The heavily fortified barracks in Forkhill was a regular target for attacks.
It was sold by the Ministry of Defence to the Northern Ireland Executive and passed on to the local council.
It is now being developed as a community garden.
The tree planting is part of a wider project called the Peace Forest Ireland initiative.
It aims to plant 4,000 trees on both sides of the border in memory of those who died.
Children from St Oliver Plunkett's Primary School in Forkhill helped with the planting.
John Haughton of Forest Friends Ireland came up with the idea of the living memorial.
"The dream of peace has been realised, and that's the most amazing thing," he said.
The project is being managed by the Ring of Gullion Partnership - a conservation group.
Darren Rice said it was part of a wider initiative to increase the low density of tree cover in the area.
"Over the past two years we have planted around 120,00 trees in south Armagh," he said.
Oak, alder, willow and rowan trees are all being planted in the six acre site at Forkhill.
Many myths grew up around the army base during the Troubles.
Among the stories the locals were told was that an underground nuclear bunker had been developed at the busy helipad.
But when contractors moved onto the site to clear it for this project they found plenty of reinforced concrete, but no evidence of any underground structure.
A thousand trees are being planted at a former south Armagh security base as a memorial to those killed in the Troubles.