Assessment of human impact on
Co2 fixation due to vegetation change Y. Honda, S.
Murai Institute of Industrial Science, University of Tokyo 7-22-1 Roppongi, Minato-Ku, Tokyo 106, Japan S. Goto Kanazawa Institute of Technology, Japan Abstract World population has doubled in the past 40 years. It is now 5.3 billion. It is estimated to double again in the next 50 years, reaching 10 billion. The impact on the global environment by human economic activities is stronger than the population increase. The human economic activities produce Co2 ( green house effect gas). Therefore it is necessary to assess of human impact based on Co2 fixation change. In this study, the authors estimated Co2 fixation change due to human activities on the earth. Inroduction Assessment of human activities in the geosphere and biosphere is one of the most important problems in environmental sciences. Vegetation changes arise from human activities. For example, in China, large forests have changed to agricultural field for agricultural development. Global change of Co2 fixation volume result from these vegetation changes. Vegetation change due to human activities is the difference between actual vegetation and potential vegetation. Co2 is the most important green house effect gas, which is produced from human activities. Therefore, human impacts should be measured based on Co2 fixation . A world vegetation map has been produced by the authors with the use of NOAA GVI ( global vegetation index ) land use because of human activities. A potential vegetation map has been produced by the authors with the use of weather data and other geographic data. This shows the virgin status of vegetation as generated only from climate and geographic conditions without disturbances due to human activities. Actual and Potential Vegetation Map 1 Actual Vegetation Map A global monthly could-free NVI ( normalized vegetation index ) can be obtained from NOAA GVI data. A new vegetation classification ( eight vegetation types ) based on monthly NVI change patterns has been defined by the authors. The author's new definition is shown in Figure 1. For example, tropical forest is defined as an NVI change pattern with a constantly high NVI ( about 0.3) all year . The minimum distance method was applied to the 3 years' ( 1985, 1986 and 1987 ) average NVI and the monthly NVI change patterns shown in Figure 1. The result, a actual vegetation map is shown in Figure 2. 2 Potential vegetation Map In this study, the potential vegetation has been proposed by the authors as follows. This process is shown in Figure 3. First, as a limit of forest growth, the temperature in the coldest month shall not less than - 5 degree. Second, in the highlands over 3000 m, there is no vegetation. Finally, regarding the arid index, the zoning criteria based on Martonne's AI ( arid index ) are shown in Table 1. Figure 4 shows the potential vegetation map. AI=P/(T+10) Where P: annual rainfall ( mm) T : he sum of 12 monthly temperatures over 0 degree divided by 12 Capacity of Co2 Fixation The litter on land surface and in the soil can fix Co2, but the amount of the capacity can't be estimated. Therefore the capacity of Co2 fixation on land is estimated by net primary productivity. The parameter linking vegetation to net primary productivity is whittaker's, it is shown in Table 1. The capacity of Co2 fixation is estimated by using the parameters of net primary productivity from Table 2 per each vegetation defined in Figure 2 and 4. The capacity of Co2 fixation in actual and potential vegetation is shown in Table 3. Carbon content can be estimated as 45% of the dry matter. In case of actual vegetation, Co2 fixation is 49.4 GtC/ year. In case of potential vegetation, that is 61.7 GtC/year/ Conclusion
Table 3. Change of Co2 fixation.
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