Old forests sequester more carbon than new ones. When you cut down a tree, you leave half of it under ground, and when the roots break down all that carbon is released to the atmosphere.
It is far from straightforward whether it is better to leave the forests standing or cut down and replant. The forestry industry is of course claiming that a cultivated forest is better for the climate. The environmentalists are claiming that old forests that are left alone are better for the climate and in addition better for ecological diversity.
I tend to believe the side whose income doesn’t depend on their claim.