The trees to make way for the greenfield project include about three lakh casuarina and as many horticultural plants, official sources said.
Local people have voiced strong opposition against the move to clear the trees, arguing that they will be exposed to cyclone, tsunami and other natural calamities.
While a large number of women guarded the forest area, male members of the Posco Pratirodh Sangram Samiti, the organisation opposing the project, posted themselves at Gobindpur village to prevent entry of security personnel and government officials to enter the plant area.
''We will discuss the matter with the local people to ensure smooth progress of work in the proposed plant site villages,'' Jagatsinghpur district collector N C Jena said.
Jena, however, assured that an afforestation exercise would be taken up to replace the trees. Also the South Korean steel giant would create enough greenery in its proposed plant premises and adjoining areas.
''The trees mostly belong to the casuarina variety, a fuel wood. In any case the trees, planted by the Forest Department after the Super-Cyclone in 1999 need to be cut at regular intervals,'' Orissa's forest and environment minister Debi Prasad Mishra said.
Saying that the Union Ministry of Environment and Forest had already approved cutting of trees in the proposed plant site, the minister claimed that the state government had been following guidelines laid down for the purpose.
''There is no old tree or forest variety trees in the area,'' the minister said adding that a Supreme Court committee had also studied over the issue.
The minister also claimed that compensatory forest cover would be created as part of the measures to make up for the loss of greenery.
''So far we have chopped trees worth Rs 10 lakh. Now we are enumerating blocks of fruit-bearing trees. Those will be removed and their owners will be compensated as per the government rates,'' additional district magistsrate of Jagatsinghpur S K Choudhury said.
Trees belonging to horticulture varieties such as coconut, mango, jackfruit and cashew were now being cut, Chowdhury said.
''In monetary terms, we have estimated the total worth of the fruit-bearing trees, which need to be cut, at Rs 4.71 crore,'' an officer said.