摘要：The shrub Artemisia halodendron and the annual herb Agriophyllum squarrosum, which
typically co-occur in a mobile sandy habitat in eastern inner Mongolia, China, were
used to determine whether the presence of A. halodendron influences seed deposition
and seedling recruitment of A. squarrosum under and around the shrub canopy in relation
to wind direction, sampling position (windward vs. leeward sides) and distance
from the shrub. The numbers of seeds deposited, seedlings emerged, and individuals
recruited of A. squarrosum around adult shrubs were sampled along four transects
aligned to the four main wind directions at 0.5, 1, 2, 3, 4.5 and 6 m from the shrub base
on both windward and leeward sides of each transect. Spatial pattern of seed deposition
was strongly altered by the presence of shrubs, but effects varied with wind direction,
sampling position and distance from shrubs. Significantly more seeds tended to deposit
on the leeward than on the windward sides in all four transects, with the exception of
transects along the least prevailing wind direction. The presence of shrubs as nursing
plants caused a marked variation in seed deposition across sampling locations, but this
effect was detected only in the most, secondary and third most prevailing wind directions,
but not in the least prevailing wind direction. In general, the shrub’s influence was
within a 2 m radius from the shrub, despite some differences among transects. Although
seed bank density had no direct effect on A. squarrosum recruitment patterns, it contributed
to the observed variation in recruitment indirectly through density-dependent
emergence of seedlings. Our findings provide further evidence of shrubs as a source of
spatial heterogeneity in seed availability and thereby a common factor determining population
dynamics of understorey herbaceous species.
