NEWS
Veld, weeds and fire: The good,
the bad and the ugly
Current Address: ARC Plant Health and Protection
E-mail Address: [email protected]
Reprinted From: http://bit.ly/2Te25Kb
Jeremy Goodall
A
sizeable part of South Africa’s
native vegetation has naturally
adapted to burn quite often and
fynbos, grassland and bushveld all burn
at some stage during their growth cy-
cles. Preventing this vegetation from
burning results in massive accumulation
of biomass that can cause devastation
when the next wildfire occurs. Farmers
are accustomed to preparing fire breaks
in the dry season and burning old veld
to stimulate the regrowth of grazing.
The advantages of the controlled burn-
ing of veld outweigh the disadvantages.
Consider alien vegetation, especially
species that invade native vegetation.
Invasive plants affect native vegetation
in many ways. This article illustrates the
effect fire can have on various invasive
plant species.
Black and silver wattle
Wattle trees are especially problematic
in the Drakensberg region. Black wattle
(Acacia mearnsii) and silver wattle (Aca-
cia dealbata) are the main culprits. Since
the inception of the Working for Water
programme in the mid-1990s, there
have been large-scale attempts to bring
wattle trees under control with ringbark-
ing and chemical control (Figure 1).
Studies that evaluated the impact of
clearing wattles in the Drakensberg,
found that most infestations where
standing trees were treated, had experi-
enced destructive wildfires one to three
years following treatment, and the soil
surfaces had been scorched. The burnt
soil surfaces became water repellent
and prone to surface wash. This resulted
in large-scale soil erosion, the worst of
which included the formation of don-
gas.
Wattle seeds have a hard seed coat that
protects the embryo from the heat of
fire. However, the heat stimulates the
germination of seeds in the burnt area
within days after the fire (Figure 2). The
29
Figure 1: A stand of wattle in Bulwer, KZN, which has died from being ringbarked
intensity of these wildfires is enormous,
and little vegetation other than wattle
regeneration remains to bind the soil
(Figure 3).
Grassland areas that are invaded by
wattles become wattle forests that burn
fiercely during wildfires and afterwards
turn into impenetrable wattle thickets
that are of little use. Felling trees, us-
ing the wood, planting grass between
staked brush lines and controlling seed-
lings would be more beneficial to the
environment.
Wattle control also needs careful plan-
ning because old wattle stands are
valuable sources of timber that can be
utilised for energy and building mate-
rial. In some areas the removal of wattle
trees has resulted in local communities
relying on indigenous forests for fire-
wood.
Paraffin weed
Paraffin weed (Chromolaena odorata)
is a tropical shrub that invades forests,
bushveld and grasslands in KwaZulu-
Natal, Swaziland, Mpumalanga and
Limpopo (Figure 4). The oil in this weed
makes it flammable in the dry season,
when plants become moisture stressed.
Indigenous forests do not burn natural-
ly, but once they are invaded by paraf-
Grassroots
Vol 20
No 1
March 2020