Over 1,200 new trees and 10 mini wooden “homes” are being placed in a Caerphilly wood to protect dormice.
The wild animals have gradually disappeared from Coed Craig Ruperra woodland since tree felling began in the 90s.
The Woodland Trust has provided hazelnut trees for mice to feed on and up to 30 mice have already been found sheltering in the nest boxes.
Planting started in November and is set to continue until 2015.
Austin Brady from the Woodland Trust said: “Dormice spend most of their waking hours in trees and shrubs looking for food.
“Over the years, habitat destruction has affected both populations so it is essential we protect woodland environments.”
The Coed Craig Ruperra project is part of the UK-wide “Foot of Forest” campaign which has received £2.1 million of funding from furniture giant IKEA.