We conducted a field experiment to test the strength of interactions among understory plants to a dominant woody species. The experiment consisted in removing all herbaceous neighbours around two target annual plant species (Fuertisimalva peruviana and Plantago limensis), which grow in the understory of the tree Caesalpinia spinosa. Treatments were four: (1) target species with neighbours (N+) under the canopy of C. spinosa; (2) target species without neighbours (N-) under the canopy of C. spinosa; (3) target species with neighbours (N+) in open nearby microsites; and (4) target species without neighbours (N-) in open nearby microsites. After the removal treatments we meadured plant height, fruit production and final biomass. The main results are as follows:
The Figure above shows that the effects of interactions as mediated by dominant plants are species specific (statistical significance is denoted with *). Mostly P. limensis displayed differences in response to removal treatments, and even those differences varied among the response variables measured.
Relative interaction indices (RIIs) also show that P. limensis responded differently in comparison to F. peuviana. For example, for 2012, the neighbours effect on biomass was stronger in open microsites. These results show that the importance of indirect effects mediated by dominant plants is species-specific, which in turn allows for coexistence in such microsites and maintains plant biodiversity at the landscape level.