Plans to create 235 acres of new native woodland will see 150,000 new trees planted.
A variety of saplings, including oak and hazel, will be introduced on farmland above Gnoll Country Park.
The £2m Woodland Trust project is aimed at preventing flooding and will be funded through grants and an appeal.
The Neath Port Talbot forest will help deliver the next stage of the Plant! scheme, which sees a tree planted for every child born or adopted in Wales.
In addition to capturing 23,000 tonnes of carbon dioxide over its lifetime, Maggie Elsey-Cox of the Woodland Trust said it would help reduce the risk of flooding.
"Research has shown that by planting trees and creating a canopy, rainwater runs off the leaves at a slower rate and enters our streams and rivers at a slower rate, preventing high risk areas like in the valley here from flooding in future years," she added.
The Woodland Trust will consult with the people of Neath Port Talbot to name the new woodland.
As well as supporting existing wildlife, there are plans to graze seven heritage Welsh White cattle, an ancient breed, in the woodland.
The trust hopes to start planting the trees next spring and estimates it will take between 20 and 30 years for the site to mature.
Half of the required funding has been secured through grants, but the Woodland Trust has launched a public appeal to raise the remaining £1m.
Wales is one of the least wooded countries in Europe, with trees covering just 15% of land against an average of 37% within the EU.
The Welsh Government has set a target of creating 100,000 hectares of new woodland by 2030.