The first one can't survive without the second, simply because trees would disappear and pretty much never return, and there would be large areas of nothing.
Forest Regrowth naturally:
Works a lot like the levels on animals near towns. They would rarely or never grow on claims or in town controlled areas. A certain distance around these areas they grow semi-rarely, and in the wilderness, they grow frequently. At a certain density, new trees stop growing.
Forest Fires:
Occur naturally at random spots and when seasons are implemented, they occur more often during summer, and with a larger distance of burning. I was thinking this could occur when a campfire was near a tree at a certain rate, but then I realized this would be extremely griefable. So this can only be naturally. Before seasons are implanted, they burn at a certain size and at a certain constant chance. If a flammable object is near such as a chest or a cabin, it catches fire. It takes a while to burn, so you would have time to throw buckets of water on the cabin to lower the fire. Only the roofs of mansions catch on fire, and they burn quickly. They would need to be repaired at full cost if it burns completely, another reason to lower the straw price on mansions. The warning would be a screen that pops up saying you see a fire in the distance maybe? Also on the mini map, the advancing fire is a light orange, and the longer an area it burns the darker shade of red and orange it gets. Eventually at a point, the middle, the fire starts to die out and the shade gets lighter until at one point the map is normal, except in that area there a ton of scorched trees. Scorched trees provide a lower quality product, say, q5. They eventually fall down and the dead logs rot slowly while new trees grow in. No animals spawn in a dead forest area, and they rarely travel there, but as the forest regrows, they slowly come back in.
Comments or suggestions to change anything?