Leave coarse woody debris in forests

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

Study locations

Key messages

  • Three studies evaluated the effects on mammals of leaving coarse woody debris in forests. One study was in Canada, one was in the USA and one was in Malaysia.


  • Richness/diversity (1 study): A replicated, site comparison study, in Malaysia found more small mammal species groups in felled forest areas with woody debris than without.


  • Abundance (3 studies): One out of three replicated studies (two controlled, one site comparison, one before-and-after) in Canada, the USA and Malaysia found that retaining or adding coarse woody debris did not increase numbers or frequency of records of small mammals. The other study found that two of three shrew species were more numerous in areas with increased volumes of coarse woody debris than areas without coarse woody debris.


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 replicated, controlled, before-and-after study in 1993–1996 of a boreal forest area in Alberta, Canada (Moses & Boutin 2001) found that retaining woody debris following harvesting did not enhance numbers of three small mammal species, relative to those in cleared areas. This was the case for estimated annual peak populations of red-backed vole Clethrionomys gapperi (debris: 53–91 voles/plot; no debris: 91–99 voles/plot), deer mouse Peromyscus maniculatus (debris: 71–115 mice/plot; no debris: 79–151 mice/plot) and meadow vole Microtus pennsylvanicus (debris: 36–118 voles/plot; no debris: 7–146 voles/plot). In a 6 × 6-km study area, trees across four plots were clearfelled during winter 1993–1994. In two plots, woody brash was spread by bulldozer to form a strip, approximately 50 m wide and 0.5 m deep, generally along block centres. Woody debris was removed entirely from the other two plots. Small mammals were surveyed using 60 or 120 Longworth live traps/6 ha block. Traps were operated for three nights and two days, at fortnightly or longer intervals, from May or June to August or September in 1993–1996.

    Study and other actions tested
  2. A replicated, controlled study in 2007–2008 of three stands of loblolly pine Pinus taeda in South Carolina, USA (Davis et al. 2010) found that increasing coarse wood debris quantity increased the abundance of two of three shrew species compared to removing debris, but not compared to leaving debris as it fell. More southeastern shrews Sorex longirostris were caught in plots with increased coarse woody debris quantities (0.057 shrews/m of drift fence) than in plots cleared of fallen debris (0.013). Numbers in neither treatment differed significantly from those in unmanipulated plots (0.026). The same pattern was seen for southern short-tailed shrew Blarina carolinensis (increased debris: 0.105 shrews/m of drift fence; debris cleared: 0.051; unmanipulated: 0.058). However, there were no differences between treatments for North American least shrew Cryptotis parva (increased debris: 0.012 shrews/m of drift fence; debris cleared: 0.014; unmanipulated: 0.015). Three plots, each 9.3 ha, were located in each of three loblolly pine stands planted in 1950–1953. In each stand, woody debris quantities were increased fivefold in one plot in 2001 by felling trees, decreased in one plot by annually removing woody debris ≥10 cm across and ≥60 cm long from 1996 and left as it fell in one plot. Shrews were sampled across plots for 14 days, during seven seasons, from January 2007 to August 2008. Shrews were caught in 19-l plastic buckets connected by drift fencing.

    Study and other actions tested
  3. A replicated, site comparison study in 2013 of a tropical forest in Malaysia (Yamada et al. 2016) found more small mammal species groups, but not individual small mammals, where woody debris was left after selective logging than in areas lacking woody debris. On average, six small mammal species groups were recorded at sites with debris compared to four at sites without. No significant difference was detected for average numbers of small mammal recorded at sites with debris (43) compared to sites without (39). Sites were compared with respect to tree density, canopy openness, understorey vegetation cover, distance to road and slope and no differences in these measures were detected between sites with and without debris. Trees were selectively logged, within a 200-ha area, in 2010–2011. Single camera traps were set, around two years later, for 10 days each at 17 locations with logging woody debris and 17 without. Camera locations were ≥50 m from logging roads and were baited.

    Study and other actions tested
Please cite as:

Littlewood, N.A., Rocha, R., Smith, R.K., Martin, P.A., Lockhart, S.L., Schoonover, R.F., Wilman, E., Bladon, A.J., Sainsbury, K.A., Pimm S. and Sutherland, W.J. (2020) Terrestrial Mammal Conservation: Global Evidence for the Effects of Interventions for terrestrial mammals excluding bats and primates. Synopses of Conservation Evidence Series. University of Cambridge, Cambridge, UK.

Where has this evidence come from?

List of journals searched by synopsis

All the journals searched for all synopses

Terrestrial Mammal Conservation

This Action forms part of the Action Synopsis:

Terrestrial Mammal Conservation
Terrestrial Mammal Conservation

Terrestrial Mammal Conservation - Published 2020

Terrestrial Mammal Conservation

What Works 2021 cover

What Works in Conservation

What Works in Conservation provides expert assessments of the effectiveness of actions, based on summarised evidence, in synopses. Subjects covered so far include amphibians, birds, mammals, forests, peatland and control of freshwater invasive species. More are in progress.

More about What Works in Conservation

Download free PDF or purchase
The Conservation Evidence Journal

The Conservation Evidence Journal

An online, free to publish in, open-access journal publishing results from research and projects that test the effectiveness of conservation actions.

Read the latest volume: Volume 21

Go to the CE Journal

Discover more on our blog

Our blog contains the latest news and updates from the Conservation Evidence team, the Conservation Evidence Journal, and our global partners in evidence-based conservation.

Who uses Conservation Evidence?

Meet some of the evidence champions

Endangered Landscape ProgrammeRed List Champion - Arc Kent Wildlife Trust The Rufford Foundation Save the Frogs - Ghana Mauritian Wildlife Supporting Conservation Leaders
Sustainability Dashboard National Biodiversity Network Frog Life The international journey of Conservation - Oryx Cool Farm Alliance UNEP AWFA Bat Conservation InternationalPeople trust for endangered species Vincet Wildlife Trust