Thin trees by girdling (cutting rings around tree trunks)

How is the evidence assessed?
  • Effectiveness
  • Certainty
  • Harms

Source countries

Key messages

  • One before-and-after trial in Canada found that thinning trees by girdling (cutting rings around tree trunks) increased understory plant species richness, diversity and cover.


About key messages

Key messages provide a descriptive index to studies we have found that test this intervention.

Studies are not directly comparable or of equal value. When making decisions based on this evidence, you should consider factors such as study size, study design, reported metrics and relevance of the study to your situation, rather than simply counting the number of studies that support a particular interpretation.

Supporting evidence from individual studies

  1. A before-and-after trial in 1992-2003 in boreal forest in Quebec, Canada (Grandpré et al. 2011) found that thinning trees by girdling increased understory species richness, diversity and cover. The number of species increased following girdling (before: 5-9; after: 7-12/1 m2 plot) and remained similar in uncut plots (before: 5-10; after: 6-12). Species diversity increased following girdling (Shannon's index before: 0.8-1.1; after: 1.2-1.7) and remained similar in uncut plots (before: 0.7-1.3; after: 0.8-1.5). Plant cover increased following girdling (before: 80%; after: 100-120%) and remained similar in uncut plots (before: 90-100%; after: 90-120%). In 1992, girdling (cutting >1 cm deep cuts around the trunks of all conifers) and uncut treatments (100 m2) were replicated in three blocks (>625 m2) at each of two sites. Data were collected before (1992) and after treatments (2003) in 5-12 plots (1 m2) in each treatment.

    Study and other actions tested
Please cite as:

Agra H., Schowanek S., Carmel Y., Smith R.K. & Ne’eman G. (2018) Forest Conservation. Pages 285-328 in: W.J. Sutherland, L.V. Dicks, N. Ockendon, S.O. Petrovan & R.K. Smith (eds) What Works in Conservation 2018. Open Book Publishers, Cambridge, UK.


Where has this evidence come from?

List of journals searched by synopsis

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Forest Conservation

This Action forms part of the Action Synopsis:

Forest Conservation
Forest Conservation

Forest Conservation - Published 2016

Forest synopsis

What Works in Conservation

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