"The lantana camara invasion is a challenge in Ngaya forest but the Lower Imenti forest is more affected because almost the whole of it has been invaded by the weed," said Mr Mukundi.
Concerted efforts by KFS, the Born Free Foundation, Kenya Wildlife Service and other partners have seen some parts rehabilitated.
"This is one of the few equatorial forests within the Mount Kenya Eco-system that must be conserved because it is a major water source. We must rid the forest of the weed to make sure rivers do not dry up. Less water in the park will drive the elephants and other animals out," said Born Free Foundation Country Director Tim Oloo.
"We have fought the weed very hard and recovered about 400 hectares in Lower Imenti forest. But about 2,000 hectares is still under threat," said Mukundi.
Peter Mugo, the officer in charge of Meru Forest, said 500 hectares of Ngaya forest was under threat and efforts were being made to protect the 3,000 hactares still uninvaded.
"Removing the weed is a very expensive exercise. Every time it is uprooted and burned, it sprouts again," said Mr Mugo.
Mugo said Ngaya forest, which is located in a very hot environment on the border of Meru National Park, must be reclaimed at all costs "because it is a very crucial water catchment area".
"Tourists visiting the Meru Park come to cool off at Ngaya. In addition, water levels would reduce if Ngaya forest is not protected," he said.
Ngaya boasts of a wonderful diversity of species and is an oasis in the desert.
Its location in a depression in the middle of a dry area bordering Kinna on the Isiolo border offers relief to locals, elephants and other species.
"Removing the weed is an expensive venture. It grows very fast. It is a species that chokes other plants," said Mukundi.
Mukundi said the weed "colonises" other plants by releasing chemicals that prevent species from growing.
"Its canopy prevents light from reaching other plants. It is an allelopathic plant, meaning it prevents neighbouring plants from growing," said Noah Okoba, a senior forester.
Mukundi said reclaiming areas under the weed would take time but locals who farm inside the forest had done 'good work'.