Wednesday, March 2, 2022

Windthrow, Windsnap and Blowdown

On March 17, at 7:00 p.m., the Maynard Public Library will present a Zoomed talk titled: “Urban Planting: 150 Years of Trees and Gardens,” sponsored by Maynard Community Gardeners. Registration (required) at

Windthrown tree, Maynard, 1938 hurricane
What a wonderful word is “windthrow.” A user of it wields word poetic. The word itself warrants this column and a definition: “In forestry, windthrow refers to trees uprooted by wind. Breakage of the tree trunk instead of uprooting is called windsnap. “Blowdown” refers to both windthrow and windsnap,” plus branches lost to high winds. And there it is - windthrow is blow me over, windsnap another evocative word, is break me in two, and blowdown encompasses all. Maynard suffered severe blowdown from the hurricane of 1938.

The risk of windthrow is related to the tree's surface area presented by its crown, the anchorage provided by its roots, its health, age, and chronic exposure to wind. The last actually reduces storm damage risk because being chronically exposed to wind causes a tree to increase and widen its root mass, and thus provide greater rooting strength.

Having experienced a hurricane first hand in Mobile, Alabama, it became clear that different species of trees are differently affected. Post-storm, helicopter views of pecan orchards showed the trees all knocked over in the same direction. Southern live oaks survived, but lost branches. In contrast, where several species of southern pine trees had been landscaped into newer suburbs because of their fast growth, many of the trees had snapped in two at heights 10 to 20 feet off the ground, leaving the shorn tops to fly through the air, in some instances stabbing down into house roofs like a toothpick through an olive.

Windthrown tree, 1938 hurricane
courtesy Maynard Historical Society
Atlantic Ocean tropical storms and hurricanes were first formally named starting in 1950 (each year as Able, Baker, Charlie…), then changed to using women’s names from 1953 onward, then switched to alternating women’s and men’s names in 1979. Naming is currently the responsibility of the Hurricane Committee of the World Meteorological Organization. This group maintains six alphabetic lists of 21 names, with one list used each year. Letters Q, U, X, Y and Z are not used. This normally results in names being recycled every six years. However, in the case of a particularly deadly or damaging storm, that storm's name is retired. To date, 94 names have been retired. There is a reserve list of names for when named storms exceed 21. To date, only two years have exceeded 21: 2005 tallied 28 and 2020 reached 30.

After-the-fact, the hurricane of September 21, 1938 was referred to as the Long Island Express because it bisected Long Island before quickly moving north through Connecticut and Massachusetts. There were more than 700 deaths across New England. Boston Edison reported that two-thirds of its customers lost power; getting power restored to everyone took two weeks. In Maynard, the official report tallied 487 trees blown down: 329 on public streets, 81 on private houses and garages. Most of the street-bordering trees lost were windthrown rather than windsnapped, their root systems weak due to being overlaid by paved streets and sidewalks. Many of the spruce trees in Glenwood Cemetery were lost to the storm, later replaced by sugar maples. That tree tally would have been in-town-only. Forested areas suffered uncounted losses. The Great Depression program WPA (Works Progress Administration) put men to work clearing downed trees and planting hundreds of new trees.

Beech tree, snapped by storm winds
Here in New England, trees known for shallow root systems are ash, beech, sugar maple, Norway maple, Norway spruce and willow. In contrast, white oak and hickory have deep root systems. Of course, any tree can end up with a shallow system if the terrain is thin soil over clay or rock, or if there is a high water table saturating the deeper soil. And hurricanes are not a requirement for windthrow or windsnap. Nor’easters can generate near-hurricane-strength winds, as can downbursts or derecho (look it up). Santa Ana winds are a southern California phenomenon that knocks down trees and makes wildfires impossible to control. Tornados primarily plague the middle states, although, surprisingly, Massachusetts averages a few each year, mostly short-track, low intensity events. On August 23, 2021, a small, short-track tornado touched down in Stow, causing minor damage along Route 117 near the police department building. Similar tornado touchdowns occurred in Marlborough and Bolton, all associated with the passage of Tropical Storm Henri.

Mark’s experience with Hurricane Frederic, September 1979, included afterwards, with no electricity for ten days, everyone was grilling whatever was thawing in their freezers before it went bad.

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