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

Abstract

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. Copyright © 2017 John Wiley & Sons, Ltd.

Can Vegetation Removal Successfully Restore Coastal Dune Biodiversity?

“…The Nizzanim LTER is an on-going collaborative project established in 2004 to monitor plants, arthropods, small mammals and reptiles [26]. The study was conducted at the Nizzanim LTER site in Nizzanim Dunes Nature Reserve (NDNR), Israel (31…”

“…The edaphic conditions and the physiognomy of the sand dunes enable numerous Saharan taxa to range northward in spite of the temperate climate that favors Mediterranean species [75], creating an unusual and highly diverse assemblage compared to other Mediterranean coastal systems [76]. Three distinct fixation states of dunes are recognized in NDNR, each state with its own characteristic species diversity and composition [26,77]. Following the declaration of the reserve, livestock grazing and wood harvesting by local communities (predominantly Bedouin) were prohibited and rapid dune fixation occurred, increasing the shrub cover from 4% to 20% of the landscape over a period of 60 years [27,72,78].…”

“…The abundance of each IS was tested using GLMM-PQL (reptiles and beetles) and LME (rodents and annuals) models similar to those used for assemblage abundances [26]. We assessed the temporal trends of each IS using a permuted Empirical Cumulative Distribution Function (ecdf ) in the R stats package [84].…”

“…Flora and fauna found on mobile dunes are often psammophilic, endemic species, highly adapted to harsh, xeric sandy conditions, and often form unique assemblages [6,[26][27][28][29][30][31]. Several researchers recognize that dune fixation, whether through succession or intentional re-establishment, can result in adverse consequences for mobile dune species [14,24,25,32,33].…”

“…Exclusion of this anthropogenic presence since the middle of the last century has led to substantial shrub encroachment and dune fixation across the reserve [69,72]. It is expected that in the absence of disturbance, the dunes in NDNR will eventually homogenize and become fixed, which will result in the loss of mobile dunes and their associated species, and an overall loss of βand γ-diversity across the reserve [26].…”