A lot of boreal forest does need low-intensity fire. This spaces trees out and prevents fuel accumulation so that the trees largely survive.

If you let things go, you end up killing all the seeds in the soil when an intense fire comes through, and depending on whether the local microclimate has changed, and what seed sources are actually available, you can end up with a very different plant community.

If you want to keep that from happening, it takes regular application of thinning and prescribed burns.