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434 THE INVESTIGATION OP SUCCESSION.
been based upon the establishment of individuals, and there has been almost
no attempt to determine the r61e of migration itself in succession, as one of the
two processes concerned in invasion. A few studies have been made of the
kind and number of migrules brought by long-distance carriage, such as that
of birds, but these have little or no effect upon succession. Local, and usually
mass, migration is the chief factor in the latter, and such movement permits
of fairly accurate measurement, even though ecesis is not taken into account.
1
4 dm. wide
Scale 1cm.= ldm.
V=yearlings
s=seedlings (older than y)
d=dead trees
Seedlings and yearlings are
without exception restricted
to free soil areas between sod
patches or mossy areas. In
holes or shallow depressions
where there is an absence of
soil cover the yearlings are
most abundant.