Thousands of herbivores at the Lake Nakuru National Park are staring at uncertain future as alien plant species continue to swamp pastureland at one of the country’s most visited wildlife sanctuaries.
Several studies conducted by environmental scientists and plant ecologists have identified more than 100 invasive plant species but zeroed in on at least 15 which they say are an immediate danger to the existence of large mammals in the park.
According to the Kenya Wildlife Service (KWS) the offending plants, which include Tarchonanthus camphoratus or mkalambati in Kiswahili, are invasive (replace other vegetation), toxic or unpalatable, meaning there’s less forage available for wildlife to feed on.
Of major concern to conservationists is that rhino habitats at the park are increasingly being walloped by Tarchonanthus camphoratus, one of the most ecologically destructive bush land species also known as the camphor bush.
In a research dubbed “The effect of invasive plants on the abundance and diversity of black rhinoceros (Diceros bicontis) food plants” conducted by Joyce Omari Kanini of University of Nairobi, School of Biological Sciences mkalambati invasive species may within a few years overtake and suppress the more palatable rhinoceros food plants, few of which grow beneath its canopies.
“Food availability and quality are major determinants of habitat suitability in order to sustain viable rhino populations. Productivity of the black rhinoceros can be increased by removing all factors that threaten food availability and quality and this includes control of invasive plants,” she states.
The Park which was declared a rhino sanctuary in 1980s and has been used as a breeding haven currently has a population of 14 white and 66 black rhinos. Two other independent findings have established that Tarchonanthus camphoratus now occupies about half of the park.
The Kenya Wildlife Service Director General, Brigadier (Rtd) John Waweru concedes that invasive plant species and habitat loss are rated as among the biggest threats the park faces.
“To sustainably conserve the park and maintain its ecological integrity, these threats need to be addressed and that is the reason we launched the Rapid Results Initiative to address factors that affect the integrity of Lake Nakuru National Park’s ecological balance.
I dispatched a team of research scientists who are carrying out a situational analysis of the park with a view to identifying areas that needed special attention to bring it back to its former glory. Greater emphasis will continue to be placed on management of species and habitats,” observes Brigadier Waweru.
A report jointly compiled by the Kenya Wildlife Service (KWS), Egerton University, Kenya Education Network (KEN) and IT University of Copenhagen titled “Monitoring Lake Nakuru Using Wireless Sensor Network (WSN)” cites prickly berry (Lantana camara), Sodom apple (Solanum incanum L.), and Jimsonweed (Datura stramonium L.) as invasive plant species that have colonized most of what used to be pastureland for buffaloes, warthogs, impala, rhinos, waterbucks, giraffes, zebras and bushbucks, among other herbivores.
Other invasive species include Long spine cactus (Opuntia exaltata L) Mexican marigold (Tagetes Minuta), castor oil (Ricinus communis L.), the Stinging nettle (Urtica dioica), black jack and (Bidens Pilosa) among a host of others.
As invasive species reduce pastureland, unexplained decline of predator species particularly lions at the Lake Nakuru National park means a steady rise in herbivore numbers and reduced food for bulk eaters such as buffaloes some of which die when drought occurs.
A World Wide Fund for Nature – Kenya census conducted last year at the Lake Nakuru National Park found only 16 lions against a widely held expectation of 60.
According to Brigadier (Retired) Waweru the park is also home to 4,100 buffaloes, about 5,000 impala, and hundreds of warthogs, waterbucks and other animals.
The KWS does not cull animals within the protected parks even when certain species increase beyond the carrying capacity.
The International Union for Conservation of Nature (IUCN) says the numbers of animals that researchers have raised a red flag over their decline at the park due to reduced pastureland include the waterbuck and the buffalo that has borne a very heavy brunt due to the invasion and destruction of their usual habitat of tall grasses and shoreline bushes.
The KWS has been reluctant to use prescribed fires as means of destroying the invasive plant species because of fear of destroying the remaining pasture. Mechanical manipulation has also been considered in the past but not implemented.
In her presentation during the launch of Rapid Results Initiative Lake Nakuru Senior Park Warden Catherine Wambani observed that invasive species may affect native species by introducing pathogens or parasites that cause disease or kill native species. Tsetse flies have been found to take cover under Lantana camara.
