Advances in the study of global forest wildfires

Wildfire is one of the most important natural disturbances in forest and multi-vegetation ecosystems, directly or indirectly affecting the structural processes and functions of forest ecosystems with varying degrees. Wildfire releases vast amounts of carbon dioxide and other substances by destroying vegetation, making itself an important topic for the study of global change and environmental impacts. Therefore, a deeper understanding of this topic is particularly crucial for managing forest ecosystems. This paper was based on a literature search of the Web of Science database for international forest wildfire research, utilizing bibliometric and quantity statistical analysis methods. The results show that forest wildfire research has been rapidly growing over the last 20 years, with the number of relevant articles generally increasing yearly at an average annual growth rate of about 22.45%. The US tops the list in terms of total and independent publications, with a total of 3111 articles (49.88%). The key journals publishing on this topic include 12 journals, Stephens S.L., Bergeron Y., and Lindenmayer D.B. are the key contributing authors to the field, and research institutions are primarily concentrated in the US Forest Service. Keyword co-occurrence analysis shows that current forest wildfire research is focused on seven main areas. This paper systematically reviewed the progress and hotspots of international forest wildfire research in recent decades, mainly focusing on occurrences, severity, management, and warning techniques for wildfires, as well as the impact of climate change and human activities on wildfires. The study concludes that research trends in this field have undergone a significant evolution in recent decades. The future forest wildfire research moves towards a combination of typical mechanisms and large-scale effects across spatial and temporal scales, deep integration of aerospace and earth observations and precise simulations, discipline fusion, and couplings research. We believe that this study provides a comprehensive and systematic overview for future forest wildfire observation, prediction, management, and investigation of ecological effects.


