The plantation are located in state forests, Wiratno told a seminar on the role of the private sector in conservation of Harimau tigers at the Andalas University here.
"Generally , they are located in state forest areas beyond effective coverage of control by government," he said here on last weekend.
The perpetrators, mostly people from other regions outside Riau cleared the forests to open plantations, he said.
He said the government could not fully control the areas partly because of limited number of officers.
The impact is narrowing forest areas and the habitat of wildlife including Sumatra tigers, he said.
Wiratno did not say if any legal action had been taken against the illegal oil palm plantations . Oil palm plantations had been blamed environmentalists for extensive damage to the countrys tropical forests.
The European Parliament has even approved a resolution to boycott the countrys palm oil and derivatives for alleged damage to the countrys forests by oil palm plantation companies.
Wiratno only said that solution has to be found for the problem as it concerns not only conversion in the function of lands but also the habitat of the rare species such as Sumatra tigers.
"Shrinking population of wildlife in the world is partly caused by loss of habitats, he said.(*)