The problem is the majority of a tree's weight is water; to turn a Kg of carbon into tree requires about 1.8 Kg of water (that's from memory but it's order-of-m

The problem is the majority of a tree's weight is water; to turn a Kg of carbon into tree requires about 1.8 Kg of water (that's from memory but it's order-of-magnitude right). This isn't necessarily a non-starter but it's a huge practical problem with trees in particular (IIRC bamboo is a better candidate).