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Vegetation pattern in lowlands between active sand dunes has rarely been studied, but it may play an important role in maintaining the biodiversity This paper aims to quantify relationships between lowland area and species richness, composition and vegetation distribution and to provide suggestions on biodiversity conservation in the active dune field. Considering each interdune lowland as a self-contained unit, we investigated species composition and vegetation pattern in 25 interdune lowlands (ranging from 0.06 ha to 9.5 ha) of an active sand dune field. Our results showed that species richness increased with lowland area following a power function. The richness of psammophytes relative to the overall species richness decreased with lowland area logarithmically, but increase in lowland area did not lead to significant decrease in psammophyte’s richness. With decrease of lowland area, frequency of psammophytes logarithmically increased, but that of nonpsammophytes logarithmically decreased. When the lowland area was about 2 ha, frequency of the psammophytes was equal to that of the nonpsammophytes (limnocryptophyte-meadow species and steppe species). Furthermore, a consistent pattern of vegetation differentiation along the direction of dune advancement occurred for lowlands larger than I ha: a psammophyte zone near the foot of leeward slope, a limnocryptophyte-meadow species zone in the central part of interdune lowland, and then followed by a psammophyte zone towards the foot of the windward slope. We concluded that lowland size is an important determinant of species diversity and vegetation pattern, and thus has implications for biodiversity conservation in sand dune fields. (C) 2007 Elsevier Ltd. All rights reserved.