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Tree species could help restore soils

Friday May 29 2015
eucalyptus

A eucalyptus plantation. A team of researchers from Makerere University and the Sorderton University in Sweden said they had identified Eucalyptus grandis, Leucaena glauca, and Cassia siamea as being able to absorb dangerous mineral components from the soil, creating a conducive environment for growth of other plant species. PHOTO | FILE

Scientists in Uganda have identified three tree species that could be used to restore vegetation in mineral polluted environments such as Kilembe and the pyrite trail in Queen Elizabeth National Park.

The team of researchers from Makerere University and the Sorderton University in Sweden said they had identified Eucalyptus grandis, Leucaena glauca, and Cassia siamea as being able to absorb dangerous mineral components from the soil, creating a conducive environment for growth of other plant species in a process called phytoremediation.

Phytoremediation refers to the direct use of green plants and their associated micro-organisms to stabilise or reduce contamination in soils, sledges, sediments, surface water, or ground water.

Hannington Oryem-Origa, principal researcher at Makerere University’s College of Natural Sciences, said the study, conducted for more than two years at the copper tailing dams in Kilembe and in the pyrite trail in Queen Elizabeth National Park in Kasese District in western Uganda, has registered a major breakthrough in ongoing efforts to restore vegetation in areas that have remained bare due to excessive pollution from copper, cobalt, lead and manganese.

“During the two years of study, our research shows that the number of plant species in the degraded environment increased from 18 to 213, meaning that the amendment of the soil with limestone and compost manure and the growth of these trees — though yet to be harvested — have absorbed the heavy metals, creating a conducive environment for the emergence of other plants naturally,” said Prof Oryem.

He added that the soil pH levels in the areas of study fell from 1.5 and 4 to 5.6, (in which a low pH means higher acidity and vice versa) as a result of the trees, which are now 15-20 metres high. Naturally, plants need mild acidic soils for proper growth.

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Prof Oryem said they expect to see a reduction in the mineral pollutants from the soil every time the trees are harvested for various uses such as construction and wood fuel.

“We expect that as you continue harvesting, you take away the heavy metals that these trees have absorbed from the soil, and subsequently with repeated harvesting, the levels in the national park or the polluted environment will be reduced, thus causing a change in the soil, and allowing other plants species to grow,” said Prof Oryem adding, “Our main objective is to reach a stage where all the vegetation is fully restored to its natural state for the purpose of feeding the animals in the national parks.”

According to the Makerere University, Kilembe area and Queen Elizabeth National Park have been contaminated by heavy metals estimated at about 15 million metric tonnes as a result of dumping of waste generated from mining copper at Kilembe Mines between 1956 and 1982.

ALSO READ: Flood havoc at Kilembe

Queen Elizabeth National Park, believed to have the highest biodiversity ratings in country, with over 500 different bird species and about 100 mammal species, covers 1,978 square kilometres, with its position providing a magnificent view of the Rift Valley floor containing Lakes Edward and George.

According to the Uganda Wildlife Authority, Queen Elizabeth National Park is the country’s third highest revenue earner after Bwindi Impenetrable National Park and Murchison Falls National Park.

Charles Tumwesigye, the chief conservation manager at the UWA said the biodiversity watchdog will analyse the research before making a conclusion on whether the trees can be planted in the national park.

In the past decade, scientists successfully applied shallow rooted plant species like Spear Grass, Common Star Grass, Kodo Grass, Bulrush millet and Copper ferns to the pyrite trail in Queen Elizabeth National Park to restore the natural vegetation. However, the shallow-rooted plants improved only the shallow depths of the soil.

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