Marange diamond fields overrun by invasive species

Giant milkweed seed


MARANGE diamond fields might not be useful for agriculture – even animal husbandry, after the mining operations end. Annexed to commerce, they are being lost to nature.

Chiadzwa is being overrun by an aggressive alien species – Calotropis procera, giant milkweed, setting up a new frontier for another long struggle with flora, as it takes over all the areas that were disturbed by years of diamond extraction without rehabilitation.

Giant Milkweed Fruit

This comes as the government is failing to contain another invasive plant – Vernonanthura polyanthes, bee bush, native to Bolivia and Brazil.

It took the government over a decade to identify it after it first being noticed in the wake of Cyclone Eline in Chimanimani in 2000 earning the then mysterious plant the moniker Cyclone.

It is yet to officially declare it invasive despite it taking over the entire eastern highlands from Chipinge to Nyanga going as far in as Bikita and Rusape. Environment Management Agency (EMA) spokesperson Amkela Sidange says they are in the process of declaring it as such.

Both giant milkweed and bee bush are wind dispersed and have been worsened by windy extreme weather events like cyclones.

Giant milkweed is fast establishing itself in Chiadzwa

Combined they threaten to completely cover the entire province with bee bush favouring humid areas and giant milkweed taking over the arid regions.

“Both take advantage of disturbed areas and are pioneering plants,” Forestry Commission Manicaland provincial manager Phillip Tomu said.

This is an observation that is also shared by National Herbarium and Botanic Garden (NHBG) experts Kudakwashe Mutasa and Anthony Mapaura.

“Disturbed areas showed a higher probability of occurrence of Calotropis procera with highest occurrence predicted in cultivated fields. In densely vegetated land areas the occurrence of the species is low. This could indicate that the species is not a very good competitor,” they noted.

Zimbabwe however has a poor record in managing problem plants as it has only had 11 species that have been declared invasive and warranting management despite having 84 plants known to be invasive in some parts of the world among its 1,449 exotic plant species.

The NHBG botanists note that the “large discrepancy between the identified invasive and declared invasive species indicates a gap in the invasive species research in the country.”

Traditional leaders raised the flag on the giant milkweed whose identity is yet to be communicated to them officially.

Even though locals do not have any access to the diamond fields they know that mineral extraction is a finite process and would want to use their land after mining ends.

“Our lands are now infested by a mystery plant. We don’t know what it is and we are concerned because it is now pervasive across all of Chiadzwa,” Tonhorai village head Livemore Rwizi said in an interview.

The plant which can grow as tall as six metres is also known as Sodom apple and has its origins in Asia as well as North and East Africa.

Giant Mikweed are now the dominant plant in Chiadzwa

It has been declared invasive in South Africa’s Northern Limpopo province which borders Zimbabwe and in western and northern Australia.

According to NHBG, although it is yet to be formally declared invasive it fits the criteria for classification as invasive.

“Based on the definition of an invasive  species  by Richardson which classifies an invasive as a plants that is able to produce self-sustaining populations and distances more than 100m from the parent plant in a period of less than 50 years, the behaviour of Calotropis procera in Zimbabwe can easily classify it as an invasive species,” the botanists said.

It is a shrub but can grow to a small tree in favourable conditions of up to 6m tall and has numerous fruits, each producing 300-500 seeds which are dispersed by wind, water, animals as well as humans, the researchers said.

According to the two botanists the plant which produces lovely pink or purple flowers making them popular ornamental shrubs might have been introduced into the country 70 years ago from Mozambique.

“In Zimbabwe it is perceived to have been introduced as an ornamental around the 1940s from Mozambique and it is currently classified as a naturalised plant even though in some areas its spatial distribution has begun to raise questions,” they said.

Ironically bee bush also came from the same country albeit with cyclone winds.

The widespread distribution and unchecked spread into productive land could result in reduced agricultural productivity for both livestock and crop production.

“If cut, the plant produces a milky sap with a chemical calotropin which is known to be toxic to livestock if ingested.

“Studies by other researchers have shown allelopathic reactions that affect germination of crops such as wheat, cotton, soya bean, tomato and cucumber which are also produced in Zimbabwe,” the national herbarium officials said.

They said it was important for the country to acknowledge that the species is a potential problem that can seriously affect agricultural productivity and ultimately the livelihoods of the general populous in the marginal areas of the country.

“Above everything else, success or failure of any management programme rests in the community, there is a need to educate the community on the effects of Calotropis procera and how they can manage its spread,” the botanists said.

Village head Tonhorai feels the community can not do anything for now as mining companies have current custody of the land for now. “We pray that when they finally move out we will still be able to access it and not leave us with impassable forests of this plant.”


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