Download Article 118 Ailanthus revisited - Botanical Society of South Africa

Weeds in our Area (Part One Hundred and Eighteen)
By Bob and Ena McIntyre – Garden Route
Ailanthus altissima (Tree of Heaven. Hemelboom)
Reading about the untold problems experienced with A. altissima in New York and elsewhere in
the USA reminded us that this plant is insidiously gaining ground in our area. We decided to revisit
the species and to share more fascinating facts. Native to China and Taiwan A.altissima was
introduced into Europe in the 1740’s and reached the United States by 1784. It was possibly
brought to South Africa during the 1800’s. Introduced to various countries all over the world it
became a problem in many.
An extract from the book, ‘A Tree Grows in Brooklyn’‘ by Betty Smith, says it all “There's a tree that
grows in Brooklyn. Some people call it the Tree of Heaven. No matter where its seed falls, it makes
a tree which struggles to reach the sky. It grows in boarded up lots and out of neglected rubbish
heaps. It grows up out of cellar gratings. It is the only tree that grows out of cement. It grows
lushly...survives without sun, water, and seemingly earth. It would be considered beautiful except
that there are too many of it.”
However, in the right environment the tree has a variety of practical uses, many of which are listed
in Chinese medical texts for its purported ability to cure ailments ranging from mental illness to
balding. The roots, leaves and bark are still used today in traditional Chinese medicine, primarily as
an astringent. The tree is grown extensively both in China and abroad as host plant for the
ailanthus silk-moth, a moth involved in silk production.
Back in the early 1950’s A.altissima’s only recommended uses as garden plants in our country
were as avenue trees or windbreaks. Gardening experts then also warned that your Tree of
Heaven would not make you popular with your neighbours and was only suitable for the very large
garden and planted well away (20m) from any cultivated area. Locally many mature A.altissima
and a profusion of saplings can be seen on the vacant site north of Heights Road opposite the
Chapel. Another ever-increasing clump thrives south of Krantz Lane and sadly they are also rapidly
spreading in the “Bird Sanctuary”.
Identification: Mature trees are tall (up to 20m) and spreading (up to 10m). Deciduous for a short
period, the dark green, yellow-tinged compound leaves and
reddish-brown stems of young plants are disproportionately
large (up to 1m). The individual leaflets are characterised by 14 basal gland-bearing teeth. The male flowers and crushed
leaves have an unpleasant smell. The small greenish-yellow
flowers appear Oct – Nov in large terminal sprays, followed by
striking rust-red seeds. The leaves and flowers are poisonous
and these and the bark are skin irritants.
Invasive Status: Ailanthus altissima are Category Three
invaders – no trade is permitted and only mature (i.e. mature
prior to March 2001) specimens may be retained - re-growth
from suckers or seed germination must be removed and
destroyed. The plants invade aggressively in mild areas such as
ours and will also grow in poor and arid soils. Once established
they sucker and spread particularly vigorously as can be seen in the areas mentioned above, to
aggravate matters even further - wherever the spreading roots are cut, suckers sprout profusely.
Control: Ailanthus altissima has a similar growth habit to Lantana camara and the same approach
is appropriate – a foliar spray on young plants and on more mature specimens, very low stem cuts
immediately followed by herbicide application to the cut surfaces. Follow-up is critical. No specific
herbicide is currently registered for this species in South Africa. In the United States both the nonselective Glyphosate and selective Triclopyr herbicides are used successfully. Both are systemic
herbicides that affect the whole plant.
Indigenous substitutes: Rooi essenhout (Trichelia emetica), Wild peach (Kiggelaria africana),
Podocarpus falcatus (Outeniqua Yellowwood) and Podocarpus henckelii (Henckel’s yellowwood).
References: Alien Weeds and Invasive Plants by Lesley Henderson, Copyright © 2001 Agricultural
Research Council. http://www.wikipedia.org