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Article

Evaluation of Litter Flammability from Dominated Artificial Forests in Southwestern China

by
Shuting Li
1,
Zihan Zhang
1,
Jiangkun Zheng
1,
Guirong Hou
1,
Han Liu
2 and
Xinglei Cui
1,3,*
1
National Forestry and Grassland Administration Engineering Research Centre for Southwest Forest and Grassland Fire Ecological Prevention, College of Forestry, Sichuan Agricultural University, Chengdu 611130, China
2
Forestry Research Institute of Ganzi Tibetan Autonomous Prefecture, Ganzi 626700, China
3
National Forestry and Grassland Administration Key Laboratory of Forest Resources Conservation and Ecological Safety on the Upper Reaches of the Yangtze River & Forestry Ecological Engineering in the Upper Reaches of the Yangtze River Key Laboratory of Sichuan Province, Chengdu 611130, China
*
Author to whom correspondence should be addressed.
Forests 2023, 14(6), 1229; https://doi.org/10.3390/f14061229
Submission received: 21 April 2023 / Revised: 8 June 2023 / Accepted: 12 June 2023 / Published: 14 June 2023
(This article belongs to the Special Issue Fire Ecology and Management in Forest)
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Versions Notes

Abstract

:
Southwestern China has a large area of artificial forests and has experienced massive environmental and social losses due to forest fires. Evaluating the flammability of fuels from dominated forests in this region can help assess the fire risk and predict potential fire behaviors in these forests, thus guiding forest fire management. However, such studies have been scarcely reported in this region. In this study, the flammability of litter from nine forest types, which are common in southwestern China, was evaluated by measuring organic matter content, ignition point, and calorific value. All these flammability characteristics of fuels varied significantly across forest types. By using principal component analysis and K-means clustering, litters were classified into three groups: highly susceptible to ignition with low fire intensity (Pinus densata, Pinus densata-Populus simonii, Pinus yunnanensis, Larix gmelini, Pinus armandii), less susceptible to ignition with high fire intensity (Abies fabri-Populus simonii), and median ignitibility and fire intensity (Abies fabri, Abies fabri-Picea asperata, Platycladus orientalis). Our study can help predict the risk and intensity of fires in the studied forests and serve as a source of information for fire management in southwestern China.

