Add woody debris to landscapes
Overall effectiveness category Awaiting assessment
Number of studies: 6
Background information and definitions
Reptile species use both fine and coarse woody debris (sometimes called downed wood) as shelter habitat. In landscapes where debris has been removed, adding debris back may improve conservation outcomes (Bunnell & Houde 2010).
For studies discussing leaving woody debris and snags in place after logging or wood harvesting, see Threat: Biological resource use – Leave standing/deadwood snags in forests and Leave woody debris in forests after logging. For other studies that discuss providing shelter habitat, see Create artificial refuges, hibernacula and aestivation sites, and Create artificial burrows.
Bunnell F.L. & Houde I. (2010) Down wood and biodiversity—implications to forest practices. Environmental Reviews, 18, 397–421.
Supporting evidence from individual studies
A replicated, randomized, controlled study in 2002–2005 of pine stands in South Carolina, USA (Owens et al. 2008, same experimental set-up as Davis et al. 2010) found that adding coarse woody debris (downed or standing) did not increase reptile abundance, species richness or diversity compared to areas with no debris added. Plots with added woody debris (downed and standing) were similar to unmanipulated plots in terms of reptile abundance (debris added: 0.3–0.5 individuals/plot vs unmanipulated: 0.4), richness (5–7 species vs. 7) and diversity (10–17 vs. x 13, Shannon-Weiner diversity index). Reptile richness was higher in plots with added downed debris (7 species) compared to plots with added standing debris (5 species). In 2002–2005, nine ha plots within three forest blocks had either downed woody debris added (3 plots, increased five-fold); standing woody debris added (3 plots, increased 10-fold) or were left unmanaged (3 plots). In 2002–2005, fourteen days of sampling were carried out each season (except in spring 2004, when there were 28 days) using drift fences with pit-fall traps.Study and other actions tested
A replicated, randomized, controlled, before-and-after study in 2007–2008 in cacao plantations Sulawesi, Indonesia (Wanger et al. 2009) found that after woody debris, or debris and leaf litter, were added to plantations, both reptile abundance and species richness did not increase compared to in areas where no debris and/or leaf litter was added. All results were reported as statistical model outputs. Overall reptile abundance remained similar after woody debris or debris and leaf litter was added, but decreased after leaf litter and woody debris were removed, or when only woody debris was removed (see original paper for details of individual species abundance changes). Reptile species richness also remained similar after the addition of woody debris or debris and leaf litter, but decreased after leaf litter and woody debris were removed. Six plots (40 x 40 m2) each in cacao plantations (number not specified) were randomly treated with: addition or removal of woody debris (trunks and branch piles), addition or removal of woody debris plus leaf litter or no management. Plots were sampled 26 days before and 26 days after habitat manipulation, three times a day in December 2007–July 2008. Active visual surveys were undertaken for 25 minutes along both plot diagonals (transects 3 x 113 m).Study and other actions tested
Referenced paperWanger 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.