Introduction
Forest wildfires are a common natural disaster, occurring almost hourly in different forests around the globe, and are the major disturbances to forest ecosystems (Phillips et al. 2022). In the USA, from 2012 to 2021, an average of 7.4 million acres of land per year affected by about 61,289 wildfires. In 2021, 58,968 wildfires burnt 7.1 million acres (Hoover and Hanson 2021). The sources of the fires are mainly divided into natural fires (such as lightning, high temperatures, volcanic eruptions, etc.) and man-made fire sources (field cooking, burning, smoking, etc.). The wildfire will begin to burn under the oxygen concentration of more than 16% (Belcher et al. 2010(Belcher et al. , 2013. Over the past decades, due to global warming and land use changes (Pachauri and Meyer 2014), the dynamics of fires are changing across the globe, while an increasingly hot planet exacerbates heat and drought, changed precipitation rhythms, and significantly increased the risk and frequency of forest wildfires (Jolly et al. 2015;Abatzoglou and Williams 2016). The severity and length of fire seasons are expected to increase globally especially in boreal high-latitude forests by the end of the century as greenhouse gas emissions increase and global climate change intensifies (Flannigan et al. 2013). According to studies, over 80% of wildfires are caused by human activities (e.g., expansion of agricultural land into forests, etc.). The forest fragmentation and degradation due to human activities have severely reduced the fire resistance of forests (Hansen et al. 2020;Xu et al. 2020). This complex interplay of socio-ecological factors is causing regional changes in forest wildfire severity and frequency trends, which may further alter global climate through biophysical feedbacks, although the potential magnitude and direction of these long-term changes remain uncertain (Tyukavina et al. 2022). Therefore, the occurrence, distribution, and ecological environmental effects of wildfires have become one of the important issues of concern for global change research. In recent years, the extreme wildfire events in Brazil (Requia et al. 2021), Australia (Boer et al. 2020), and California (Dillis et al. 2022) have also drawn public attention to the issue. These extensive and severe recurrent wildfires may be a precursor to changing fire conditions elsewhere in the world, which can provide valuable experiences in guiding responses in other environments subject to widespread fires (Lindenmayer and Taylor 2020).
Despite the growing damage of wildfires has caused massive destruction of forest resources and atmospheric pollution, wildfires are a fundamental part of the global ecosystem that society has used to manage the landscape for thousands of years (Shuman et al. 2022), which play an important role in the renewal of forest ecosystems and the reshaping of landscape patterns (Moura et al. 2019). In other words, wildfires are an important part of the process of material exchange between the land and the atmosphere and also an important driver of ecosystem succession. In the long term and overall, moderate, naturally occurring wildfires enhance forest patchiness (i.e., small communities), create more diverse microhabitats (Fordyce et al. 2016), and improve ecosystem service functions essentially. Forest wildfires could, on the one hand, promote tree species turnover, optimize above-ground species patterns, alter the composition of surface vegetation, help to reduce canopy transpiration and intercept water, and significantly regulate hydrological processes on a landscape and regional scale (Guinto et al. 1999a(Guinto et al. , 2000Bastias et al. 2006a;Reilly et al. 2006), and on the other hand, help to reduce the spread of pests while improving soil nutrients (Guinto et al. 1999b(Guinto et al. , 2001(Guinto et al. , 2002. Specifically, wildfires could warm the soil by burning off dead leaves, help accelerate the decomposition of organic matter, and kill pathogenic bacteria, inducing the release of nutrients and minerals, the improvement of soil nutrient availability, and the growth of new plant roots (Caon et al. 2014). At the same time, the reconstruction of the overfired area lead new animals to move in and seeds (like spruce and fir, which need to burst the seed shell with the help of high temperatures) to sprout (Shepherd et al. 2021), which alter the original plant, microbial, fungal and other animal composition, increase the biodiversity of forest ecosystems, and further affect the biotic patterns of adjacent ecosystems (Guinto et al. 1999b;Bastias et al. 2006a, b). At the global scale, wildfires contribute to the carbon-water cycle (Poulter et al. 2014), surface albedo (Rother and De Sales 2021), and effects of atmospheric aerosol and cloud properties (Chan et al. 2006); it is possible to eventually alter the surface energy balance. In addition, wildfires themselves are still the best way to reduce the risk of large-scale wildfires (Reverchon et al. 2012(Reverchon et al. , 2020Hamilton et al. 2018). Allowing a portion of wildfires to burn naturally or to burn out first is a means to prevent and control forest wildfires.
Current international forest wildfire field has done a lot of research on fire occurrence, distribution, and ecological effects in the past three decades as shown in Fig. 1. However, there is a lack of systematic combing and quantitative analysis of past literature. Bibliometrics is a good way to do this and has been widely used in forest ecology (Juárez-Orozco et al. 2017), grassland ecology (Li et al. 2022a, b), remote sensing , and other fields. It is an innovative way of research in important disciplines that have been proven to fully exploit a large amount of information in the literature and can generate new academic content (Chen 2017;Li et al. 2022a). Therefore, the purpose of this paper was to conduct a bibliometric analysis of forest wildfire research from the perspectives of general trends, major authors, research areas, journal distribution, research countries and institutions, and keyword clustering, in order to extract current research trends and identify cutting-edge issues and development directions, providing important theoretical basis and useful reference for international forest wildfire research and forest management. Since most forest wildfire studies do not distinguish between "man-made" and "natural" causes, the literature covered in this paper includes and does not distinguish between the above two categories and is collectively referred to as "forest wildfire" studies.

Research methods
The methodology used in this study provides a bibliometric analysis of literature data on global forest wildfires. The use of this type of analysis was motivated by the need to assess scientific outcomes (Ellegaard and Wallin 2015). Bibliometric research is referred to as the "science of science" , a way to quantitatively analyze large amounts of large data from the literature, which in turn can help researchers determine the current state of research, sort through and identify new research trends, and provide potential for future collaborative research by researchers (Viana-Lora and Nel-lo-Andreu 2022). The data for this study were obtained from the core collection of the Web of Science (WOS), a database with a high-quality index. The time period of the literature search was 1991-2022, the language was chosen as English, and "forest wildfire" was used as the keyword, the keyword search, and sorting tool applied after repeated testing finally produced 6975 publications, as shown in Fig. 2; after screening and eliminating irrelevant, a total of 6236 publications were obtained. Finally, all information such as title, author, institution, country, abstract, and keywords of these publications was exported in WOS as target files for further software analysis and visualization.
In this study, VOSviewer and R (bibiliometrix package) were used for data analysis and visualization. VOSviewr is an important analytical tool in the field of bibliometric research and has been widely used as a key technique that can help to achieve the construction of relationships in bibliometric data and can visualize current in its software to show the relationships between bibliometric data as well as grouping Waltman 2010, 2017;Li et al. 2021). The larger the circle formed, the higher the number of papers published is represented. The connections of different colors are other clustering modules. R (bibiliometrix package) provides a set of tools for bibliometric studies. It is based on the R language, an open-source statistical programming environment with many efficient, high-quality statistical algorithms and integrated data visualization tools that allow a one-step decomposition and parsing of raw literature data (Li et al. 2022b). The specific findings of the study are presented in detail below.

