The felling of 6,500 larch trees in Belvoir Forest – home to the oldest known trees in Ireland – is now under way.
The drastic measure was decided upon after trees in the Belfast forest were found to be infected with the virulent Phytopthora ramorum fungus, which has devastated Japanese larch plantations across Northern Ireland.
The disease is spread through the release of infective spores and affected trees are soon killed.
A spokesperson for the Environment Agency said some of Belvoir's trees were present when Belfast was little more than a village.
"Many of these veteran trees are growing within the larch plantations that need to be felled. In many ways, this felling should ultimately benefit the veteran trees and we have worked closely with Forest Service to ensure that the felling of disease-affected trees is carried out as sympathetically as possible to minimise the potential threat to the veterans.''
More than 220,000 trees have now been felled across Northern Ireland after becoming infected.