Document: JOS-3-38-6

Effects of shrubs on annual plant communities in temperate arid lands of Australia.

FACELLI, J.M.* and A.M.TEMBY

University of Adelaide. Adelaide, South Australia 5005 Australia ¹

Abstract:
Interactions among plants are often asymmetric and size dependent. In arid lands the presence of large perennial plants may produce spatial heterogeneity that affects the distribution and performance of annual plants. The soil under Atriplex vesicaria (one of the dominant shrub species in the system) had higher total N content than soil in open spaces, while soil under Maireana sedifolia (the other dominant shrub) had lower available P than open spaces. The germinable soil seed bank, and the annual plant community under A. vesicaria shrubs were substantially different from those in open spaces. While annual plant densities under A. vesicaria were higher than in open spaces, experimental removal of shrubs increased plant density, suggesting that the shrubs have simultaneously facilitative and competitive effects through different mechanisms. Trenching of open areas close to shrubs (to sever any lateral shrub root) decreased annual plant density, probably because water is moved laterally by shrub roots, in a process akin to hydraulic lift, increasing water availability for the annual plants. Protection against grazing had a stronger effect on annual plant biomass in open spaces than under shrubs, suggesting that shrubs provide some shelter against grazers. Our results demonstrate that shrubs have both positive and negative effects on the annual plant community. These effects are spatially - and most likely temporarily - heterogeneous, which should contribute to the maintenance of species diversity in the community.

Keywords: facilitation, competition, arid lands, annual plants

This abstract is being presented at: 9:30 AM in session:
Oral Session #72: Plant Competition.