Obviously, you do not know the difference between soft wood or sapling forests and those of hard wood ancient growth that spurred growth, and to some extent hindered it as well. Ancient forests were both a bane to early agricultural development but also a boon to lumber barons that used it for great wealth and production.
One could argue with any of the extended resources if it deserves attention in the game. It truly comes down to the vision of the designer, because anything in the game can be explained by hypothetical discussions of use or insignificance. I made the post to offer an idea, not to demand adding it -- to spur discussion not derision.
The same as Copper? Iron? Yes, early cutltures that do not have the hardwood resource would be at a disadvantage, but that is the strategy of the game, right? If you do not have horses, then you don't get cavalry. If you don't have copper, you lose out in axemen? Hardwood would simply offer another possibility for a civilization to utilize a resource for growth -- perhaps even conquest.
My main point boils down to the balance issue, and to the "you can't build ships without this" idea, which strikes me as a serious problem for the game at large.
Again, I wish to underline that every tile on the map is tens of thousands of square miles of land. If we look at what realistic terrain is like without human involvement, then except for the flattest prairies, tundras, and actual deserts, there are trees
everywhere. Even places like the African savanna have trees, just not very many of them.
Large, tall trees suitable for construction are harder to come by- but not
that hard, as demonstrated by the fact that except for civilizations that evolved in deserts and river valleys, nearly everyone managed to make things out of wood whenever they chose.
Remember that forested tiles represent much larger forests, ones that are hundreds of miles across, and since they're there from game start they are going to be old growth forest. It's not unreasonable to assume that decent building timber can be found in any forest tile on the map- maybe not the best timber, but still useful timber. They
do "hinder growth," particularly agricultural growth, though adding Camps to the game changes that balance in History Rewritten. And they're everywhere- any civilization on a normal map can be assumed to contain forest tiles. Getting rid of that more or less requires that the civilization deliberately chop down its forests for the hammers... which is quite logical, and which plenty of cultures did in real life.
But, to underline the point, forests, including old-growth forests of the sort that produce plenty of hundred-foot trees, are ubiquitous in a game set up on the scale of Civilization IV. That's why I don't think that you should need any special resource to build ordinary thing in ancient times- because wood was never that hard to come by for the ancients, except for a few very specific places like ancient Egypt and Mesopotamia.
Now, making Prime Timber (a la Colonization; I have fond memories of the original Colonization) give a
bonus to ship construction works- I wish I'd thought of it, or that you'd suggested it earlier. That would work all right, because it doesn't unduly penalize players without the resource, or create an ahistorical situation where my Greeks can't build triremes out of the trees growing on their own hillsides, as the historical Greeks could even though Greece isn't famous for its forests.
in our cities, but if an increased number of resource types are at the same time reduced in their occurence (and made really rare, like just two or three of them), the sum of 
