Environmental Engineering Reference
In-Depth Information
Regulatory services (carbon sequestration, water filtration, crop pollination),
Cultural services (fulfillment of human needs: spiritual, cultural, aesthetic, intellectual)
(Aronson et al.
2007
)
Wetlands continue to be destroyed worldwide, as well as in South Africa, a
trend which sacrifices long term societal benefit for short term private gains
(Ashton
2002
). Major threats to wetlands and associated river systems are agri-
culture, forestry, invasive alien species and poor land and fire management
(Mooney et al.
1986
; Rowntree
1991
; Groombridge
1992
; Rejmánek and Randall
1994
; Grundling et al.
1999
; David et al.
2000
; Brinson and Malvárez
2002
;
Collins
2005
; Kotze et al.
2009
). Invasive woody alien trees, such as Acacia
mearnsii, commonly known as Black Wattle, are one of the greatest threats to
South Africa's water supply because of high water consumption rates (Dye and
Jarmain
2004
). Alien plants had invaded about 10.1 million ha of South Africa and
Lesotho to various degrees by 1996, resulting in the loss of an estimated 3,300
million m
3
of water per annum (Le Maitre et al.
2000
) (Figs.
16.2
,
16.3
).
Acacia mearnsii(Black Wattle)
Black Wattle is arguably one of South Africa's most aggressive alien invasive plants. It is
a tall woody tree, a competitive invader with extremely rapid growth rates, high seed yield
and drought tolerance (Crous et al.
2011
). It transpires large volumes of water and,
together with other woody alien invasive plants, has been shown to decrease river flow,
base flow and yield of South African River Systems (Bosch and Hewlett
1982
; Dye
1996
;
Le Maitre et al.
2009
). It has shallow root systems and thus is not able to withstand flood
waters, resulting in trees being ripped out which causing significant channel instability and
erosion in river systems (Scott et al.
2004
; Grenfell et al.
2005
). Black Wattle shades out
native plant species, such as the wetland plant, palmiet (Prionium serratum) (Boucher and
Withers
2004
; van Wilgen et al.
2008
). Black Wattle originates from Australia and as such
has adapted to fire. Consequently it is very difficult to eradicate as burning simply stim-
ulates the germination of its sizeable seed banks and many trees resprout. Black Wattle
poses a significant threat to attaining water security in South Africa.
Fig. 16.2 The flowers of a
Black Wattle (Acacia
mearnsii) tree
Search WWH ::
Custom Search