Natural target pruning and the Shigo school: what the research record says

This page is a history of one idea in pruning, told from the papers and the trade magazine that record it. It reports what each source says. It does not say how any cut should be made, and it takes no side between schools. The standards that govern pruning are on the pruning standards guide, and the biology behind the idea is on the compartmentalization guide.

The sequence, source by source

Work	What the source says it found, and who reports it
Shigo and Larson, 1969, photographic summary of discoloration and decay patterns	Observational, not experimental. One finding was that covering pruning wounds with dressings neither improved closure nor reduced decay. Reported by: Clark and Matheny, 2010.
Shigo and Marx, 1977, Compartmentalization of decay in trees	Called the seminal report. It introduced the CODIT concept. Reported by: Clark and Matheny, 2010.
Shigo and others, 1979, flush cuts in black walnut	Linked flush cuts to internal decay and other defects. The authors noted that late in a tree's life care must be taken not to remove the branch collars at the bases of dead and dying branches. Reported by: Clark and Matheny, 2010.
Shigo, 1984 and 1985, compartmentalization and how branches attach to trunks	The papers where the CODIT model culminated. Clark and Matheny say the vast bulk of this work was observational. Reported by: Clark and Matheny, 2010.
Neely, 1988, Journal of Arboriculture 14(11), closure of conventional and Shigo cuts	Four-year test on pin oak, sycamore and Norway maple branches of 25 to 35 millimetres. Shigo-cut wounds were 4 to 6 percent wider than the branch, conventional cuts 32 to 51 percent wider. Callus grew faster at conventional cuts, and after the second growing season more conventional cuts than Shigo cuts had closed completely. Reported by: Arboriculture and Urban Forestry, abstract.
Neely, 1991, Arboriculture and Urban Forestry 17(8), branch pruning wound closure	Ten species, branches of 50 to 75 millimetres. Conventional cuts made wounds 30 to 50 percent larger than Shigo cuts, with little closure of Shigo wounds in the first year. After four years conventional wounds were smaller than Shigo wounds on six species, about the same on one, and larger on three. Reported by: Arboriculture and Urban Forestry, abstract.
Lonsdale, 1993, UK research note on beech	Four-year-old wounds on European beech: wood discoloration spread more beneath flush cuts than beneath cuts at the natural stem and branch junction. There was no difference between target cuts and stub cuts in that respect. Flush cuts grew callus fastest but closed proportionately less because of their size, and the note says the fastest occlusion came with cuts between target and flush. Reported by: Arboricultural Advisory and Information Service, research note.

Who Shigo was, in the trade's words

Tree Care Industry Magazine's October 1, 2021 tribute by a retired city forester describes Shigo as the USDA Forest Service's chief research scientist in the late 1970s and early 1980s. It says his compartmentalization work and his proposed natural target pruning contrasted at that time with Dan Neely's ideas on flush cuts, and that Shigo had retired from the Forest Service by September 1986, when the author attended the first of his New Tree Biology workshops. It lists his books, says he was dubbed the father of modern arboriculture, and gives October 2006 as the month he died.

What a 2010 review concluded

Clark and Matheny compiled 201 research publications for the International Society of Arboriculture in a review published in 2010. They name Shigo and Dirk Dujesiefken as the most frequently cited authors. They write that research by Shigo, and by Dujesiefken, has supported the branch collar, natural target approach to choosing where a removal cut goes. They also record Shigo's 1990 booklet on pruning near electric utility lines as not research-based but a key element of utility practice, since largely superseded by Kempter's 2004 best management practices summary. They stress that Shigo was neither the only scientist interested in tree response to wounding nor the first, and name foresters before him.

Where the sources do not agree

The two Neely papers measure the same thing and differ on the long-run result, and the UK note found the quickest closure at neither extreme. Lonsdale's note records that earlier practice was divided between stub cutting and flush cutting, and says that flush cutting had come to be viewed with disfavour because it injures tissue that belongs to the parent stem.