Publications general development trend, main journals, authors, and research categories in WOS
The general growth trend of a publication reflects the regularity presented by research findings in a time series of development. The time series facilitates the understanding of trends in forest wildfire research and the exploration of specific phases of research. Figure 3a shows the dynamics in time of the number and the average number of citations of annual publications over the past 30 years. From 1991 to 2021, the paper growth curve shows an exponential growth trend with an average annual growth rate of 22.45%. However, during 1991However, during -2003, the number of papers published per year was less than 20, but the number of citations of individual papers was high. After 2004, forest wildfire research entered a phase of high growth, increasing from the number of annual articles of 20 to 680, which was not considered in view of the incomplete data for 2022. From a journal perspective, forest wildfire research appeared in 267 journals, and the study revealed that the top 12 (4.48%) journals published 2041 (32.72%) of the literature. In contrast, 152 journals (56.92%) published only 1 paper and 76 journals (28.46%) published 2 to 5 papers on forest wildfire research. As shown in Fig. 1b, the top 3 journals with the highest number of published papers were Forest Ecology and Management (654), International Journal of Wildland Fire (299), and Forests (212). According to Bradford's law, the results show that the forest wildfire research literature also exhibits a high degree of dispersion, with a large proportion published in Top 12 journals, as shown in Fig. 3b. These journals are the core sources of research in this area that play a crucial role in forest wildfire research and are a common source of interest for scholars.
A network analysis of the primary author groups can help understand the scholarly community in the field of forest wildfires. The author information of the sample papers was visually analyzed, and a network graph of key author collaborations was extracted. Clustering based on research content can further highlight academic and research communities (Fig. 3c). Figure 5 shows the authors who published more than 5 papers, where no separate distinction was made between the first and corresponding authors, and the authors who published more than 50 papers were Stephens S.L.  A co-authorship network analysis has identified five major clusters of researchers, each representing distinct research interests (RI). RI 1 focuses on the interactions between wildland fires and ecosystems, as well as the effects of fire and fuel treatments on forests. RI 2 centers on the effects of forest growth dynamics and disturbances, such as fire, on the forest ecosystem function. RI 3 represents research interests in the sustainable management of boreal forests in the face of climate change. RI 4 is concerned with forestry wildlife management and the environment. Finally, cluster 5 focuses on forest ecology and vegetation dynamics in relation to natural and anthropogenic disturbances, particularly those related to climate variability.

Main countries and the main affiliations of the authors
The analysis of research countries and institutions allows to clarify the distribution of research forces in specific research areas and to pinpoint the contribution of each research institution. The country clustering collaboration network is shown in Fig. 4a, and the organizational collaboration map is shown in Fig. 4b. The results of the study indicate that forest wildfire research is characterized by a large scale and wide scope, involving more than 100 countries and more than 2342 research institutions. At the national scale, the countries with the highest number of publications are concentrated in North America (US, 3111; Canada, 888), Europe (Spain, 685; UK, 287; Portugal, 280, etc.), and Australia (612), in which the USA being the most central to this area of research in terms of collaborative networks. Figure

Keywords co-occurrence
In this study, a total of 12,738 keywords were detected in the literature on forest wildfire research from 1991 to 2021. The visualization of the 30 keywords with the highest co-occurrence and frequency of the main keywords is summarized in Table 1 and further high-frequency keywords are displayed in Fig. 6. In addition to the keywords "wildfire" and "fire", the most frequent keywords were "climate change" (397), forest (236), management (236), boreal forest (231), fire severity (229), disturbance (228), remote sensing (167), and prescribed fires (146). This indicates that the ecological effects and feedback processes on forest wildfires in the context of global climate change, as well as the management of forest ecosystems and wildfire management, and the application of remote sensing technology for wildfire monitoring are the hot topics and priorities of current research. Figure 5 shows the keyword network selected from the total literature based on the keyword co-occurrence method, and these keywords formed seven clusters, which are shown in Fig. 2 based on the relationship between the link attribute weights of different keywords and the total link strength. Specifically, the seven clusters of keywords and their links in Table 1 are grouped together, with each group identified by a different color. The size of each cluster represents their relative contribution to the clusters with keywords, and the thickness of the link line between two clusters refers to the number of interactions established between two different clusters. Table 1 shows the seven clusters that were examined. These are labeled with the most frequent keywords and are ordered by the percentage of keywords they contain, as follows: cluster 1, red, forest fire; cluster 2, green, fire severity; cluster 3, dark blue, wildfires; cluster 4, yellow, disturbance; cluster 5, purple, fire; cluster 6, light blue, climate change; cluster 7, orange, California. It is also including the link weight and total link strength contributed by each representative keyword and provides the 10 most important keywords. These clusters can better help to understand the research hotspots. Based on the results of the above analysis, the fourth section will discuss the research hotspots in the field of forest wildfire in depth (Table 2).