“To untrained persons some of these invasive species are very beautiful flowers and ornamentals. Alien plant species have negatively affected the habitats and ecosystems at the park environmentally and ecologically. They have altered the diversity of native plants and posed unfair competition. The balance of nutrient cycling and hydrology has been disrupted.
Both old and newly established invasive species contribute to land degradation through soil erosion and the drawing of water resources, reducing resources available to people and indigenous plants” she explained.
According to a study headlined “The Effect of Invasive Species Lantana Camara on Soil Chemistry in Wildlife Protected Areas and National Parks”, the author, Marystella Nango’ni Wekhanya, a plant ecologist indicates that protected areas close to human settlements such as Lake Nakuru, Nairobi National Park and Ol- Donyo Sabuk National Parks face an increased risk of being invaded by both native and non-native invasive species.
“In Kenya protected areas like Nakuru National Park, Nairobi National Park, Oldonyo-Sabuk National Park, prickly berry (Lantana camara), is threatening the habitats and biodiversity. Besides drastically altering soil chemical properties such as pH, mineral composition and mineral levels invasive plant species have also led to deaths of wildlife when they feed on poisonous species.
Alien plant species are a threat that cannot be wished away as they have special survival traits that native species do not possess such as ability to reproduce both asexually as well as sexually, rapid growth, early sexual maturity and high reproductive output.
They have been found to possess the ability to disperse young widely, tolerate a broad range of environmental conditions, high phenotypic plasticity (ability to alter growth form to suit current conditions) and allelopathy (production of chemicals which make the surrounding soil uninhabitable, or inhibitory, to other competing species). As native plants are displaced, animal populations that rely on the plants for food and shelter also decline”, states the Plant Ecologist.
Some of the invasive species choking Lake Nakuru National Park are native to Mexico, Central America, tropical South America and the Caribbean. They were introduced during colonialism as garden plants and windbreaks.
Wekhanya observes that prickly berry (Lantana camara) that was introduced in Kenya in 1950s as an ornamental plant has now completely established itself and out-competed the indigenous species as shown by its high-densities in wild life protected areas.
The KWS Assistant Director Central Rift Conservation Area, Aggrey Maumo noted during the Lake Nakuru National Park Recovery Strategy meeting that increased human encroachment and climate change were critical factors contributing to emergence of new invasive plant species in both flora and fauna at the once highly acclaimed wildlife refuge and international tourism site.
“This park entirely surrounded by settlements hence the inherent biodiversity is being adversely affected by invasive species. Any control and management strategies put in place in the park will incorporate the surrounding community areas. Their spread must be addressed through research, monitoring and active management to ensure that the food plants of all herbivores are in large supply, maximize productivity and hence sustenance of native plant and animal life.
Invasive plants at this park have reduced or displaced both native plant and animal species and altered the ecosystem function. Others have transformed grazing fields by producing chemicals which make soils that support grasslands unfavourable” explained Maumo.
The researchers are in concurrence that spread of invasive plant species in the park is bolstered by findings that primates (mainly Olive Baboons) and several feeding guilds of birds within the park were active feeders of seeds and nectar from most of these alien plants.
“Several species of birds were noted to move from one type of invasive plant species to another. This was more often during the dry season surveys and could be a coping strategy to reduced food but can also play a role in hybridization of closely related species. Mammals and especially primates and squirrels were recorded as active feeders of the invasive species” reveals Ms Wekhanya.
The Environmentalists further warn the threat posed by invasive plant species at the Lake Nakuru National Park may be aggravated as natural bio-geographical barriers like oceans, mountains, rivers and deserts that provided the isolation essential for unique native species and ecosystems to evolve have lost their effectiveness due to increased global trade and tourism.
“Modern technological advancements mean increased global movement of people. This has resulted in an exponential increase in the movement of organisms from one part of the world to another. There has been tremendous ecosystem damage which has translated into immense decline of native plant species”, states the joint report compiled by the Kenya Wildlife Service (KWS), Egerton University, Kenya Education Network (KEN) and IT University of Copenhagen.
The environmentalists have suggested several methods for control and management of invasive plants including chemical, biological and mechanical methods. Management aspects entail eradication, containment, control and mitigation strategies.
They say that the most applicable option in a given area should be based on the intensity of infestation that will inform eradication through physical or mechanical removal and minimizing the factors that are related to dispersal.
By Anne Mwale