Natural grass fires are evidently more important for the ecology of
savannahs than has previously been assumed. This is the finding of a
study carried out in Etosha National Park in the north of Namibia.
It is the first study to have investigated the complex interplay of
the factors fire, competition, moisture and seed availability in
relation to a grass species. Periodic fires in semi-arid regions can
lead to older tufts of grass disappearing, thereby making room for
younger grasses. Writing in the Journal of Ecology, the researchers from
the Helmholtz Centre for Environmental Research (UFZ), the University
of Frankfurt am Main and the University of Cologne say that fire
therefore plays an important role in regeneration.
The findings are particularly significant for the management of
semi-arid nature reserves, in which, in the absence of natural plant
eaters, fires are the only practical means of renewing the grass canopy.
For the study, the researchers selected an area measuring 500 by 500
metres in Etosha National Park because it has one dominant grass species
and because it was possible to rule out interference such as grazing
and other human influences. Etosha National Park in the north of Namibia
is the second largest nature reserve in Africa, measuring 20,000 square
kilometres. The temperatures in the semi-arid savannah fluctuate
between 6 degrees centigrade in the winter and 35 degrees in the summer.
The area under investigation is one of the driest areas in which plants
can still grow, with annual rainfall of just 380 mm. That is less than
the rainfall in the rain shadow of the Harz mountains.
Stipagrostis uniplumis is the dominant grass species and lives for
several years. The researchers observed the growth of these grasses at
weekly intervals for one season and measured the most important climate
parameters. They also experimented on small areas by sowing additional
seeds, carrying out controlled reconstructions of fires, planting
competing grass species and using artificial irrigation. They found that
the dead grass layer significantly hindered the recruitment of young
Fire can break up the old grass layer, thereby creating opportunities
for regrowth. By contrast, artificial irrigation and the addition of
seeds did not result in higher recruitment of seedlings.