Those are among the findings of a series
of research studies conducted by a University of Maine biologist who combined
data from a 33-year population study of rodents with experiments in the Holt
Research Forest, Penobscot Experimental Forest and Acadia National Park.
“Small mammals can reach extremely
high densities; in some years up to 100 individuals per acre,” said Alessio
Mortelliti, assistant professor of wildlife conservation. “They can actually
eat every single seed of the species they like, which means they can have a
massive impact on forest regeneration.”
By pointing trail cameras at plates
left in the forest with different tree seeds, Mortelliti found strong
preferences among different animal species. None of the animals liked the seeds
of balsam fir, for instance, which Mortelliti said is one reason why there are
so many balsam firs in Maine forests. Paper birch seeds were also avoided by
most of the animals. Mice had a preference for red oaks, which voles ignored,
and all of the animals liked white pine, spruce and maple seeds.
In another study, the researcher found
that different seeds affect the vole population differently, and the effects
were largely dependent on the animal’s population density. White pine seeds
were found to be especially important when vole populations were low by helping
them survive and reproduce in greater numbers. The animals only ate paper birch
seeds when the vole population was high and few white pine seeds were
available.
Mortelliti hopes to use his research
findings to help forest managers minimize the impact of small mammals on the
most commercially valuable tree species.
“With a little more research, we
should be able to figure out how to optimize timber production by understanding
how small mammals are affecting the regeneration of the forest,” he said. “We
hope to be able to give timber companies prescriptions for the best way to
manage the forest so they can maximize the regeneration of the trees they
want.”
He said this will become especially
important as the climate changes and new tree species expand their ranges
northward.
“Tree species composition is going
to change, and small mammals will play a key role in affecting the expansion,”
Mortelliti said. “They’re the gatekeepers. They’re going to decide which plants
will regenerate. The results of our studies will tell us what tree species will
be blocked by the animals and which will be favored, and that will inform the
management actions that can be taken to deal with this process.”
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