Shrub Encroachment Effects on Habitat Heterogeneity and Beetle Diversity in a Mediterranean Coastal Dune System

Coastal dunes are fragile dynamic environments characterised by low productivity and high levels of bare and shifting sands. They are highly threatened by urbanisation and human development. The dunes in Nizzanim Dunes Nature Reserve, Israel, have additionally incurred shrub encroachment following exclusion of grazing and wood extraction from the area. The temporal changes over the last few decades have been monitored in the Nizzanim Long-Term Ecological Research project and are reflected by spatial heterogeneity. Some dunes are fixed with high plant cover and associated characteristics, while other dunes are still in semi-fixed and mobile states. Measures of beetle abundance, richness and diversity showed significant differences, among dune states. Cluster analysis and ordination of species composition revealed distinct assemblages for three different states, with more psammophilous species found in mobile dunes than in other dune states. Variation within a dune state was not significant for any dune state, while among states species composition was significantly different, demonstrating high β-diversity between dune states. Landscape heterogeneity contributes to high β-diversity and γ-diversity in the coastal dunes and continued shrub encroachment, and the associated fixation of mobile dunes will lead to habitat homogenisation and a decline in γ-diversity. This finding highlights the importance of disturbance in dynamic Mediterranean coastal dunes. We recommend a restorative intervention that promotes disturbance and heterogeneity at the landscape level by conserving all three dune states.