Adverse impacts of off-road vehicles on coastal dune vegetation are widespread, substantial, and long-lasting : Evidence from a global meta-analysis of sandy beach-dune systems

1: Ocean shores are among the most spectacular and sought-after sites for leisure activities, including ‘nature and wilderness experiences’. Some of these activities can involve the use of off-road vehicles (ORVs) driven across extensive stretches of sandy coastlines. Yet, this recreation mode can be controversial because of environmental, cultural, social, and ethical concerns. However, ORV users often question the putative impacts, especially the ecological aspects.

2: Here, we review the available published data about the ecological impacts of vehicles on coastal plants. We focus on vegetation because of its critical role in coastal resilience and its foundational role in the structure and function of dune-beach systems. The principal type of evidence is a formal meta-analysis of effect sizes that can be unambiguously linked to ORV use.

3: The evidence of serious ecological harm caused by ORVs to plants of beach-dune habitats is geographically widespread, extensive in taxonomic coverage (253 species, 174 genera, and 64 families), sizeable in the magnitude of reported impacts (443 records) and statistically robust (significant negative departures from zero responses).

4: Vegetation stressed by ORVs typically has substantially reduced abundance, cover, biomass, area, occurrence, diversity, and productivity. ORVs also significantly alter the composition and structure of assemblages.

5: Degradation occurs rapidly, with the first few vehicle passes causing most of the damage. Thresholds of impact can be exceptionally low (one or two cars separated by weeks), implying that in many cases, dunes and the back-shore of beaches have extremely limited resilience to repeat traffic by off-road vehicles: No ‘safe threshold’ of use may exist.

6: Recovery after closure to off-road vehicles is highly variable, depending on species traits (slower for woody shrubs) and habitat conditions (slower for back-dunes). It can be protracted, with some assemblages typically taking around a decade or more to recover.

7: The exceptionally low tolerance of many coastal plant species and habitats translates into policies to phase out ORV use on ocean shores and dunes. Spatial closures and strict controls should be the mainstay of management interventions, supplemented by novel approaches seeking to identify where and when environmentally safe and benign practices may exist and whether these can be culturally and ethically acceptable.