Acacia polyacantha Willd

Acacia polyacantha Willd

 

Botanical Name:

Acacia polyacantha Willd

Family:

fabaceae

Common name:

White-stem thorn, Falcon's claw acacia, Hook thorn, Catechu tree

 

Description of species

A deciduous, straight cylindrical tree, occasionally basally swollen with prickly branches, and a light, spreading flat or slightly rounded crown. Grows up to 18 m high and 0.6 m diameter. The prickles are pale brown, strongly hocked and broad, laterally compressed bases. Bark is pale brown or grey, scaly, slush pinkish with white pith, soft and fibrous and exudes a clear brown gum. Leaves: Alternate fatherly, bipinate with 15-30 pairs of pinnae, each with 10-40 pairs of minute, linear oblong leaflets, and 1-2 glands at base of each leaf. Flowers: White spikes produced in October – December. Fruits: Dark brown, flat oblong, thin shelled smooth, gloss pods to 8 cm long. Ripen in June – December and contain 4-8 round flat dark green seeds

 

Dispersal:

Birds, animals and human

Pathways:

 

Taken to botanical garden/zoo, forestry ignorant possession, human

Vectors:

Water, human, litter plants and Wind

Reproduction:

Seeds sprouting

Biological form:

Tree

 

Introduction

It spread along Batoka-Mamba road as people shared it for aesthetic purposes as well as using it as a source of fuel.  

Cause of introduction:

Means:

Place:

Date:

People sharing resources

Intentionally

Along the Batoka-Maamba Road

Chongwe

 

By forestry interests

Intentionally

 

     

Economic Use

Fuel, construction materials, medicine, other food uses,religion or ceremony. The white-stem thorn tree yields gum that is normally used in confectionery and as an adhesive, while the bark is used in tanning. The root and possibly bark are used for medicinal purposes. In rural areas, the root is placed on crossing areas in the rivers to ward off crocodiles. Root infusion is used to treat snake-bites, and also to bathe children who are restless at night. The tree is also used as larvae food plant for the butterfly Anthene crawshayi. Acacia polyacantha is further used for timber, building shelter (e.g. live fencing), land improvement (nitrogen fixing, soil reclamation), used as fuel (firewood) and for ornamental purposes.

 

Impacts

They form impenetrable thickets along water courses blocking access to people and livestock to water, and obstruct the flow of rivers particularly during floods, when fallen trees create logjams and blockages that cause further flood damage. Alien Acacia polyacantha generally have higher water requirements than the indigenous vegetation they replace, so infestations in catchment areas and along water courses reduces runoff and hence river flow. This is detrimental to riverine and wetland ecosystems.

 

Dense stands of Acacia also reduce the productive potential of land by taking over agricultural valuable areas, and increases the risk and intensity of fire by increasing the fuel load. Very hot fires destroy the seeds of indigenous Species, compromising post fire generation. Like mentioned earlier these have high water requirement than indigenous vegetation. This translates to less water in dams for agriculture.

With its strong odour, the root of Acacia appears to be avoided by animals. Therefore animals that can not adapt to such environments are displaced. The roots are also poisonous which can be dangerous to human beings as well as animals. The thickets formed by Acacia along water courses prevent people and livestock from accessing water.

Risk assessment

Risk assessment and analysis to be conducted before the plant specie spreads to other areas.

Prevention measures

Ensure that farmers as well as the community are fully informed as to how best the can manage and make full use of the introductions. Also review risk of spread by assessing seed production, seed longevity, seed dispersal mechanisms, and further review potential methods of control such a susceptibility of seedlings and trees to grazing (thorns, toxins, anti-palatability will reduce animal access); susceptibility to fire, chemical and mechanical methods and occurrence of insect predators and pathogens to native range.

 

Mechanical control

It can be done by uprooting and cutting down the acacia trees before they can spread to other areas. Seedlings and saplings can be pulled out by hand when soil is damp.

 

Chemical control

Chemical control s often preferable if growth is very dense as large-scale uprooting results.

