Changes in Morphology of Nitraria tangutorum Nebkhas at different Successional Stages in the Oasis-Desert Ecotone, Northwest China

Nebkhas play a tremendous role in maintaining the ecological functions of deserts and in slowing land desertification processes. Numerous nebkhas are distributed in the northwestern edge of the Ulan Buh desert, Nitraria tangutorum nebkhas are the most typical dunes in this area. However, our knowledge of the effect of those factors on the succession of nebkhas, including their succession in different sandy land types, is limited. The goal of this study was to reveal their factors influencing the morphological characteristics of N. tangutorum nebkhas in different sandy land types (shifting sandy land, semi-fixed sandy land, and fixed sandy land) in the Ulan Buh desert. Our results showed the densities of N. tangutorum nebkhas were 34, 51, and 77 dunes per ha in the shifting, semi-fixed, and fixed sandy lands, respectively. The density of N. tangutorum nebkhas gradually increased and N. tangutorum nebkhas started to degenerate with the increasing fixation of sandy land. The successional stage had significant effects on all the morphological characteristics, and sandy land types had significant effects on the length (L), height (H), volume (V), horizontal scale (D) and ratio of width to height (H/W). Almost all of the morphological parameters of N. tangutorum nebkhas were correlated at different successional stages, indicating a strong interrelationship among the morphological parameters of nebkhas. The successional stages of N. tangutorum nebkhas had significant effects on the density of branch (M), height (h), coverage (C), deadwood rate (DR), and length of new branches (LB) of the N. tangutorum shrub. The M, h, C, and LB first increased and then decreased, and DR increased with the succession of N. tangutorum nebkhas. These results indicated that we should focus on nebkhas succession to ensure the ecological stability of oases in a dessert.