1. Introduction

Wildfire has become a global problem, although wildfire is a natural component of the earth system [1,2]. Due to climate change, land-use change and human activity, many places around the world have experienced, and are predicted to experience, more frequent and intense wildfires [3,4,5]. For example, the annual burned area in California, United States, increased fivefold during 1972–2018 [6]. In China, an average of 5688 forest fires occurred each year, with a burned area of burning 73,964 hectares (the data was calculated based on the information from 2000–2021, China Statistical Yearbook: http://www.stats.gov.cn/tjsj/ndsj/, accessed on 5 May 2023). The wildfire problem can cause devastating consequences for both human and natural systems. Frequent wildfires can have potentially catastrophic impacts on aquatic ecosystems, soil ecosystems, biodiversity, community infrastructure, and even public health [7,8]. Wildfires also can cause significant economic and social losses, creating heavy economic burdens for governments [9,10]. For example, in the United States, wildfire damage and management costs have increased dramatically in the last decade [11,12]. Therefore, better wildfire management and increased efforts are urgently required in many places around the world to minimize the negative effects of wildfires.
Wildfires are affected by many factors, including weather, topography, ignition resource and fuel. Fuel characteristics, including physical and chemical properties, play important roles in determining fire behaviors [13]. Therefore, scientific investigation of fuel characteristics and fuel treatment, such as reducing surface fuels, increasing the height of live tree crowns, decreasing crown density, and creating fuel breaks, are useful approaches to mitigate wildfires [14,15,16,17,18]. For example, Pinus pinaster plantations are highly susceptible to fires. Timely removal of litter and debris can effectively reduce the impact of fires on the ecosystem, including tree damage and mortality, and improve the efficiency of firefighting efforts while preserving the value of the timber [19].
In nature, plants, including live and dead plant materials, are the main fuel for wildfires [20,21]. The great variation in plant functional traits contributed to the variation in fuel characteristics across plant species. Previous studies have shown that fuel characteristics varied greatly across species and forest types, thus contributing to the fire behavior variation [22,23,24]. For example, flammability was found to vary greatly across plant species [25,26]. Zhang et al. [27] conducted a study analyzing the physicochemical properties of dead surface fuels under five typical forests in the Daxing’anling Mountains, Inner Mongolia. They investigated properties such as moisture content, crude fat content, ash content, ignition point, and calorific value. The researchers ranked the comprehensive flammability of dead surface fuels in different forest types and found significant variations in the flammability of litter among the different forest types. Curt et al. [28] studied the flammability of Quercus suber (corkoak) woodland and shrubland mosaics in Mediterranean fire-prone areas and found that the flammability of litters varies with vegetation types. The great variation in flammability characteristics of fuels contributed to the difference in fire behaviors across different forests.
There are three types of wildfires: ground fires, surface fires, and crown fires. Surface fire is the most common forest fire type, as litter is the most easily ignitable fuel in the wild and can reach really low moisture content due to weather effects [29,30,31,32]. Surface fires can become severe crown fires when litter loading is high and continuous “ladder fuels” exist [33,34]. Therefore, characterizing the flammability of litter fuels is significantly important for assessing wildfire risk and behavior, thus informing fire management [28]. However, the flammability characteristics of litter from different forest types have been scarcely studied, especially in southwestern China, where forest fire is a common occurrence.
Southwestern China has the second-largest forest area in China. However, due to its unique plateau, mountainous terrain, and diverse climate, this region is at high risk of wildfires [35]. Frequent wildfires not only destroy precious forest resources but also cause severe damage to the lives and property of people in forested areas [35,36]. Therefore, the evaluation of forest fuels in this region is urgently needed to guide forest fire prevention. However, the pyric properties of forest fuels in this region have not been adequately quantified. Here, we aim to investigate the flammability of litter of common forest types in southwestern China and predict the fire behaviours in these forests, thus providing information for fire management. In this study, we collected litter samples from nine common forest types in southwestern China. Ignition point, calorific value and organic matter content were measured to assess the flammability of the litters, as ignition point, calorific value and organic matter content are important parameters in the physicochemical properties of combustible materials. All these flammability characteristics of fuels varied significantly across forest types. We employed principal component analysis (PCA) and K-means clustering to categorize the litter into three groups. The results of this study will provide valuable information for predicting fire behaviours in these forests and developing effective fire management strategies to reduce the risk of forest fires.

2. Materials and Methods

2.1. Study Area

The study was carried out in the Ganzi prefecture, which is located in western Sichuan Province. The prefecture is situated in the upper reaches of the Yangtze River in southwestern China and is positioned on the eastern edge of the Qinghai–Tibet Plateau (Figure 1). Ganzi prefecture has a climate typical of the Qinghai–Tibet Plateau, with an average annual temperature of around 10 °C. The region receives strong sunlight and ample sunshine and has distinct dry and rainy seasons. The winters are cold and dry with abundant sunshine and low precipitation, while the summers are hot and rainy with an annual precipitation of 347–922 mm. Due to its climatic characteristics, forest fires are frequent in Ganzi Prefecture from October of each year to June of the following year [36]. The tree species in Ganzi Prefecture are rich, but in terms of their community-building roles in the forests, most of the dominant species in this region belong to Pinaceae, Cupressaceae, Fagaceae, Betulaceae, Salicaceae, and Juglandaceae.