EVERY CONTROL ACTION MUST BE PERFORMED WITH ADEQUATE SAFETY
EQUIPMENT. WHEN USING CHEMICAL PRODUCTS, FOLLOW LABEL INSTRUCTIONS AND CARE NOT TO GENERATE PARALLEL IMPACTS ON THE ENVIRONMENT

 

Biological control

Biological control offers the most sustainable control method in the long term. The Acacia seed weevil Melanterius servulus is mostly used in that during spring, when mating occurs in the adult beetles feed on Acacia polyacantha flowers and developing seeds. The female beetles then chew small holes through the walls of developing pods and lay their eggs singly on young seeds, so that the larvae will have a ready food supply after they hatch. The larvae burrow into and feed on the seed tissue, destroying the developing seeds in the process. After six weeks they chew their way out of the pods and drop to the ground, where they pupate in the soil until they emerge as adult beetles six to eight weeks later(December-March). The beetles spend the remainder of the year over-wintering under bark, becoming active in spring to begin the cycle again.

By destroying the viability of seeds, seed weevils not only reduce the rate of spread of Acacia polyacantha and other invasive acacias, but also limit regeneration from the soil seedbank after mechanical and chemical clearing.

 

Native range

Sri Lanka, Sudan, South Africa, India, Eritrea, Australia and Botswana.

Natural habitat

Wooded grassland, deciduous woodland and bush land, riverine and ground water forests in altitudes between 1800m.

Preferred habitats for invasion

Disturbed areas, forest plantations - native species, river banks.
It prefers sites with a high ground water table, indicating eutrophic and fresh soils. It
occasionally prospers on stony slopes and compact soils. However, in Kenya it can be
found at the coast, in the central highlands and the lake region.
Invaded habitat

Disturbed areas

Local reference

Luanshya

City/District - State/Province

LUANSHYA / COPPERBELT

Population level

Established

Invaded habitat

Disturbed areas

Local reference

Lake Mweru

City/District - State/Province

KAWAMBWA / LUAPULA

Population level

Established

Invaded habitat

Disturbed areas

Local reference

Chilanga

City/District - State/Province

CHILANGA / LUSAKA

Population level

Established

Invaded habitat

Forest

Local reference

Chongwe

City/District - State/Province

CHONGWE / LUSAKA

Population level

Invasive

Description of invasion

It grows rapidly with a lot of water requirements, hence dominating the habitats and forming impenetrable thickets.

Invaded habitat

Disturbed areas

Local reference

North Luangwa National park

City/District - State/Province

LUANGWA / LUSAKA

Population level

Established

River basin

Luangwa

Invaded habitat

Disturbed areas

Local reference

Luangwa

City/District - State/Province

LUANGWA / LUSAKA

Population level

Established

Invaded habitat

Disturbed areas

Local reference

Mbala

City/District - State/Province

MBALA / NORTHERN

Population level

Established

Invaded habitat

Disturbed areas

Local reference

Kabompo

City/District - State/Province

KABOMPO / NORTH-WESTERN

Population level

Established

Invaded habitat

Disturbed areas

Local reference

Jirundu national forest reserve

 

References

Sue Mathews, Africa Invaded: The Growing Danger of Invasive Alien Species, 2004 Edition, South Africa, Kobie Brand, 2004, Book, http://www.gisp.org Van Dijk,G, Vallisreria and its Interactions with other Species, 1985, Journal Smit, N., Guide to the acacias of South Africa, Pretoria, 1999, Book Coates Palgrave, M., Keith Coates Palgave Trees of Southern Africa, Cape Town South Africa, 2002, Book Mulafwa.J,S.Simute and B.Tengns, Agroforestry:Manual for Extension Wokers in Southern Province., Zambia, Swedish International Development Authority(SIDA), Regional Soil Conservation Unit(RCSU) in Nairobi, Kenya., 1994, HandBook Timberlake, J., Hand Book of Acacias; Ministry of Agriculture., Botswana, 1980, HandBook

Schmitz, D., The Invasion of exotic and wetland Plants in Florida: History and efforts to prevent new introduction. 1990, Book Butler L. G, Chemical communication between parasitic weed Striga and its host crop, a new dimension in allelochemistry, (ed), Washington DC, 1995, Book