Action: Use patch retention harvesting instead of clearcutting
Key messagesRead our guidance on Key messages before continuing
- Three studies evaluated the effects on mammals of using patch retention harvesting instead of clearcutting. Two studies were in Canada and one was in Australia.
COMMUNITY RESPONSE (0 STUDIES)
POPULATION RESPONSE (3 STUDIES)
- Abundance (3 studies): Two replicated, controlled, before-and-after studies and a replicated, site comparison study in Canada and Australia found that retaining patches of unharvested trees instead of clearcutting whole forest stands increased or maintained numbers of some but not all small mammals. Higher abundances where tree patches were retained were found for southern red-backed voles, bush rat and for female agile antechinus. No benefit of retaining forest patches was found on abundances of deer mouse, meadow vole and male agile antechinus.
BEHAVIOUR (0 STUDIES)
Removing trees, through clearcutting or clearfelling, can have substantial, usually negative, effects on forest mammals, through alteration of habitat and removal of food and shelter. Patch retention is the act of leaving groups of trees during harvesting, which may act as refugia to support forest fauna and enable its recolonisation of the remainder of the forest as it regrows.
Supporting evidence from individual studies
A replicated, controlled, before-and-after study in 1993–1996 of a boreal forest area in Alberta, Canada (Moses & Boutin 2001) found that retaining patches of unharvested trees enhanced numbers of red-backed voles Clethrionomys gapperi, but not of deer mice Peromyscus maniculatus or meadow voles Microtus pennsylvanicus, relative to those in fully harvested areas. Following harvesting, yearly peak red-backed vole population estimates were higher with retained tree patches (101–172 voles/plot) than without (53–91 voles/plot). Deer mice had similar abundance between treatments (patches: 107–148 mice/plot; no patches: 71–115 mice/plot). Meadow vole numbers were higher in fully harvested plots (patches: 0–24 voles/grid; no patches: 36–118). In a 6 × 6-km study area, four plots were managed during winter 1993–1994. In two plots, trees were felled, but leaving undisturbed 40-m diameter patches, comprising 10% of total tree basal area. In two other plots, trees were felled entirely. Small mammals were surveyed using 60 or 120 Longworth live traps/6 ha block. Traps were set for three nights and two days, at fortnightly or longer intervals, from May or June to August or September, in 1993–1996.
A replicated, controlled, before-and-after study in 2002–2009 of forest across three districts in Victoria, Australia (Lindenmayer et al. 2010) found that retaining forest islands when clearfelling reduced subsequent abundance declines after brash burning for some small mammal relative to in clearfelled areas. Average bush rat Rattus fuscipes abundance declined less following burning in island retention patches (before: 2.1; after: 1.6/grid) than in clearfelled patches (before: 1.2; after: 0.4/grid). Female agile antechinus Antechinus agilis abundance declined less following burning in island retention patches (before: 2.2; after: 1.5/grid) than in clearfelled patches (before: 1.0; after: 0.1/grid). However, male agile antechinus abundance declines were similar following burning in island retention patches (before: 1.1; after: 0.4/grid) and clearfelled patches (before: 0.5; after: 0.2/grid). Forest patches (coupes) of ≥15 ha were established in six blocks. In each block, one patch was entirely clearfelled, one was clearfelled, but retaining a 1.5-ha forest island and one was clearfelled, but retaining three 0.5-ha islands. Post-felling, blocks were prescribed burned to clear brash. Small mammals were surveyed using four live-trap grids in each patch. Three grids/patch were in retained forest islands. Surveys took place before felling, after felling and after burning. Treatments were staggered, so surveys spanned 2002 to 2009.
A replicated, site comparison study in 2015–2016 of a coniferous forest site in British Columbia, Canada (Sullivan & Sullivan 2017) found that retaining patches of trees when harvesting sustained higher southern red-backed voles Myodes gapperi populations compared to clearfelling. Nineteen to 20 years post-harvest, there were more red-backed voles in patch retention plots (5.7/ha) than in clearfelled plots (3.3/ha). Harvesting, in 1996, comprised three replicate plots each of tree patch retention (10 m2/ha basal area, retained as a group – group sizes not stated) and clearfelling. Plot sizes ranged from 3.6–12.8 ha. Forest overstorey was mostly lodgepole pine Pinus contorta and Douglas fir Pseudotsuga menziesii, of average ages of 82–228 years. Following harvesting, sites were planted with lodgepole pine, Douglas fir and interior spruce Picea glauca × engelmannii seedlings in 1997. Small mammals were sampled at four-week intervals in May–October of 2015 and 2016. One live-trapping grid (49 traps across 1 ha) was located in each plot. Traps were set for two nights and one full day on each occasion.
- Moses R.A. & Boutin S. (2001) The influence of clear-cut logging and residual leave material on small mammal populations in aspen-dominated boreal mixedwoods. Canadian Journal of Forest Research, 31, 483-495
- Lindenmayer D.B., Knight E., McBurney L., Michael D. & Banks S.C. (2010) Small mammals and retention islands: An experimental study of animal response to alternative logging practices. Forest Ecology and Management, 260, 2070-2078
- Sullivan T.P. & Sullivan D.S. (2017) Green-tree retention and recovery of an old-forest specialist, the southern red-backed vole (Myodes gapperi), 20 years after harvest. Wildlife Research, 44, 669-680