The Forests Where The Trees All Lean The Same Way

In southeast Alaska, researchers worked out which way storms blew four centuries ago. They did it by noting which way the fallen trunks pointed. A forest that leans one way is a record, and what it records changes every time. The lateral blast at Mount St. Helens, one summer storm over northern Minnesota. A wind that came over the Rockies from the wrong side, ground that will not hold still. Eight national forests carry a reading of that kind, and the force behind each one lasted a different length of time.

Gifford Pinchot National Forest, Washington

Two hundred and thirty square miles of forest in southwest Washington went down or died standing north of Mount St. Helens on May 18, 1980. Geologists later sorted that ground into three rings. Within about eight miles of the volcano almost nothing survived, and geologists call that inner ring the tree-removal zone. Beyond it came the tree-down zone, where the blast flattened everything and the trunks stayed where they fell. Federal geologists say the force and direction of the blast show in the parallel alignment of the toppled trees. Each one snapped off at the base.

The outer ring is the odd one. Trees in it stayed upright, killed by the heat but never pushed over. The dead poles are still there. Blast Edge Viewpoint, 3.9 miles up Forest Road 99, marks the eastern entrance to the national volcanic monument. Calculations put the blast near 220 miles per hour at the outset, rising to roughly 670. The three rings differ by nothing except distance from the volcano.

Superior National Forest, Minnesota

The storm crossed the Boundary Waters Canoe Area Wilderness early in the afternoon of July 4, 1999. The swath it left ran 12 miles wide and 30 miles long. Derecho is the term for a windstorm of that scale. The July storm qualified easily. Its damage path covered about 6,000 nautical miles, reaching Quebec, the open Atlantic, and finally the Gulf of Mexico. No other recorded derecho has spent more than a day at sea and then returned to shore to resume.

Weather Service meteorologists also traced part of its fuel. Two months of heat and near-record rain had left the northern Minnesota canopy lush. Evapotranspiration from that canopy and its undergrowth then supplied an important share of the storm's moisture. The forest helped feed the thing that flattened it. Federal forecasters state plainly that damage inside the wilderness came from straight-line winds alone. Tornadoes from the same system appear to have stayed north of the Canadian border. The wreckage left 60 tons of dead fuel per acre. Most of it snapped high on the trunk. Very little of it touched the ground, so the timber dried.

Medicine Bow-Routt National Forests, Colorado

Colorado's damaging mountain winds arrive off the Continental Divide from the west. On the morning of October 25, 1997, the wind ran the other way. Strong easterly flow met very cold air near the ground, and the combination sent wind pouring down the western slope. About 13,000 acres of old-growth spruce, fir, and lodgepole pine went flat along the west boundary of the Mount Zirkel Wilderness. The team that later modeled the storm found no earlier study of a high-wind event driven by easterly winds crossing the Divide in Colorado.

No instrument stood in the blowdown itself. The strongest reading anyone recorded that morning, a gust of 114 miles an hour out of the east, came from a ski area far to the south. Agency staff put peak winds in the blowdown near 120 miles an hour. That figure came from looking at what the wind had done to the trees. The forest's own monitoring report went on to say that windstorms of this size are very rare at that altitude. Little was known about how such ground recovers. Much of the forest plan monitoring effort was aimed at finding out.

Francis Marion National Forest, South Carolina

Close to three quarters of the overstory came off the Francis Marion in a single night. Hurricane Hugo crossed the South Carolina coastal plain on September 22, 1989. The forest sat on the right-hand side of the storm track. A hurricane's rotation there runs with its forward motion, and the two speeds add together. The Weather Service recorded how the trees failed. Trunks sheared off 10 to 25 feet up and left the stumps in place.

A study followed these woods for 27 years afterward. Species made no difference to what survived on the Santee Experimental Forest or the surrounding national forest. Size did. Bigger trees failed and smaller ones came through, whatever kind they were. Fire crews then found that their tractor-plows could not work through the wreckage. Those machines had been the mainstay of suppression. South Carolina asked for a 12-month voluntary halt to prescribed burning across the affected area. Logging operations on the forest ended permanently.

