MessageHi Colin and others
Giles is actually quoting outdated Eurocentric theories. Our grasslands are
in fact primary grasslands maintained by climatic factors including
lightning ignited fires. These grasslands are all in areas with a high
density of lightning strikes to ground and trees and shrubs will only invade
them if fire is ARTIFICIALLY excluded from the area by means of firebreaks,
overgrazing (i.e. the grass is too short to burn), etc. They once probably
covered as much as 60% of Africa, but are now virtually restricted to
southern Africa. Other climatic factors include warm wet summers followed
by cold dry winters with heavy frosts and sometimes snow.. This results in
a high preproduction of dry, highly flammable aerial parts of the plants
(the nutrients having been withdrawn into the plant root systems) which
would have been set alight by dry electrical storms experienced in these
areas in our spring around September/October.
Unfortunately I have been out of Grassland ecology for quite a few years now
so can no longer quote any references, but there are many articles and
papers on the subject. This theory is also supported by the presence of so
many endemic species in our grassland biome (12 bird species alone - which I
know is not great by Aus standards but it is the highest of any South Africa
Biome). These species could surely not have evolved over the last 400
years - the time period that anthropogenic fires have been a major factor in
our grasslands. Another indication is that the vast majority of Africa's
famous antelope species are grazers, not browsers indicating that they
evolved when grasses not trees or shrubs were the dominant vegetation. Our
grasslands are under tremendous threat in South Africa and around 80% of
then have been irreversibly transformed by agriculture, livestock ranching,
tree plantations, urban sprawl, mining, etc.
Fire is thus an indispensable part of our grassland ecology. The
"wildfires" of the past are no longer a major feature, but this is due to
human factors such as fire control, overgrazing, planting to alien species
such as eucalypts, wattles, pines, etc. Fires are now indeed mostly
anthropogenic, but that is due to human needs or interference in curbing
them.
I hope that you'll excuse my rambling, but it is a subject close to my heart
and is closely related to birds - the majority of our threatened species are
grassland endemics or dependant on grasslands to a large extent for their
survival. If anyone is interested in reading further on the subject the
South African National Botanical Institute in Tshwane (Pretoria) has plenty
of literature on the subject and I would imagine that a Google search would
turn up their contact details.
Cheers
John McAllister
Wakkerstroom (in one of the last remaining "near pristine" grassland areas
of South Africa)
South Africa
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