Kenya's Masai Mara Threatened by Invasive Species of Plant

Flowers of the Eurasian Asteraceae species of feverfew (Tanacetum parthenium). Kenya's pasture is threatened by the North American Asteraceae genus (Parthenium hysterophorus). Photo courtesy: Corbis via guardian.co.uk

One of the most sacred and revered places on the planet - the Masai Mara - is under attack from an unlikely source. Feverfew, a non-native species, is threatening to colonize the Mara; thereby, causing local herbivores to starve.

No one knows how feverfew reached south-west Kenya. But the threat it poses led to a recent alert from the International Union for Conservation of Nature (ICUN) issued to the international scientific community: "The Serengeti – Masai Mara ecosystem in Africa, which hosts the largest wildlife migration known to man, is under attack from a noxious weed."

Masai Mara, which runs along the border with Tanzania, is home to Africa's largest herbivore population. At the start of the annual rainy season, millions of wildebeest, gazelles, zebras and giraffes leave the Tanzanian savanna for the plains of Kenya in search of fresh pastures. A few months later, towards December, they circle back completing a round trip of several hundred kilometres. But what would happen if the weed, originally from Central America, colonised this wildlife sanctuary?

Parthenium hysterophorus, commonly known as Santa Maria feverfew or whitetop weed, is one of the world's 10 most dangerous weeds. It can grow two metres tall. Until now it has only been seen on tracks crossing the wildlife reserve and on the shores of the river Mara, which flows through the Serengeti.

"It is very hard to say how long it will take for the invasion to spread to the whole park, because that depends on many factors, in particular climatic conditions," says Arne Witt, Invasive Species Co-ordinator at the Centre for Agricultural Bioscience International (Cabi). "But the example of neighbouring Uganda shows that it may be very quick. The plant was first spotted three years ago and it is now seen all over the country. Bearing in mind that it can grow from seed to maturity in four to six weeks and can produce 10,000 to 25,000 seeds, contamination can happen very quickly," Witt adds.

Unlike Central America, there are no predatory insects in Africa to thwart its spread. Scientists are all too familiar with the destruction wrought by feverfew, which has been on the red list of invasive species in Australia and India for decades. Feverfew pollen is also a skin irritant and causes respiratory difficulties.

Its first landfall in Africa was in Ethiopia in the early 1980s. The most widespread, though unconfirmed, explanation is that the weed was imported with food aid to combat the famine then affecting the Horn of Africa. It then spread to Uganda, Tanzania, Mozambique, Zimbabwe, Somalia and South Africa.

"Unless action is taken immediately to eradicate known infestations in the Masai Mara National Reserve it is not unrealistic to expect a drastic reduction in wildlife populations in the long term," says Geoffrey Howard, at IUCN Kenya. "The animals won't eat feverfew, at least at first, but they won't have any alternative if they are starving."

Witt's organisation, Cabi, has drawn up a plan to eradicate the species in conjunction with the Kenyan wildlife service, the public body that manages all the national parks. This involves several options. "Ideally we should mount a biological response – for example by introducing an insect predator – but that is extremely expensive. Another solution is to use weedkiller, but that wouldn't be too popular with the donors who fund our programmes," Witt admits. "So we will almost certainly be doing the work by hand, helped by local communities."

The operation could be carried out in a few weeks, but that would only be the first step. "Feverfew seeds can lie dormant in the soil for several years before germinating, so it is essential to keep watch over the next five years," Witt explains. He reckons a monitoring programme would cost at least $65,000.

It may seem a ridiculously small figure in view of the natural heritage at stake. But "for us it is a large amount of money and we will need outside support", says Dr Judith Nyunja of the wildlife service. The decision to implement the plan is now in the hands of the Kenyan authorities.