68
THE ESSEX NATURALIST.
to seek the aid of Biology in the case of animals and birds,
whether permanent residents or migrant visitors, exploited as
game. The acceptance of advice from Biology as to the age, the
sex, or the number of victims to be sacrificed during a season,
and as to the dates at which exploitation may begin and must
end, has made it possible to avoid the extermination of particular
species: the promotion of Nature reserves, as asylums for
interesting creatures hitherto destroyed as vermin, is a more
recent extension of the same principle. Now the help of Biology
is sometimes sought with a view to the maintenance of health
or the treatment of disease in such assemblages of protected
creatures. Occasionally Human Society has shown its want
of regard for the interests of posterity by introducing animals,
useful in one area, to another area where agencies capable of
preserving the balance of Nature are absent. Examples of
damage from this cause have followed the transfer from India
to the West Indies of the ichneumon; from North America to
Europe of the musk-rat; from Europe to Australia of the rabbit.
Cases in which the exploitation of plants, when unguided by
advice from Biology, has damaged the interests of posterity,
have been if possible more striking. The face of the globe shows
many areas where the belief of Human Society that the world's
forest resources are unlimited has resulted in the creation of
deserts. The denudation of mountain ranges of their forest-
covering goes on heedless of the warning that this course is not
justifiable unless provision be made in advance for simultaneous
re-afforestation on a scale adequate to ensure an annual growth-
increment that, when the young trees reach maturity, will
compensate for the contemplated timber-fall. Neglect of this
precaution has over and over again unbalanced the annual
rainfall and disturbed the natural drainage of a region: has
swept much of the fertile soil away and buried part of it under
barren detritus: has modified the climate, replaced forest by
savannah, and made the area uninhabitable. Carelessness on
the part of individuals has at times led to results as disastrous
as those of over-exploitation; the effects of forest-fires may
resemble those of intensive lumbering. Human Society now
adopts methods, based on the principle that "prevention is
"better than cure," of forest-protection and conservancy which
keep exploitation under a control that prolongs indefinitely