By Alastair Lawson BBC correspondent in Dhaka

Members of Bangladesh's indigenous community are holding a demonstration in Dhaka on Saturday.

Omilla Nicola: angry about disruption to indigenous life

They are protesting at what they describe as ongoing encroachment by Bengali settlers into their ancestral homelands.

Representatives from most of Bangladesh's 45 indigenous groups will take part in the demonstration, staged to coincide with Indigenous Peoples' Day.

The protestors are especially angry over government plans to build a giant wall in the ancestral homelands of the Garo community in the north of the country.

Under threat

75-year old Krishna Nicola and his wife Omilla have cut wood in the forest of the Madhupur National park in northern Bangladesh for more than 50 years.

They are members of the Garo indigenous community and speak their own language and maintain their own cultural traditions.

In contrast to the rest of predominantly Muslim Bangladesh they are mostly Christian and inherit property through the female line.

But now they feel that a way of life which has remained mostly undisturbed for centuries could be seriously disrupted.

The government says the wall is needed to protect the forest

The Bangladesh government has begun work on a nine-foot wall in the National Park which ministers say is necessary to stop poaching and illegal logging.

It will span an area of more than 3,000 acres and separates Garo villages from their farmland and hunting grounds in the forest.

"This wall will make it a lot harder for us to go out and come into an area of the forest that is our ancestral homeland," Krishna Nicola says.

"We have been hunting and growing small plantations on this land for centuries. Now we are being obstructed.

"I cannot see why there is any need for this wall."

Omilla, is equally indignant.

She says that once the wall is completed, all the main roads going through the forest will be blocked, forcing them to pay a toll every time they want to sell agricultural produce in the nearby town of Mymensingh.

"It will disturb us enormously."

"All the indigenous people of this area feel angry that their homeland in the forest is either being cut down or made into a holiday destination for outsiders."

Human rights

There are few schools in the Madhupur area - apart from those run by Christian missionaries.

So there's not much opportunity for the children of indigenous people formally to learn their native language.

All over the north of Bangladesh, indigenous people say they are concerned over what they call encroachment onto their traditional homelands by Bengali settlers.

Nonimon Koch is a member of the Koch indigenous community.

He lives west of the northern town of Mymensingh.

"We received a notice from the forest department to vacate the area where our community have lived the last 600 years," he said.

"They gave us no explanation, we were only told to vacate the area within a few weeks."

Our communities are under threat," he said, "because Bengali customs are very different from tribal customs Albert Mankin, human rights activist

Indigenous people in Bangladesh are becoming more and more vociferous in asserting their legal rights.

Some like Albert Mankin have even formed human rights groups to campaign against the migration of Bengali settlers into indigenous areas in the east of the country.

"Our communities are under threat," he said, "because Bengali customs are very different from tribal customs.

"We are seeing our culture being systematically undermined by the majority community."

Mr Mankin says that while Bangladesh may be a unitary state, the government shows little enthusiasm for pluralism.

"The prime minister recently said that there are no minorities in Bangladesh, even though there are around 50 indigenous groups."

"In my view there should definitely be restrictions on the relocation of Bengali people to tribal areas."

Forest protection

The Bangladeshi Government argues that the reason it does not accept that minorities live in the country is because everyone is equal under the law to move around.

The Garo community have their own language and distinct cultural traditions

Ministers say that does not mean different customs and traditions are not respected.

The Environment and Forests Minister, Shajahan Siraj, says the wall being built in Madhapur is to protect the ecosystem of the national park.

"We want to make it a forest again in that area after so much illegal logging, and we want to make this somewhere that people outside the wall - tribal people and non tribal people - can enjoy."

Mr Siraj said that no-one was being forcibly evicted from Madhupur national park and no-one who lived in the area would be made top pay any tolls.

He said that the area surrounded by the boundary wall was in any case uninhabited.

But in one of the most densely populated countries in the world -- where pressure for land is immense -- its hardly surprising that Bangladesh's indigenous community feels threatened.