2.2. Sample Collection

Our study was conducted in western Sichuan, where nine common artificial forest types were selected, including Pinus densata forest, Pinus yunnanensis forest, Abies fabri forest, Platycladus orientalis forest, Pinus armandii forest, Larix gmelini forest, Abies fabri-Populus simonii mixed forest, Abies fabri-Picea asperata mixed forest and Pinus densata-Populus simonii mixed forest. The composition ratio of the two species in mixed forests is approximately 1:1. Fresh litter was collected from the forest understory in April–May 2021. Each forest stand is set up with a standard plot of 20 m × 20 m. Three 1 m × 1 m subplots are set up along the diagonal, and all surface litter in each subplot was collected (Figure 1). Therefore, the total number of plots was nine, and the subplots sampled were 27. The altitude and GPS coordinates of each plot were recorded when collecting samples.

2.3. Flammability Characteristics Measurement

Calorific value refers to the heat released by the complete combustion of a unit mass of combustible material. A higher calorific value means that more heat can be released per unit mass of plant material [37]. The sample is dried to a constant weight in a 105 °C oven, crushed using a grinder, and then sieved through a 15-mesh (1.35 mm) screen. The calorific value was measured using the water equivalent method of a calorimeter. Accurately weigh the combustible sample to 0.500 ± 0.001 g into the combustion dish and measure using a microcomputer automatic calorimeter (ZDHW-9, Jiangsu Tianyuan Testing Equipment Co., Ltd., Yangzhou City, China) for three repeated measurements of each sample.
The ignition point is the temperature of the combustible material when it catches fire. The sample is dried to a constant weight in a 105 °C oven, crushed using a grinder, and then sieved through 40-mesh (0.45 mm) screens. Before the test, the combustible sample and sodium nitrite were placed in an oven in advance to ensure absolute dryness during the measurement. An accurately weighed dry combustible sample of 0.1 ± 0.001 g was taken and mixed thoroughly with 0.075 ± 0.001 g of sodium nitrite powder. The ignition temperature of each sample was measured three times using an ignition temperature tester (TYRD-6A, Jiangsu Tianyuan Testing Equipment Co., Ltd., Yangzhou City, China).
Organic matter, which includes carbohydrates, fats, and proteins found in plants, plays a crucial role in fire behavior as it can significantly influence the spread of fire and is positively correlated with flammability [38]. The dry ashing method is used to indirectly calculate the organic matter content by measuring the ash content. One gram of pulverized sample is separately weighed and placed into a crucible, which is then carbonized in an electric furnace until the sample stops smoking. After cooling the carbonized sample together with the crucible, it is subjected to ashing in a muffle furnace at around 650 °C for about 4 h. After cooling for 30 min, the residue was weighed and calculated as
Organic matter content = 1 − ash mass/(total oven-dried mass) × 100%

2.4. Data Analysis

The variation of flammability characteristics across forest types was analyzed by using the least significant difference (LSD) multiple comparison method. Differences are considered significant at the α = 0.05 level. The correlation across the three flammability characteristics was analyzed by using Pearson correlation coefficients. Principal component analysis (PCA) was conducted by using Origin2021. The K-means clustering algorithm was used to classify the flammability types according to the flammability characteristics and was performed in R 4.1.1 by using the R package cluster 2.1.2. The range normalization method was used in this article to calculate the comprehensive combustibility ranking of each forest type. This calculation was based on the weighted contribution of variances corresponding to each principal component [39]. All statistical analysis and plotting were performed by using R 4.1.1 (R Foundation for Statistical Computing, Vienna, Austria) and Origin2021 (Origin Lab Corporation, Northampton, MA, USA).

