Hierarchical Effects of Tamarix aphylla Afforestation in a Sand Dune Environment on Vegetation Structure and Plant Diversity

Abstract

Abstract One method of controlling dune encroachment is afforestation, which may result in biodiversity loss because of habitat change and adverse effects of trees on ecosystem functioning. We carried out a study on the effects of planting discrete areas with Tamarix aphylla (L.) Karsten trees, over 50 years ago, in a semiarid dunefield in the northern Negev, Israel. We surveyed the vegetation and sampled litter and soil in five microhabitats formed by this afforestation scheme. Afforestation had spatially and functionally hierarchical effects on vegetation and plant diversity. The strongest effect was associated with land-use change, showing reduced species richness (by 30–50 percent) and litter production following afforestation. The second strongest effect was associated with salt accumulation in T. aphylla leaves and litter, which increases soil salinity under T. aphylla canopies by 4–5, forming “salinity islands,” and leading to over 30 percent decrease in plant cover and aboveground biomass. The assumed effect of trees in blocking solar irradiance and wind was observed only outside canopies and had a weak impact on plant cover. Therefore, afforestation can increase plant diversity at the regional scale, but at the local (microhabitat) scale it has an overall adverse effect on measured ecosystem functions.