Hardy bigleaf maple is a tree for open spaces

HALL OF MOSSES TRAIL, Hoh Rain Forest — Shaggy and hulking as Sasquatch, these bigleaf maples smothered in moss and ferns are lush, primeval, mysterious.

No other tree in the rain forest is home to hanging gardens of moss and fern like the bigleaf. A single tree can be landlord to 40 species of moss, lichen and fern, a biomass five times the weight of its leaves.

That's really saying something on a tree that sprouts leaves a foot long — the biggest of any maple in the country.

The bigleaf can benefit from its tenants. As pads of moss grow ever thicker, quilting the branches and crooks of the tree, a nutritious layer of humus is slowly formed on the bark of the bigleaf.

The maple's branch can grow roots that dig right into the luscious soil formed beneath the mosses, a discovery by Nalini Nadkarni, now on the faculty at The Evergreen State College.

"These trees have evolved the capacity to stick roots of their own into these mats of moss 50, 60 feet in the air. It would be like your arm sprouting a toe," Nadkarni said. "It made us rethink the way forests work."

Why the bigleaf is so emphatically the host of choice of ferns, mosses and lichens is a mystery.

Some scientists think it may simply be the worried, furrowed brow of the bigleaf's bark and its broad, horizontal branches, perfect for gaining a purchase and then a perch.

The bigleaf's bark is also rich in calcium, a mineral mosses crave. And unlike evergreens, the bark is not acidic or laced with chemicals that may deter epiphytic growth.

Another theory is that the bigleafs provide access to both sun and moisture when they drop their leaves in the fall, just in time for the drenching autumn and winter rains.

"No one knows for sure," said Nadkarni, who stitched a thigh-length cape of moss gathered from a bigleaf together with dental floss. "I have to trim it back every year; it keeps growing," she said of the cape. "I have to wear it outside, because it tends to shed, but it makes a big hit when you walk in with a moss cape. It's very heavy and very warm."

Our biggest, most sumptuous, deciduous native, the bigleaf can live 150 to 200 years and longer, and reach 70 to 80 feet high. Its limbs can soar 50 feet upward from hulking trunks as much as 5 feet in diameter.

Native people still use this noble tree, cutting planks as food platters. Its wood is also used for smoking meat and fish. The giant leaves once made a work surface for food preparation, served as lids in cooking, and as a kind of wax paper on which to dry berries.

The bark was made into rope, the wood into canoe paddles.

Acer macrophyllum are adaptable trees, with their shape forming a living history of sunlight: Grown in an open field, the terminal buds of the branches reach and stretch without hindrance, forming a full, rounded crown with branches reaching in all directions.

But in a crowd, the bigleaf adapts. It takes a columnar shape as its top-most branches stretch to pierce a canopy.

A maple's leaves emerge soft and crumpled in the early spring, so tender they are silent in the wind, says Gordon Hempton of Port Angeles, who specializes in recording the sounds of nature.

"You just will not hear them," Hempton said. "They flow like seaweed in the sea; there is movement, but no sound. It's a total contrast to where the tree is headed in the fall.

"That I call the great applause, as the wind blows up the valley, and these maples are just in a final crescendo. And in the Hoh (rain forest), which can be as quiet as a recording studio, you will hear the sound when a single leaf gives up — it has done its duty.

"You will hear one land at a time. To witness something that simple in our fast-paced life, well, you would think you would have to wait forever to hear that sound."

But what a fine forever: Beautiful year round, the bigleafs are never as glorious as at this moment, their peak autumn color.

An afternoon spent in the shining company of bigleaf maples is a succession of slow, golden glissandos of leaves kiting through shafts of sun, each taking its own graceful flight to the ground.

Sink a finger into the moss on a bigleaf's branches and it disappears to the knuckle. Lean on a moss-swaddled trunk and it feels like the bigleaf is wearing a down jacket.

Found west of the mountains from British Columbia to Southern California, bigleaf maples keep to the lowlands; they are seldom found above 1,500 feet on the Olympic Peninsula. They grow best in moist, gravelly alluvial soils in river bottoms, soils other trees shun.

In spring, the entire tree is covered with 6-inch-long clusters of yellow -green, sweet-scented flowers that evolve to hairy, helicopter-winged seeds.

The seeds hang on into winter, providing abundant food for squirrels and birds. The nectar-laden flowers are sweet and can be eaten right off the tree.

"A sweet, honey crunchiness," is how Sarah Reichard, assistant professor of conservation biology at Seattle's Center for Urban Horticulture, describes them. Their burls are treasured by woodworkers.

Cut it down, and the bigleaf maple will spring right back. The many-trunked stump sprouts all over Puget Sound country are testimony to the bigleaf's vigor.

The tree is banned in Seattle for planting as a street tree because of its sidewalk-bursting roots and widow-making branches.

Plagued by compacted soil from parked cars and foot traffic, pavement and construction, the bigleaf is prone to root rot, said Linda Chalker-Scott, associate professor at the Center for Urban Horticulture.

Rot can make it more vulnerable to shattering in stormy weather.

The trees are also just too big to fit into street tree-planting strips, said Nolan Rundquist, city arborist for Seattle.

He has cut many a chunk of sidewalk out to make room for burgeoning bigleafs, and Rundquist remembers one sidewalk muscled up 18 inches by bigleaf roots.

"You had to just kind of fly over that part."

It's a tree for wild, open places, not the straitjacket life of a street tree. "Everything has its place," Rundquist said. "It's place just isn't between the sidewalk and the street."

Lynda V. Mapes: 206-464-2736 or lmapes@seattletimes.com. Natural Wonders appears every other Monday.