The broad plains of Mugie, a huge estate on a high plateau northwest of Mount Kenya, are crisscrossed with cattle trails and the wildlife is mostly gone.

The knee-high grass remains, but not for long, reckons manager Josh Perrett.

Tensions between semi-nomadic pastoralists and settled landowners are nothing new, nor is competition between livestock and wildlife, but in Kenya's central Laikipia highlands they are taking a destructive, sometimes violent turn.

Last month perhaps 30,000 livestock arrived on Mugie, displacing wildlife. The illegal herders -- some armed with spears, others with AK47s -- cut through fences, making off with wire and posts. The shooting, looting, poaching and rustling that accompanied them left Perrett despondent.

"Twenty years of time, effort, sweat, money... it's fallen apart in two weeks, destroyed," says the 35-year-old.

"Before, you would see elephant, a few hundred head of buffalo, Jackson's hartebeest, oryx, Grant's gazelle, impala. Now you see thousands of head of cattle, a lot of sheep and goats."

At the 44,000-acre (17,600-hectare) Suyian ranch, south of Mugie, thatched huts for tourists were burned down and shots fired this week as herders swept in. Black and white landowners alike speak of invasions, fear and siege.

- Too many people, too much livestock -

The dangerous situation in Laikipia is an acute expression of a chronic and complex tangle of population growth, livestock increases, overgrazing, erratic rainfall, climate change, weapons, money and politics.

A recently published four-decade study by the International Livestock Research Institute in Nairobi uncovered "catastrophic... widespread" declines in Kenyan wildlife as herds of livestock displace wild animals.

The data was Kenya specific but the problem is continental.

"At the basis of all this is the human population explosion," says lead author Joe Ogutu.

The report blamed "policy, institutional and market failures" and said regulation was needed to reduce livestock numbers, which have increased 76 percent while wildlife fell by 68 percent.

As pastoralist populations have grown so have their herds, grazing sparse pasture into desert. Exacerbating the situation, the value of cattle has increased dramatically, making it a smart investment for urban elites, a mobile bank account hidden from scrutiny and taxation.

When land can no longer sustain their livestock, the people move.

In Kenya, Laikipia's private and community reserves and ranches are the grassy frontier between the pastoralist north and the agricultural south.

"Population growth, livestock growth, that's the pressure on conservation," said Tom Silvester, the 49-year-old manager of Loisaba, a 56,000-acre conservancy to the east of Mugie which is recovering from large-scale illegal grazing last year.

Tens of thousands of cattle a day reduced Loisaba's grass plains to tufts of dry sedge and stubble, spike thorn, acacia and shimmering croton bushes.

- Legal vs. illegal grazing -

Well-managed, grassland acts like a reservoir in tough times.

Loisaba, Mugie and others have established controlled grazing programmes with neighbouring communities enabling the survival of both livestock and wildlife, but the system breaks down when huge herds arrive.

"We are neighbours with Loisaba, we are part of the whole thing," says 70-year-old Lesibia Larari, with 70 cows and silver rings in his stretched earlobes. "We have a stake in it but the others do not care about being good neighbours."

Adowan Letowon, a 28-year-old Samburu "moran" or warrior, with a long knife in his belt and a mobile phone in his hand, has relied on Loisaba to get his cattle through every dry season and drought since he was 13.

"We have been here for long. Our children, our cattle do not die because of this land," he says.

In easier times neighbouring communities are a buffer against illegal grazers, but when they come in their hundreds with tens of thousands of cattle they are unstoppable.

Nevertheless, "the answer is not fences and guns, it is conversation and understanding," says Charles Lekalasimi, a 24-year-old Samburu university student interning at Loisaba.

Like most of the herders -- legal and illegal -- Lekalasimi is a moran.

He understands the social value of cattle and, he says, his agemates listen when he tells them 50 fat cows are better than 200 skinny ones. But, he warns, the warlike culture of morans means, "If you try to be aggressive or violent, they will knock you down!"

- A looming disaster -

Conversation and understanding look a lot like capitulation.

Perrett is negotiating with the Samburu and Pokot to leave their guns and dogs behind, stop killing the wildlife and keep sheep and goats out in return for access for less destructive cattle.

But he expects Mugie to be "a dust bowl" by the time they leave.

Meanwhile, the wildlife tourism that drives the conservancy's business model is suspended. "What we were selling, you can't sell that now," he says.

Managing coexistence in an evermore crowded world is a challenge for individuals and government, but residents and landowners criticise Kenya for not playing its part.

Last month President Uhuru Kenyatta condemned those who "invade land" in Laikipia but took no action against lawbreakers, while local leaders have stoked tensions by encouraging pastoralists to take grass they say belongs to the herders.

With national elections due in August, few expect vote-costing action against the illegal grazers, while the ethnic logic of Kenyan politics means some candidates stand to benefit from a favourable shift in population dynamics ahead of the vote.

"The solution is coexistence, talking, dialogue. Recognising that resources are limited and working out how to equitably divide it between wildlife and livestock," says Silvester.

But if that fails, if the law is not applied to protect land, if livestock herds are not reduced to a sustainable level, if land management is not improved, the coming disaster will hit everyone and everything, he says.

"If we don't succeed, the terrible, apocalyptic vision is the guy sitting on a rock in the desert, with a begging bowl waiting for food aid."