A 91-year-old woman has spent 4½ hours locked to a gum tree in Victoria's west in an attempt to save it from being knocked down.

Isabel Mackenzie chained herself to the river red gum on the side of the Western Highway near Buangor, 74 kilometres west of Ballarat, about 7am on Monday.

Isabel Mackenzie, left, has locked herself to a rover red gum in protest at its slated removal. Credit:Ararat Advertiser

Helen Lewers, who was chained to the tree with Mrs Mackenzie, said VicRoads should reroute the highway between Buangor and Stawell to preserve the native roadside vegetation.

The protest ended at 11.30am, when the pair decided to unlock themselves.