That was a completely forested green area, and it is now absolute desert.

It is thus possible to allow destructive processes to proceed to a point of no return unless one envisages Herculean attempts at reconstruction. One hopes that the United States will prepare itself to prevent this from happening over most, if not all, of the productive land which may be damaged in a nuclear war.

THE DUST BOWL

However, we should not overestimate the vulnerability of ecological systems. The drought of the thirties in the United States created a dust bowl in the Middle West. The extreme lack of moisture, dust, and erosion killed off much of the plant cover. Overgrazing and grasshoppers added to the destruction of plant life.

The first chart will show the extent of this damage. Over a period of years, the destruction on the overgrazed land went down almost to zero. And then it stayed until about 1940 or so at a very low level, and then when the moisture and other conditions became proper, it recovered back to its normal coverage in a rather short period of time.

The blue line here represents the ungrazed land and the grey line, the moderately grazed.

In all cases, it went down to less than 25 percent of the normal cover. This is the extent of damage over a large area which we may equate with the kind of picture that might be drawn following a thermonuclear attack.

The loss of ground cover over a period of 8 years was recouped fairly well in a short period of time when proper moisture conditions again prevailed. This is an excellent example of large-area recovery on a natural basis after considerable damage. (See fig. M-2, p. 336.)

FIGURE M-2.-DECREASE IN PERCENTAGE OF BASAL COVER IN THE SHORT-GRASS TYPE DURING DROUGHT AND INCREASE DURING RECOVERY AFTER DROUGHT

We might mention here that much work is being done to assist natural processes in the recovery effort. There is an interesting project on the use of the airplane for reseeding depleted and burned out areas of range land. This is a fast method and can be used for covering large areas but further research on materials and methods is needed.

Work on the improvement of brushland is also germane to our problem. Some of these methods actually start with fire. Then clearing, artificial seeding, fertilizing, and grazing management are brought into play. It is possible to establish a rich grassy surface of land in 4 to 5 months. Such an area can be so managed that it will be highly productive for 3 to 5 years. After that, the soil will have become sufficiently enriched to support heavy crops of grain, etc.

Along with the reestablishment of rangeland it will be necessary to replenish livestock. Some of the requirements for this are:

(1) Specialized breeding farms.

(2) Veterinary services.

(3) Education of farmers.

Reforestation can also be artificially augmented. And there is a wealth of information on this subject which should be brought to bear on our problem of reconstruction in the postattack environment. Our own Forestry Service has a good deal of information and one of the most dramatic things going on in the world today is the Israel Government's attempts to reforest the destroyed lands in Israel, land that actually has been uncultivatable for centuries, which at one time consisted of forests.

What seems to come out of all this is that an inventory and research effort in the "biological economy" sector should be instituted at a level of intensity comparable to that going on in the industrial economy (from the postattack recuperation point of view). The resources of the agricultural bureaus of Federal and State Governments, as well as academic departments in universities and agricultural schools, undoubtedly contain information and personnel which could be brought to bear on the problems of concern to us. The Department of the Interior, the Forestry Service and the Army Corps of Engineers are still other agencies whose knowledge and skill should be utilized for study of the problems involved.

RADIATION EFFECTS ON THE ENVIRONMENT

Two problems are raised by the presence of radioactive material in an environment. There is the direct effect on individuals and populations and the total effect will depend upon the total response of the ecosystem. The second problem relates to the passage and concentration of particular isotopes through food chains leading to selective hazards to man and possibly to particular organisms of vital interest to the human economy.

Natural radiation interacts with biological material and in one way or another (for example, mutation effects) is an integral part of the equilibrium of life, whether of one generation or of all evolutionary history. The levels of radiation we will be concerned with in the postattack environment will far exceed these natural radiations for some limited period of time, and new responses will appear at these higher levels. Whether or not radiation will create ecological problems will depend upon the level of radiation in an area and the relative sensitivities of living forms in any particular ecosystem.

There is a tremendous range of radiation dose which encompasses phenomena of ecological interest. (See fig. M-3.)

