A decision on whether to route Tullamore bypass through an area designated for conservation will be made by Offaly County Council within weeks.
The council is looking at three possible routes for the £30 million Tullamore bypass but has said its preferred route was one through part of Charleville estate, a woodland designated as a candidate special area of conservation (SAC).
The plan has met with opposition both from the local community and environmental activists.
Mr George Smith of Trinity College's botany department said it was ironic that the Millennium Forests Committee was planning to grow oak forests from acorns collected in the very native woodland the local authority was proposing to knock down.
"One is a perfect example of the direction we need to be heading in and the other would be taking two steps backwards. There is no point in planting new trees if we can't conserve what is there. The trees that are there already are much more valuable," he said.
The proposal to route the bypass through part of Charleville wood was an appalling prospect, he said. "These woods comprise one of the very few fragments of tall, well-grown native woodland left to us today.
"Ancient woodland in good condition is so rare in Ireland as to make this a living historic monument," he added.
Charleville wood was designated as a candidate SAC due to the presence of the vertigo moulinsiana, a rare species of snail, and the old oak woodland habitat.
Mr Charlie Fox lives next to the wood and is chairman of the Ballard-St O'Haras Residents' Association, which was formed to oppose the proposal. He said his main concern was preserving the wood but he also had concerns about increased traffic and pollution in the area if the bypass went through Charleville.
However, Mr Fox was optimistic that the Council, in making its decision, would not approve the destruction of the local heritage.
Another local man, Mr Cathal Byrne, said there was only a handful of heritage sites in Co Offaly of such European importance that they were designated candidate SACs. "We find it difficult to believe, given that there are all kinds of alternative routes, that the county council would want to put a road through one of the few sites we have," he said.
"Tullamore should have a bypass but there is no need to put it through Charleville wood. The county council certainly has not demonstrated up to now that this is the only viable option," he said.
The Offaly county engineer, Mr William Wall, said the council's preferred route "skirted" an area designated as a candidate SAC. Explaining the remark, he said the proposal was to "take in a small bit of it (the SAC)".
However, he said the council had not made up its mind on the bypass route and would not do so until Duchas, the heritage service, had examined the preferred proposal and reported back on how important it viewed the woods as being. He expects to have this report within weeks.
Mr Wall said the council was anxious to have the bypass go ahead to ease traffic congestion in Tullamore, but he said it had no intention of building the bypass through a sensitive area if Duchas felt this was not acceptable.
"We don't disregard environmental issues," he insisted.
Officials from the Department of Arts, Heritage, Gaeltacht and the Islands have met representatives of Offaly County Council and told them of the Minister's concerns about the proposal.
Ms de Valera has indicated she was anxious to have an ecological survey of the area to determine if the boundary of the candidate SAC should actually be extended.
Her private secretary said if this survey was incomplete before a planning permission decision was arrived at, Duchas would examine the environmental impact of the proposal and object if the bypass was likely to have a significant adverse impact on the conservation of the site.