Adverse effects of Tamarix aphylla afforestation in a sand dune environment on vegetation structure and plant biodiversity

One method of fighting dune advancement is planting trees in dunefield heads. However, dune afforestation comes at the cost of mobile sand dune habitat and biodiversity loss. Further negative effects may arise from planting drought- and salinity-adapted allelopathic trees. We have carried out a study of the effects of a T. aphylla forest planted in the 1960s on local vegetation and plant biodiversity. T. aphylla afforestation had clear adverse effects on vegetation cover, plant biomass and plant biodiversity. The greatest and most important effects are of afforestation itself. Compared with non-forested sand, the forest demonstrated reduced species richness, species heterogeneity and dominance. These differences are attributed to reducing sand movement and creating relatively uniform afforested sand fields, hence removing a diversity of mobile dune microhabitats and the species that are uniquely adapted to them. The second tier of effects are of T. aphylla allelopathy. Areas directly under T. aphylla canopies have very low plant cover, plant aboveground biomass and species richness. Third tier effects are of T. aphylla shading, and are observed in differences between areas north and south of trees and outside the direct influence of tree canopies. Plant cover and species richness were greater north of trees, possibly because they block sun irradiance and wind, and thus provide less arid and more protected conditions. Plant community composition among study units varied accordingly, with the CA axes hierarchy matching the three effect vectors described above.