Ecological restoration of former agricultural land can improve soil condition, recover native vegetation, and provide fauna habitat. However, restoration benefits are often associated with time lags, as many attributes, such as leaf litter and coarse woody debris, need time to accumulate. Here we experimentally tested whether adding fine and coarse woody debris to a decade-old restoration sites can accelerate restoration benefits. We used a Multi-site Before-After / Control-Impact design to test the effects on 30 response variables over a period of two years, including those describing soil physical and biochemical properties, herbaceous vegetation and ant communities. We analysed the data using linear mixed-effect models and perMANOVAs. Of the 30 response variables, a significant effect of mulch or log additions was found for just four variables: volumetric water content, decomposition of tea leaves, native herbaceous species cover and species richness of opportunistic ants. Mulch addition had a positive effect on soil moisture when compared to controls but suppressed growth of native (but not exotic) herbaceous plants. Whilst other soil properties such as organic matter and dissolved organic carbon showed a positive response to mulch addition, the effect was not statistically significant. On plots with log additions, decomposition rates of tea leaves decreased, and species richness of opportunistic ants increased. However, we found no effect on total species richness and abundance of other ant functional groups. The benefit of mulch to soil moisture was offset by its disbenefit to native herbs in our study. Logs increased species richness of opportunistic ants, but given time, may provide habitat for cryptic species. Indeed, benefits to other soil biophysical properties, vegetation and ant fauna may require longer timeframes to be detected. Further research is needed to determine whether the type, quantity and context of mulch and log additions may improve restoration outcomes.

Dominant and non-dominant plants could be subject to different biotic and abiotic influences, partially because dominant plants modify the environment where non-dominant plants grow, causing an interaction asymmetry. Among other possibilities, if dominant plants compete strongly, they should deplete most resources forcing non-dominant plants into a more constrained niche space. Conversely, if dominant plants are constrained by the environment, they might not fully deplete available resources but instead ameliorate some of the environmental constraints limiting non-dominants. Hence, the nature of the interactions between the non-dominants could be modified by dominant species. However, when plant competition and environmental constraints have similar effects on dominant and non-dominant species no difference is expected. By estimating phylogenetic dispersion in 78 grasslands across five continents, we found that dominant species were clustered (underdispersed), suggesting dominant species are likely organized by environmental filtering, and that non-dominant species were either randomly assembled or overdispersed. Traits showed similar trends, but insufficient data prevented further analyses. Furthermore, several lineages scattered in the phylogeny had more non-dominant species, suggesting that traits related to non-dominants are phylogenetically conserved and have evolved multiple times. We found some environmental drivers of the dominant—non-dominant disparity. Our results indicate that assembly patterns for dominants and non-dominants are different, consistent with asymmetries in assembly mechanisms. Among the different mechanisms we evaluated, the results suggest two complementary hypotheses seldom explored: (1) Non-dominant species include lineages adapted to thrive in the environment generated by the dominant species. (2) Even when dominant species reduce resources to non-dominant ones, dominant species could have a stronger effect on—at least—some non-dominants by ameliorating the impact of the environment on them, than by depleting resources and increasing the environmental stress to those non-dominants. The results show that the dominant–non-dominant asymmetry has ecological and evolutionary consequences fundamental to understand plant communities.