Action

Remove or control non-native/invasive plants

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

Study locations

Key messages

  • Four studies evaluated the effects of removing or controlling non-native/invasive plants on reptile populations. Two studies were in Australia and one was in each of South Africa and the USA.

COMMUNITY RESPONSE (1 STUDY)

  • Richness/diversity (1 study): One replicated, randomized, controlled, before-and-after study in Australia found that areas where invasive Bitou bush were sprayed with herbicide had similar reptile species richness compared to unsprayed areas.

POPULATION RESPONSE (4 STUDIES)

  • Abundance (3 studies): Two of three replicated, controlled studies (including two randomized and two before-and-after studies) in the USA and Australia found that areas where invasive Bitou bush or para grass were controlled had a similar abundance of reptiles and combined reptiles and amphibians compared to areas with no control. One study also found that the abundance of delicate skinks was lower in areas with invasive control compared to unmanaged areas. The other study found that removing invasive non-native Sahara mustard had mixed effects on the abundance of Coachella Valley fringe-toed lizards and flat-tailed horned lizards.
  • Reproductive success (1 study): One replicated, controlled, before-and-after study in South Africa found that in areas where an invasive plant was removed, nesting activity by Nile crocodiles increased more than in places with no removal.

BEHAVIOUR (0 STUDIES)

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, before-and-after study in 1993–1997 in shoreline habitat on a lake in Kwazulu-Natal, South Africa (Leslie & Spotila 2001) found that manual removal of the invasive plant Chromolaena odorata from nesting sites increased Nile crocodile Crocodylus niloticus successful nesting attempts over three breeding seasons. Results were not statistically tested. Known nesting sites where invasive vegetation was removed had 40% (2 out of 5 sites nested), 80% and 60% success over three breeding seasons following removal, compared to 40% nesting success before removal. Newly created nesting sites, where invasive vegetation was completely removed, had 33% (2 out of 6 sites nested), 33% and 67% success over three breeding seasons following removal, compared to 0% success before removal. Nesting success in sites where invasive vegetation was not removed was 100% (5 out of 5 sites nested), 60%, 40% and 40% over four breeding seasons. In 1993, sixteen nest sites were chosen: five known nesting sites where the invasive plant was present and manually removed from 1994; six sites newly created by manually clearing of all invasive vegetation and root stock (4 x 4 m area); and five where the invasive plant was present and was left untreated. In 1994–1997 (three breeding seasons) invasive vegetation clearing was carried out each season. In 1993–1997, all sites were monitored using foot, boat and aerial surveys in mid-December to determine use of nesting sites.

    Study and other actions tested
  2. A replicated, paired sites, controlled, before-and-after study in 2002–2007 in a site of dunes and desert scrub in California, USA (Barrows et al. 2009) found that manual removal of invasive non-native Sahara mustard Brassica tournefortii resulted in an increase in Coachella Valley fringe-toed lizard Uma inornata abundance but not flat-tailed horned lizard Phrynosoma mcallii abundance. Overall abundance of fringe-toed lizards was higher in invasive removal plots (2.5 lizards/plot) compared to plots with no removal (1.6 lizards/plot), but flat-tailed horned lizard abundance was similar in both (removal: 0.1 lizards/plot; no removal: 0.1 lizards/plot). In yearly comparisons, fringe-toed lizard abundance was higher in removal plots in one of three years during or after removal in active dunes (2nd year of removal: 6.6 lizards/plot; no removal: 3.5 lizards/plot), but not in stabilized sand fields (removal: 1.9–2.3 lizards/dune; no removal: 1.2–2.5 lizards/dune).  Paired plots (10 x 100 m plots) of mustard removal and no mustard removal were established in stabilised sand fields (15 removal plots, 15 no removal plots) and active dunes (6 removal plots, 6 no removal plots). Mustard removal was carried out by hand in 2005–2006. Reptiles were surveyed at each site six times/year from May to July 2002–2007 in the morning using sightings and tracks left in the sand. 

    Study and other actions tested
  3. 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
  4. A replicated, randomized, controlled study in 2004–2006 in a seasonal wetland in Queensland, Australia (Bower et al. 2014) found that overall reptile and amphibian abundances were not affected by combinations of burning and grazing to remove invasive non-native para grass Urochloa mutica, but that the abundance of one skink species Lampropholis delicata was reduced. When non-native para grass was controlled, overall reptile and amphibian abundance was similar in grazed, burned, grazed and burned and unmanaged plots (results presented as statistical model outputs) but abundance of Lampropholis delicata was lower in all managed plots (burned: 3 skinks/plot; grazed: 4 skinks/plot; burned and grazed: 1 skink/plot) compared to unmanaged plots (14 skinks/plot). Para grass dominated habitat in a conservation park (3,245 ha) was divided into 12 plots (200 x 300 m each) and each plot was either burned, grazed, burned and grazed, or not managed (3 plots/management type). Burning took place in August 2004, September 2005 and November 2006. Cattle grazing took place after burning in September–December 2004, October–December 2005 and November–December 2006. Stocking levels were calculated to consume 50% of the grass biomass present/plot. Reptile and frog communities were sampled four times between 2005–2007 using three pitfall/funnel trap arrays/plot (see original paper for details). Reptiles were individually marked by toe clipping prior to release.

    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.

Where has this evidence come from?

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Reptile Conservation

This Action forms part of the Action Synopsis:

Reptile Conservation
Reptile Conservation

Reptile Conservation - Published 2021

Reptile synopsis

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