I agree that my estimate could be too big, but I do think there is a potential to increase the forestation in the north. Because of the warmer climate, Iceland can grow aspen. The government is planning to grow tree in a large part of the island, but the have a problem with free roaming sheeps. The land the can only sustain shrubs and moss could grow trees now.

Some countries are increasing the forestation as well https://www.citylab.com/environment/2018/01/northern-forest-...