Discussion
Forest wildfire research has gained the attention of many scholars globally, who come from different research regions and research institutions and have produced a large amount of literature. Based on the analysis of key co-occurrences, we obtained seven important clusters, which epitomize the most important current research content, so it is necessary to review the relevant literature behind them and then further explain and sort out the research hotspots formed by the keywords of the clusters.

Forest wildfire occurrence and severity
The 2021 wildfire season broke global records, scorching vast swaths of land from California to Siberia. A United Nations report released in February warned that the number of wildfires will increase by 50% by 2050. Over the past 50 years, the Arctic has warmed three times faster than the rest of the planet (Rantanen et al. 2022), and recent studies suggest that wildfires in the Northern Hemisphere appear to be contributing to the discrepancy. Assessments through the Australian Academy of Science suggest that some aspects of the current 2019-2020 wildfires are unprecedented (Lindenmayer and Taylor 2020). These wildfires are estimated to have burned 12 million hectares of forest and agricultural areas in southeastern Australia (Lindenmayer and Taylor 2020). It is estimated that over 1 billion Australian animals have been killed and it is estimated that 700 species may be driven to extinction (Boer et al. 2020). Several decades have seen a dramatic increase in the length of fire seasons as far away as the Arctic, as well as intense fires from the tropical wetlands of the Pantanal in South America to the peatlands of tropical Asia.
In the western United States, warmer and drier conditions have spurred fires that have burned almost twice as much area in the twenty-first century compared to the late twentieth century (Shuman et al. 2022).
The most important hazard is reflected in the risk posed by forest loss (Anderegg et al. 2022). Researchers have attempted to quantify the risk to forests, carbon storage, biodiversity and forest loss using vegetation models, the relationship between climate and forest properties, and the impact of climate on forest loss (Anderegg et al. 2022).  Wildfire fire events can wipe out large areas of forests, directly contributing to the potential risks described above. When fire itself determines when, where, and how it burns, it can be very dangerous to encounter uncontrollable fires (Dupuy et al. 2020). This is an underestimated risk. In addition, fires are becoming more extreme, with longer fire seasons, which are increasingly overlapping in southern and northern Europe.

Wildfire and management
Prescribed fire is a proactive approach to wildfire prevention and control by setting fires to remove combustible material from the forest by artificially controlling the intensity and extent of the fire (Mayer et al. 2020;Jones et al. 2022). In the controlled areas, low-intensity, controlled fires with little risk of spread are used to remove ground combustible material, allow old-growth stands to fall and breed new forests, and bring back the natural ecology to health. There are uses of low-intensity, controlled wildfires with little risk of spread to remove combustible material from the forest floor, dead wood that have not fallen, prescribed fires to prevent and control the major wildfires and allow forests to regenerate (Wang et al. 2015;Zhang et al. 2018a;Tahmasbian et al. 2019;Reverchon et al. 2020;Jones et al. 2022). Allowing a portion of the wildfire to burn naturally or to burn out first is about removing flammable material from the forest for planned burning (Wang et al. 2014(Wang et al. , 2015(Wang et al. , 2020a. But the central question is how much to burn, where to burn, and how to burn it. Some scientists want to use mathematical equations to simulate fires (Quintero et al. 2021), to study where fire risk is greatest and how "planned burns" can minimize the risk of forest wildfires under different models of specific weather conditions, vegetation types, topography, fuel loads, etc. (Guinto et al. 1999a, b;Long et al. 2014;Ma et al. 2015;Wang et al. 2015Wang et al. , 2020c. Under the simulation model, planned burning is theoretically effective. Burning all the flammable material in the forest that needs to be removed, regardless of any restrictions, is effective in reducing the occurrence of wildfires (Wang et al. 2014;Taresh et al. 2021). However, there are also problems in the simulation such as uncertainty of future severe fire weather. For example, the simulation model showed that on average, prescribed burning reduces wildfire extent in dry forested grasslands by only 1 ha per 3 ha. This suggests that it is almost impossible to reduce the occurrence of forest wildfires by prescribed burning alone, but such planned burning has been proven by many studies to be one of the important and useful disturbance methods to effectively reduce forest wildfires and manage forest ecosystems (Davis et al. 2022). However, if planned burns are used blindly to remove, it may also bring negative effects such as damage to young forests on forest land. Therefore, future research should adhere to this planned burn management, but further efforts in simulation accuracy and scale are needed. Species composition across a large bioclimatic gradient had the greatest effect on fire intensity in a long-term unburned area of northeastern Washington State, USA, with results suggesting that prior fire, harvesting, Fig. 6 The loop between forest wildfires and global climate change clearcutting, and especially planned burning can reduce fire intensity in subsequent forest fires (Cansler et al. 2022).

