Limit or exclude off-road vehicle use

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

Study locations

Key messages

  • Two studies evaluated the effects of limiting or excluding off-road vehicle use on reptile populations. Both studies were in the USA.


  • Richness/diversity (1 studies): One replicated, site comparison study found that restricting access of off-road vehicles and sheep had mixed effects on lizard species richness.


  • Abundance (2 studies): One of two replicated, site comparison studies (including one randomized study) in the USA found that areas where off-road vehicles were completely excluded using fencing that also excluded livestock grazing had higher densities of Agassiz’s desert tortoises compared to areas with some restrictions or no restrictions. The other study found that restricting off-road vehicle and sheep access had mixed effects on lizard abundance.
  • Survival (1 study): One replicated, randomized, site comparison study in the USA found that in areas where off-road vehicles were completely excluded, death rates of Agassiz’s desert tortoises were lower than in areas with some restrictions or no restrictions.


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, site comparison in 1994–1996 in desert shrub and grassland in south-central California, USA (Brooks 1999), found that lizard abundance and species richness was higher inside a fenced protected area that excluded vehicles and sheep, compared to outside of the fence, depending on survey month and plot. Lizard abundance was higher in three of six survey comparisons in a fenced protected area with restricted vehicle use (4–10 lizards/transect) compared to outside of it (2–4 lizards/transect) but similar in the remaining three comparisons (inside protected area: 2–5 lizards/transect; outside protected area 1–3 lizards/transect; see original paper for details). Lizard species richness was higher in one of six comparisons inside the protected area (2 species/transect) compared to outside of it (1 species/transect) but similar in the remaining five comparisons (inside protected area: 2–3 species/transect; outside protected area: 1–3 species/transect; see original paper for details). In 1994, two sites were selected near the north-eastern and southern boundary of the Desert Tortoise Research Natural Area (where off-road vehicles were prohibited from 1973, sheep grazing prohibited from 1978 and the boundary was fenced in 1980). Two 2.25 ha plots were established/site: one ≥400m inside the boundary and one outside the boundary (used by off-road vehicles until 1980 and grazed by sheep until 1994). In each plot, lizards were surveyed using 1.25 km transects in July 1994 and May and July 1995 (six surveys/site).

    Study and other actions tested
  2. A replicated, randomized, site comparison study in 2011 in desert shrub and grassland in California, USA (Berry 2014) found that Agassiz’s desert tortoises Gopherus agassizii were more abundant and had a lower mortality rate in a protected area fenced to exclude recreational vehicle use and livestock grazing. Desert tortoise densities were approximately six-times higher in the most protected area, the Tortoise Natural Area (15 tortoises/km2) than designated tortoise critical habitat with some vehicle restrictions (2 tortoises/km2) and four-times higher than on private lands with no vehicle restrictions (4 tortoises/km2). Tortoise annual death rates over the preceding four years were estimated as lowest in the Tortoise Natural Area (3% mortality/year) compared to private lands (6%) or in tortoise critical habitat (20%, results were not statistically tested). Tortoises were surveyed in 240 1 ha plots across three different management areas (80 plots/area): Tortoise Natural Area (1973: closed to recreational vehicles; 1980: fully enclosed and closed to mining and livestock grazing, 2010: 12 km of fencing extended to prevent tortoises leaving), tortoise critical habitat areas (1994: recreational vehicle use restricted but not enforced with some annual closures, 1990: closed to sheep grazing) and private lands (unregulated sheep grazing, intensive recreational vehicle use, hunting and trash dumping). In April–May 2011 plots were surveyed on foot twice in a day for live or dead tortoises and field signs.

    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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