0428-B1

Direct Carbon Emissions from Chinese Forest Fires, 1991-2000

Tian Xiaorui^[1], Shu Lifu, Yang Xiaohui and Wang Mingyu

Abstract

Many studies have indicated that the products of biosphere burning have short and long-term effects on the atmosphere. Vegetation burning can produce some gases that have a significant influence on environment, including some greenhouse gases, like CO₂ and CH₄ etc. Smoke aerosols produced from burning also influence global climate and atmospheric chemistry.

The paper calculates the consumed biomass due to forest fires according to the statistics of forest fires from 1991 to 2000 and research results of biomass of Chinese forests. During the study period, forest fires burned an average of 5~7 Gt biomass each year and directly emitted 20.24~28.56 Gt carbon. In 1991-2000, average emission of carbon dioxide and CH₄ account for 2.7~3.9% and 3.3~4.7% of the total emission of China (calculating with the data of 2000) respectively.

The recent researches show that the emissions from biomass burning have short and long-term effects on atmosphere. Biomass burning is the burning of the world’s vegetation, including forests, savannas, and agricultural lands, for land clearing and land-use change. Forest fire is the most important part. The immediate effect of burning is the production and release into atmosphere of gases and particulates resulting from the combustion of biomass matter (Joel et al. 2000). The instantaneous combustion products of vegetation burning include CO₂, CO, CH₄, nonmethane hydrocarbon (NMHC), nitric oxide (NO), and methyl chloride (CH₃Cl). Even if the forest ecosystem can recover or be re-established after burning, the vegetation through photosynthesis will only absorb carbon dioxide, the other emissions cannot be reabsorbed into biosphere. Longer-term effects of biomass burning include enhanced biogenic soil emissions of NO and N₂O following burning. Some emissions including greenhouse gases such as carbon dioxide and methane have significant influences on global change (Eric et al. 2000). Biomass burning is also an important global source of atmosphere bromine in the form of methyl bromine (Mano and Andreae 1994). In addition to gaseous emissions from biomass burning, smoke aerosols also influence globe climate and atmosphere chemistry (Radke et al. 1991). Smoke can arouse regional environment pollution (Radke et al. 1991; Ward et al. 1991; Lenoble 1991). It makes the respiratory diseases of local people and affects transportation and tourism industries. The 1997-1998 fires in Indonesia absorbed the attention of the world due to its serious air pollution (UNEP 1999). Some projects were conducted to study the fire impacts on environment (Awang et al. 2000; Goldmmer 2000). China also developed some projects for the forest effects on carbon cycle (Jingyun 2001; David et al. 2001). Some attempts were made to evaluate the greenhouse gases emissions from forest burning (Wang Xiaoke et al. 2001). To date, interaction between fire and climate change is becoming a main topic of fire research (Levine 1991; Crutzen and Goldmmer 1993; Goldmmer and Furyaev 1996; Levine 1996; Van Wilgen et al. 1997). The goal of the paper is to calculate the direct C emissions from forest fires according to forest fire statistics and its biomass research results, which will be helpful to better understand the forest fire effects on global change and make a suitable forest fire management strategy.

1 Data and methods

1.1 Data

Statistics data of annual forest fires were gotten from State Forestry Administration and aboveground biomass data come from more than sixty typical forest communities’ investigation and 1989-1993 national forest resources survey results.

1.2 Methods

The gaseous emissions from forest fires can be calculated from consumed biomass. First, the consumed biomass can be calculated using the following equation (Seiler and Crutzen, 1980):

M=A×B×E (1)

Where M = total mass of forest consumed by burning (tons), A = burned areas (ha), B = biomass loading (t/ha), and E = burning efficiency.

Assuming carbon accounts for 45 percent of the mass of the forests and 90 percent of the carbon is released in the form of CO₂ (Andreae 1991), then the mass of CO₂ released to the atmosphere is:

M(co₂)=0.9×0.45×M (2)

Once the mass of CO₂ produced by burning is known, the mass of any other species, X_i(M(x_i)) can be calculated with the knowledge of the CO₂-normalized species emission ratio (ER(x_i)). The emission ratio is the ratio of the production of species X_i to the production of CO₂ in the fire.

M(x_i)=ER(x_i)×M(co₂) (3)

X_i=CO, CH4, NOx, NMHC, NH3

2 Results and discussion

2.1 Consumed biomass by forest fires

Table 1 shows the burning areas during 1990-2000 in China. Because the forest fires statistic were undertaken by provinces, some data will be added together according to the biome for the consumed biomass calculation. Tibet autonomous region characterized by large area of natural forests and higher biomass loading is calculated by itself. At present, there are few research papers about the biomass in Tibet autonomous region and no paper about the average biomass loading in the region. We can know the average forest stocking (311m³/ha) from the state forest investigation results (Li Yucai 1997). The forest stocking (V) and biomass loading (B) have the relationship as the following expression: B = aV+b, where a and b are coefficients respectively. Here we adopt the formula B = 0.52V (Fang Qignyun et al. 1996) to calculate the average biomass loading in Tibet autonomous region (162t/ha). The aboveground biomass is 75% of the total biomass (Xu Deying et al. 1997). Finally, we can calculate the average aboveground biomass loading in Tibet autonomous region (121 t/ha).

Table 1 Burned Areas by Classes Used in the Calculation (1991-2000) (ha)

Table 2 The Average Aboveground Vegetation Combustibles in Different Biome in China

(Liu Shirong 1997) (dry matter, tons · ha^-1)

*Calculated from the state forest investigation results.