Wildfires and forest ecosystem changes
From an ecological point of view, wildfire is inherently part of nature and a key driver of ecosystem structure, condition, composition, and change processes. It can alter vegetation population structure, soil physicochemical properties, microbial and insect population structure, nutrient cycling pathways, etc., with a variety of positive and negative effects (Gomes et al. 2018;McLauchlan et al. 2020). Forest wildfires dramatically alter the export processes and pathways of stored and unstable soil organic matter (SOM) as well as dissolved organic matter (DOM). Ecosystem recovery after forest fires depends on soil microbial communities and revegetation (Taresh et al. 2021), and these processes are easily limited by the amount of nutrients in the soil, such as nitrogen and unstable water-soluble compounds, which both strongly influence ecosystem recovery after forest fires (Wang et al. 2020a, b, c). The results of related studies show that the enrichment of SOM and DOM at different soil burning intensities is important for ecosystem recovery and water quality in the soil (Wang et al. 2020a, b, c;Bahureksa et al. 2022).
Previous studies have shown that wildfires can reduce microbial biomass in soils and alter the composition of the soil microbiome (Zhou et al. 2019;Mayer et al. 2020;Singh et al. 2021;Babur et al. 2022), both of which can have implications for forest regeneration and overall ecosystem health. Recent studies have shown that 1 year after fire, many of the key ecosystem functions performed by microbes in unburned soils were absent in burned samples. In particular, the absence of ectomycorrhizal fungi following highintensity fires may affect the ability of pine seedlings to reestablish and grow in fire-affected soils (Rodriguez-Ramos et al. 2021). Such studies will provide new information for the overall recovery of forest ecosystems after wildfire disturbance (Nelson et al. 2022).
Savannas are beginning to take hold in tropical and subtropical regions with the effects of wildfires. It is a natural landscape that is highly dependent on wildfire, with most of the trees being snuffed out at a young age. What is more, in places where water and heat conditions are adequate for forest growth, trees continue to struggle to become forested and continue to sustain the grassland landscape (Hoffmann et al. 2012;Belcher et al. 2013;Maurin et al. 2014;Zhang et al. 2018b;Benton et al. 2022;da Rocha et al. 2022). Smaller and smaller overfire areas reduce aerosol concentrations, alter vegetation structure, and then increase the total terrestrial carbon sinks. Reducing fire is beneficial to combat warming but may go against natural ecosystems. Frequent fires are a necessary part of ancient grassland ecology and play an important role in species conservation.
For fire-resistant plants and plants that depend on fire for reproduction, wildfire is a positive force. In Australia, plants including mountain lobelia (Banksias) have evolved reproductive strategies that use fire (Rokich and Dixon 2007) and its fruit spikes need to be scorched at high temperatures to burst open smoothly, releasing seeds that have been dormant for years and quickly occupying the open spaces and nutrient-rich land after wildfire burns.

