@b92dcc07 This article is very informative.

Black spruce dominated ecosystems are under threat. Not from black spruce, but from hotter, dryer conditions which mean that black spruce is being out-competed by other species such as white spruce, aspen and birch. 

Black spruce has dominated boreal forests for the last five to ten thousands years. The climate is beginning to change that dominance. 
 https://www.woodwellclimate.org/black-spruce-regeneration-failure/