Action

Manage vegetation using herbicides

How is the evidence assessed?
  • Effectiveness
    not assessed
  • Certainty
    not assessed
  • Harms
    not assessed

Study locations

Key messages

  • Seven studies evaluated the effects of managing vegetation using herbicides on reptile populations. Four studies were in the USA, two were in Australia and one was in the US Virgin Islands3.

COMMUNITY RESPONSE (3 STUDIES)

  • Community composition (1 study): One replicated, randomized, controlled, before-and-after study in Australia found that areas where an invasive shrub was sprayed with herbicide had similar composition of reptile species compared to unsprayed areas.
  • Richness/diversity (3 studies): Three replicated, randomized, controlled, before-and-after studies in Australia and the USA found that areas where vegetation was treated with herbicides had similar richness of reptile species or combined reptile and amphibian species compared to areas not treated with herbicide.

POPULATION RESPONSE (6 STUDIES)

  • Abundance (4 studies): Three of four studies (including three replicated, randomized, controlled, before-and-after studies) in the USA and Australia found that areas where vegetation was treated with herbicides had similar abundance of all or most reptiles compared to areas not treated with herbicide. The other study found that after glyphosate was applied to pond vegetation, fewer mangrove salt marsh snakes were found compared to immediately before application.
  • Reproductive success (2 studies): One of two controlled studies (including one replicated study and one randomized study) in the USA and US Virgin Islands found that exposure of red-eared slider eggs to high levels of glyphosate caused a reduction in hatching success. The other study found that leatherback turtle nests in areas treated with herbicide had similar hatching and emergence success compared to nests in untreated areas.
  • Survival (1 studies): One randomized, controlled study in the US Virgin Islands found that in areas treated with herbicide, fewer leatherback turtle hatchlings became entangled in vegetation than in untreated areas.

BEHAVIOUR (1 STUDY)

  • Use (1 study): One replicated, randomized, controlled study in Australia found that pink-tailed worm-lizards were not found in restored rocky areas treated with herbicide, but were found in restored areas not treated with herbicide.

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 study in 2005 in a laboratory in Louisiana, USA (Sparling et al. 2006) found that the herbicide (glyphosate), which may be used to manage vegetation, when applied to eggs of red-eared sliders Trachemys scripta elegans, reduced hatching success and the health of hatchlings, but only at the highest glyphosate concentration. Hatching success at the highest concentration of glyphosate and the surface-active agent was 73%, compared to hatching success of 80–100% with lower concentrations or no glyphosate. Hatchlings from eggs that had been exposed to the highest concentration of glyphosate and surface-active agent also weighed less both at hatching and after 14 days, compared to those from eggs that had been exposed to lower concentrations. Eggs of red-eared terrapins were exposed to either a single application of glyphosate (68–11,206 ppm wet weight of glyphosate in Glypro, 15 eggs/concentration) with a surface-active agent (LI700) or to no glyphosate (16 eggs). After exposure, eggs were incubated in vermiculite and the number to hatch successfully was recorded. Fourteen days after hatching, size and weight of hatchlings was recorded.

    Study and other actions tested
  2. A before-and-after study in 2006–2007 in two connected stormwater run-off ponds in Florida, USA (Ackley et al. 2010) found that after glyphosate herbicide was applied in summer to remove ground vegetation, fewer mangrove salt marsh snakes Nerodia clarkia compressicauda tended to be recorded in the autumn. Results were not statistically tested. In the autumn after glyphosate herbicide was applied to pond vegetation, mangrove salt marsh snake abundance was estimated as 47 snakes, compared to 95 snakes in spring immediately before herbicide was applied, 94 snakes in the summer while herbicide was being applied and 33 snakes in the spring of the year prior to herbicide being applied. Two man-made ponds (0.2–0.4 ha) were treated with glyphosate herbicide (‘Aquamaster’) monthly during summer 2007 (exact start date not known). Salt marsh snakes were monitored at night for three nights at a time in April 2006 (spring), March–April 2007 (spring), May–July 2007 (summer) and August–October 2007 (autumn). Snakes were caught by hand, individually marked with PIT tags and released. Snakes >40 cm long were used to calculate abundance.

    Study and other actions tested
  3. A randomized, controlled study in 2007 on coastal sand dunes in St Croix, US Virgin Islands (Conrad et al. 2011) found that using herbicide to remove the native plant ‘beach morning glory’ Ipomoea pes-caprae did not increase leatherback turtle Dermochelys coriacea nest productivity compared to plots with untreated vegetation, but fewer hatchlings became entangled in plant roots in herbicide treated plots compared to in untreated, vegetated plots. Herbicide treated plots had similar hatching success (24% hatched/total yolked eggs) and emergence success (21% hatched/total yolked eggs) compared to untreated vegetated plots (hatching: 20%; emergence: 15%), but lower hatching and emergence success compared to naturally unvegetated plots (hatching: 50%; emergence: 38%). However, the number of hatchlings that became entangled in plant roots was lower in herbicide-treated plots (17 of 393, 4% of hatchlings trapped) compared to untreated vegetated plots (36 of 314, 12% of hatchlings trapped). Ten herbicide-treated plots and 10 untreated vegetation plots (5 x 5 m) were randomly allocated across two experimental blocks. Ten unvegetated plots were established seaward of the experimental blocks. Herbicide (3% Roundup Pro ConcentrateTM) was applied once, 72 days before the nesting season. In April–May 2007, nests laid in areas of the beach liable to flooding were relocated to either herbicide-treated plots, untreated vegetated plots or naturally unvegetated plots (2 nests/plot; 16–20 nests/treatment). Nylon mesh nets were placed over nests before hatching. All nests were excavated 1–3 days after the main period of hatchling emergence and the number of hatched and unhatched eggs was counted.

