DR GW Cross (Letters, February 2) argues that a field of trees and a field of crops have the same productive equivalence as they both fix similar amounts of carbon during an annual growing cycle. This is true but, aesthetics aside, the annual carbon extracted from the atmosphere by a stand of trees will likely stay fixed for many decades to come, whereas that fixed by a field of crops will be re-released into the atmosphere in a very short time period.

Growing trees can help reduce atmospheric carbon dioxide and thus play a role in combating anthropogenic global warming. Crops, on the other hand, are good to eat.

Bob Downie,

66 Mansewood Road, Glasgow.