Bonn Political Protocol and Malagasy Protocol reckoned that developed countries could counteract some portion of greenhouse gas emission through implementing the project of forestry carbon-sink.It symbolized the confirmation of ecological functions of forest in economy through out the world.Consequently, the compensation of ecological beneficial forest has been a focus in its research in recent years (Qi, 2004).Most studies on the compensation reported in China applied the traditional methods of economic analysis such as expense-input and compensation for equal loss (Xie, 2000;Zhou et al., 2000;Song et al., 2001; Xu et al., 2004), which could hardly evaluate the actual value of the ecological benefit of forest (Song et al., 2001).Emergy Synthesis, founded by Odum(1988), can compare and analyze various ecosystem energies by transforming different energies into the emergy.This method has since been proved to be appropriate in evaluating the real value of natural resources and service functions of ecosystem (Lan et al., 2001).Emergy synthesis was applied in this paper to study the ecological benefits and compensation rate for the ecological beneficial forest in Guangdong Province, so as to draw other further researches.

1 Research area and methods 1.1 Research area

Guangdong Province lies within 20°13′-25°31′N and 109°39′-117°19′E.Its terrestrial area is 18 million km².The area of ecological beneficial forest is 3.45×10⁶ hm², of which 47.6% is broad leaved forest, and mixed conifer and broad leaved forest and 53.3% is conifer forest.The hypsography becomes lower from north to south and mountains, plains and hills all appear in the province.The climate is subtropical monsoon with long summer and warm winter.Rainfall is abundant with a mean annual rainfall of 1 500~2 000 mm.The annual average temperature is 19~23 ℃ and the mean annual irradiance is 1 750~2 200 hours.

1.2 Research methods

With the object of the ecological beneficial forest in Guangdong Province, the input and output data of material and energy in 2002 were collected by referring to annals.The data of human input (feedback of capital)were obtained by peasant inquiry. Five representative locations were selected to inquire human input and study the ecological benefit and photosynthesis reaction. Five locations were respectively on north, middle, south, east and west of Guangdong Province such as Renhua County, Sanshui County, Shenzhen, Meizhou County and Gaozhou County.We inquired 100 peasants in every location.The average of all ecological beneficial forest in Guangdong Province was calculated based on the inquiry.The ecological benefit and the compensation rate for the ecological beneficial forestwere studied through Emergy Synthesis of ecosystem (Shu et al., 2000; Lan et al., 2002), combined with the reaction mechanism of photosynthesis (Pan et al., 1995).

2 Result and analysis 2.1 Emergy input analysis

The total emergy flow of the ecological beneficial forest in Guangdong Province was estimated at 5.69 ×1021 sej (sej, i.e., solar emjoule), including environmental input energy and capital feedback (human input).The environmental input energy, which consists of renewable and nonrenewable resource, was 5.52 ×1021 sej, accounting for 97.1%of the total emergy, and the human input was 1.67×1020 sej, or 2.9%of the total emergy (Tab. 1).

Rain chemical energy was the main environmental renewable resource, whose emergy input in the system was related mostly to the mean annual rainfall and the area of ecological beneficial forest in Guangdong Province.The amount of emergy input of rain chemical energy would not change much if the climate did not appear the worst situation, e.g., drought, waterlog.Therefore, the environmental renewable resource of ecological beneficial forest system could be considered as a constant.The environmental nonrenewable resource was the depletion of forest soils, which only took 0.02% of total emergy input, and could be ignored. The ecological beneficial forest not only depleted less soil, but also could fix up nutrition, reserve water and soil.

The capital feedback (human capital investment)accounted for little proportion of total input emergy, i.e.2.9%, so the ecological beneficial forest was mainly depended on environmental input to make contribution to human being by absorbing CO₂ and releasing O₂ with sunlight energy.

3.2 Emergy output analysis

The total annual emergy output of the ecological beneficial forest in Guangdong Province was 0.337 billion ＄(Tab. 1). The materiality output, i.e., lumber weight 1.7×10⁷ t, and its emergy value took 15.4% of total output.The immateriality output, i.e.the ecological benefit of ecological beneficial forest, included fixation of CO₂, release of O₂, groundwater reservation, pollution reduction, water and soil reservation and dirt fixation and so on.This paper computed the benefit emergy of the six ecological functions.The existing ecological beneficial forest in Guangdong Province could fix 41.4 billion t of CO₂, release 30.3 billion t of O₂, reserve 0.711 billion t of groundwater and 65.5 billion t of water and soil, absorb 0.643 billion t of SO₂, and fix 29.4 billion t of dirt.The output emergy value of ecological benefit was 0.285 billion,＄or 84.6% of total output, and was more five times than the output emergy value of the materiality.

