Stepping up its campaign to protect avenue trees, the Paristhithi Samrakshana Samithi has started marking them as “protected trees.” The environmental agency's volunteers have decided to drape red ribbons around these trees to indicate that they should not be damaged. A spokesman for the group said here on Thursday that there had been attempts to cut branches of these trees so that the public could have a clear view of the advertisement boards put up on them by shopkeepers and advertising agencies. Volunteers of the samithi had recently foiled attempts to fell two trees on Mavoor Road. More recently, about 10 trees were badly damaged to put up advertisement hoardings near the bus stand. The samithi's campaign was jointly inaugurated recently by Murukesan, a cobbler; Sulochana, lottery-seller; Vishnu, a tender coconut vendor, and Harish, who sells tea by the roadside. All of them earn their living under the shade of avenue trees.