At these kinds of scales, the effects can be enormous. Just across the sea, Japan went on their own replanting crusade, and ended up with a huge pollen allergy problem [0]

Hopefully they have thought through the problem well enough that they don't run into anything major, but putting in the same trees that were there is logically the least dangerous. In BC Canada, the government required replanting on forest licensed crown land HAS to be a representative mix of seeds gathered from that forest, and its for a reason.

[0] https://www.nytimes.com/1995/01/17/science/japan-s-cedar-for...