    Study and other actions tested
  4. A replicated, randomized, controlled, before-and-after study in 2010–2012 in shrubland in New South Wales, Australia (Martin & Murray 2013) found that spraying invasive Bitou bush Chrysanthemoides monilifera ssp. rotundata with herbicide did not increase reptile abundance or species richness in the year after spraying. Reptile abundance and species richness was similar after shrubland was sprayed (0.4–1.0 individuals/100 m2; 0.4–0.5 species/100 m2, respectively) compared to before spraying (0.6 individuals/100 m2; 0.5 species/100 m2) and compared to sites where Bitou bush was unsprayed (0.9–1.0 individuals/100 m2; 0.3–0.5 species/100 m2) and unsprayed sites without Bitou bush (0.6–1.3 individuals/100 m2; 0.3 species/100 m2). Species composition was similar before-and-after spraying and between sprayed and unsprayed sites. Reptiles were surveyed in 10 sites in March–April 2010, November 2010, and February 2011. Two sites contained invasive Bitou bush and were treated with glyphosate herbicide in May–June 2010. Eight sites were not sprayed: three contained invasive Bitou bush and five did not. Where Bitou bush was present, it comprised 40% cover in a mosaic with native vegetation. Reptiles were surveyed morning and evening (15 minutes/transect) using active searches (for example, turning over logs and rocks, raking leaf litter, lifting loose bark).

    Study and other actions tested
  5. A replicated, randomized, controlled, before-and-after study in 1999–2007 in six pine plantations in Mississippi, USA (5) found that herbicide application did not increase reptile and amphibian diversity in six out of seven years of monitoring, although eastern fence lizards Sceloporus undulatus abundance did increase in the year after management. In six of seven years after herbicide application, species richness, diversity measures and most species abundances were similar in plots treated with herbicide and plots receiving no treatment (data reported as statistical model outputs, see paper for details). Eastern fence lizard abundance was higher in plots treated with either herbicide only, herbicide in combination with burning or burning alone (0.02 lizards/plot; abundance for herbicide only plots not provided separately) in the first year after management compared to unmanaged plots (0.002 lizards/plot; abundance in other years not provided). Four 10 ha plots were set up in six intensively managed 18–22-year-old commercial pine stands (59–120 ha). Plots were either treated with herbicide (‘Imazapyr’) in September 1999, burned in the dormant season (December–February) in 2000, 2003 and 2006; or treated with herbicide then burned; or unmanaged. Reptiles were monitored using drift fences with pitfall and funnel traps in May–June 1999–2007 (one year before management and seven years after management began).

    Study and other actions tested
  6. A replicated, randomized, controlled, before-and-after study in 2008–2014 in an upland mixed oak forest in the Appalachians, USA (Greenberg et al. 2016) found that mid-storey vegetation removal using herbicides did not increase the abundance or species richness of total reptiles, snakes or lizards when compared to no management. Abundance and richness of total reptiles was similar in herbicide treated plots (Abundance: 0.4–0.7 average captures/100 fence nights; richness of total reptiles provided as statistical model result) compared to unmanaged plots (Abundance: 0.2–0.5 average captures/100 fence nights). In 2008, mid-storey vegetation removal was carried out using herbicides. Reptiles were surveyed in herbicide-managed plots and unmanaged plots (4–5 plots/type each 225 x 225 m) using drift fences, pitfall and funnel traps in May–August one year pre-management (in 2008) and up to 5 years after management (in 2010, 2011, 2013, 2014).

    Study and other actions tested
  7. A replicated, randomized, controlled study in 2014–2015 in six rock and grassland areas in Australian Capital Territory, Australia (McDougall et al. 2016) found that pink-tailed worm-lizards Aprasia parapulchella did not recolonise restored rocky areas replanted with grasses that were treated with herbicide, but did recolonise restored areas not treated with herbicide. When herbicide was used following native grass and rock cover restoration, pink-tailed worm-lizards did not recolonise rocks (no lizards observed), but four lizards and one lizard skin were observed in restored rock outcrops not treated with herbicide. There was no evidence of lizards in unrestored sites in poor quality habitat, but four lizards and three shed skins were observed in unrestored sites near high quality lizard habitat. In April–May 2014, plots (4 x 4 m) in six sites (150 m apart) were managed with: rock addition (30% rock cover) and native grass restoration; or rock addition and grass restoration with herbicide application (Glyphosate, 1:100 glyphosate:water). In February 2015, all plots were surveyed for lizards (live sightings and skins) including two unmanaged plots/site (one in poor, the other near high-quality lizard habitat).

    Study and other actions tested
Please cite as:

Sainsbury K.A., Morgan W.H., Watson M., Rotem G., Bouskila A., Smith R.K. & Sutherland W.J. (2021) Reptile Conservation: Global Evidence for the Effects of Interventions for reptiles. Conservation Evidence Series Synopsis. University of Cambridge, Cambridge, UK.

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