Action: Leave coarse woody debris in forests
- Two replicated, controlled studies in the USA found that there was no significant difference in abundance in clearcuts with woody debris retained or removed for eight of nine amphibian species, but that the overall response (population, physiological and behavioural) of amphibians was more negative where woody debris was retained.
- Two replicated, controlled studies in the USA and Indonesia found that the removal of coarse woody debris from standing forest did not decrease amphibian diversity or overall amphibian abundance, but did reduce species richness in one study.
- One replicated, controlled study in the USA found that migrating amphibians used clearcuts where woody debris was retained more than where it was removed.
- One replicated, site comparison study in the USA found that within clearcut forest, survival of juvenile amphibians was significantly higher in piles of woody debris than in open areas, and was similar in wood piles to unharvested forest.
Coarse woody debris consists of fallen dead trees and cut branches (> 10 cm diameter) that are left during harvesting. Coarse woody debris increases the structural diversity at the forest floor and provides a valuable microhabitat for animals that are moisture and temperature sensitive such as amphibians.
Studies investigating the effect of adding woody debris to forests are discussed in ‘Habitat restoration and creation – Create refuges’.
Supporting evidence from individual studies
A randomized, replicated, controlled study in 2004–2009 of mixed coniferous and deciduous forest wetlands in Maine, USA (Patrick, Hunter & Calhoun 2006) found that there was no significant difference in amphibian abundance in clearcuts with woody debris retained or removed for eight of nine amphibian species (see also Popescu et al. 2012). Abundance of spotted salamander Ambystoma maculatum juveniles was significantly higher in clearcuts with woody debris retained than in those where it was removed (11 vs 7%). Although not significant, captures tended to be higher in clearcuts with woody debris retained for three of nine species and with woody debris removed for five species. Treatments extended 164 m (2 ha) from each of four created breeding ponds and were clear-cut in 2003–2004. Drift-fences with pitfall traps were installed around each pond at 1, 17, 50, 100 and 150 m from the edge. Wood frogs were marked. Monitoring was in April-September 2004–2005.
A randomized, replicated, controlled study in 1998–2005 of pine stands in South Carolina, USA (Owens et al. 2008) found that the removal of coarse woody debris did not effect amphibian abundance, species richness or diversity. Plots with all downed and standing woody debris removed did not differ significantly from controls in terms of abundance (1–2 vs 2), species richness (7 vs 7) or diversity (17–18 vs 19). The southern leopard frog Rana sphenocephala had greater capture rates with removal rather than addition of woody debris (0.11 vs 0.02/night). Treatments were randomly assigned to 9 ha plots within three forest blocks. The first set of treatments was undertaken in 1996–2001 and a second set in 2002–2005. Control plots had no manipulation of woody debris. Five drift-fence arrays with pitfall traps/plot were used for sampling in 1998–2005.
A replicated, site comparison study in 2005–2006 of microhabitats within clearcut oak–hickory forest in Missouri, USA (Rittenhouse et al. 2008) found that survival rates of juvenile amphibians were significantly higher within piles of woody debris than within open areas in clearcut forest (0.9 vs 0.2). Survival within clearcut brushpile was similar to that within unharvested sites (0.9). The proportion of water loss from animals was lower within woody debris than open areas for American toads Anaxyrus americanus (0.2–0.3 vs 0.3–0.6), green frogs Lithobates clamitans (0.2–0.4 vs. 0.6–0.7) and wood frogs Lithobates sylvaticus (0.1–0.4 vs 0.6–0.7). Water loss in unharvested sites was 0.2–0.4, 0.2–0.3 and 0.1 respectively. Open habitat and piles of coarse woody debris were selected within two clearcuts, where tree crowns had been retained during harvest in 2004. Unharvested forest was used as a reference. Captive-reared American toad and wood frog juveniles and wild-caught green frog metamorphs were placed in individual enclosures within treatments. There were four replicates. Animals were weighed every six hours for 24 hours.
A replicated, controlled study in 2003–2009 of 12 ponds in deciduous, pine and mixed-deciduous and coniferous forest in Maine, Missouri and South Carolina, USA (Semlitsch et al. 2009) found that overall, retaining coarse woody debris during clearcutting had a greater negative effect on amphibian population, physiological and behavioural responses than removing debris, when compared to unharvested forest (-32 vs -19%). However, 14 of 33 response variables were less negative, four less positive, three more negative and 12 the same when debris was retained compared to removed, when compared to unharvested controls. Four treatments were assigned to quadrats (2–4 ha) around each breeding pond (4/region): partial harvest (opposite control), clearcut with woody debris retained or removed and an unharvested control. Treatments were applied in 2003–2005. Monitoring was undertaken using drift-fence and pitfall traps, radio-telemetry and in aquatic (200–1,000 Litres) and terrestrial (3 x 3 m or 0.2 m diameter) enclosures. Different species (n = 9) were studied at each of the eight sites. Response variables were abundance, growth, size, survival, breeding success, water loss, emigration and distance moved.
