Wellington Monument champion John Greenshields has planted an oak sapling along the avenue at the landmark.
The sapling replaces a dead oak tree which would have been there when the monument was built 200 years ago.
Emma Jones, National Trust community engagement and fundraising officer (Wellington Monument), said: “This is a wonderful way to celebrate the Wellington Monument renovation project in 2019.”
The Blackdown Hills Woodland Association and The Woodland Trust gave the tree.
Some 600 other saplings have been planted in the area surrounding the monument as part of an environmental project to replace trees affected by Ash die back.