New Zealand Journal of Botany abstracts
Below-ground morphology of Cordyline australis (New
Zealand cabbage tree) and its suitability for river bank stabilisation
Alexander Czernin
Hasnerstrasse 105/10
1160, Vienna, Austria
Chris Phillips*
Landcare Research
P.O. Box 69
Lincoln 8152, New Zealand
*Author for correspondence.
phillips@landcareresearch.co.nz
Abstract Observations and measurements on the
below-ground characteristics of the New Zealand cabbage tree, Cordyline
australis, from river bank environments near Christchurch, New
Zealand, revealed a unique structure of peg-like rhizomes and fine
spaghetti-like roots. By age 25 years, root depths reached
1.75–2.00 m, root spread reached 3.00 m, and below-ground
root biomass, including the rhizome, exceeded 50 kg or 38% of the
total tree biomass. Fine C. australis roots of diameters
0.6–3.8 mm had mean tensile strengths in the range of 26.7–17.5
MPa, 30% less than those of most willow (Salix) species. The
pullout resistance of five c. 8-year-old self-seeded Cordyline
australis trees ranged between 5.57 and 14.2 kN. In terms of
the parameters assessed against published information for willows, it
appears that C. australis falls short on both growth rate and
tree anchoring parameters (tensile strength and resistance to pullout)
for use as a river bank protection plant in all rivers. However, when
grown with other native riparian colonising plants such as flax (Phormium
spp.), river bank protection may be comparable, especially in
low-order streams with silty soils and lower hydrodynamic forces.
Keywords Cordyline australis; cabbage
tree; biomass; rhizome; root tensile strength; erosion control;
biodiversity
B05023; Received 27 May 2005; acepted 26 September 2005; Online
publication date 1 November 2005
New Zealand Journal of Botany, 2005, Vol. 43: 851–864
0028–825X/05/4304–0851 © The Royal Society of New Zealand 2005
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