Tongass National Forest, Alaska

Wildfire is rare in the coastal rainforest of southeast Alaska, so wind does the work fire does elsewhere. Gales run hardest in fall and winter. Those gales rotate counterclockwise around a low-pressure core and reset whole stands at a stroke. Each storm leaves an even-aged patch of forest, all of it grown up at once. Those patches can be dated.

Researchers picked out even-aged stands on Kuiu Island from aerial imagery, then checked them in the field. About 40% proved to be roughly 110 years old, which put their origin at a severe cyclone in October 1880. The other 60% traced back to at least four more major storms between 50 and 400 years ago. The team then worked out the direction those storms had come from using nothing but the way the trees had fallen. South, southeast, and southwest. Across the whole region in 2025, aerial survey mapped only nine fresh patches of windthrow. The old ones were still legible a century and more later.

Siuslaw National Forest, Oregon

The Forest Service lists four habitats inside the 2,700-acre Cape Perpetua Scenic Area, and one of them is defined by wind. Old-growth Sitka spruce and western hemlock make up the first, including a spruce 15 feet across. Shore pine, shrubs, and grasses take the ground immediately next to the beach. Between those two the agency records wind-sculpted strand communities dominated by spruce. The phrase describes a kind of forest that the wind itself has shaped. Wind here is not damage but a growing condition, and the trees take the form it allows.

Cape Perpetua is a basalt headland 800 feet above the Pacific, with 26 miles of trail and an auto road to the top. The paved shoreline path below passes wind-sculpted spruce on its way to the tidepools. Agency guidance for visitors makes the conditions plain. Rain and high winds can move ashore quickly, and spring is when they do it. One of the trails there carries the name Whispering Spruce Trail.

Shoshone National Forest, Wyoming

Tibbs Butte rises 2.3 miles southeast of the Beartooth Pass summit. The conifers on top grow in a pattern that can be read. Trees at treeline do not settle at random. One takes root in the shelter of a rock or a shallow hollow and survives. Others then establish downwind of it, in the shelter it makes, until the group becomes what ecologists call a tree island. The windward tree carries a title of its own. That tree is the initiator, and every tree behind it is classed as leeward. Direction is the whole structure.

A research team surveying four treeline sites in the Yellowstone region, two of them on the Shoshone, needed the prevailing wind at every plot. The method used was to examine the flagged branches of nearby conifers and take the reading off the trees themselves. Whitebark pine made up 91.3% of the conifers at Tibbs Butte, against 42% at the wettest of the four sites. Of the conifers on Tibbs Butte, 95.5% stood alone rather than in islands.

Grand Mesa, Uncompahgre and Gunnison National Forests, Colorado

The ground beneath the Slumgullion earthflow moves as much as 24 feet a year, and it has kept moving for roughly three centuries. The Routt blowdown, in the northern part of the same state, records moving air. The Slumgullion records moving ground. An older slide dammed the Lake Fork of the Gunnison River 800 to 900 years ago and made Lake San Cristobal. A younger flow now travels across the top of that older deposit. Geologists separate the active part from the still country around it by watching for a strip of tilted evergreens.

In the hopper, where the slide narrows, the ground surface tilts inward from both flanks. Trees on the tilted section lean uniformly toward the middle of the slide. The trunks stand square to that ground rather than to gravity, and the slope beneath them runs as steep as 50%. At the front edge the flow advances like the tread of a bulldozer. Trees in its path are pushed over and buried. One spruce lower down straddles a fault that leaves no crack at the surface, only a trough about three feet deep. Ground moving apart under its roots has pulled that tree into four pieces.

What The Trees Wrote Down

A leaning forest is a measurement nobody took on purpose. Forest Service staff put a number on the Routt winds by reading broken trunks. A survey team in Wyoming found its wind direction in flagged branches. Geologists in Colorado pick the moving part of an earthflow out of still country by the tilt of its evergreens. The instruments were already in place, and they kept the reading.