Results/Conclusions We found that relationships varied with elevation, and taxonomic and functional groups. Total arthropod abundances and proportions of introduced species (mostly the Argentine ant) increased with the presence and abundance of particular species and milder physical condition (i.e, sampling effect and facilitation), while arthropod diversity increased with total plant complexity of the plot (i.e., facilitation). Proportions of several herbivores responded to a mix of plant complexity and the abundance and quality of particular species (i.e., complementarity), and proportions of predators increased mostly with increased plant complexity (i.e., facilitation). We see that multiple mechanisms are acting across space and trophic hierarchies. Our findings in this young system are informing current efforts to restore native plant and arthropod communities.