3. Results

3.1. The Flammability Characteristics of Litter Varied Significant across Forest Types

Litters were collected from nine forest types. Ignition point, organic matter content, and calorific value varied significantly across the litters collected from the nine forest types (Table 1). The ignition point of litters ranged from 263.94 to 271.65 °C, with a mean value of 266.45 °C. Litter from Abies fabri-Populus simonii forest has the highest ignition point (271.65 °C), followed by Platycladus orientalis forest type. The organic matter content of the litter ranged from 78.18% to 95.87%, with a mean value of 90.30%. The litter of Abies fabri-Populus simonii forest exhibited the highest organic matter content. Conversely, the Platycladus orientalis forest type displayed the lowest organic matter content among all forest types. The gross calorific value (GCV) of each forest type exhibited a range of 21.09 to 23.27 KJ·kg−1, with a mean value of 21.74 KJ·kg−1. Notably, the Abies fabri-Populus simonii forest type displayed the highest calorific value, while the Pinus armandii forest type exhibited the lowest calorific value.

3.2. Evaluation of the Flammability of Litters from the Nine Forest Types

Ignition point, organic matter content, and calorific value were not related significantly to each other (Table 2). In order to evaluate the flammability variation of litter comprehensively based on the three flammability characteristics, PCA was conducted with the three flammability characteristics. The first two axes of the principal component analysis explained 62.76% and 29.43% of the variation, respectively (Figure 2).
By using the K-means clustering algorithm based on the values of PC 1 and PC 2, the litters were classified into three groups (Table 3). According to the values of the three flammability characteristics of each group, we have ranked the combustibility of nine forest types and classified them into three groups: highly susceptible to ignition with low fire intensity (Pinus densata, Pinus densata-Populus simonii, Pinus yunnanensis, Larix gmelini, Pinus armandii), less susceptible to ignition with high fire intensity (Abies fabri-Populus simonii), and median ignitibility and fire intensity (Abies fabri, Abies fabri-Picea asperata, Platycladus orientalis).