FIGURE M-3.-DOSE RANGE IN ROENTGENS FOR EFFECTS OF POSSIBLE ECOLOGICAL

Starting with the mammals, we begin to get ecological effects such as limitation of fertility at accumulated doses as low as 50 roentgens, and we can go up to as high as over a million roentgens in our attempts to sterilize an area by killing off the bacteria.

Now, bacteria in the soil, for instance, are needed for the healthy agricultural quality of the soil. So that we actually are concerned with this whole range of interest when we think of ecological problems.

Now, some of these, of course, are going to be thrown out when we look at the various levels of attack and realize that we don't come to these. Nevertheless, these problems at least have to be looked at.

The chart, indicating an overall range of 50 to 1 million roentgens, implies that minor effects (such as reduction in fertility) in mammals may be observed at the lower dosage whereas in excess of 1 million roentgens would be needed to kill bacteria.

RADIOSENSITIVITY OF A SPECIES

It is also important to know the extent of radiosensitivity of one species during different phases of its life cycle. (See fig. M-4.) (Fig. M-4 illustrates this and follows:)

FIGURE M-4.-RADIOSENSITIVITY OF DROSOPHILA

Stage in life cycle

Embryo (3 hours)

LD50 dose (roentgens) of X-rays*

Embyro (4 hours).

Embyro (7.5 hours).

Pupa

Adult.

*LD50 dose of radiation lethal for 50 percent of organisms.

170-200

500

810

2,800

85,000

You will notice that the adult drosophila has a particular sensitivity as measured here of 85,000. But if you will look at the other aspects of the life cycle of this particular organism, you find that there is a sensitivity in the embryo as low as 170 to 200. So it becomes obvious that the radiosensitivity of the adult insect is not enough. Whenever we come to a particular life form which is of interest to us it is important that we have the radiosensitivity profile of the whole life cycle of the organism if we are to be really qualified to say what the radiosensitivity in this organism is. This is just an illustration of that. The chart shows the response of drosophila to X-rays. It is obvious that only knowledge of the resistence of the adult would be very misleading.

The reproductive behavior of a species must also be considered in assessing effects. Bacteria, for example, will repopulate an area very quickly even though only a small number survive.

It is also worth mentioning that small organisms might be killed by external beta radiation which would cause only local surface lesions in large animals. This should be watched for in the evaluation of fallout patterns from an ecological point of view.

Figure M-5 shows the radiosensitivity of several species of seed plants.

TABLE M-1.-Tolerance of various plants to chronic gamma radiation

1 Dose rate is in roentgens/24-hour day; however, the actual dosage/day averaged about 90 percent of the dose rate shown.

? This dose rate is not necessarily the lowest rate which will produce a severe effect.

This is a highly selective list from the literature. The literature, itself, is very, very sparse in terms of the food crops that we are concerned with. There is a widespread range of sensitivity. Actually, this is a cumulative dose with exposure given daily for weeks and going from a dose rate per 24-hour day of 20 roentgens up to 4,100 roentgens to encompass the differences in sensitivity of particular plants to radiation.

Now, the same thing exists with regard to seeds themselves. Here are dormant seeds and if you will notice the critical dose, which is the beginning of reducing the ability of seeds to grow, we have a range from 5,000 roentgens for rye, going to 100,000 roentgens for cabbage. (See fig. M-5.)

FIGURE M-5.-RESPONSE OF DORMANT SEEDS TO VARYING DOSES OF COBALT 60 GAMMA RAYS AS MEASURED BY SEEDLING GROWTH IN A GREENHOUSE

1 Critical dose is the lowest dose-reducing growth below that of unirradiated controls.

One more thing that I would like to put in, just to give you the range of doses which are important, is that when we get into the sensitivity of mammals to radiation we are now talking about the killing dose for 50 percent of the mammals within 30 days, and the numbers run 281 up to 805, starting with dogs and going through the rabbit. (See table M-2, p. 340.)

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