COS 93-5
Indirect effects in a desert plant community: do nurse-plants mediate interactions between understorey species?
In deserts nurse plants usually facilitate entire plant communities below the influence of their canopies. Although much attention has been given to the direct consequences of these interactions in terms of species richness and abundance/biomass, the understanding of indirect effects between beneficiary plants is still limited. Here, we tested the hypothesis that nurse plants mediate indirect effects between understorey plants by increasing their competitive interactions. To better understand the conditionality of indirect effects we tested this hypothesis along a stress gradient in coastal Southern Peru. Our design consisted in the removal of neighbors of 2 target understorey species (Plantago limensis and Fuertisimalva peruviana) in a 0.3 m radius in 2 microhabitats: under the canopy of Caesalpinea spinosa and in open nearby spaces where the target species also occurred. We recorded plant height, number of fruits and final biomass of the target species in response to our treatment removals and non-removal controls.
Results/Conclusions
We found overall significant differences along the stress gradient and between our target species in relative growth rate, fruit production and biomass. We also found that the neighborhood removal of Plantago limensis resulted in a biomass and fruit production increase, but not for Fuertisimalva peruviana indicating a species-specific effect of direct competition. However, we did not find differences between microhabitats for any of the target species showing that nurse plants do not mediate indirect effects in their under-storey. These results provide evidence that in arid ecosystems direct effects are stronger than indirect effects, however further tests should be carried out to extend the scope of this finding.