The question was simple: What trees are the parents of seedlings growing in the forest fragments? Finding the answer would have been nearly impossible even a decade ago until the invention of sensitive techniques that allow researchers to determine the exact genetic makeup of individual plants in an ecosystem. Even now, the problem is daunting, since there were more than 800 possible parent pairs.
"In trying to tell who the parents are, we had to use the same
techniques used in forensic analysis to determine a child's parents," said
Hamrick. "We were able to do this only because Preston was able to develop the
techniques for our specific genetic analysis himself."
The breakthrough came in using segments of DNA called microsatellites as
specific markers for S. globulifera. These markers allowed Aldrich and Hamrick
to determine the pedigree for a number of seedlings and saplings in a one
hectare forest fragment on their 38.5- hectare research area. (A hectare is a
metric unit of area equal to 2.471 acres.) The scientists knew the genetic
composition of all the adults, 42 individuals, in the study area.
The results of the genetic analysis were startling. Out of nearly 250
seedlings studied from a single forest fragment, some 68 percent were produced
by adults in pastures -- not from adults within the fragments themselves.
Moreover, of the seedling produced by pasture trees, 77 percent came from only
two trees. Adults left in the fragment produced less than 5 percent of the
seedlings in their own patches. The importance of the discovery lies in the fact
that the genetic diversity of seedlings in forest fragment may be relatively
small indeed.
"If you looked at the number of seedlings superficially, you might say
that this is a healthy rate of regrowth," said Hamrick. "But in truth, the
effect is ecological
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Contact: Phil Williams
philwpio@arches.uga.edu
706/542-8501
University of Georgia
3-Jul-1998