The author seems to assume that deserts are lifeless places, which is incorrect. Converting billions of acres of desert to a monocrop forest would kill the billions of plants and animals which have become adapted to that environment, which could also negate the emissions reductions. Monocrops are also ecologically unstable and easily destroyed by disease.
This is also being done in locations that were forests a few hundred years ago before humans cut them down. The mature forest is a self-sustaining ecosystem, but it needs extra water for a few decades until it reaches that point. https://www.westhawaiitoday.com/2020/01/12/hawaii-news/yisha...