Action: Remove woody debris after timber harvest
- One of six studies (including two replicated, randomized, controlled studies) in the USA and France found that woody debris removal increased understory vegetation cover. Three studies found no effect or mixed effects on cover. Four of the studies found no effect or mixed effects on understory vegetation species richness and diversity and two found no effect of woody debris removal on coverand species diversity of trees.
- Six studies (including two replicated, randomized, controlled studies) in Canada, Ethiopia, Spain and the USA examined the effect of woody debris removal on young trees. One study found that debris removal increased young tree density, another study found that it decreased young tree density, and three studies found mixed effects or no effect on young tree density. One found no effect of woody-debris removal on young tree survival.
Coarse woody debris consists of fallen dead trees and cut branches (> 10 cm diameter) that are left during tree harvesting. Removal of coarse woody debris uncovers the ground and allows sunlight to reach it, which may enhance seed germination and increase plant biodiversity.
Supporting evidence from individual studies
A replicated, controlled study in 1992 in Afro-montane forests in Ethiopia (Sharew, Legg & Grace) found that woody debris treatments had mixed effects on seedling establishment of African Juniper Juniperus procera and East African yellowwood Afrocarpus gracilior trees. Seedling density (individuals/m2) of African juniper was higher in burned than control and similar to both in raked plots (control: 0-5; raked: 8-12; burned: 13-14), while seedling density of East African yellowwood was lower in burned than control and raked plots (control: 4; raked: 5; burned: 1-3). Data were collected in December 1992 in three plots (10 × 10 m) of each treatment: control, raked (all logging waste and ground vegetation removed, seedbed raked) and burned (logging waste, ground vegetation and litter burned). Plots were established in a 40 × 40 m study site in March-April 1992
A controlled study in 1995-1998 in temperate coniferous forest in Spain (José Martínez-Sánchez et al. 1999) found no effect of burnt wood removal on the emergence and mortality of Aleppo pine Pinus halepensis seedlings. Emergence rates were similar between treatments (cleared: 0.0-3.2%; control: 0.0-2.6%) and mortality (cleared: 3-18%; control: 2-9%). In June 1995, two treatment plots (2,500 m2), one cleared (all burnt pines cut down and removed) and one control (untreated) were established in an area that was burnt in August 1994. Seedlings were sampled in 20 plots (4 × 5 m2) in each treatment plot on six dates during the first three post-treatment years: October 1995, January 1996, June 1996, January 1997, June 1997 and June 1998.
A replicated, controlled study in 1988-1991 in temperate coniferous forest in Washington State, USA (Scherer et al. 2000) found that different woody debris removal treatments had mixed effects on understory vegetation cover but not on species richness. At one site, vegetation cover was higher in control than other treatments (chopped: 1.8%; spring burn: 2.5%; pulled off site: 4.2%; control: 7.1%). At a second site, cover was higher in control, pulled off and autumn burn treatments (2.9, 1.2 and 1.2% respectively) than spring burn and chopped treatments (0.2% in both). At the other two sites it was similar among treatments (chopped: 2.7-2.8%; spring burn: 2.9-5.7%; autumn burn: 3.8-4.7%; pulled off: 1.2-5.7%; control: 2.1-2.2%). The number of species/m2 was similar among treatments at all four sites (chopped: 7-26; spring burn: 7-22; autumn burn: 8-20; pulled off: 5-20; control: 10-18). In 1989, five treatment plots (0.25-3.2 ha) were established in each of four sites: control (untreated); pulled off (woody debris pulled off the site); chopped (debris chopped); spring burn (low intensity burn); autumn burn (low to medium intensity). All plots were clearcut in 1988. Data were collected in 1991 in 15 quadrats (1 m2) in each treatment plot.
A replicated, randomized study in 1995-2000 in boreal forest in British Columbia, Canada (Kabzems & Haeussler 2005) found that woody debris removal treatments increased tree sapling density and decreased their height. Trembling aspen Populus tremuloides sapling density was higher in plots were all parts of the trees removed (tree removal) (44,000 stems/ha) than in plots were only saleable stems removed (stem removal) (34,000). The saplings dominant height was higher in stem removal and tree removal plots (225 and 245 cm respectively) than in plots were the hole forest floor was removed in addition (complete removal) (120 cm). White spruce Picea glauca total height was higher in stem removal plots (71 cm) than in tree removal and complete removal plots (54 and 42 cm respectively). Trembling aspen density was monitored in nine stem removal, nine tree removal and nine complete removal 40 × 70 m treatment plots. The height of more than 12 aspen saplings and of 200 randomly selected white spruce saplings was measured in each plot. Treatments were applied in 1995, data were collected in 2000.
