Chapter 1: New Plant-Production Chart

How much aboveground plant-matter (dry weight) would have been able to grow on central Taimyr during the height of the Last Glaciation on this very dry zonal steppe? Could it have fed this elephant? Could it have fed large herds of woolly mammoths? I have worked out now a completely new type of chart, to answer these questions. I have drawn these different values on millimeter-paper. This chart is based on the following basic values:

The average annual aboveground production of plant matter (dry weight) in gDM/m². The average annual precipitation (mm/yr). The average annual aboveground production of plant matter (dry weight) and average annual precipitation combined into gram dry matter per millimeter of precipitation year (gDM/mm ppt yr). The average annual net radiation at the earth’s surface (kcal.cm².yr). The average annual solar net radiation at the earth’s surface can be easily changed into potential evapotranspiration, into transpiration power.

The plant needs enough heat and water, to grow properly. But there must also be the needed nutrients in the soil, where it is growing. And there must be enough water, so that the plant will be able to take these nutrients out of the soil. In many dry parts of the northern hemisphere, in the dry desert and desert steppe of Central Asia, in the dry steppe of the Tibetan High Plateau, and in many places on the Great Plains in North America, on the short grass plains, the plant is not able to grow properly, because at certain times in summer, there is enough heat, but not enough water. So the plant is not able, to use the nutrients in the soil, or not enough. And as a result, only little fodder will grow there.

With this chart, it will be now possible, to find out, how much aboveground plant-matter (dry weight) is able to grow at which amount of net radiation and at which amount of potential evapotranspiration. And also the other way around: With this chart, it will now be possible, to find out, in what kind of a climate the food will be able to grow, where the elephant is able to live.

This chart is based on the annual aboveground production of plant matter (dry weight) of dry steppe, of dry grasslands. That is, where there is a dry season in summer, where the plant depends mainly on the water coming down from above, not on the water coming up from below. This chart does not tell us, how much aboveground plant matter (dry weight) will grow in wet meadows, which are flooded in spring, after breakup, or which are growing in wet areas near ponds and lakes. I have used the data about climate and aboveground plant-production in my new chart from the following places, starting from the South:

Tsavo East National Park, Kenya, East Africa

Tsavo East National Park lies near 7°S, 39°E, southeast of Lake Victoria, near the coast of the Indian Ocean, just south of the Equator. Annual average net radiation at the earth’s surface in Tsavo East National Park, in Kenya, East Africa, is about 80 kcal.cm² yr, according to Budyko 1974, in: A. Kessler, World Survey of Climatology (1985) Fig. 7. Annual average potential evaporation in Tsavo East National Park, in Kenya, East Africa, is about 1600 mm. In World Climate Atlas, 1972, Moscow. Leningrad, by I.A. Golzberg, p. 22.

The African elephant is still able to live in the semi-desert, where there is at least 300 mm of rain per year, according to the British zoologist R. M. Laws, University of Cambridge (1970:3). These 300 mm of rain per year are producing in East Africa about 255.33 gDM/m² per year. That is 0.8511 gDM.m²/mm ppt yr.

During the years 1969-72, 235 mm of rain in the southern part of Tsavo East National Park, in Kenya, East Africa, produced about 200 gDM/m² per year. (J. Phillipson 1975:176-182). 200 gDM/m² yr : 235 mm ppt yr = 0.8510638298 gDM/m²/1 mm ppt.yr. In Tsavo East National Park, in Kenya, East Africa, in the years 1969-72, as published by John Phillipson (1975) and Timothy F. Corfield (1973).

Some workers have tried to calculate annual aboveground plant production in different parts of the world by using only one value: some have used annual precipitation, some annual net radiation at the earth’s surface, or potential evaporation, or even the annual temperature. But that does not really work. The plant is only able to grow, where it gets enough heat and water (besides the other nutrients). I first noticed this, when I compared the annual aboveground plant production in central East Africa with that of northwestern North America and northern Siberia. I found out: 1 mm of rain in East Africa produces more aboveground vegetation, than 1 mm of annual precipitation in the Yukon and Alaska. Why? Because in Africa it is much warmer, than in the Far North.

In my new chart, I have used three values: (1) The annual solar net radiation at the earth’s surface, in kcal.cm².yr. And (2) the average annual precipitation and (3) aboveground plant-production (gDM/m².yr). Annual precipitation and aboveground plant-production I have then combined. This shows me, how much aboveground plant matter (dry weight) 1 mm of annual precipitation produces there (gDM.m²/mm.ppt.yr)

From this chart, I may find out, how much aboveground plant matter (dry weight) is able to live in a certain climate, by starting with the annual net radiation or with annual potential evaporation. When starting with annual potential evaporation, I just need to convert it first into annual net radiation. 1 kcal.cm².yr net radiation (= 1 kly) at the earth’s surface is 16.95 mm potential evaporation (evaporating power) (P.E.).

1 mm of potential evaporation (evaporating power) is 0.05899705015 kcal.cm².yr. According to: R. A. Bryson and F. K. Hare (Eds.) 1974, Climates of North America, World Survey of Climatology, Vol. 11, Fig. 29, page 116.

Using the new Plant-Production Curve

This shows us, how much aboveground plant matter (dry weight) the dry steppe or dry meadow will be able to grow per year from annual precipitation. This does not include wet meadows, growing near ponds and lakes, flooding the meadows in spring at breakup or during the whole summer.

200 gDM/m² yr : 235 mm ppt yr = 0.8510638298 gDM/m²/1 mm ppt.yr

The African elephant is still able to live in the semi-desert, where there is at least 300 mm of rain per year, according to the British zoologist R. M. Laws, University of Cambridge (1970:3). These 300 mm of rain per year are producing in East Africa 255.33 gDM/m² per year. That is 0.8511 gDM.m²/mm ppt yr. In Tsavo East National Park, in Kenya, East Africa, in the years 1969-72, as published by John Phillipson (1975) and Timothy F. Corfield (1973). Tsavo East National Park lies near 7°S, 39°E, southeast of Lake Victoria, near the coast of the Indian Ocean, just south of the Equator.

During the years 1969-72, 235 mm of rain in the southern part of Tsavo East National Park, in Kenya, East Africa, produced about 200 gDM/m² per year. (J. Phillipson 1975:176-182).

200 gDM/m² yr : 235 mm ppt yr = 0.8510638298 gDM/m²/1 mm ppt.yr

Annual average net radiation at the earth’s surface in Tsavo East National Park, in Kenya, East Africa, is about 80 kcal.cm² yr, according to Budyko 1974, in: A. Kessler, World Survey of Climatology (1985) Fig. 7.

Annual average potential evaporation in Tsavo East National Park, in Kenya, East Africa, is about 1600 mm. In World Climate Atlas, 1972, Moscow. Leningrad, by I.A. Golzberg, p. 22.

The elephant is still able to live in tropical Africa, where about 250 gDM/m² has grown per year during 8-9 wet months from 300 mm of rain, if it contains enough protein. That is its lower limit. Because the elephant will already starve to death with a full stomach, where only 200 gDM/m² has grown per year. The elephant is able to live, where 300-400 gDM/m² have grown per year during 8-9 wet months. The remaining 3-4 months of the year are dry.