Mr Hill described last week's resolution to allow only eucalypts likely to grow no more than five metres high to be planted within eight metres of the roadside as "hasty and ill-informed."

Council had ignored the advice of its own experts in passing the resolution at last week's meeting, he said.

"The problem is not so much that the resolution was passed because it is probably legally unenforcable, but because it shows an abysmal lack of understanding by the majority of councillors about the importance, value and underlying processes of the natural environment in general and the roadside reserves in particular," said Mr Hill.

"It is a bit like having the National Parks run by accountants and real estate agents who weren't prepared to consult experts on the things that they did not understand."

Mr Hill said that as the width of most road verges was less than eight metres, the resolution would effectively exclude all eucalypts from roadsides.

"To be healthy, the vegetation on roadside reserves needs to be constituted with the natural three layers of a tree canopy, an understorey of shrubs and a groundcover.

"There are few eucalypt species in the Southern Highlands that grow to less than five metres, and there would be large areas that do not have any such species that are native to the area and thus be available to recreate the canopy," he said.

Mr Hill said the reserves could be the last refuge of threatened and endangered plants and animals, and might be the only connection to other isolated areas of bush.