Remote sensing and wildfires
Evaluating the impact of wildfires on forest landscapes is a research component that is increasingly supported by remote sensing technology (Santos et al. 2021). Remote sensing technology has been proven by many studies as a very feasible and effective tool to comprehensively characterize the pattern and extent of fire occurrence in forest ecosystems. The interpretation of satellite imagery is an important process by which the extent of fire expansion can be delineated, and the intensity or severity of fire reached can be described over the past decades (Chuvieco 2012;Allison et al. 2016). Through field measurements of wildfire burning, satellite remote sensing, and model simulations, a large amount of sample point data on the amount of combustible material, burn rate, and burn volume have been accumulated. Meanwhile, online satellite imagery resources have significantly improved the efficiency and coverage of wildfire mapping, such as in the Babeldaob watershed, with the expansion of wildfire mapping efforts to provide a more accurate picture of fire area and patterns (Dendy et al. 2022) and provide important practical value to simulation efforts. Elucidating the impact of wildfires on climate by altering radiative forcing at the global scale, either by coupling remote sensing models, vegetation models with climate models, or by inputting information on greenhouse gas emissions and aerosols generated by wildfires into climate models, will provide an important reference for accurate management of wildfires. The main methods for quantitatively assessing carbon emissions from wildfires are calculations using the amount of combustible material, the percentage burned, and the area burned by the fire. One study specifically was conducted with a bibliometric analysis from the perspective of forest wildfires and remote sensing and obtained four main research aspects: (1) analysis of forest changes caused by wildland fires over the years and the use of spectral indices in the analysis of climate change; (2) development of systems for monitoring, mapping, and detecting wildland fires based on satellite imagery; (3) studies on the relationship between emissions impacts, especially in various biomes; and (4) model-based analysis of the relationship between studies of burned areas, using remotely sensed data, and anthropogenic effects (Santos et al. 2021). Currently, research on extreme wildfires is just beginning and is expected in the future (Mathew et al. 2018); thanks to advanced remote sensing technology and artificial intelligence data analysis technology support, parties will be able to predict forecasts and environments under extreme fires.

Wildfire and black carbon
Wildfires are the largest source of carbonaceous aerosols globally (Andreae and Rosenfeld 2008), and organic carbon and black carbon in aerosols scatter and absorb radiation, while black carbon adds heat to the clouds so that they evaporate and change the radiation balance (Lohmann and Feichter 2005). Meanwhile, aerosols and greenhouse gases emitted from forest fires are transported over long distances with the atmospheric circulation, affecting regional air quality and radiation. Aerosols from forest fires in Russia have led to a 57% reduction in solar radiation in Korea and an increase in PM 10 concentration to 258 μg m −3 (Lee et al. 2005) and increased ozone and aerosols in the lower troposphere of the Tibetan Plateau due to forest fires in South Asia (Chan et al. 2006).
On the one hand, greenhouse gas emissions may accelerate the decomposition of organic carbon in permafrost at high latitudes. Observational analysis and numerical simulations show that the warming effect of water-soluble brown carbon over the Arctic is about 30% of that of black carbon, and biomass burning at mid and high latitudes in the Northern Hemisphere contributes about 60% of the warming effect of brown carbon in the Arctic. As future warming intensifies, the frequency, intensity, and extent of wildfire burning at mid and high latitudes in the Northern Hemisphere are likely to increase, thus releasing more brown and black carbon aerosols and further accelerating Arctic warming, forming a positive feedback loop. The contribution of brown carbon aerosols to Arctic warming is expected to be more important in the future. The results of the study suggest that enhancing effective management of wildfire burning in the northern hemisphere at mid and high latitudes will play an important role in mitigating Arctic and global climate change (Yue et al. 2022).
Disturbance of vegetation by wildfire significantly increases surface albedo and produces significant cooling effects (Tsuyuzaki et al. 2009). Finally, atmospheric emissions and climate impacts from wildfires also have feedbacks on vegetation growth, thus forming a feedback loop among various factors (Gatebe et al. 2014). The impact of wildfire on terrestrial vegetation carbon cycle is an important aspect to evaluate the ecological role of wildfire. The contribution of wildfire to the terrestrial vegetation carbon cycle also includes the increase in plant photosynthesis due to CO 2 emissions and the effect of wildfire on vegetation succession dynamics (Lehmann et al. 2014). Meanwhile, many simulation studies of the effects of fire on global and regional ecosystem carbon cycles using dynamic vegetation simulation models have been conducted, and the results agree that wildfire reduces terrestrial carbon sink capacity, but with great uncertainty in magnitude (Dendy et al. 2022).

