When Carl Roland was hiking the high country in an Alaska national park not long ago, he thought the landscape looked different than any park in the Lower 48. The alpine zone seemed to be carpeted with more plant species than the much-larger forests and wetlands in the valleys below.
When Roland looked at plant inventories from a large chunk of Denali National Park, he confirmed a pattern that seems unique: An increase in plant species diversity in alpine areas compared to adjacent lowlands. While a patch of vegetation within a Denali lowland black spruce bog might contain a dozen species, a typical high-country gathering of crowberry, mountain avens and other small plants was part of a community with 40 to 50 species in the same area.
"It's a glimpse into the way the past has shaped the present," said Roland, a plant ecologist with Denali National Park.
Roland figures that Denali's plant geography is perhaps a reflection of what middle Alaska used to be. Cut off from the rest of North America by giant ice sheets, the landscape now dominated by boreal forest was for a longer time occupied by open steppe and tundra, supporting alpine plants that don't like shade.
"Over the last million years, the area has been much more tilted toward well-drained open landscapes than boreal landscapes," Roland said.
Since the height of the ice age 20,000 years ago, a warmer and wetter climate, combined with receding ice sheets and an open connection to North America, has allowed spruce, birch and alders to expand and other plants to creep in. The boreal forest has been established in Denali Park for more than 7,000 years, not very long compared to the grasses, mountain avens and alpine sedges that had been there eons before.
That long-term availability of alpine habitat in Denali might be why plant species diversity there is different from places outside Alaska. As ice sheets were advancing and obliterating large sections of landscape, tundra and other open-landscape plants persisted. The plants didn't have to find their way back like spruce and other boreal forest plants.
Though he has only looked at the alpine vs. lowland equation for Denali, Roland thinks other Alaska parks probably have the same tendency for more plant species up high. And he's happy Alaska has enough room to make such a phenomenon detectable.
"The unique thing about our parks is that they contain intact lowland ecosystems," Roland said. "Plant geography is so interfered with in other places. There are so many weeds. Eighty percent of species are non-native in meadows (on the coast of California)."