Dot-meshed areas in the Figure 4 indicates high-production zone (10t and above). We can see that the high-production zone is relatively narrow compared to the vast lands on the Earth.
To quantify those, the area-frequency distribution curve with different NPP-values has been expressed in Table 2.
The areas of high production with its NPP of 10t/ (ha・year) and above account for only 36.1% of the entire lands (14.889 billion ha). Especially, subtropical and tropical rain forests with the NPP of 25t (ha・year) occupy make only 3.5%. On the other hand, the biological borders with the NPP of 1t/ (ha・year) or below are as much as 22.5%. This means that the real combinations of temperature resources, water resources, and solar energy resources on the Earth - in other words, geographical distribution of continents and oceans on the Earth - are not so favorable for plant production. How the expected global warming, caused by man, in the next century affects the results in Figure 4 and Table 2 is a crucial issue for not only the human beings but all the living things on the Earth.
From Figure 4 and Table 2, the maximum dry-matter production of ferrestrial vegetation under the present climate (the potential net primary production in ton/year) can be obtained. The results, the dry-matter production when taking into account human being's land utilization (actual net primary production), and the amount of plant production utilized by human beings are shown below (Uchijima, 1997)：
Potential net primary production： 1,360 (100 million ton/year)
Actual net primary production： 816
Yields of foods and timbers： 122
Production needed for the yields of foods and timbers： 204
Natural vegetation areas have been ceaselessly destroyed to exploit and construct farming, residential, industrial, and transportation lands. This tendency makes the actual net primary production as low as 60% the potential net primary production. Out of the former, human beings harvest and use 12.2 billion ton (15% of the actual net primary production).