A replicated, controlled study in 2000-2003 in temperate coniferous forest in Québec, Canada (Lorenzetti et al. 2008) found no effect of woody debris removal and raking in artificial gaps on the survival of yellow birch Betula alleghaniens seedlings. Seedling survival was similar between treatments (debris removal and raking: 45-50%; removal: 22-40%; control: 23-38%). Data were collected in 2003 in six control, six debris removal (mechanically pushing all debris to the edges of the gap), and six removal and raking (pushing all debris followed by raking) artificial forest gaps (900 m2). Gaps were created and treatments applied in 2000.
A replicated study in 1994-2003 in temperate broadleaf forest in Missouri, USA (Ponder 2008) found that after wood harvest, removal of the whole tree decreased the density but not the height of young trees compared with removal of main stems only, or removal of the whole tree plus debris from the forest floor. The number of individuals/m2 plot for trees was lower in whole tree removal plots (3.9) than in main stem removal plots (4.6) and forest floor debris removal plots (4.6). For shrubs (main stem removal: 2.8; whole tree removal: 3.2; forest floor debris removal: 3.3), woody vines (main stem removal: 4.9; whole tree removal: 3.7; forest floor debris removal: 3.5) and herbs (main stem removal: 7.7; whole tree removal: 7.7; forest floor debris removal: 8.9) numbers of individuals was similar between treatments. Height (m) of trees (main stem removal: 2.6; whole tree removal: 2.6; forest floor debris removal: 2.4) and of all other plants (main stem removal: 0.6; whole tree removal: 0.5; forest floor debris removal: 0.5) was similar between treatments. Data were collected in 2003 in three plots (8 m2) in each of three replicate treatment plots (0.4 ha): main stem removal, whole tree removal and forest floor debris removal. Harvest and removal treatments were applied in 1994.
A replicated, randomized, controlled study in 2001-2006 in temperate coniferous forest in Alberta, Canada (Landhäusser 2009) found no effect of woody debris removal on the density and height of pine seedlings. The density (1,308 seedlings/ha) and height (20 cm) of seedlings were similar between treatments. Twelve removed (woody debris removal in winter 2001) and 12 unremoved plots (30 × 30 m) were established in 2002. Density and height of regenerated seedlings were measured in 2006 in five subplots (10 m2) within each plot.
A replicated, controlled study in 2003-2006 in temperate coniferous forest in Colorado USA (Owen et al. 2009) found that woody debris removal treatments had mixed effects on plant cover and species richness. Six to 18 months after treatment, percentage cover and species richness/m2 of plants were higher in untreated plots and those where debris was cut up and left (46-50% cover, 7 species) than where debris was piled and burned (1% cover, <1 species). After 2.5-3.5 years the percentage cover and species richness/m2 of plants were highest where debris was cut up (46% cover, 8 species), lower in untreated plots (26%-29% cover, 6 species) and the lowest where debris was piled and burned (4% cover, <1 species). Three treatments were applied in three sites (1-2 km2): untreated, piled and burned (cutting trees, piling debris and burning in areas 3–6 m2) and cutting and leaving mulched material (areas 10–12 m2). Monitoring was in a total of 75 untreated, 50 piled and burned and 50 cut up treatment plots (1 × 1 m).
A replicated, randomized, controlled study in 1999-2006 in temperate coniferous forest in Washington State, USA (Peter & Harrington 2009) found no effect of removing all woody material after clearcutting on plant species richness and diversity compared with removing only tree trunks. Species richness (trunk removal: 17; complete-removal: 16) and diversity (Simpson's index: trunk removal: 0.36; complete removal: 0.27) were similar between treatments. Data were collected in 2006 in two plots (30 × 85 m) of each treatment, trunk removal only and removal of all woody material. Treatments applied after clearcutting in 1999 in each of four blocks. In all plots Douglas-fir Pseudotsuga menziesii seedlings were planted in 2000 and vegetation-control herbicide was applied annually.
