Regeneration properties of a Populus euphratica riparian forest located in the vicinity of the Ejina Oasis, Inner Mongolia, China

To explore the regeneration properties of a Populus euphratica Oliv. forest under unstable environmental conditions, we performed replicate censuses to determine the sapling dynamics of a P. euphratica population in the vicinity of the Ejina Oasis (Inner Mongolia). Even when the stands were established on riverside flatland, we detected slight variations in ground levels and salt concentrations. Due to leaching by flood water, the salinity of topsoil was lower in the riverbed than on the riverbank. Newly recruited saplings grew on riverbanks with high-salinity soil. Saplings were distributed over a wide area via fluctuating water levels, and those growing where salt levels were relatively low were able to grow more easily and become canopy trees. Small individuals comprise a sapling bank on the forest floor that is relatively stable. The dieback of larger saplings results in few reaching a height of more than 2 m. The growth of saplings (including new recruits) is balanced by the death of smaller saplings and the dieback of larger saplings. Individual saplings persist for about 4 years on the forest floor. In summary, hydrological events coupled with soil conditions may drive vegetation distribution patterns in riparian areas in arid regions. P. euphratica forests regenerate via a sapling bank rather than a seed bank. Yearly fluctuations in water flow facilitate the spread of the sapling bank, which guarantees regeneration of the forest. Dieback through partial defoliation is a mechanism used by saplings to escape adverse conditions, thereby maintaining a stable state in arid regions.