Quotations
are EXTRAORDINARILY rare in scientific writing--perhaps one in every 50
manuscripts (just a rough guess here but you should get the point!).
Your job as the author is to
relate the work of others to your project. As a result, the preferred
tact is to paraphrase the
work of others and more directly relate this citation to your point.
One much less wordy way
of using the ideas of Aldo Leopold would be:
A knowledge of social systems has long been
considered of great importance to the
conservation of a species (Leopold 1948)