A replicated, controlled study in 2005-2008 in temperate forest in France (Pellerin et al. 2010) found no effect of clearing of woody debris on species richness and diversity of trees and herbs. Numbers of woody plant species (control: 7-8; cleared: 10 m2) and diversity (Shannon's index control: 2.1-2.5; cleared: 1.9-2.1), and number of herbaceous species (control: 17-20; cleared: 13-17 m2) and diversity (Shannon's index control: 2.9-3.5; cleared: 3.1-3.4) were similar between treatments. Data were collected in May 2008 in 60 pairs of control (woody debris left) and 60 cleared (woody debris cleared of) plots (1 m2) in one site, and 42 similar pairs at a second site. Plots were set up in May 2005.
A replicated, randomized, controlled study in 1999-2006 in temperate coniferous forest in Washington State and Oregon, USA (Peter & Harrington 2012) found no effect of different woody debris removal treatments after clearcutting on cover of Douglas-fir Pseudotsuga menziesii and understory vegetation. At all three sites (respectively), cover was similar between treatments for Douglas-fir (control: 13%, 13% and 62%; piled/removed: 11%, 15% and 70%) and understory vegetation (control: 92%, 118% and 73%; piled/removed: 81%, 117% and 5%). Four blocks of 8-16 plots where woody debris had been piled or removed after clearcutting and 8-16 control treatment plots (0.26 ha) were established in each of three sites, all clearcut and planted with Douglas-fir in 1999-2003. Data were collected five years after clearcutting.
A controlled study in 2007-2009 in Piñon-juniper woodland in Utah, USA (Ross, Castle & Barger 2012) found that shredding woody debris (mulching) increased understory vegetation cover. Cover of understory plants was higher in mulched (66%) than control plots (4%). Two treatment sites (0.4-0.9 km2) were established in 2007: mulching (using a tractor with an attached brush-cutter) and control (untreated). Data were collected in 2009 along ten transects (35 m) in each site.
- Sharew H., Legg C.J. & Grace J. (1997) Effects of ground preparation and microenvironment on germination and natural regeneration of Juniperus procera and Afrocarpus gracilior in Ethiopia. Forest ecology and management, 93, 215-225
- Martı́nez-Sánchez J.J., Ferrandis P., De L.H.J. & Herranz J.M. (1999) Effect of burnt wood removal on the natural regeneration of Pinus halepensis after fire in a pine forest in Tus valley (SE Spain). Forest Ecology and Management, 123, 1-10
- Scherer G., Zabowski D., Java B. & Everett R. (2000) Timber harvesting residue treatment. Part II. Understory vegetation response. Forest Ecology and Management, 126, 35-50
- Kabzems R. & Haeussler S. (2005) Soil properties, aspen, and white spruce responses 5 years after organic matter removal and compaction treatments. Canadian Journal of Forest Research, 35, 2045-2055
- Lorenzetti F., Delagrange S., Bouffard D. & Nolet P. (2008) Establishment, survivorship, and growth of yellow birch seedlings after site preparation treatments in large gaps. Forest Ecology and Management, 254, 350-361
- Ponder F. (2008) Nine-year response of hardwood understory to organic matter removal and soil compaction. Northern Journal of Applied Forestry, 25, 25-31
- Landhäusser S.M. (2009) Impact of slash removal, drag scarification, and mounding on lodgepole pine cone distribution and seedling regeneration after cut-to-length harvesting on high elevation sites. Forest ecology and management, 258, 43-49
- Owen S.M., Sieg C.H., Gehring C.A. & Bowker M.A. (2009) Above-and belowground responses to tree thinning depend on the treatment of tree debris. Forest Ecology and Management, 259, 71-80
- Peter D.H. & Harrington C. (2009) Six years of plant community development after clearcut harvesting in western Washington. Canadian journal of forest research, 39, 308-319
- Pellerin M., Saïd S., Richard E., Hamann J., Dubois-Coli C. & Hum P. (2010) Impact of deer on temperate forest vegetation and woody debris as protection of forest regeneration against browsing. Forest Ecology and Management, 260, 429-437
- Peter D.H. & Harrington T.B.P.D. (2012) Relations of native and exotic species 5 years after clearcutting with and without herbicide and logging debris treatments.
- Ross M., Castle S. & Barger N. (2012) Effects of fuels reductions on plant communities and soils in a piñon-juniper woodland. Journal of Arid Environments, 79, 84-92