Forests in Imperialism are of two types: scrub and hardwood, the latter being eventually much more valuable.
A scrub forest tile yields one load of timber per turn and cannot be improved.
A hardwood forest tile yields one load initially but can be improved by a forester up to three loads: $100 for the second, $1,000 for the third. The improvements are shown as little logging huts.
Forests can have railroads driven through them (and depots and ports built on them) as soon as railroads are invented, which is right at the start of a standard game.