Climate change and wildfires
Forests absorb about a quarter of the carbon dioxide emitted into the atmosphere, so they play an extremely important role in buffering the Earth's contribution to the rise of carbon dioxide in the atmosphere (Anderegg et al. 2022). Since 2000, research on wildfires and climate change has been increasing (Succarie et al. 2022), and the effects of climate change on fire occurrence include increased temperatures and increased atmospheric CO 2 concentrations. First, warming and increased CO 2 concentrations lead to longer growing seasons, increasing forest and grassland biomass and thus surface combustible loads. Second, global warming increases the number of lightning bolts in the temperate atmosphere. The number of lightning bolts will increase by 50% in the continental, US (Romps et al. 2014), increasing wildfire risk significantly (Veraverbeke et al. 2017;Succarie et al. 2022). Study predicts 19.1% increase in lightning fires in California, USA, from 2020 to 2049 (Lutz et al. 2009). Stocks et al. (2002) find that lightning causes much larger single fires than man-made fires in Canadian boreal conifer wildfires. Third, warmer temperatures increase atmospheric evaporation, thereby exacerbating drought and increasing wildfire risk, especially in forested areas with abundant combustible material. In addition, the seasonal distribution of wildfire frequency is also changing (Succarie et al. 2022). Recent North American fire seasons have seen a significant increase in wildfire frequency in the late season, with greater fire intensity resulting in greater CO 2 emissions. Climate change is already significantly increasing wildfire risk, with drought-affected areas significantly (Turetsky et al. 2011;Jolly et al. 2014). Climate change is likely to be a major driver of increased fire activity. As the planet continues to warm, extreme weather such as high temperatures and heat waves are expected to become more frequent (Leigh et al. 2015). Higher temperatures dry out the landscape and help create the perfect environment for larger, more frequent forest fires. This, in turn, leads to increased emissions from forest fires, further exacerbating climate change and contributing to more fires as part of a fire-climate feedback loop that also exacerbates the occurrence of extreme fires ), the whole process as shown in Fig. 6.
If forests are tapped to play a more important role in climate mitigation, then a huge scientific effort will be needed to better articulate when and where forests can withstand climate change in the twenty-first century (Anderegg et al. 2022). The increasing intensity, extent, and frequency of boreal forest wildfires may exacerbate carbon emissions and transform the region from a globally important carbon sink to a carbon source. Some findings highlight the climate risks posed by boreal wildfires and point to fire management as a cost-effective way to limit emissions (Phillips et al. 2022). Boreal forests in the more productive southern part of central Canada already suffer from relatively high fire frequency (of disturbance) and thus could be used for future simulations of carbon dynamics in more boreal forests (Parisien et al. 2020). Fire-related carbon dynamics in southern boreal forest systems have been relatively poorly studied, with limited research on pre-fire carbon stocks and the drivers of subsequent burning. The latitude-based approach underscores previous research that northern boreal forests have the risk of sequestering less carbon under changing disturbance conditions (Dieleman et al. 2020). Therefore, assessing the effects of wildfire on the carbon cycle of forest ecosystems in high latitudes in the context of climate change which requires a holistic approach to ground-air interactions. The understanding of a range of fire-related processes, including the effects of fire on soil hydrothermal transport, on high-latitude forest dynamics, and on other vegetation composition, is refined through multiple pathways.

Forest wildfires and the environment and human health
Wildfires can affect the institutions, processes, and functions of forest ecosystems and also have far-reaching effects on the atmosphere and human well-being to a certain extent. The months-long forest wildfires that occurred in Australia in 2019-2020 caused very serious impacts on local ecosystems as well as on social life (Sullivan et al. 2022). Wildfires are a growing threat to people's lives, property, and livelihoods (Dillis et al. 2022). Wildfires can also threaten crops and human health in the immediate vicinity of forests (Dillis et al. 2022). In addition to the direct damage caused by forest wildfires to local ecosystems, the air pollution caused by the fires also affects more distant areas with the atmospheric circulation. Forest wildfires directly contribute to elevated PM2.5 concentrations, for example, more than 20% of PM2.5 in the USA in 2014 was due to wildfires. Stanford University researchers have found that wildfire smoke is undermining decades of air quality gains and that fire smoke is exposing millions of Americans to dangerous levels of fine particulate matter each year, seriously jeopardizing human health levels (Childs et al. 2022). Moreover, wildfires are an important cause of tropospheric O 3 pollution . One study suggests that wildfires in Brazil may have led to a 23% increase in respiratory admissions and a 21% increase in blood circulation admissions. The impact of air pollution from forest fires on human health also varies spatially, in the northern region of Brazil (Ye et al. 2021), which is mostly a tropical rainforest area, and was estimated to have increased respiratory admissions by 38% and circulatory admissions by 27%. Epidemiological evidence between air pollution from forest wildfires and human health, i.e., air pollution from wildfires, is significantly associated with higher risk of cardiopulmonary disease admissions (Requia et al. 2021).

