Drought-tolerance of an invasive alien tree, Acacia mearnsii and two native competitors in fynbos riparian ecotones
Date
2012Author
Crous, C.
Jacobs, S.J.
Esler, K.J.
Format Extent
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Show full item recordAbstract
successfully
invaded many riparian zones in South Africa,
especially Australian Acacia spp. which are prevalent
along riverbanks in the south-western Cape of South
Africa. This Mediterranean-type climate region is
predicted to endure severe future water shortages
under likely scenarios of increased population growth
and climate change, and IAPs aggravate this problem
due to their profligate water use. Acacia mearnsii
competes aggressively with native species, however, it
remains unclear what physiological advantage the
species has over co-occurring native species under the
predicted reduced streamflow scenarios. A mechanistic
approach was used to investigate how key native
fynbos riparian woody tree species compare in
vulnerability to drought-induced cavitation against
A. mearnsii by comparing findings from three Mediterranean-
type fynbos river systems that differ in
streamflow. A. mearnsii showed lower water potential
at 50% hydraulic conductivity loss (P50 values)
compared to native species at certain sites, an indication
of drought-tolerance. This suggests it is likely to
persist under future drier conditions and it therefore
remains a top priority for control. The native Brabejum
stellatifolium had consistently higher water
potentials across all sites than the other studied
species, and is a potentially valuable species for
restoration of south-western Cape riparian zones.
Consistency in the shapes of species vulnerability
curves across sites illustrated a species-specific
hydraulic response to different water availability,
strengthening the argument that this approach to
distinguish site-level drought-tolerance between trees
is a practical technique, with great application in
understanding future geographic distribution under
climate change, and potential for use in restoration
research. Additionally, streamflow was an inaccurate
predictor of species drought-tolerance along these
riparian systems.
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- RESEARCH: Esler K [140]