Page 53 - Research & Innovation Report 2020

SCIENCE

events). These dry-period flows, the lifeblood of drought-stricken
catchments, are pivotal for maintaining water security.

In tandem with clearance of invasive alien vegetation, reversing
the destruction of wetlands, with their well-adapted indigenous
plant species, is an important solution to water conservation
efforts. A 2020 journal article, “Water-use characteristics of Palmiet
(Prionium serratum), an endemic South African wetland plant”,
co-authored by Prof Cowling, described the potential benefits of
restoring the habitat of this often misunderstood species.

In precolonial times, the entire length of the Kromme floodplain
was covered in palmiet wetlands; today, they cover barely 15%.
Palmiet is a sedge-like plant with an extraordinary capacity to trap
moisture, silt and organic matter, accumulating as massive (up
to 6 m deep) peatlands. Runoff is held in this natural sump, or A dense stand of water-thrifty palmiet on the Kromme River.
‘supersponge’, seeping slowly downstream and persisting, even Photo: Richard Cowling
during prolonged droughts, as baseflow that ensures low but
significant flows into water storage areas. So trapping run-off in a spectacular intermontane valley. The valley walls, which once
palmiet wetlands makes perfect sense for water conservation. supported dense spekboom thicket, have been denuded by
livestock overbrowsing. Where once there was a dense, green
Spekboom too has an important role in water conservation. West canopy that absorbed rainfall and slowly released clean water into
of the Kromme lies the Kouga River catchment. A major tributary the Baviaans River, there is now eroded earth that allows precious
of the Kouga – the Baviaans River – drains the iconic Baviaanskloof, rain to run unabated in silt-laden flows. Restoring degraded thicket
by planting spekboom cuttings (or ‘truncheons’) is known to reduce
erosion and improve baseflows, while also restoring biodiversity
and sequestering unusually large amounts of carbon dioxide for
semi-arid vegetation.

In a recently published journal article, “Herbivory and
misidentification of target habitat constrain region-wide restoration
success of spekboom (Portulacaria afra) in South African subtropical
succulent thicket,” Prof Cowling and his colleagues highlighted
some of the key elements required for the successful reintroduction
of the species to degraded landscapes.

Prof Cowling explains: “We were particularly interested in the
relative role of factors related to human actions (e.g. location of
plot in target habitat, protection of plots from herbivores, influence
of the restoration contractor) and those related to factors beyond
the control of managers – such as rainfall patterns after planting –
and the role of soil physical and chemical factors.” He continues:
“Adopting a region-wide approach and evaluating an experiment
replicated across the full extent of environmental variability in
spekboom thicket vegetation, has provided insights that will benefit
future spekboom restoration projects. Our principal conclusions
are that sites must be protected from browsing, especially by
wildlife, and that every effort must be made to ensure that they are
located in the appropriate spekboom thicket habitat.”

Prof Cowling concludes: “While state-funded restoration
programmes have made some progress, these have been
inadequately supported and have faltered in recent years.
Reducing the risk of running out of water and compromising
the capacity of municipalities to foster economic growth and
development will require radical action to restore the functioning
The Kouga River, winding through wilderness on its way to the
distant Kouga Dam. The wetlands and floodplain are densely of these catchments.” Avoiding another Day Zero depends on our
invaded by black wattle, a thirsty tree that can deplete efforts to conserve water in these critical source areas, as well as
baseflows during dry periods. Photo: Richard Cowlings reducing wasteful consumption.

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