Level of habitat fragmentation determines its non-linear relationships with plant species richness, frequency and density at desertified grasslands in Inner Mongolia, China

Aims This study aimed to examine the changes in plant species richness,frequency and density along a habitat fragmentation gradient(with varied degrees of habitat fragmentation[DHFs])in a desertified grass-land of Horqin Sandy Land,northeastern Inner Mongolia,China.Methods In this study,six landscape plots(500×500 m each)along a habi-tat fragmentation gradient were established.A new fragmentation index was formulated to study the effects of habitat fragmentation on biodiversity indices(species richness,frequency and density).Regression analyses(linear-or non-linear regression)were con-ducted to assess the changes in species richness,frequency and density along the habitat fragmentation gradient at plant commu-nity,functional group and species scales,respectively.Important Findings There was a non-linear relationship(following a quadratic function)between total species richness and the DHF.Total species richness reached its peak when the DHF was 0.2,beyond which species richness decreased along the fragmentation gradient.Plant func-tional groups showed their specific responses to habitat fragmenta-tion,and some non-linear relationships and thresholds existed.The relative richness of rare species also showed a non-linear response to habitat fragmentation,with the threshold being DHF=0.6.Species became rarer(both some common species and rare spe-cies)with the intensifying habitat fragmentation.Our study dem-onstrates the importance of the non-linear relationships and plant functional groups in exploring the effects of habitat fragmentation on biodiversity and implementing effective biological conservation in sand dunes.