A replicated, randomized, controlled study in 1996–2008 in a loblolly pine Pinus taeda forest in South Carolina, USA (Davis et al. 2010, same experimental set-up as Owens et al. 2008) found that increasing downed coarse woody debris had no effect on lizard or snake abundance, species richness or diversity compared to not manipulating debris. After adding debris, snake abundance, richness and diversity were similar (abundance: 0.03 individuals/m drift fencing, species richness: 0.02 species/m drift fencing, diversity: 0.003 Shannon-Wiener Index), to unmanipulated plots (0.04, 0.04, 0.01), but less than in plots with debris removed (0.07, 0.04, 0.01). For lizards there was no difference between adding (abundance: 0.15 individuals/m drift fence, species richness: 0.07 species/m drift fence, diversity: 0.02 Shannon-Wiener Index), not managing (0.01, 0.07, 0.02) or removing debris (0.15, 0.07, 0.02). Nine ha plots in three pine stands (approximately 45 years old, three plots/stand) were managed by: increasing volume of downed woody debris five-fold by felling trees (initiated 2001, to 59 m3/ha in 2007); no manipulation of woody debris (initiated 1996, 13 m3/ha woody debris); removing all downed woody debris ≥10 cm diameter and ≥60 cm in length by hand (initiated 1996, to 0.24 m3/ha in 2006). All plots were prescribed burned in 2004. Reptiles were sampled for 14 days/plot in each of seven seasons (January 2007–August 2008) using drift fences with pitfall traps.Study and other actions tested
A replicated, controlled study in 2007–2010 in two grassy woodland reserves near Canberra, Australia (Manning et al. 2013) found that adding coarse woody debris in clumps only, or dispersed and in clumps, increased reptile abundance over four years, although the effect size depended on vegetation density and grazing intensity. Adding coarse woody debris (20 tonne/ha clumped or 40 tonne/ha clumped and dispersed) increased overall reptile abundance in one site and overall reptile abundance and small skink abundance in another site compared to not adding debris (results reported as model outputs). The effect of adding coarse woody debris was greatest in open vegetation compared to mid- or high-density vegetation, particularly when vegetation was subject to high-intensity grazing by kangaroos Macropus giganteus (see paper for details). Reptiles were monitored in 96 plots (1 ha) in 24 sites across two nature reserves (4 plots/site). In October 2007, coarse woody debris was added to 1 ha plots as follows: 20 tonnes/ha evenly dispersed (24 plots), 20 tonnes/ha in clumps (24), 40 tonnes/ha clumped and dispersed (24), or no coarse woody debris (24). In December 2007, six sites were fenced to exclude kangaroos and grazing levels were classed as low (fenced: 0.4 kangaroos/ha) or high (unfenced: 2.1). Reptiles were surveyed at each site using 30-minute active searches from March to April in 2007–2010.Study and other actions tested
A replicated, randomized, controlled study in 2011–2012 in upland forest in Queensland, Australia (Shoo et al. 2014) found that reptile captures and species richness tended to be higher one year after coarse woody debris was added to restoration plantings compared to no debris added, or debris removed. Results were not statistically tested. One year after coarse woody debris was added to restoration plantings, reptile captures and species richness tended to be highest in restoration plantings with added coarse woody debris (captures: 3.7–4.0 individuals/site; species richness: 2.0 reptiles/site), followed by restoration plantings without added coarse woody debris (1.5, 0.7), and lowest in remnant forest without management (0.8, 0.5) or remnant forest with coarse woody debris removed (0.3, 0.2). In November 2011–January 2012, five treatments were applied four times each in four sites (60 m x 40 m sites): restoration planting (native trees and shrubs) with added salvaged log piles; restoration planting with added fence post piles; restoration planting with no debris added; remnant forest with no debris added; and remnant forest with all woody debris removed. Restoration plantings were 0–7 years old when coarse woody debris were added. Reptiles were surveyed in either March or August 2012 and again in December 2012.Study and other actions tested
A replicated, paired study in 2013–2015 in 12 pastures adjacent to grassy woodland in New South Wales, Australia (Pulsford et al. 2017) found that pastures with timber added had lower rare reptile abundance and similar species richness compared to pastures without timber, although abundance did increase underneath the timber over time. Rare reptile species abundance was lower in pastures with timber added (0.4 individuals/paddock) compared to pastures without timber (0.7 individuals/paddock). Rare reptile richness was similar in pastures with (1.4 species/paddock) and without timber (1.9 species/paddock). Reptile counts were higher at 15 months after timber installation (3.5 individuals/paddock) than at 12 months (1.4 individuals/paddock). In January 2014–March 2015, reptiles were surveyed in 12 farms grazed by sheep Ovis aries or cattle Bos Taurus with paddocks directly adjacent to remnants of native open grassy woodland. On each farm, two 80 m transects were surveyed: grazed pasture, and grazed pasture with timber added (50 x 50 x 40 cm timber pieces laid at 0.5 m intervals from the edge to 80 m into the pasture 2 months before the first surveys). Surveys were carried out using drift fences, pitfall traps and funnel traps set at 20, 50 and 80 m intervals/transect. Surveys took place for 5 days at a time in austral spring–summer. Rare species were defined as those captured in ≤4 sites with <70 total captures. Timber was checked for reptiles at 12 and 15 months after installation.Study and other actions tested