Question: Do shrubs influence the spatial pattern of soil seed banks in herbaceous vegetation and are these effects influenced by wind direction, sampling position (windward vs leeward sides of the shrub) and distance from the shrub?
Location: Horqin desert in eastern Inner Mongolia, China.
Methods: A pioneer shrub, Artemisia halodendron, occurring in a mobile sandy habitat was used as a case study. Species composition and abundance of the seed bank and established herbaceous vegetation around six target shrubs were sampled along transects aligned to the four main wind directions and at 0.5, 1, 2, 3, 4.5 and 6 m from the shrub base on both windward and leeward sides of a transect.
Results: The presence of shrubs significantly modified the spatial pattern of seed deposition, but effects varied with wind direction, sampling position and distance from the shrub. More seeds were deposited on the leeward side than on the windward sides in all four transects, especially on transects with the most prevailing wind directions. Shrubs also caused a marked variation in seed deposition across sampling locations; this effect was more pronounced on the leeward side of transects with the most prevailing wind directions, suggesting the mean range of the shrub's influence is within ca. 2 m.
Conclusions: The study shows clear evidence of shrubs as a source of spatial heterogeneity in seed availability in the herbaceous layer. Shrub presence effects were strongly influenced by complex interactions between wind direction, sampling position, and distance from the shrub.