4. Discussion

Litter is the most susceptible fuel to ignition in the wild and provides the main fuel for surface fires. Evaluation of the flammability characteristics of litter is very important for assessing wildfire risk and behavior, thus informing fire management. However, many previous studies focused on the flammability of plant issues, such as foliage and branches [40,41]. Investigations on the flammability characteristics of litter across different forest types have been scarcely reported. We employed two different evaluation methods, namely K-means clustering and normalization method, to assess the research subjects, aiming to gain a better understanding of their flammability differences. However, the ranking can only reflect the overall flammability of each forest type, while grouping can provide a clearer view of the burning characteristics of different forest types, which is more meaningful for specific fire prevention and control measures. Our results classified the litter into three groups: highly susceptible to ignition with low fire intensity, less susceptible to ignition with high fire intensity and median ignitibility and fire intensity. The vegetation type known as “highly susceptible to ignition with low fire intensity” refers to vegetation that can quickly ignite with relatively low heat input, but its burning intensity is relatively low. On the other hand, the vegetation type “less susceptible to ignition with high fire intensity” has a higher ignition temperature but releases high levels of heat and energy during combustion. This characteristic leads to rapid fire spread and increased burning intensity. The vegetation type “median ignitibility & fire intensity” requires a moderate amount of heat to ignite. While the fire spread rate is not as rapid as highly flammable vegetation, it still poses a significant fire risk. Our study can help predict the risk and intensity of fires in studied forests and serve as a source of information for fire management in southwestern China. For example, for high fire intensity forest types (Abies fabri-Populus simonii), establishing firebreaks of appropriate width, timely removal of dead branches and leaf piles from the ground, paying attention to pruning branches at high points, changing the spatial distribution structure of combustible materials and reducing the gradient of combustible materials in the vertical direction can effectively reduce fire risk and fire intensity [42]. For forest types that are highly susceptible to ignition (Larix gmelina, Pinus armandii, Pinus densata, Pinus densata-Populus simonii, Pinus yunnanensis), it is important to strengthen monitoring of wildfires, prevent human-caused fires, and pay attention to weather conditions. Irrigation management also can be implemented to maintain the humidity of the plants and prevent drought conditions, thus, forest types [43].
Moisture content and loading of litter are also important parameters in evaluating fuel characteristics [44,45]. For example, fuel moisture conditions showed a significant influence on patterns of fuel consumption [46]. When the moisture content is low, the flame tends to exhibit vertical propagation because the dry, dead leaves and bark can burn quickly. When the water content is high, the flame will show horizontal propagation characteristics because the moisture absorbs part of the heat so that the flame can not spread upward quickly [43]. Fuel loading also affects fire behaviors. For example, excessive fuel loading can lead to greater surface fire intensity and increase the likelihood of crown fires [47]. However, moisture content and loading of litter varied greatly with weather and stand density [48]. Our aim of this study was to evaluate the inherent flammability traits of litter from different forests. Therefore, only three main physicochemical traits, namely organic matter content, calorific value and ignition point, were selected in this study, as the physicochemical properties are stable with varying weather and stand density and largely determined by plant species. The oil content, lignin content and cellulose content are also important characteristics of fuel. For example, fuels with high oil content, such as pine needles, tend to have higher flammability. In future research, these metrics can be measured to better assess the differences in combustion characteristics of litter between different forests.
