Conservationists have warned that without work, the ancient gnarled tree which was made world famous by William Shakespeare could split in half.
The celebrated oak, which is at least 500 years old, featured in the "Scottish play" Macbeth and attracts thousands of visitors to the region each year.
Interest in the woodland was recently re-energised after last year's highly acclaimed film adaption of the Shakespeare tale starring Michael Fassbender.
The Perth and Kinross Countryside Trust hatched a plan to preserve the Birnam oak a study earlier this year revealed major concerns about its condition.
A spokeswoman said: "The ancient tree's trunk is hollow, but its long branches are still growing. Without remedial action, the significant strain they are exerting could cause the trunk to split in half.
"Based on recommendations from one of Scotland's top tree surgeons, the trust will carry out remedial works to mitigate these problems and keep the tree alive for years to come.
"The works planned include the removal of dead wood and some of the top and outer branches to help reduce the weight on the tree trunk."
For health and safety reasons, the popular walking route past the tree will be closed off from 7.30am to 7.30pm each day. The work is scheduled to finish on Friday, July 1.
The trust's spokeswoman added: "We are dedicated to the continued preservation of this historic tree and the improvement of its surroundings for the future us and enjoyment of the local communities."
Trustees assessed the oak and a neighbouring sycamore of a similar age after the woods were flooded in December, when Storm Desmond battered the region.
Although the floodwater is not thought to have cause much damage to the trees, it did affect the soil.
In Macbeth, the huge branches of trees in the Birnam wood are used as camouglage by soldiers as they advance on the Scottish king.
It is believed that the bard was inspired during a visit to the area in 1599.
The trust was set up to carry out projects to improve and promote access to the Perthshire countryside. It is an independent charity supported by the Gannochy Trust, Perth and Kinross Council, Scottish Natural Heritage and Forestry Commission Scotland.