery time of global forests remain unclear. Here, we rigorously identified 3,281 global large-scale (>10 km2) single-time fire events (LSFs) from 2001 to 2021, and used multiple indicators to understand the post-LSF recovery dynamics from different perspectives and comprehensively reveal major driving factors across regions and forests types based on multiple models. Compared with pre-2010, LSFs after 2010 caused greater forest damage, with the fire severity expanding further from low to high latitudes and from humid to arid regions, particularly affecting evergreen needleleaf forests. Fewer than one-third of the forests recovered successfully within 7 years, and most of these were tropical, moisture-rich broadleaf forests. The average time required for three indicators to recover to pre-fire conditions increased by 7.5% (vegetation density), 11.1% (canopy structure) and 27.3% (gross primary productivity). Moreover, the positive sensitivity of recovery time to increased fire severity was significantly intensified. Notably, more forests experienced recovery stagnation with increased severity, especially in boreal forests, further extending recovery time. The negative impact of the severity of LSFs on forest recovery was much stronger than that of post-LSF climate conditions. Soil moisture after LSFs was identified as the primary facilitating factor. Temperature generally had a positive role before 2010, but a strong negative influence on post-LSF forest recovery after 2010. These findings provide a useful reference for better understanding global forest recovery mechanisms, estimating forest carbon sinks and implementing post-LSF management accordingly.

Integrated fire management as an adaptation and mitigation strategy to altered fire regimes

Altered fire regimes are a global challenge, increasingly exacerbated by climate change, which modifies fire weather and prolongs fire seasons. These changing conditions heighten the vulnerability of ecosystems and human populations to the impacts of wildfires on the environment, society, and the economy. The rapid pace of these changes exposes significant gaps in knowledge, tools, technology, and governance structures needed to adopt informed, holistic approaches to fire management that address both current and future challenges. Integrated Fire Management is an approach that combines fire prevention, response, and recovery while integrating ecological, socio-economic, and cultural factors into management strategies. However, Integrated Fire Management remains highly context-dependent, encompassing a wide array of fire management practices with varying degrees of ecological and societal integration. This review explores Integrated Fire Management as both an adaptation and mitigation strategy for altered fire regimes. It provides an overview of the progress and challenges associated with implementing Integrated Fire Management across different regions worldwide. The review also proposes five core objectives and outlines a roadmap of incremental steps for advancing Integrated Fire Management as a strategy to adapt to ongoing and future changes in fire regimes, thereby maximizing its potential to benefit both people and nature.

Wildfires: Burning our way to a 'hot house Earth'?

A new global analysis shows that wildfires turn temperate and boreal forests into major emitters of greenhouse gases - instead of storing carbon. Without sustainable forest fire management, forest fires may amplify climate change, leading to irreversible ecological changes.

Disentangling the drivers of wildfires

The risk of wildfires varies across regions with different vegetation.

Recovery Following Recurrent Fires Across Mediterranean Ecosystems

In fire-prone regions such as the Mediterranean biome, fire seasons are becoming longer, and fires are becoming more frequent and severe. Post-fire recovery dynamics is a key component of ecosystem resilience and stability. Even though Mediterranean ecosystems can tolerate high exposure to extreme temperatures and recover from fire, changes in climate conditions and fire intensity or frequency might contribute to loss of ecosystem resilience and increase the potential for irreversible changes in vegetation communities. In this study, we assess the recovery rates of burned vegetation after recurrent fires across Mediterranean regions globally, based on remotely sensed Enhanced Vegetation Index (EVI) data, a proxy for vegetation status, from 2001 to 2022. Recovery rates are quantified through a statistical model of EVI time-series. This approach allows resolving recovery dynamics in time and space, overcoming the limitations of space-for-time approaches typically used to study recovery dynamics through remote sensing. We focus on pixels burning repeatedly over the study period and evaluate how fire severity, pre-fire vegetation greenness, and post-fire climate conditions modulate vegetation recovery rates of different vegetation types. We detect large contrasts between recovery rates, mostly explained by regional differences in vegetation type. Particularly, needle-leaved forests tend to recover faster following the second event, contrasting with shrublands that tend to recover faster from the first event. Our results also show that fire severity can promote a faster recovery across forested ecosystems. An important modulating role of pre-fire fuel conditions on fire severity is also detected, with pixels with higher EVI before the fire resulting in stronger relative greenness loss. In addition, post-fire climate conditions, particularly air temperature and precipitation, were found to modulate recovery speed across all regions, highlighting how direct impacts of fire can compound with impacts from climate anomalies in time and likely destabilise ecosystems under changing climate conditions.