Wildfires have become increasingly frequent and severe in many parts of the world, causing significant ecological, economic and social impacts. In southwestern China, wildfires are particularly common and have become a problem threatening society and ecosystems. Coniferous forests accounted for a large percentage of forests, both in the wild and in plantations, and a majority of forest fires occurred in coniferous forests [49,50]. Coniferous forests usually have high fire risk due to a number of factors, including the high flammability of conifer needles, high resin content, the presence of dead wood in conifer forests and simple stand composition [51,52]. For example, the Camp Fire in Paradise, California, in 2018 was a large wildfire that broke out in the coniferous forests in northern California, leading to 85 deaths, over 1000 missing persons and the destruction of 18,000 structures, with a total area of about 620 square kilometers. The high flammability of these plants, combined with the dry and hot climate conditions, led to the rapid spread and severe damage of the fire, making it one of the deadliest wildfires in California’s history [53]. Therefore, the high fire risk and wide distribution of coniferous forests suggested that investigating the flammability characteristics of fuels in these forests was highly important. A study conducted a mesocosm experiment with 39 widely distributed gymnosperms of diverse genetic lineages, which demonstrated that the majority of gymnosperms are highly flammable. Surprisingly, some needle-leaved species previously considered highly flammable were found to be the least flammable in litter fuel beds, highlighting the influence of species-specific litter traits on surface fire regimes [54]. In our study, all the species tested were conifers and planted widely not only in southwestern China but also in many places around the world. For example, Abies fabri and Platycladus orientalis were planted widely around the world to produce timber. Our data can provide useful information for other areas as well, as the physicochemical traits we tested is unlikely affected by environmental factors.
Fire management will be increasingly challenged by the frequent occurrence of large fires in the future due to climate and land use changes [55]. More investigation on the flammability of fuels and more efforts in fuel management are urgently needed. Previous studies usually measure the flammability characteristics of fuels and rank fuels from highly flammable to low flammable based on their flammability characteristics. For example, Wang et al. [41] measured moisture content, calorific value, extractives content, and ash content of fresh leaves from 12 species of garden trees in Kunming and ranked the flammability of different species based on their results. But fuel flammability involves multiple aspects. Generally, the flammability of fuels has four components: ignitability (ease of ignition), combustibility (the speed or intensity at which fuel burns), sustainability (the length of burning time) and consumability (proportion of biomass combusted) [56,57]. Simply ranking fuels from high flammability to low flammability can not reflect the real burning conditions of fuels. For example, grasses are easily ignited and spread rapidly but burn at a low temperature and with low intensity. Woody plants are difficult to ignite, but once ignited, they will burn with high fire intensity [58]. Here, we divide nine common vegetation types in the western Sichuan region into three groups based on their flammability characteristics of litter and suggested fire prevention measures for different groups. Our study is useful for evaluating fire hazards caused by different forests’ litter and can provide a reference basis for future fire prevention.
The physical and chemical properties of vegetation tested in the laboratory are relatively stable. The pro of this approach is that they are less influenced by environmental factors and experimental errors. This enables us to obtain objective and reliable data that can be replicated and compared. Laboratory tests of fuel traits do not fully reflect the actual conditions of field combustion [13]. Many traits, including chemical and physical characteristics, and their interactions affect fuel flammability. Recently, the burning experiment has been used by many researchers to test the flammability of fuels. The burning experiment is a good approach to measure flammability, as it can directly reflect fire behaviors. For example, Wyse et al. [25] demonstrated that burning tests could reflect how plants burn in real fires. Varner et al. [59] conducted burning experiments for litter from five co-occurring species and evaluated potential shifts in flammability after tanoak was replaced with different species. However, this method primarily reflects the burning conditions of plants when exposed to crown fires. Currently, there is no standardized method for accurately determining the actual flammability of plants. In future studies, burning experiments and traits measurement can be used collaboratively to better evaluate the flammability of fuels. However, it is important to note that fire risk and fire behaviors are also affected by other factors, such as weather and terrain. For example, strong winds and steep slopes can increase the spread speed of fire. Therefore, all these factors should be taken into consideration in order to better manage wildfires and mitigate their impacts in our more fire-prone world.

