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Providing evidence to improve practice

Individual study: Understory response to repeated thinning in Douglas-fir forests of western Oregon

Published source details

Berger C.A., Puettmann K.J. & McKenna J. (2012) Understory response to repeated thinning in Douglas-fir forests of western Oregon. Journal of Sustainable Forestry, 31, 589-605


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Thin trees within forests: effects on understory plants Forest Conservation

A replicated study in 1975-2006 in temperate coniferous forest in Oregon USA (Berger, Puettmann & McKenna 2012) found that a second thinning treatment increased the cover and abundance of some understory plant groups. The percentage cover of ferns (43 vs 30%) and exotic plant species (1.0 vs 0.1%) was higher in twice thinned than in once thinned plots, while percentage cover of all forest understory species was similar between treatments (95% in both treatments). Frequencies were higher in twice thinned than in once thinned plots for ferns (2.0 vs 1.6 respectively), grasses (2.2 vs 1.3), open site species (4.1 vs 2.2) and exotic species (0.7 vs 0.1).The frequency of all forest understory species was similar between treatments (10.3 vs 9.9). Two treatments: once thinned (thinned from below in 1975-1982 to densities of 270-590 trees/ha) and twice thinned (re-thinned in 1997-2000 to 100-150 trees/ha) were replicated in four sites. Understory vegetation was monitored six years after the second thinning in 6-12 once thinned and 12-13 twice thinned 0.1 ha plots at each site.