Conclusions and perspectives
This study is the first to use bibliometrics and terminology analysis to provide a centralized, unified analysis and in-depth interpretation of the literature related to the topic of forest wildfires published in the WOS database over the past 30 years . Mainly from the journals, authors, countries, and institutions involved in research on the abovementioned topics, and the most relevant keyword networks used during this period were mapped, and seven main research hotspots were formed based on clustering features. The results show that despite the large amount of literature reporting on the occurrence of forest wildfires, technical methods of monitoring, spatial and temporal patterns of wildfires and their ecological, environmental and evolutionary effects, and the impact of global change on wildfire activity, the combing and description of the traditional approach in our study shows clear research advantages, especially for the combing of the current research in general and the description of the research hotspots is an important guide. The results of the study show an exponential increase in the number of publications on these topics over the past 30 years, and the trend of increase, especially in the last 15 years, indicates that there is a growing academic interest in this topic, which is widely appreciated. Among all publications, 54% are related to forestry, ecology, and environmental science, showing the interest and connection between the analyzed topics and environmental dynamics. Forest Ecology and Management, as the core journal of publications, has a significantly higher number of publications than the other journals, being the subject of the seven themes formed by the keyword clustering. The seven thematic directions formed by keyword clustering are the hot content of current research, focusing on anthropogenic management of wildfire, monitoring and model simulation by remote sensing technology, ecosystem response and feedback, reciprocal feedbacks mechanisms of forest wildfire in the context of global climate change, and environmental and human health effects of aerosols.
There are still many challenges that need to be addressed. Current research further provides significant room for improvement. Firstly, wildfire research is isolated within disciplines such as forestry and atmospheric chemistry, but wildfire is a biophysical and social phenomenon that cannot be understood through the lens of any single discipline currently. It is necessary to integrate disciplines by promoting coordination among physical, biological, and social sciences. Future research needs to promote greater proactivity like societies and ecosystems becoming more resilient to reply increasing fire risks by increasing funding and getting better coordination.Furthermore, the accuracy in forest wildfire model simulations needs to be further improved, as numerical simulations are limited by a variety of factors such as climate, hydrology, atmosphere, soil, and topography. How to optimize model simulations and the integration with the interpretation of remote sensing imagery, while aiding ground verification and wildfire mapping needs to be further studied. Therefore, developing coupled models that include the human dimension to better predict future fire activity and its effects is essential. Scientists need to develop more advanced computer modeling systems that incorporate both human and non-human aspects of fire. Moreover, the impact of global climate change on wildfire landscape patterns is mainly reflected in the warming and aridity of some regions, as well as the control of wildfire frequency and overfire area by anthropogenic activities. Therefore, the dynamic assessment and early warning of wildfire risk, prefire prevention, and post-fire vegetation restoration will be important elements of wildfire research in the future, especially for the study of different vegetation zones and the disturbance and response of different wildfires (type, fire extent, area, etc.) to the ecosystem. Finally, future research should further enhance the extent to which wildfires pose risks to human well-being and health, such as the effects of forest fires on neighboring crops and haze on the human respiratory tract and on children and pregnant women.
In conclusion, although there are still many challenges in forest wildfire research, it has developed considerably and received a lot of attention in the past 30 years. We believe that forest wildfire, as an important driver and key disturbance factor of global climate change and forest ecosystem succession, will receive more attention and in-depth study from the scientific community in the future.
Acknowledgements Thanks to all authors for contributing to this manuscript. The authors acknowledge Griffith University and Centre of Planetary Health and Food Security. Comments and suggestions from anonymous reviewers, the academic editor, and the managing editor are greatly appreciated.
Funding Open Access funding enabled and organized by CAUL and its Member Institutions. This research was funded by the CAS Strategic Priority Research Program (XDA20050103) and TL received the Griffith University Postgraduate Research Scholarship for his Ph.D. project. Open Access funding enabled and organized by CAUL and its Member Institutions.
Data Availability Data available from the corresponding authors upon request.

Conflict of interest
The authors declare no competing interest.
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