But these are, after all, exceptional, and
characterise those regions only where the climate is little favourable
to forest vegetation. In the tropical and all the warm temperate parts
of the earth, where there is a sufficient supply of moisture, the
forests present the same variety of species as does the turf of our old
pastures; and in the equatorial virgin forests there is so great a
variety of forms, and they are so thoroughly intermingled, that the
traveller often finds it difficult to discover a second specimen of any
particular species which he has noticed. Even the forests of the
temperate zones, in all favourable situations, exhibit a considerable
variety of trees of distinct genera and families, and it is only when we
approach the outskirts of forest vegetation, where either drought or
winds or the severity of the winter is adverse to the existence of most
trees, that we find extensive tracts monopolised by one or two species.
Even Canada has more than sixty different forest trees and the Eastern
United States a hundred and fifty; Europe is rather poor, containing
about eighty trees only; while the forests of Eastern Asia, Japan, and
Manchuria are exceedingly rich, about a hundred and seventy species
being already known.
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