I totally agree with covok48.
Forest tiles will give you 1 food and 2 production shields. And even with railroads the amount of food won't increase. And every inhabitant in your city will require 2 food. So starvation will occur if you 'reforest' your island.
Plains = max 3 food, Grassland tiles = max 4 food, forest = max 1 food.
So you 'lose' 1 or 1.5 inhabitants for each forest tile. You win back 2 or 3 shields, but I don't see why this shields would be more valuable than civilians. In most cities the production is not a big issue at the era you refer to (a advanced network of railroads). Maybe you can keep / recreate some forest tiles near 'producing cities' (cities that keep your army at strenght)