By Dr. Elizabeth Migongo-Bake, Chair, FoNNAP’s Habitat & Wildlife Committee

Nairobi, July 14 – The Nairobi National Park and the neighouring private wildlife sanctuaries are under a major threat from parthenium hysterophorus, a weed that is rapidly eating into the grazing area for wildlife, reducing fodder and grasses by replacing its indigenous annual species vegetation.

Parthenium hysterophorus (here going by just the name parthenium) of the family Asteraceae (Compositae), is a weed of semi-arid, subtropical, tropical and warmer temperate regions. It is particularly aggressive in degraded or disturbed pastures in semi-arid environments. From its origins in the South and Central American tropics, Parthenium has become a widespread invader of rangelands and cropping fields in at least 34 countries in Africa, Asia, Australia, and the Middle East where it is invasive and threatens food security, biodiversity, and human and animal health.

Its adaptability to a wide range of habitats, drought tolerance, ability to release toxic chemicals against other plants (allelopathy), rapid growth rate, and prolific seed production allows the invasive weed to colonize new areas quickly and extensively.

Parthenium was declared a noxious weed in Kenya in 2010 under the Suppression of Noxious Weeds Act (CAP 325), yet there is no national programme for its removal. Its presence has been reported in the Serengeti, the Maasai Mara Game Reserve, Amboseli and in most of Uganda’s Protected Areas, especially Queen Elizabeth National Park. Hence, it could become, if not already, an East African regional crisis.

Parthenium is unpalatable to grazers so its invasion results in grazing shortages. If left to spread unchallenged, the weed can replace native vegetation and remove the food sources of many herbivores. Given the current widespread nature of the invasive weed in the park and the potential threat it poses to the food source of herbivores in the park, its removal has, in 2021, become the main focus for Friends of Nairobi National Park (FoNNaP), led by its Habitat and Wildlife Committee, in collaboration with the Kenya Wildlife Service (KWS). FoNNaP has been given the leadership by KWS to ensure a scientific and systematic approach to the removal process.

Starting in May 2021, FoNNaP in collaboration with KWS has made parthenium removal a weekly event with youth drawn from the Community Scouts allocated to KWS through the national government’s scheme to create employment for the youth. Also, once a month FoNNaP holds a removal event where other youngsters from all walks of life in Nairobi, such as universities and informal sectors are supported by KWS and FONNaP members to come for a day in the park and help with the parthenium removal.

There are also other groups working directly with KWS on invasive species removal. The programme is proving successful and the combined effect of these concerted efforts has seen remarkably large areas of the park cleared of this weed. This is only for now, though, as the thousands of seeds in the soil from the last several flowering seasons of the weed will germinate with the right moisture and temperature conditions. It may, therefore, take 4-5 years with continuous removal of new growth before the park can be completely free of parthenium.

Under ideal conditions, parthenium can mature in 4-6 weeks and produce anything from 10,000 to 25,000 seeds from a single plant. The soil seed bank contains millions of seeds that can survive in the soil for several years, waiting for the ideal conditions to germinate.