Similar term(s): timberline, tree-line.
The northern limit of tree growth; the sinuous boundary between tundra and boreal forest.
Glossary of Meteorology
Climate change is projected to cause vegetation shifts because rising temperatures favor taller, denser vegetation, and will thus promote the expansion of forests into the arctic tundra, and tundra into the polar deserts.
Northward shifting treeline
Impacts of a Warming Arctic
To read about this term in context:
GreenFacts Summary on Arctic Climate Change: