"Many forests are destroyed in Cambodia - Areng is the last of our great forest areas", says Sothea Khmer a women's activist from Phnom Penh, explaining why she is here at the road blockade protest camp:

"We want to stop the Chinese company here. We don't want them to bring their machinery here to cut the trees, build a dam or dig mines in the Areng valley. The commitment from youth and monks joining us is that they have to stop the company. So they will dedicate their lives here."

Her words highlight the dramatic decline of Cambodia's forests which just ten years ago covered large swathes of the country. With some of the highest logging rates in the world it is estimated that since 1990, Cambodia lost 84% of its primary forests [UN FAO].

Now the struggle to save the untold natural riches of these ancient forests has closed in on this patch in the Cardamom mountains, still home to Asian elephants, clouded leopards and the most important breeding site of only 250 wild Siamese crocodiles found globally. Home in all to 31 endangered species.

The Areng dam is 'a criminal enterprise'

Here the last stand is being played out by activists and local indigenous Chong people. A protest camp hurriedly set up in March [2014] to stop Chinese dam builders entering the Areng Valley to start construction, has since been successful at repelling the dam-builders on several occasions.

As the tropical rain thunders down on the tarpaulin Meng Kheang Seang explains he has come from Phnom Penh to share his experiences. He supports local resistance by people being thrown off their land to make way for Government development schemes.

His friend Phoung shows photos of villagers in Kratie who have had their houses burned to the ground for refusing to move.

Alejandro Gonjalez Davidson asks to "add a little word to your description" when I ask about the Government's role in the dam: "it is a criminal enterprise, they have assassinated people and they are able to put people in jail and threaten people."

He explains how senior government officials often leading regional cartels, have systematically plundered the rich natural resources of the country with impunity.

A reluctant leader emerges

Quitting his job 18 months ago to dedicate himself to the campaign, Anglo-Spanish Alex speaks fluent Khmer having been living in the country for 11 years.

He has become the figurehead of a rapidly growing movement, which is attracting youth groups, activists and monks. It is a role he is wary of and he bemoans his bearded face gracing the new banners.

At the same time he cannot deny that the viral popularity of his Facebook videos, has been useful at spreading the message among Cambodia's youth.

They have even attracting funds from the many Cambodians overseas that fled the regime and along with at least half the population, deeply want to see the end of Prime Minister Hun Sen's 29 year rule.

The opposition party has been boycotting the parliament at what it sees as the unfair rigging of the elections in July 2013. This caused huge protests that were finally crushed by a bloody military crackdown which killed striking garment workers.

Still Alex claims the situation has improved as in the past the authorities would have been much quicker to reach for the gun and these days are prepared to negotiate - up to a point.

Fearful of deportation and wanting to play down his leadership role, Alex decides not to join the activists at the blockade now bracing themselves for the arrival of a platoon of soldiers to be stationed near the protest camp to support Sinohydro, the Chinese state-owned dam building company.

No environmental impact assessment has ever been published

The 1,640 mainly indigenous people living in the valley were due to be moved to a nearby relocation site called Veal Thom.

This has recently been rejected due to an outcry by conservation organisations keen to protect the elephant migration route that it would have severed. As yet no alternative has been put forward leaving villagers uncertain about their future.

Dam construction plans show it would include a pipeline, power station, accommodation for 1,200 workers and access roads. These would all add to the affected forest area, making the overall footprint of the dam site far greater than the proposed 20,000 hectare reservoir.

Forest observers are worried. The announcement to clear the neighbouring Tatai dam reservoir site, led to a feverish stampede of hunting and logging as outsiders flocked for rich pickings and inevitably the exploitation spilled into neighbouring forest areas.

Building of the almost complete Tatai dam has been carried out in secrecy at a high security Chinese compound off limits to most Cambodians and foreigners. Rumours circulating of poor working conditions at the site have proven difficult to verify.

Ame Trandem, Cambodia country director of NGO International Rivers, says details of the project under the new management remain obscure. "The project's Environmental Impact Assessment has not been released to the public, so has never been up for public scrutiny."

She adds that Sinohydro is notoriously difficult to contact and requests by the author to interview them were met with silence.

Huge cost, huge impact, for little electrical output

The Areng dam would be the fourth hydropower plant in the Cardamoms to provide energy to several provinces. It would be the first in the Cardamoms to displace people, the others having been constructed in forested areas.

This is all part of plans to increase electricity capacity to meet a national demand forecast to double by 2020.

With over 60 projects worldwide, Sinohydro is China's biggest dam-building company and is the third company to take on the controversial project. First China Southern Power Grid pulled out citing the fragile environment and more recently China Guodian Corporation departed saying that it was not economically viable.

This economic view is supported by the Japanese International Cooperation Agency. Its report for the Cambodian government concludes that the £200 million price tag will result in a high cost of electricity per unit compared with other dams, for the modest 108 megawatt output it would provide.

It also says the 16 mile long valley to be flooded is large compared to the electricity it would generate. Financing for the project is already guaranteed by the Chinese state Exim bank.

Is it just an excuse to log and grab land?

Comparing the dam with similar projects, activist Sothea says that it is primarily an excuse to exploit the natural resources through logging and mining. She sees eventual dam construction as merely the conclusion of an exploitative process.

Soon it becomes clear that the Minister of Mines and Energy is visiting regional capital Koh Kong to instruct local officials to carry out a series of meetings with the villagers in the valley.

Sothea explains the purpose: "The commune Chief calls meetings to force people to agree with him and to accept the compensation from the Government. He uses his role and brings the words from the top management especially from the Minister of Industry, mines and Energy."

Camp activists decide to attend the first meeting to support the villagers. Early morning, mist shrouding the forest canopy, a fleet of laden scooters sets out down the waterlogged trail through the jungle to the valley.

Locals have packed the local school of Chum Noeb village. The commune headman speaks first and seeks opinions about the government's compensation offer of five hectares of land for each family.

'We will destroy the company's machinery'

Mrs Hom Khat is the first of many women to speak out and flatly rejects the offer saying, "We don't need any compensation because we are staying here on the lands of our ancestors. Our children will never forgive us if we move."

Sothea speaks out reminding the audience that the project has not been officially approved and that the Government and company have recently stated that it will only go ahead after feasibility studies and fresh Environmental and Social Impact Assessments have been done.

She highlights that under these circumstances talk of compensation is premature and inappropriate.

The government official sent to oversee proceedings intervenes to say that this meeting is only for villagers to speak and that no more members of the youth group may do so and in future they must report to police. The youth group react angrily with passionate speeches about their freedom of speech, strongly rejecting the official's demand.

Kum Chae, the commune Chief of neighbouring valley commune Prolay, is feared locally for his past role as a Khmer Rouge official. Locals say he has been circulating photos of Alex and a fellow activist in the community in an attempt to discredit them.

But residents of the valley are growing wise to the official line and are increasingly joining the growing movement of resistance. Boek Sowan of the Chong tribe in the Areng valley remains defiant: "If the company try to build a dam in the valley we will destroy their machinery."

Rod Harbinson is a journalist, filmmaker and photographer who has reported on some of the biggest environmental issues confronting the developing world for over 20years. He has particular experience of the Southeast Asian region where he has documented and supported the struggles of indigenous and local people to protect their lands in the face of development.

Watch ‘Defenders of the Spirit Forest', a 25 minute documentary on the Cardamom Mountain forests by Rod Harbinson at: www.spiritforest.org

Sign the petition by Rainforest Rescue to Save the Areng Valley.

Support the campaign to save the Areng valley with Cambodian Campaign group Mother Nature.