Response of three semi-arid savannas on contrasting soils to the removal of the woody component
Date
2015-09-11
Authors
Scholes, Robert John
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Abstract
A t h r e e - y e a r study was un dertaken in the semi-arid (500mm p a . )
n o rth -eastern lowland area of South Afric a. All the woody plants were
removed from one -hectare savanna plots on three d i f f e r e n t soil types ,
and key hydrological and biological changes were monitored relative to
adjacent controls.
Runoff increased initially, but decreased once the grass cover increased.
Deep drainage and lateral subsurface flow increased on the sandiest site.
Evaporation from the soil surface increased on the heavier t e x t u r e d soils.
The duration of plant - available water in the soil increased on all cleared
p l o t s .
&
The p re - c l e a r in g woody plant abo veground biomass was in the range of
of which 0 . 6 6 to 0 . 8 0 t ha was 5.6 to 11.2 t ha -1 leaf biomass. The
annual herbaceous production was stron gly rainfal' dep endent, averaging
1 to 1.5 t ha -1 , and increased by 0 . 4 - 0 6 t .ha -1 except on the most
f erti le site ( 0 . 6 - 2 0 t ha ) . Total available forage increased with c l e a ring,
but so did its variability The observed changes in herbaceous layer
palatability could not be a t trib u t e d to clearing.
Woody plants and grasses wore shown to have w a te r- u s e niche separation
in both rooting depth and time of water use. Simulation over forty years
of wetting patterns indicated 75 to 85 % niche overlap, w t h separation
on the depth axis more important in sandy sites, and on the time axis
in clayey sites. Competition between woody plants and grasses was
strongly asymmetrical in favour of woody plants.
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Description
A thesis submitted to the
Faculty of Science
University of the Witwatersrand, Johannesburg
for the
Degree or Doctor or Philosophy
October 1987