The last figure of the above is the value obtained assuming the harvest index (= yields/total crops) as follows.
Cultivated crops = 0.3, Timber production = 0.5
Grassland crops = 0.8.
With the harvest index employed, the amount of plants human beings harvest and use for themselves alone is as much as 25% of the actual net primary production.
As explained earlier, the amount of plants produced from vegetation is the base for lives of all organisms on the Earth. The above figures, therefore, imply that the species (i.e., the human beings) alone uses 25% of the net primary production of ferrestrial vegetation. In view that the world population will be almost 10 billion in the mid 21st century, even simple arithmetic clearly tells us that the human beings consumption will exceed 50% of the total plant production. Taking into consideration that natural vegetation, especially various forests, plays the roles below to support a number of wild lives, we can conclude that the human beings on-going monopolization of the plant production will lead to drastic decrease of wild species in a wide range in the near future. In other words, there is a risk that it will cause artificial massive extinction of species.
1] Natural vegetation areas produce and supply many kinds of energies for lives.
2] Natural vegetation areas are safe habitats for wild lives.
2) Plant/Food Production and Water Resources
As implied in Equation (4), the efficiency of conversion from solar energy to dry matters in plant production sharply decreases as the dryness of the climate that controls water supply to plants, i.e., radiation dryness, increases. This logic can be applied to crop production. As described in Figure 5, the dry matter production of maize is approx.
