Trees creep into mountain meadows

MOUNT RAINIER NATIONAL PARK, Wash. – Nothing lures visitors to Paradise like the transitory displays of wildflowers that populate Mount Rainier’s high mountain meadows. But summer sojourns could fade into memory and panoramic vistas vanish as alpine asters, rosy pussytoes and purple lupines are crowded out by trees.

Add disappearing high mountain meadows to the catalog of effects wrought by global warming.

“There aren’t very many places where you can visually identify the changes affected by climate. This is one,” said David Peterson, a U.S. Forest Service research biologist.

The problem is snowfall, or more precisely, the lack of it. A long-term decline in mountain snowpack also to blame for many shrinking glaciers permits trees to grow in places where they couldn’t otherwise establish a foothold.

“As soon as you get less snow, there are more opportunities for trees to come in,” said botanist Regina Rochefort, a National Park Service science adviser.

Plant ecologist Mignonne Bivin, Rochefort’s Park Service colleague, put it this way: “Meadows stay open because of snowpack. That’s what restricts trees temperature and water availability. As we get less snow and more rain, we get more trees.”

Rochefort began exploring the pattern of tree encroachment at Mount Rainier in the early 1990s. Her research focused on subalpine meadows at elevations between 5,000 and 7,000 feet above sea level.

It’s the transition zone, where forests give way to open ground, and also below the treeless alpine areas, where snow persists year-round.

This is a battle zone, where trees compete for space with other species, said Peterson, who advised Rochefort on her research. The study was the subject of a 1996 article in the journal Arctic and Alpine Research.

“It’s definitely going from meadows to forests,” Rochefort said. “These are dynamic landscapes. They are changing, but none of us really expect it to change in our lifetime.”

Even nonscientists take note. On a recent summer research trip to check alpine research plots near Panorama Point, high above Paradise, Rochefort said she and Biven encountered a man in his 70s out for a day hike. A resident of nearby Randle, the Lewis County man was on familiar terrain. “He definitely notices more trees,” Rochefort said.

The correlation between warmer, wetter winters and vanishing high mountain meadows is not unique to the Cascades. “This does appear to be a West-wide phenomenon,” said Peterson, who, with Rochefort, has reviewed other research.

In Mount Rainier National Park, subalpine parklands cover about 23 percent of the landscape. The high mountain meadows are home to hordes of summer wildflowers, sedges and grasses, heather and huckleberries plus many stunted-looking and, in some cases, aged trees.

Just how old they are is one of the things Rochefort discovered when she and others set up test plots, dissected fir saplings and counted growth rings. A 3- to 5-foot tree could be 100 years old, she said. Some that stood less than 6 inches tall were 20 years old.

Once trees take hold, they tend to proliferate. “It’s self-sustaining in some respects,” Peterson said. Established stands warm their surroundings, melting the snow.

Rochefort, 55, was based at Mount Rainier from 1984 until 1998. She now works out of an office near North Cascades National Park.

She first became aware of the significance of trees in mountain meadows earlier in her career when a former Mount Rainier park ecologist questioned a tree removal program.

In the 1960s, park workers mowed down hundreds of thousands of small trees, Peterson said. The goal was to maintain the vistas around Paradise. “People don’t go up there to look at the trees,” he said.

Tree removals ended in 1979, but uncertainty about the effects of climate change persists, Rochefort said.

“We are trying to get a better handle on what changes we will see, where we will see the most rapid changes and how we can use that information to help manage parks,” she said.

While snowpack is the primary factor limiting tree growth, other local influences also come into play, scientists said. They include moisture, soil conditions, exposure to sun, wildfires and past land uses, such as grazing.

Rochefort studied five sites on Mount Rainier and concluded that since about 1930, trees have consistently crept into meadows near Paradise and other relatively wet spots.

In meadows in the mountain’s rain shadow, such as near Sunrise, new trees are more dependent on cool wet summers, she found.

In the future, this might mean people who flock to Mount Rainier in summer could have a better chance to see wildflowers at Sunrise than at Paradise, she said.

Park Superintendent Dave Uberuaga has seen the trees move into the park’s high mountain meadows. Officially, the plan is to leave them be.

“It is just going to take its natural course,” he said. “That’s what we’re about, I guess.”