# Can Vegetation Removal Successfully Restore Coastal Dune Biodiversity?
## 4 Discussion
### Effect of ORV Disturbance  
Off-road vehicle (ORV) disturbance is an anthropogenic press disturbance that is increasingly threatening coastal ecosystems [108; 109]. In general, recreational disturbances result in a decrease of species diversity [110; 111; 112]. Motorbikes, \(4\times 4\) vehicles and quad bikes are driven on beaches and dunes for recreation purposes [113]. These vehicles can cause more widespread damage than human trampling [109; 114; 115], another disturbance that is a widely reported issue for fragile coastal biodiversity [110; 111; 112; 115; 116; 117]. The negative impacts ORVs cause include damage of the physical properties and stability of the substrate, destruction of vegetation, and disturbing, injuring or killing fauna [108; 114; 118; 119; 120; 121]. In California, dunes exposed to ORV disturbance showed significant decline in Coleoptera diversity and species evenness [122]. The effect of disturbance on species composition depends on whether the disturbance exacerbates or reduces environmental harshness, and the conditions that favor specialization ([PERSON] 2006). Since recreational driving in the dunes reduces perennial shrub cover and facilitates sand remobilization, this disturbance could theoretically benefit dunes. The situation is complex because we were not able to quantify the start date, frequency, or intensity of vehicular usage. It is speculated that dunes used by ORVs are most likely to have been mobile dunes, but we do not know what trends would have occurred naturally without disturbance over this time period. However, by comparing the disturbed dunes with both mobile and control (un-treated) semi-fixed dunes, we were able to quantify the outcomes of ORV disturbance on species composition. While disturbed dunes were significantly different to mobile dunes in many samples, these dunes were still the most similar to mobile dunes relative to other treatments for all faunal taxa. Nevertheless, there was undoubtedly a negative impact of ORV disturbance in Nizzanim reserve; firstly, annuals were almost entirely absent due to the intensity of disturbance preventing seedling establishment. Secondly, a significant reduction in total abundance and overall richness of reptile species was seen compared to both mobile and semi-fixed states. Reptiles are known to be particularly sensitive to the presence of vehicular disturbance, affecting the relative abundance and proportional use of preferred microhabitats in coastal systems of Argentina [123]. [PERSON] and [PERSON] [124] found that a gradual reduction in beach vegetation over a decade was accompanied by population declines of a lizard in coastal Brazil. [PERSON] & [PERSON] [120] reported heavy impacts of ORVs on lizards, mammals and arthropods in California. We also found that the populations of the ground beetle _S. striatus_ were significantly lower than on mobile dunes. If the state of disturbed dunes prior to disturbance was more similar to semi-fixed dunes, then the ORV disturbance achieved a much greater shift in composition on these dunes (towards reference) than either of the pulse treatments achieved. Indeed, if the restoration goal was to increase the abundance of MIS, the response to ORV disturbance in the study site could be perceived as positive. The abundance of the desert gepil _G. pyramidum_ was significantly higher in ORV disturbed dunes, compared with both semi-fixed control and mobile dunes. Thus, the overall rodent assemblage was almost entirely composed of this species. Plausibly, the 'hypermobile' conditions created are only inhabitable by highly adapted sand specialist species. Both gerbils are found in sandy habitats, but _G. pyramidum_ is better adapted to exposed, harsh conditions, while _G. a. allenbyi_ needs some shrub cover for protection [97; 125]. Population levels of the beetle _S. striatus_ were also significantly higher in ORV dunes than in semi-fixed dunes, although still somewhat lower than numbers found in mobile dunes. This species is also highly adapted to sandy desert conditions.