A replicated, controlled study in 2004–2007 of four seasonal wetlands in pine forest in southeastern USA (Todd et al. 2009) found that migrating amphibians used clearcuts where woody debris had been retained more than where it had been removed. By the final year, the proportion of both salamander species emigrating through clearcut with woody debris retained was significantly higher than in clearcut without woody debris (0.2 vs 0.1). The same was true for immigrating Southern toads Bufo terrestris (0.3 vs 0.1) and frogs Rana spp. (0 vs 0.5). There were four wetland sites, each surrounded by four randomly assigned treatments extending out 168 m (4 ha): partial harvest (15%), clearcut with or without coarse woody debris retained and unharvested. Harvesting was undertaken in spring 2004. Immigrating and emigrating amphibians were captured using drift-fencing with pitfall traps from February 2004 to July 2007.
A replicated, controlled, before-and-after study in 2007–2008 of a cacao plantation in Sulawesi, Indonesia (Wanger et al. 2009) found that removal of woody debris and/or leaf litter did not significantly effect overall amphibian abundance, but did decrease species richness. However, the abundance of Hylarana celebensis and Asian toad Duttaphrynus melanostictus increased following removal of woody debris and leaf litter. The abundance of Sulawesian toad Ingerophrynus celebensis decreased following removal of woody debris. Forty-two plots (40 x 40 m2) were divided into four treatments: removal of woody debris (trunks and branch piles), removal of leaf litter, removal of woody debris plus leaf litter and an unmanipulated control. Monitoring was undertaken twice on two occasions, 26 days before and 26 days after habitat manipulation. Visual surveys were undertaken along both plot diagonals (transects 3 x 113 m).
In a continuation of a previous study (Patrick, Hunter & Calhoun 2006), a randomized, replicated, controlled study in 2004–2009 of mixed coniferous and deciduous forest wetlands in Maine, USA (Popescu, Patrick, Hunter Jr. & Calhoun 2012) found that overall there was no significant difference in abundance in clearcuts with woody debris retained or removed for four forest specialist and four generalist amphibian species. This was true for adults and juveniles immigrating and emigrating from breeding ponds. The one exception was that the abundance of spotted salamander Ambystoma maculatum metamorphs was significantly higher in clearcuts with woody debris retained than in those where it was removed (2 vs 1). Treatments extended 164 m (2 ha) from each of four created breeding ponds and were cut in 2003–2004. Drift-fences with pitfall traps were installed around each pond at 2, 17, 50, 100 and 150 m from the edge. Monitoring was in April–September 2004–2009.
- Patrick D.A., Hunter M.L. & Calhoun A.J.K. (2006) Effects of experimental forestry treatments on a Maine amphibian community. Forest Ecology and Management, 234, 323-332
- Owens A.K., Moseley K.R., McCay T.S., Castleberry S.B., Kilgo J.C. & Ford W.M. (2008) Amphibian and reptile community response to coarse woody debris manipulations in upland loblolly pine (Pinus taeda) forests. Forest Ecology and Management, 256, 2078-2083
- Rittenhouse T.A.G., Harper E.B., Rehard L.E. & Semlitsch R.D. (2008) The role of microhabitats in the desiccation and survival of amphibians in recently harvested oak-hickory forest. Copeia, 2008, 807–814
- Semlitsch R.D., Todd B.D., Blomquist S.M., Calhoun A.J.K., Whitfield-Gibbons J., Gibbs J.P., Graeter G.J., Harper E.B., Hocking D.J., Hunter M.L., Patrick D.A., Rittenhouse T.A.G. & Rothermel B.B. (2009) Effects of timber harvest on amphibian populations: understanding mechanisms from forest experiments. BioScience, 59, 853-862
- Todd B.D., Luhring T.M., Rothermel B.B. & Gibbons J.W. (2009) Effects of forest removal on amphibian migrations: implications for habitat and landscape connectivity. Journal of Applied Ecology, 46, 554-561
- Wanger T.C., Saro A., Iskandar D.T., Brook B.W., Sodhi N.S., Clough Y. & Tscharntke T. (2009) Conservation value of cacao agroforestry for amphibians and reptiles in South-East Asia: combining correlative models with follow-up field experiments. Journal of Applied Ecology, 46, 823-832
- Popescu V.D., Patrick D.A., HunterJr. M.L. & Calhoun A.J.K. (2012) The role of forest harvesting and subsequent vegetative regrowth in determining patterns of amphibian habitat use. Forest Ecology and Management, 270, 163-174