Why is this study
important?
Rangelands are ecologically
complex and dynamic systems
in which vegetation responses
to some management practices
are strongly influenced by subtle
nuances of the management
actions and by differences in
climate, vegetation type, soil
and other ecosystem properties.
There’s increasing pressure
on rangeland managers to
preserve ecosystem services
flowing from the veld.
Anecdotal evidence of
increased production or
ecosystem services is often
used in the advocacy of high-
density grazing management,
but claims seldom emerge under
experimental manipulation
where confounding variables
such as rainfall are controlled.
Critics of academic studies often
claim that experimental trials
fail to capture the complexity
of adaptive management
decisions that bring about long-
term vegetation changes at the
landscape scale. That is why we
supplemented our experimental
trials with a study of working
farms, all of which had been
consistently practising a certain
grazing approach for many years.
The national survey, experimental
trials, and global reviews
conducted by our research group
all lend weight to the growing
global literature showing that
continued advocacy for extreme
forms of rotational grazing
management is without basis
and potentially risky. Increasing
grazing densities in arid veld
seems especially unreasonable
because it requires large
investment not only in fencing,
but also watering infrastructure,
with little to no gain in
productivity to offset these costs.
Our survey also confirmed
that HPG practitioners were
closely aligned to other forms of
rotational grazing approaches,
in contrast to the claim that HPG
is unique. Interestingly, other
work within the research group
indicates that corralling animals
at high densities for a short time
can be used for specific purposes,
such as fertilisation, disturbance
and stimulating plant growth
when ground cover is low. Thus,
high stocking densities could well
have restoration applications, but
this requires further research.hoW did grazing
practices affect
Woody plants?
We tested whether intensive
grazing would increase
herbaceous growth while
decreasing woody plant invasionlivestock Rotational Grazing
ABOVE:
According to the
researchers, the
previously untested
hypothesis that
rotational grazing
alters woody
plant cover was
not supported
in the study.
FW Archiveby reducing selective grazing.
Other studies suggest that
increasing browser densities
combined with increasing
fire frequencies is a useful
tool to combat woody plant
encroachment. The principle
is that both fires and browsers
remove woody plant material,
thus favouring grass growth and
increasing grass-tree competition.
Since the selected fence lines
had not burnt in 10 years, it
was an opportunity to test
whether increased livestock
densities alone might reduce
encroachment by invasive wattle
or even indigenous woody plants.Most of the fence-line contrasts
showed no significant effect of
relatively high grazing densities
on woody plant cover. Increasing
stocking rate and shifting
livestock composition to include
more browsers also appeared to
have no effect on woody plant
cover across the studied farms.
The lack of effect of livestock
density on woody plant cover at
this local scale was likely due to
the absence of recent fires, but
also because the fence lines were
in areas with low overall woody
cover. An effect of grazing density
may only emerge at higher
woody cover and in combination
with fire. This remains an
interesting topic, especially given
the increase in woody plant
encroachment over sub-Saharan
Africa with climate change and
trends of fire suppression and
reduced numbers of browsing
animals, including wildlife.- Email Dr Heidi-Jayne Hawkins
at [email protected]. - Visit doi.org/10.1016/j.
agee.2019.05.019 to read the article,
‘National veld survey raises questions
about rotational grazing effects’,
by Hawkins, Dr Zander Venter,
and Prof Michael Cramer.
▪
FW38 farmer’sweekly 2 august 2019
do not increase
grazing
densities in
arid veld