At this time of year hundreds of thousands of wildebeest charge across the Mara River on their way to fresh grazing lands. In one of nature’s great spectacles, they run the gauntlet of rushing waters and snapping crocodiles, in a display that is quintessential Africa.

Campaigners warn, however, that the destruction of Kenya’s biggest forest threatens this natural wonder. “At the moment the river crossings are not a tourist spectacle,” said Brian Heath, chief executive of the Mara Conservancy, where water levels on the river are now among the lowest ever recorded.

About a quarter of the 400,000ha Mau Forest that sprawls across the rolling hills of the southern Rift Valley has been destroyed by politically motivated land grabbing, illegal timber felling and charcoal production. The Mau is Kenya’s most important water catchment, acting as a huge sponge absorbing rainfall and controlling its release into rivers. Without that control the rivers flood or dry up.

Conservationists say that the deforestation has already taken its toll on Kenya’s wildlife. Some blame destruction of the Mau for the floods that drowned 15,000 wildebeest during the 2007 migration. “Without the Mau Forest there will be no Masai Mara,” said Tuqa Jirmo, Kenya Wildlife Service (KWS) chief warden for the area.

The destruction of the forest threatens not just East Africa’s most famous safari parks — the Masai Mara and Serengeti — but its economic future. Rainfall over the Mau feeds a dozen rivers and five lakes, including Lake Victoria. The rivers irrigate farmlands and turn the hydroelectric turbines that drive Kenya’s economic development; the lakes are home to a multitude of birds and wildlife and the forest-clad escarpment ensures the constant moisture needed for growing tea — one of Kenya’s biggest exports.

“What we’re dealing with here are the core economic sectors for Kenya: energy, tea and tourism,” said Christian Lambrechts, at the United Nations Environment Programme.

Areas that were once thick virgin forest are now patchworks of maize fields, or have been cleared for the valuable hardwood. Elsewhere there are apocalyptic landscapes of blackened tree stumps dotted with smouldering charcoal kilns.

Mwalimu Mati, chief executive of Mars Group Kenya, a media watchdog, said: “The Government uses land titles to win votes [so] there is a pattern of land allocations coinciding with elections.”

The vote-buying and distribution of the Mau began with multiparty democracy in 1992 under President Moi and continued today, he said.

As many as 150,000 settlers now live among the increasingly sparse trees, and with each new national poll has come another round of land theft — and subsequent deforestation — in exchange for votes.

However, last month the Prime Minister, Raila Odinga, signalled that the political parcelling out of the Mau may be at an end as he handed Parliament a list of 49 individuals and companies that were wrongly given 18,000 hectares of the forest. The Government has approved plans that settlers be evicted while others — if they can produce the right title deeds — will be compensated.

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