Effects of Tamarix ramosissima on the distribution of Populus euphratica in various soil water and salinity environments in the Ejina Oasis, Inner Mongolia of northern China

  Objective  The population of Populus euphratica recovered to a certain extent following the ecological water conveyance project, but its restoration result was far less significant than for Tamarix ramosissima, which overlaped its ecological niche. To provide scientific reference for protecting and managing P. euphratica forests and developing ecological water conveyance projects in oases, this study explored whether the adaptability advantages of P. euphratica population were affected by symbiosis with T. ramosissima in different soil water and salinity environments.

  Method  P. euphratica and T. ramosissima forests in the arid area in northwestern China were selected as the key constructive species of riparian forest communities, and two common soil water and salinity habitats with high and moderate soil moisture and salinity were established as a means of analysing the spatial distribution of both species and their relationships with saline water.

  Result  (1) In an environment with relatively high water and salt content, the P. euphratica population demonstrated a declining trend, with relatively few young woods and a limited amount of regeneration, whereas the T. ramosissima population was stable. The population structure of P. euphratica was found to be stable with little difference between each age class, whereas T. ramosissima was found to have a growing population. (2) In different salt and water environment, both species were mainly distributed in aggregation as a means of resisting the stress of an adverse environment, and P. euphratica seedling growth was inhibited by T. ramosissima. (3) Different soil water and salinity environments resulted in differences in the abundance of both species. The ratio of T. ramosissima to P. euphratica was found to have a positive correlation with salinity, but as the water content increased, the number of T. ramosissima decreased and P. euphratica increased with lower salt content.

  Conclusion  The results further verify that competition is an important factor for the decline of P. euphratica during the succession process, with the exception of environmental filtering. T. ramosissima will gradually replace P. euphratica in high-salt habitats, but the improvement of water conditions could slow down the occurrence of this trend.