Allow me to repost one of BLubmuz' screenshots here, to make my text easier to understand:
When setting up a "path" for a Fast Worker to pre-chop or straight chop Forests, sometimes you will find that two Forests are equally adjacent to the current square, so you can pick between them.
So, which should you choose?
Well, a Forest can grow horizontally or vertically into a non-Forested square. That non-Forested square has to be of a type that can grow a Forest (so a Desert or a coast won't work), not have a Resource on it (except for a couple of exceptions, such as a Deer or a Fur), not have an improvement on it, and not already have a Jungle on it. Let's call such a non-Forested square that can actually get a Forest a "Forest Eligible" square.
The more horizontally and vertically surrounding squares that have a Forest surrounding a Forest Eligible square, the greater the chance of a Forest growing in the Forest Eligible square.
So, the best Forest to chop is one that has Forested squares on 4 sides of it. Such a square is "wasting regrowth potential," as none of the surrounding squares can currently receive a "new" Forest until the old Forest is chopped down, while the square that has 4 Forests around it also can't receive a "new" Forest.
Since we want to maximize our chances of Forest regrowth, the more Forest squares that we chop which could potentially "spread" a Forest, the less chances for spreading we will end up with.
So, there needs to be a balance between selective chopping (chopping Forests that are likely to regrow) and clear-cutting.
Other squares to target early on are those that will hardly ever see any chance of Forest regrowth and will hardly help horizontally or vertically adjacent squares to regrow. For example, a square that has a city and 3 improved Resources surrounding it will never regrow, nor will it help any other Forests to regrow. Such a square is our 1S of Delhi Grassland Forest River square.
Such a square is not benefiting us at all by being a Forest, except for the long-term potential to use it for Hammers or 1/2 of a Healthiness point. But, if we're planning on chopping most Forests eventually, we might as well chop one now that "doesn't encourage Forest regrowth" before chopping one that might spread to a nearby square.
Here's another example: the Grassland Forest River to the NE of Delhi is a good one to chop. It is surrounded (horizontally and vertically) by 3 Forests and 1 Resource, meaning that it can't spread anywhere. Once it is chopped, there are 3 squares that could spread a Forest back onto it.
Here's yet another example: The Grassland Forest River square to the SE + S of Delhi is not a great Forest to chop, as no Forest exists to regrow there, while two squares (the Tundra Hills square 1E of it and the Grassland 1S of it) can get a Forest spreading from this square.
Here's another example, that may appear to contradict a previous example: a square that is surrounded by 4 Forests might be a good square NOT to chop. Instead, chop all of the surrounding Forests and hope that one of those squares gets a Forest to spread back onto it. Here's a location that might apply: W + W of our capitol. While chopping the square W + W of our capitol would have the greatest chance of regrowth, 3 of the surrounding Forests can ONLY grow in 1 direction--back onto the W + W of the capitol square (and only after that W + W of the capitol square is chopped). The only "surrounding" square that can grow elsewhere is the one to the north of the W + W of the capitol square, as that Forest can also spread 1N of itself (i.e. spread to the square that is 1NW of the Copper). By chopping this centre square instead of the surrounding squares, the Forests that we "leave" will have a total of 5 "regrowth possibilities."
For this example, if we instead chopped all of the surrounding squares, we'd end up with 7 "regrowth possibilities": W + W -> 1E, W + W -> 1S, W + W -> 1W (and two other Forests would also potentially regrow said Forest), and W + W -> 1N (and one other Forest would also potentially regrow said Forest). By just chopping the W + W square, we'd only be have 5 regrowth possibilities, while only being able to chop 1 of said Forests, as opposed to getting 2 extra regrowth possibilities PLUS 4 chops out of the bargain!
This example is SLIGHTLY skewed, because the Forest 1S of the W + W square should actually be saved to help chop Moai Statues in Silverado, but the overall idea still holds, since we'd still have 6 regrowth possibilities (as opposed of 5 regrowth possibilities from chopping the W + W square) while being able to chop 3 Forests in the bargain (as opposed to just 1 chop).
Why am I telling you all of this stuff?
Well, if you've read this far, you're interested in learning. You probably also like thinking about math problems.
But really, it's so that we can come up with a chopping plan that meshes together well, instead of just chopping hap-hazardly without considering the impact that the current chop will have in dictating where the next chop should occur.
