Present address: Institute of Ecological Science, Vrije Universiteit, De Boelelaan 1085, 1081 HV Amsterdam, The Netherlands
Desert shrubs have negative or neutral effects on annuals at two levels of water availability in arid lands of South Australia
Article first published online: 6 AUG 2008
© 2008 The Authors. Journal compilation © 2008 British Ecological Society
Journal of Ecology
Volume 96, Issue 6, pages 1230–1237, November 2008
How to Cite
Weedon, J. T. and Facelli, J. M. (2008), Desert shrubs have negative or neutral effects on annuals at two levels of water availability in arid lands of South Australia. Journal of Ecology, 96: 1230–1237. doi: 10.1111/j.1365-2745.2008.01427.x
- Issue published online: 15 OCT 2008
- Article first published online: 6 AUG 2008
- Received 17 January 2008; accepted 30 June 2008; Handling Editor: Fernando Maestre
- Carrichtera annua;
- chenopod shrublands;
- fertility islands;
- Maireana sedifolia;
- Tetragonia tetragonioides
- 1Perennial plants have been shown to facilitate understorey annual plant species in arid lands through the modification of spatial patterns of resources and conditions. This effect can result from a balance between simultaneously positive and negative interactions, both direct and indirect. This balance may shift with temporal variability in water availability.
- 2We conducted a field experiment in a chenopod shrubland in South Australia to separate the effects of shade, below-ground competition, and soil modification by shrubs on the performance of annual plants, and to determine if the strength and direction of the interaction shifted with changes in water availability.
- 3Annual plant diversity and seedling density was highest in plots established in open sites away from the dominant shrubs (Maireana sedifolia). Experimental removal of M. sedifolia increased seedling density compared to plots under undisturbed shrubs and plots where the removed shrub was replaced with artificial shade. Shading of open plots also reduced seedling density. Annual plant biomass was highest in areas where shrubs had been removed and was reduced by artificial shading. Biomass was higher in open plots than under intact shrubs. Experimental water addition did not alter plant density, but increased biomass across all treatments, particularly in artificially shaded bush plots.
- 4Synthesis. Our results show that the overall effect of shrubs on the annual plant community in the system is negative under the range of water availabilities experienced during the experiment. This negative net-effect results from a combination of simultaneous facilitation via soil modification, and above- and below-ground competition. Assessment in different systems of different combinations of mechanisms that have simultaneously positive and negative effects will allow us to refine hypotheses seeking to explain the relative importance of facilitation across spatial and temporal gradients.