5. Conclusions

Many places around the world are predicted will experience more wildfires due to climate and land use changes. Investigations into the flammability characteristics of fuels can facilitate forest fire management. Our study evaluates the flammability characteristic of litter from nine different artificial forests in this region. We hope our study can help predict the risk and intensity of fires in the studied forests and serve as a source of information for fire management. Our data can also provide useful information for other areas, as the physicochemical traits we tested are unlikely affected by environmental factors. In future research, burning experiments and characteristic measurements can be used in conjunction to better assess fuel flammability.

Author Contributions

This idea was developed by X.C., S.L. and X.C. led the writing of the manuscript, with input from all co-authors. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by by the National Natural Science Foundation of China (grant number 32101532), Natural Science Foundation of Sichuan Province (grant number 2023NSFSC1278), Postdoctoral Science Foundation of China (No. 2122999010).

Data Availability Statement

Data presented in this study are available from the authors upon request.

Conflicts of Interest

The authors declare that they have no conflict of interest.

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Forests 14 01229 g001 550
Figure 1. Study area and sample plots set-up. Red circles indicate the collection sites, and the left box represents the sample plot.
Figure 1. Study area and sample plots set-up. Red circles indicate the collection sites, and the left box represents the sample plot.
Forests 14 01229 g001
Forests 14 01229 g002 550
Figure 2. Principal components analysis (PCA) of flammability characteristics. In the analysis, the negative values of ignition point for each forest type are used to present ignitibility, and the higher the value of ignitibility, the easier it is to be ignited. Dots represent forest types, and color of dots represents different groups based on k-clustering.
Figure 2. Principal components analysis (PCA) of flammability characteristics. In the analysis, the negative values of ignition point for each forest type are used to present ignitibility, and the higher the value of ignitibility, the easier it is to be ignited. Dots represent forest types, and color of dots represents different groups based on k-clustering.
Forests 14 01229 g002
Table
Table 1. Flammability characteristics of litter varied significantly across different forest types. The values in the table are presented as mean ± SE. Different lower-case letters across the same physical and chemical traits indicate significant differences (p < 0.05).
Table 1. Flammability characteristics of litter varied significantly across different forest types. The values in the table are presented as mean ± SE. Different lower-case letters across the same physical and chemical traits indicate significant differences (p < 0.05).
Forest TypeLocationIgnition PointOrganic Matter ContentCalorific Value
(°C)(%)(KJ·kg−1)
Abies fabri101.4711° E, 31.2967° N266.86 ± 1.02 b95.79 ± 1.02 a21.82 ± 0.50 ab
Abies fabri-Picea asperata99.4237° E, 30.2610° N266.47 ± 0.88 b91.31 ± 2.04 abc21.10 ± 0.05 b
Abies fabri-Populus simonii101.0231° E, 30.7741° N271.65 ± 3.09 a95.87 ± 0.47 a23.27 ± 0.75 a
Larix gmelini99.8472° E, 28.6820° N263.94 ± 1.18 b86.82 ± 4.62 bc21.38 ± 0.48 b
Pinus armandii101.8556° E, 30.9240° N265.79 ± 0.88 b86.22 ± 2.03 c21.09 ± 1.27 b
Pinus densata102.0771° E, 30.5617° N264.69 ± 0.70 b93.35 ± 2.10 ab22.43 ± 0.23 ab
Pinus densata-Populus simonii99.6015° E, 29.1319° N264.97 ± 1.49 b92.47 ± 1.01 abc21.85 ± 0.37 ab
Pinus yunnanensis101.8244° E, 28.5245° N265.62 ± 2.04 b92.68 ± 2.47 abc21.45 ± 0.21 b
Platycladus orientalis101.8334° E, 30.8963° N268.08 ± 1.64 ab78.18 ± 2.63 d21.27 ± 0.35 b
Table
Table 2. Pearson’s correlation coefficient among the three flammability characteristics.
Table 2. Pearson’s correlation coefficient among the three flammability characteristics.
Ignition PointOrganic Matter ContentCalorific Value
(°C)(%)(KJ·Kg−1)
Ignition point
(°C)		Pearson’s1
p value-
Organic matter content (%)Pearson’s−0.121
p value0.76-
calorific value
(KJ·Kg−1)		Pearson’s−0.560.601
p value0.120.09-
Table
Table 3. The values of PC1 and PC2 for each forest type, along with their classifications based on K-means clustering and flammability rankings.
Table 3. The values of PC1 and PC2 for each forest type, along with their classifications based on K-means clustering and flammability rankings.
Forest TypePC 1PC 2GroupFlammability Ranking
Pinus densata0.410.10Highly susceptible to ignition with low fire intensity1
Abies fabri0.490.57Median ignitibility and fire intensity2
Abies fabri-Populus simonii2.27−1.02Less susceptible to ignition with high fire intensity3
Pinus densata-Populus simonii−0.010.78Highly susceptible to ignition with low fire intensity4
Pinus yunnanensis−0.170.58Highly susceptible to ignition with low fire intensity5
Abies fabri-Picea asperata−0.370.11Median ignitibility and fire intensity6
Larix gmelini−0.890.40Highly susceptible to ignition with low fire intensity7
Pinus armandii−0.83−0.31Highly susceptible to ignition with low fire intensity8
Platycladus orientalis−0.90−2.11Median ignitibility and fire intensity9
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Li, S.; Zhang, Z.; Zheng, J.; Hou, G.; Liu, H.; Cui, X. Evaluation of Litter Flammability from Dominated Artificial Forests in Southwestern China. Forests 2023, 14, 1229. https://doi.org/10.3390/f14061229

AMA Style

Li S, Zhang Z, Zheng J, Hou G, Liu H, Cui X. Evaluation of Litter Flammability from Dominated Artificial Forests in Southwestern China. Forests. 2023; 14(6):1229. https://doi.org/10.3390/f14061229

Chicago/Turabian Style

Li, Shuting, Zihan Zhang, Jiangkun Zheng, Guirong Hou, Han Liu, and Xinglei Cui. 2023. "Evaluation of Litter Flammability from Dominated Artificial Forests in Southwestern China" Forests 14, no. 6: 1229. https://doi.org/10.3390/f14061229

APA Style

Li, S., Zhang, Z., Zheng, J., Hou, G., Liu, H., & Cui, X. (2023). Evaluation of Litter Flammability from Dominated Artificial Forests in Southwestern China. Forests, 14(6), 1229. https://doi.org/10.3390/f14061229

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