Effects of a nurse shrub on seed deposition and seedling recruitment of the annual <i>Agriophyllum squarrosum</i>

Abstract

Abstract. 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.

Plant–plant interactions: from competition to facilitation

“…For instance, Rey Benayaset et al 2007studied different management techniques of the use of low-cost, low-impact techniques on restoration of Quercus coccifera oak forests, finding that competition had a strong impact on oak recruitment and that simple clipping of competing vegetation resulted in similar effects to those of more thorough and expensive treatments of competition removal. Other studies (Li et al, 2007) did try to detect facilitation between pairs of species but found prevailing competition between two species inhabiting mobile dunes, although the presence of one species created a wind barrier that modified prevailing airstreams and strongly influenced the spatial pattern of seed dispersal of the second species. This provided further evidence of the effect of shrubs as a source of spatial heterogeneity.…”