1044 RADIATION ECOLOGY
been conducted involving small ecosystems in an attempt to
determine what would happen on a large scale. In one study,
10,000 acres of land surrounding a nuclear reactor where
exposed to radiation ranging from lethal levels to levels no
higher than the natural background radiation. The ecosystem
on this land consisted mainly of an oak-hickory-pine climax
forest. The forest was exposed to a mixture of gamma radia-
tion and neutrons, with an intensity similar to that expected
from fallout after a nuclear attack. The radiation reached
about 37,00 trees, plus many more herbaceous species and
many more shrubs. Ecologists examined thousands of plants
in order to differentiate between the effects of ionizing radia-
tion and the effects of frost, disease, insect damage, drought,
and other natural factors. In still another study, a community
of spring and summer annuals was exposed to gamma radia-
tion for nearly 4 months during one growing season and then
was observed over the next 3 yrs. In still another study, gamma
radiation was applied daily throughout one winter and spring
to a forest and to an open field with a well-established cover
of annual plants.
On the basis of these and other studies, radioecologists
have formulated a scenario depicting how ionizing radiation
would affect the plants and animals of our forests and fields
if a nuclear attack occurred during the summer growing
season. People emerging from shelters several weeks after the
attack would find little change in their surroundings, except
in areas of extremely high radiation. All plants and animals,
both large and small, would have been killed in these high
radiation areas, and as the plants died they would subject
the surrounding areas to further danger from fire. However,
most fields and woodlands would appear unchanged by
radiation when viewed from a distance. Closer inspection
would reveal more clearly the extent of the damage. The
ground would be littered with the bodies of birds and ani-
mals killed by the radiation. Inspection of lakes, streams,
ponds and marshes would show that the lower animals had
fared better. Fish, frogs, toads and salamanders would be
alive and healthy. The sound of insects would be heard as
before. Among the plants the damage would be least seri-
ous to those that appear early in a natural succession pattern.
Mosses and lichens would be undamaged, annuals would be
somewhat affected, shrubs more so, and trees most of all. The
damage to pine trees would be most apparent. Pines nearest
the radiation zone would have turned a brilliant red brown
within a few days after the attack. Other plants in the forest
and fields would undergo little change during the remainder
of the summer.
In the autumn the oaks, hickories and other hardwood
trees would lose their leaves earlier than usual—perhaps as
much as 7 weeks earlier in areas nearest the high-radiation
zone. The following spring these areas would remain in their
state of winter dormancy 7 or 8 weeks longer than usual.
Examination of the hardwoods (oaks, hickories, etc.) at this
time would reveal severe damage to the buds, resulting in the
development of fewer leaves and of abnormal leaves. Near
the high-radiation zones, the trees might be leafless. The
distribution of annuals in the open fields and on the forest
floor would also be changed from previous years. Certainspecies would grow in greater numbers, partly as a result
of the stimulation of their seeds by radiation and partly as
a result of the radiation in seed germination among other
competing species. The delay in development of leaves on
the trees would give these annuals an extra long growing
season. In the abundance of sunshine, weeds would grow on
the forest to heights of 8 ft or more. The absence of a leafy
canopy would also cause changes in the forest soil. With
greater wind flow through the bare trees and higher tempera-
tures from direct sunlight, the soil would become drier and
harder during sunny weather. In rain storms the harder impact
of rain drops would wash away topsoil in areas not covered
by weeds or shrubs. Throughout the first summer follow-
ing the attack, birds and animals from outside the irradiated
areas would move in to replace those that were killed.RADIOACTIVE TRACERSWith the threat of nuclear war receding, and nuclear reac-
tors being equipped with ever more elaborate safe-guards
to reduce radioactive releases to the environment, the thrust
of radioecology is changing. Activation products in con-
trolled quantities are now being used as radioactive tracers
to follow the pathways of chemical elements in the bodies
of organisms and in the complex interactions of ecosystems.
The radioactive materials have the advantage of being easily
detected and quantitatively measured in biological materi-
als without elaborate chemical separation of the elements
otherwise necessary.
For example, the radioisotope^137 Cs was added to the
upward flow of water in trunks of yellow poplar trees in
Tennessee about 18 years ago. In the ensuing years radio-
ecologists have followed the movement of this relatively
inert tracer into leaves of the trees, into leaf-eating insects,
into the insect eating birds, into the forest litter as the dead
leaves fell, into soil insects, and so forth. Periodic sam-
pling has confirmed the recycling of natural materials in
this forest ecosystem. The radioecologists, in concert with
systems analysts, are currently developing computer simula-
tion models to mimic the ecological cycles revealed by this
cesium tagging experiment. Comparable information on the
exchange of materials from one component of the ecosys-
tem to another could never have been obtained without the
knowledgeable use of radioactive materials by these trained
radioecologists.
Other activation products such as calcium-45 or
phosphorus-32 find use in studies of metabolic processes
in organisms, populations or communities. Such studies
lead to an understanding of regulatory processes and struc-
tural characteristics of living systems. Other examples of
experimental use of radioactive tracers may range ecologi-
cally, from studying the uptake of^45 Ca tagged fertilizer by
corn, to following the pathways of^32 P in a stream, includ-
ing its distribution in the non-living as well as the living
components.
Radiation ecology is now an area of ecological research
and teaching that encompasses far more of the impacts ofC018_001_r03.indd 1044C018_001_r03.indd 1044 11/18/2005 11:04:28 AM11/18/2005 11:04:28 AM