# Can Vegetation Removal Successfully Restore Coastal Dune Biodiversity?
## 4 Discussion  
Coastal dune habitats have declined globally over the last several decades due to urbanization. Within remaining dune systems, substantial dune fixation has resulted in further losses of mobile dunes with negative impacts on their associated species [15; 19; 25; 27; 36; 49; 78]. Some studies suggest vegetation removal can initially promote habitat heterogeneity, and increase availability of suitable habitats for psammophile, seric and endemic mobile dune species, but longer term responses are generally unknown [15; 24; 28; 40; 54]. We investigated the temporal trends of four taxonomic groups (including fauna) to determine the effect of vegetation removal on dune assemblages over a 12-year period. Detecting community level responses to restoration can be difficult. Indeed, two studies in Californian coastal dunes were unable to show significant assemblage level responses for terrestrial arthropods [32] or plants [24] despite intensive vegetation removal. Our study found only marginal restoration effects in most cases.  
This large-scale project across multiple taxa and multiple treatments meant that our samples sizes were relatively small, and some caution is needed to interpret the results. Nevertheless, some inferred conclusions can be made. Comparison of control dunes only supported \(H_{I}\) for annual plants (% cover increases with perennial cover) and \(H_{2}\) for annuals and reptiles (richness increases with perennial cover). Composition level parameters showed only small shifts away from the control dune, suggesting high levels of resistance at the community level. Although many of these changes were not statistically significant, they were usually in the direction desired by the manipulation, towards mobile dune status. Semi-fixed dune responses were more pronounced than fixed dune responses. The ORV-disturbed dunes shared more aspects with mobile dunes for faunal taxa compared to both semi-fixed and fixed treated dunes, while annuals were effectively absent. Most mobile dune indicator species also showed some trends in the intended direction in response to most treatment types suggesting that treatment did increase habitat availability for these species, while not removing suitable habitat for fixed dune species. Our results suggest that more pronounced responses might occur given a longer time frame, and that press disturbance is more effective than pulse disturbance for restoring mobile dune habitat.  
Overall, abundance and richness measures were not appropriate indicators for treatment success (since there were few differences between control dune states). Richness did correlate with the gradients of increasing PPC across control dune dunes, but the effects of treatment detected for this parameter were marginal. Both abundance and richness are important to monitor in restoration projects, but they are more appropriate for assessing whether any unexpected artefacts resulted from the intervention. Composition is known to a better parameter for detecting changes [26; 28]. The indicator species that were selected also were highly suitable for detecting changes. Both composition and indicator species showed a temporal trend in treated semi-fixed dunes, away from the control dunes towards the reference dunes over time; this trend was more consistent in the faunal taxa. Over a period of 12 years, we found that the response at the assemblage level was between \(-9\%\) to 30% in semi-fixed treatment, compared to just \(-17\%\) to 6 % in fixed dunes.