Action: Thin trees by girdling (cutting rings around tree trunks)
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- 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.
Girdling, i.e. thinning trees by cutting rings around their trunk, is used as a conservation management practice to increase forest structural diversity. This method imitates the natural death of a tree without using chemicals or cutting trees.
Supporting evidence from individual studies
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.