Trail builders and riders were caught off-guard by the decision to remove almost a quarter of the forest, and with it the many hundreds of hours of volunteer work to design and create the recreational drawcard.

Kowalski Brothers volunteer trail builders co-ordinator Alan Vogt said he was told about the plans on May 24, just two weeks before the forestry operations were slated to begin.

He said some of the work was expected, having been discussed for the past two years, but it was the first time they had learned of the Millpost Road clear-felling plans.

There were concerns the annual Kowalski Classic, which attracted almost 1000 riders last year, would not go ahead, but organisers were told on Saturday that forestry works could be halted to allow it to proceed.

"We had not expected this," Mr Vogt said.

"It's actually a massive impact when overlayed on the trail network. It looks to remove as much as 70 per cent of the trail network over the next five years. That was a bit of a surprise."

Mr Vogt said the trails were built with the permission of the land manager, and there was always the knowledge that logging operations would impact the network. However, he said the new plans were "going to create a lot of change in a short period of time and dramatically affect the riding out there".

"It looks to be something like 85-90 trails will be removed over the five-year plan," Mr Vogt said.

The initial winter plan will affect 31 trails at East Kowen. There are about 120 kilometres of trails overall, Mr Vogt said, built and funded completely by volunteers. He expected if they were commercially built, it would have cost between $2 and $3 million.

Mr Vogt said he believes the trails could be reinstated following the forestry work, but it would be down to volunteer builders. He said losing the large amount of trails would impact cycle tourism.

A University of Canberra health and wellbeing expert believes if the government could quantify the tourism and recreational benefit of the area, it could outweigh the income from forestry operations.

UC Canberra urban and regional futures recreation consultant Anthony Burton described the forest as a once in a generation asset.

Mr Burton said at the very least, the government should hold off on the clear-felling until the tourism cycling strategy was completed.

"I think we need to be holding back and going let's wait and see until we've got it right before we rush to chop down those trees. We won't have anything like this out there again for 20-25 years."

A spokesman for the ACT government said 200 hectares per year for the next five years would be clear-felled, returning about $5 million per year to the territory. The spokesman said the plan was communicated with the mountain biking community.

"The primary purpose of Kowen Forest is commercial forestry. Kowen Forest supports 4,500 hectares of softwood plantation," the spokesman said.

"Mountain bike track builders have been engaged by the Parks and Conservation Services since they have been actively constructing trails and always with the express knowledge that harvesting operations would one day impact on the trail network."

"Clear felling operations will attempt to preserve as much of the mountain bike trails as possible, and once clear felling is completed, the area is once again open to the construction and maintenance of trails."

The spokesman said the government remained committed to supporting the mountain bike community in the ACT.