I always get this stuff wrong by using too many/few zeros but say 1 tree needs 100 sq. metres of land (10 by 10). 2 billion trees would need 200 billion square metres. According to the internet that = 77,000 sq. miles. The UK has an area of 96,000 sq. miles

Bit of a squeeze.

Actually, it’s easy. By keeping 1.9 billion trees that would otherwise train to become nurses & planting a paltry 100 million we would have 2 billion more trees! Simples!