Black spruce and fir are the dominant tree species in the boreal forest.

黑云杉和冷杉是北方森林的优势树种。

It's burning off the organic layer of soils that support species like black spruce.

它正在燃烧土壤的有机层，而这些有机层正是黑云杉等物种赖以生存的土壤。

This showed forests that transitioned to birch and aspen would accumulate carbon four times faster than forests dominated by black spruce.

这表明过渡到白桦和白杨的森林积累碳的速度是黑云杉为主的森林的四倍。