3.3 Emergy indices analysis 3.3.1 Emergy investment ratio (EIR)

EIR is the ratio of the feedback emergy from the human economic system to the input emergy of natural environment system (Lu et al., 2003).The former, for example, artificial forestation, cultivation and regeneration and so on, is called "Purchased emergy" for need of capital input.The latter is called "Free emergy" because it come from free input of nature, which includes renewable (sunlight, rain and so on) and nonrenewable resource (soil)(Lan et al., 2002).EIR can evaluate the degree of development in economy and the loading capacity of environment.The larger value of EIR, is the higher degree of economy development.On the other hand, the smaller value of EIR shows the lower economy development level and also indicates that the system is more depended on environment (Odum, 1996).

EIR of ecological beneficial forest in Guangdong Province was 1.84×10^-2 in 2002 (Tab. 2), which is much smaller than the average value, i.e., 2, in the world (Lan et al., 2002).It showed that the economy development of ecological beneficial forest was still on rather low level in Guangdong Province.The environment resource had not been utilized well and could not achieve good benefit consequently.Therefore, the compensation for the ecological beneficial forest should be increased in order to improve development of the ecological beneficial forest and utilize the environmental resource effectively.

3.3.2 Environmental loading ratio (ELR)

ELR is the ratio of all nonrenewable emergy input to all renewable emergy input (Lu et al., 2003).In this paper all nonrenewable emergy meant the "Purchased emergy" and the emergy of nonrenewable resource depleted by system (soil), and all renewable emergy meant the emergy of free renewable resource(sunlight, rain and so on).ELR reflected the pressure of natural environment received from the forest system.

ELR of the ecological beneficial forest in Guangdong Province was 1.85×10^-2, which is much smaller than the average of the world, i.e., 1.15 (Odum, 1995)(Tab. 2).However, the exploitation and planting of ecological beneficial forest will not only give little pressure to environment, but also improve its quality.It should emphasize the importance of ecological beneficial forest planting, fulfill the compensation for ecological beneficial forest so as to enhance ardor for ecological beneficial forest exploitation and planting and accelerate environment improvement.

4 Discussion and conclusion

The essential of compensation for ecological beneficial forest is to make a price for ecological products and services.The compensation rate should be established in term of total output.Table 1 showed that the compensation fee was 0.337 billion ＄ and contributing to 0.24% of GNP of 2002 in Guangdong Province which was 1.41×10¹¹ ＄.However, because of uncomplete availability of statistic data, the paper only took into account six ecological functions and ignored others, such as biodiversity conservation, entertainment provided by natural environment, esthetics, society science, education, spirit, culture.Therefore, it was the lowest compensation rate of ecological beneficial forest, equaled to 99 ＄·hm^-2a^-1.

At present, the highest compensation rate for ecological beneficial forest, is 23.6 ＄·hm^-2 a^-1 of Guangzhou City (Zhang et al., 2004).However, this highest compensation only takes 23.8% of total output emergy of ecological beneficial forest per hm².If the compensation rate is not increased, the enthusiasm for ecological beneficial forest planting will be depressed, and the development of ecological beneficial forest will be hampered.

Because of the region difference of ecological beneficial forest distributing, the expenditures of earth exploitation, ecological beneficial forest management and fireproofing were rather different, and had not been computed in the benefit analysis in this paper.In fact, these expenditures were necessary payout for the ecological beneficial forest operators and were usually from ecological beneficial forest earnings by selling lumber.Therefore, the compensation fee should consist of the expenditures of management, protection and fireproofing in different regions.The average of these expenditures was 37 ＄·hm^-2a^-1 in terms of average earnings per person in Guangdong Province which is 500 ＄·hm^-2a^-1.To sum up, the compensation rate should be 136 ＄·hm^-2a^-1.

According to this criterion, the total compensation rate of ecological beneficial forest in Guangdong Province is 0.408 billion ＄·a^-1 or 0.33% of total GNP in Guangdong Province in 2002 (1.41×10¹¹ ＄).Therefore, the compensation rate will be reasonable and feasible.