A treatise on improving the lands of Erebus.
Firstly, I want to preface this with the caveat that all elves have a natural synergy with the forest, and are somewhat foolish to not exploit this synergy via the Fellowship of Leaves religion. For most other races, while FoL may be useful in appeasing the masses for a time before something better comes around, almost any other religion will serve them better. This is due to the fact that forests (and therefor Ancient forests as well) are simply over rated. I will elaborate later.
First of all, to establish a standard for comparison, we must look at two things. The first being the base values of your common terrain:
Flat grass produces 2 food, Grass hill = 1 food, 1 hammer
Flat plain = 1 food, 1 hammer, Plain hill = 2 hammers
Ignoring forests, which are effectively a terrain bonus (for the most part) we can see that 1 food is roughly equivalent to to 1 hammer or:
1.) 2 food ~ 2 hammers
Now, this tells us nothing of commerce, so for that we shall look to specialists. Whiles specialists are not exactly the best analog for terrain improvement, they will serve our purposes in establishing a basis for comparison between the terrain improvements. This is because, while specialists generally require and are limited by certain buildings, the resources they provide are relatively static, save for some fairly substantial wonders and late game civic options. So, lets take a look...
Engineer = 2 hammers
Merchant = 3 gold
Sage = 3 beakers
Bard = 1 beaker 4 culture
Priest = 1 hammer, 1 gold
Here we can see that culture is clearly an inferior resource to gold and beakers, which both compare to hammers at essentially 3 to 2. Given that, we can say that:
2.) 3 commerce ~ 2 hammers
Combining this with 1.) we get our standard for comparison and establish that:
3.) 2 food ~ 2 hammers ~ 3 commerce
Now, to make this even simpler, I'm going to assign these all point values. So that we can stick with whole numbers, we'll take the common denominator of 6, making food and hammers worth 3 points each, and commerce worth 2.
With that settles, lets start looking at the improvements.
Farms start at +1 food (3pts) and become +2(6pts) by midgame.
Under Agrarianism you trade 1 hammer for 1 food, thus on plains the value of a farm is essentially unchanged, but grasslands, having no hammers, are boosted with an extra food (6 or 9pts). If you throw in Aristocracy you trade 1 food(3pts) for 2 commerce(4pts) (ignoring the Financial trait for this comparison) and so Aristo/Agro farms are basically worth 7pts and eventually 10pts. Without Agrarianism you're looking at a simple 1 point boost to farm value from 3 and 6, to 4 and 7pts.
Staying on the flat lands, we have towns next. These ramp up from 1 commerce (2pts) cottages to 4 commerce (8pts) towns after plenty of working and get another commerce with currency (for 10pts). (Kuriotates eventually get enclaves with an extra food and commerce for 15pts!) Then there's the simple workshop which trades a food for a hammer and throws in a commerce (for 2 pts) then with smelting gets another hammer (for 5 pts) and eventually gets another 2 hammers from guilds (for 11pts).
Now, lets talk about forests. They give you 1 hammer (3pts) and a minor health bonus which, in the long run, could potentially be worth half a food, so lets give it a point for that (for 4pts). The only thing you can really do with a forest is build a lumbermill which is going to add a hammer (for 7pts). (I'm not even considering the commerce you get along rivers, as without the forest, you would get that anyway.) If you happen to be persuing the Fellowship of Leaves/ Guardians of Nature strategy you'll be looking at another food from Ancient forests (for 10pts), but you cant build a lumbermill in ancient forests, so if it's not there when the forest changes you're only looking at ~7pts. (You could chop it down and plant a new forest and build a lumbermill when that new forest matured but before it became an ancient forest; it's just tedious.)(There's also the extra health and happiness under GoN, but that's harder to put a value to.)
Those exact same numbers apply to forests and ancient forests on hills, which makes for a good segue to mines. Mines start out at 2 hammers (6pts) gaining another in the late game at blasting powder (for 9pts) and can also get one from Arete (for 9pts, or 12pts with both). Last of all, there is the windmill, which can't even be built until the mid-game and gives 1 food, 1 hammer, 1 commerce (8pts). It gains another hammer and commerce with the next tech down (for 13pts).
So, a summary:
Farms = 3pts -> 6pts
w/Agr = 6pts -> 9pts (grasslands only)
w/Arist = 4pts -> 7pts
w/both = 7pts -> 10pts (grasslands only)
Town/Cottage = 2pts -> -> 10pts
<Enclave = 15pts (Kuriotates only)>
Workshop = 2pts -> 5pts -> 10pts
Lumbermill = 7pts (10pts w/ ancient forest)
Mine = 6pts -> 9pts (9pts -> 12pts w/ Arete)
Windmill = 8pts -> 13pts
Final notes: I tried not to dwell on it too much, but I want be sure I'm clear about forests. While the FoL/GoN strategy is a perfectly viable one (and can be quite powerful) it is also pretty limiting. If you're an experienced player, it's worth considering, but not something for the novice (unless playing elves). Outside of that, or being elves in general, forest are fairly weak. If you have no hills, you're definitely going to want to use those forests for a while, but for most well balanced city locations, forest are there to be chopped.
Kuriotate, embrace the megalopolis.
Always mine a hill, you may find some goodies.
Towards the late game, if you are at or near your health or happiness caps, start converting a few plots to workshops.
If you've made it to machinery and haven't started blanketing the countryside with windmill, you are a food.
I generally cottage plains and farm grasslands (and floodplains), and tend to lean towards Runes of Kimorph so usually follow the 3As (Agriculture, Aristocracy, and Arete) for much of the game.
There are many strategies, and your opinion may vary, but hopefully this clarifies some of the nuances.
