Re: Savannah and Grassland

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RE: Fire and Maintenance of Open Savannah

A recent special on PBS (I think) showed that the situation is much
more complex than has been discussed in this thread.

During normal rainfall years, the grassland is maintained by the
continuous grazing of large ungulate herds. During drought
periods, the grazers move to other areas and trees become
established and can convert the grassland to a broken forest type
environment. Even when normal rainfall returns, ungulates cannot
reopen the grassland. Elephants then enter the picture, as they
are quite willing to push down trees to get to the higher leaves.
This reopens the grassland so that the cycle can begin.

All this presupposes that the grassland can support trees. Various
environmental conditions could preculd this. The N. American
plains are too cold, for example (I recently found out there are no
hardwood decidious trees in Calgary, for example, for this reason).

So I think we need a wider outlook on this question.

Mark Fagan, Toronto, Ontario

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