The Green Glacier: What is conifer encroachment and why is it bad?
Extensive research shows us that native conifer trees, primarily juniper and pinyon pine, but also other conifers, have been increasing their footprint on the landscape at an unprecedented rate over the last 150 years or so, especially in places like the Great Basin. This is part of a global phenomenon of trees encroaching into and replacing adjacent grasslands and shrublands.
Some of that change is expansion in the traditional sense, that is, trees moving from higher elevations or fuel-limited sites protected from fire where they historically existed into areas where they never grew before. But much of the change is what we call ‘infill,’ which is what happens after trees colonize and continue to populate previously tree-less landscapes, turning them from sagebrush or grasslands with just a few trees per acre into closed-canopy woodlands – what you might think of as a forest.