Download Article 21 Hakea sp - Botanical Society of South Africa

Weeds in our Area (Part Twenty One)
By Bob and Ena McIntyre – Garden Route Branch.
Hakea sp.
One of the major threats to our mountain fynbos is posed by Hakea species. Three species of
Hakea were introduced into South Africa from Australia in the 1830’s and by 1900 they were well
established in the Mountain Fynbos area of the Cape coastal region. Since then it has spread with a
vengeance throughout the mountainous regions of the Cape - its spread exacerbated by fire.
Hakea are extremely flammable and said to be “born to burn”. The fruits of all Hakea are very hard
wooden capsules that protect the seed during fire, opening afterwards releasing the seed. The
heat intensity of fire in Hakea infested fynbos is about 5 times that of a fire in pristine fynbos,
resulting in the destruction of most of the fynbos seed bank. The masses of released Hakea seed
quickly germinate in the fire ravaged area and the Hakea seedlings’ rapid growth completely
smothers what little fynbos regeneration may have occurred.
All three of the originally introduced Hakea (H. sericea {silky hakea}, H. gibbosa {rock hakea} and H.
drupacea {sweet hakea}) are Category One weeds that require eradication. Willow hakea (H.
salicifolia), introduced later, appears on the proposed new list as category three.
Identification. The big woody capsules that contain and
protect a single seed make identifying all Hakea species
reasonably simple. The plant itself is an almost delicate looking
tree. Silky, rock and sweet hakea are all characterised by very
sharp needle shaped leaves (like pine needles) while the leaves
of willow hakea are leathery, flat and linear to lanceolate.
Locally rock and silky hakea is common in Constantia Kloof and
Wilderness Heights.
Control. Bio-control is having a limited effect in containing the
spread of silky hakea. Manual intervention is needed on all
other species. Hakea does not coppice readily. Therefore providing that no branches or twigs are left intact below a cut,
no treatment with herbicide is required. Bear in mind that
small branches or even spines can develop into a new plant.
The felled hakea should have all branches with ‘fruit’ removed and stacked separately, preferably
on level ground to prevent the seed washing away during rain, The stack should be thoroughly
weighed down. The seeds will release in time and mostly be eaten by rodents. Some will inevitably
germinate. Eradicate the seedlings by hand pulling.
Photo with acknowledgements to “ALIEN WEEDS AND INVASIVE PLANTS” by Lesley Henderson.
Copyright © 2001 Agricultural Research Council