Table 2 shows the average aboveground biomass in different biome in China. Although there is a little change on the total forest area and average biomass loading in China during 1991-2000, As far as the whole country is concerned, the variation can be ignored. We can use research results of the average biomass investigated in 1995-1996. Using the expression (1), we can calculate the consumed biomass from burned area, average aboveground biomass loading and burning efficiency. Table 3 and table 4 show the burning efficiency in different vegetational zones and the consumed biomass in China during 1991-2000 respectively. Because the burning efficiency changes with the forest fire type and forest characteristics, table 3 just gives the estimation range. At present, there are few documents or literature on biomass burning in China. We will calculate the consumed biomass with the burning efficiency in references to existing literature (Joel S.L. et al., 2000; Aulair et al. 1993). The results show that the consumed biomass by forest burning is, mainly in cool temperate zone, average 3.19 ~4.79Tg(1 Tg =1,000,000 tons), which accounts for 63.8~67.9% of the total. During 1991-2000, China have consumed about 49.97Tg ~70.51Tg aboveground biomass by forest fires, average 5~7Tg aboveground biomass per year.

Table 3 Burning Efficiency in Different Vegetational Zones

Table 4 Consumed Biomass by Forest Fires in China, 1991-2000 (Tg)

Table 5 Emission Ratios Normalized with CO₂ (Laursen et al. 1992; Yokelson et al. 1997)

*Total particulate matter (TMP) emission ratios are in units of tons/kiloton. (tons of total particulate matter / kiloton of biomass consumed by fire)

Table 6 The direct emissions from forest fires in China, 1991-2000 (Tg)

2.2 Calculation of the burning emissions from forest fires

We can calculate the consumed carbon by forest burning with the equation (1). 90% of the total carbon sends in form of carbon dioxide. So we can know the carbon amount in the carbon dioxide emitted directly from forest burning.

The total carbon in the direct emissions by forest burning in China during 1991-2000 is 20.24~28.56Tg, CO₂ 74.2~104.7 Tg, CH₄ 1.797~2.536 Tg, NMHC 0.856~1.208 Tg and smoke particulate 0.999~1.410 Tg. In 2000, China emitted total carbon dioxide 2690 Tg (David et al. 2001). The average carbon dioxide emitted from forest burning in 1991-2000 accounts for 2.7~3.9% of the total amount of China (calculating with the emission amount in 2000). The amount of CH₄ emitted from forest fires accounts for 3.3~4.7% of the total emission in China (5.45Tg in 2000, David et al. 2001).

The rate of soil respiration and decomposition will increase after the fire. The remainder will decompose gradually. Forest productivity decrease and it will recover in 20-30 years. We just estimate the direct emissions from forest fires. Many models estimate that the direct carbon emission is just a half of the total carbon loss by forest burning (Auclair and Carter 1993; Dixon and Krankina 1993; Kasischke et al. 1995; Kurz and Apps 1999). So it can be estimated that the average carbon dioxide emission by forest burning is about 148~209 Tg each year, which accounts for 5.4~7.8% of the total CO₂ (in 2000).

China has confirmed to sign the Kyoto Protocol in 2002. In future, all the member countries will limit their carbon emission. If we do well on fire management and most forest fires can be controlled, the carbon emission from forest fires will reducewhich will benefit the industry development and prompt the economy development.

3 Conclusion

3.1 Consumed biomass from forest fires

During 1991-2000, China have consumed about 49.97Tg ~70.51Tg aboveground biomass by forest fires, average 5~7Tg aboveground biomass per year. 63.8~67.9% of the total is burned in cool temperate forests, average 3.19 ~4.79Tg per year.

3.2 Emissions from forest fires

During 1991-2000, forest burning in China products emissions 20.24~28.56Tg C. It is estimated that the emissions include CO₂ 74.2~104.7 Tg, CH₄ 1.797~2.536 Tg, NMHC 0.856~1.208 Tg and smoke particulate 0.999~1.410 Tg. The average carbon dioxide emitted from forest burning in 1991-2000 accounts for 2.7~3.9% of the total amount of China (calculating with the emission amount in 2000). The amount of CH₄ emitted from forest fires accounts for 3.3~4.7% of the total emission in China (5.45Tg in 2000, David et al. 2001).

3.3 The main factors affects emissions from forest burning

The amount of biomass burning emissions has close relationship with the fire severity. Although the Chinese fire management has developed continuously and the ability of control big fires rose, the total burned area has not decreased obviously. Considered the present control ability of the fire agency, the people can just prevent some areas with communities and property. They cannot control the conflagration in natural forests. The burned area and fire severity is mainly depended on the fuel and weather conditions.

3.4 The tendency of fire occurrence in China

At present, China adopts the policy of attacking all forest fires. Although the forest fire is controlled in some degree, in the long term it will bring a problem with the increasing fuel loading and forest areas. The forest will be easy to catch a high intensity fire and difficult to be controlled. Since the 1980s, China has paid attention to environment protection. The forest area enlarges continuously. Now with the six-forestry projects implementation, the forestry gets developing greatly and the fire prevention will be becoming urgent. It is obvious that the globe will be getting warm and many models forecast that in the future the globe will be warmer, especially in the northern hemisphere. The days with abnormal weather condition will increase, which will make the forest fire serious (IPCC 1998). Forest fires have influence on globe change and globe carbon cycle. Fire brings the change of vegetation; in return, the change of vegetation affects the fire regime. In order to make a rational fire management policy for the future, much more studies are needed on forest fire occurrence mechanism.

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