Dynamics of Hedysarum scoparium seed rain in the southeastern margin of the Tengger Desert

The natural regeneration of artificial sand-fixation forests is crucial for the success of afforestation efforts aimed at stabilizing sands. Seed rain dispersal plays a vital role in the natural regeneration process of plants. Accurately understanding its dynamic characteristics is significant for assessing the effects of vegetation establishment and formulating effective forestry practices. To investigate the seed rain dispersion pattern in artificial sand-fixation forests, this study focuses on a typical sand-fixation plant, Hedysarum scoparium, located at the southeastern edge of the Tengger Desert. We employed a method of continuous, fixed-point field observations to compare and analyze the seed rain dispersion pattern and seed dispersal capability of artificial H. scoparium populations. The results showed that the density and composition of the complete seed rain of H. scoparium with different crown sizes were significantly different (P < 0.05); however, no apparent difference in seed vitality was observed as canopy width increased. Seed dispersal of H. scoparium populations began in early November and lasted approximately 90 days, following a unimodal curve pattern. The seed rain density peaked in the initial month of dispersal, with values of 3,777.76, 742.06, and 455.35 seeds·m⁻² for large-, medium-, and small-crown populations, respectively. After peaking, seed dispersal gradually declined and essentially ceased by February of the following year. Spatially, the dispersion pattern was concentrated, and maximum dispersal quantity occurred within 0～2 m downwind (east and southeast directions) of large-crown plants. Minimum dispersal distance was observed in south and northwest directions. More than 70% of seeds were deposited within 1～2 m under the maternal crown, with dispersal quantity decreasing sharply as distance from the parent plant increased. In conclusion, the results showed that large-crown H. scoparium populations of the southeastern Tengger Desert exhibit high seed viability and concentrated dispersal patterns, which confer advantages in natural regeneration. We recommend prioritizing the retention of large-crown individuals during forest management, and implementing supplementary planting within 1～2 m of their crown edges to enhance regeneration efficiency. Future studies should address the impacts of extreme climate events on seed rain dynamics and the long-term stability of seed dispersal patterns.