Spatial homogenization of understorey plant communities under eCO₂ in a mature Eucalyptus woodland

Understorey plant communities comprise a large portion of biodiversity of forests and woodlands globally, where they contribute to tree species dynamics, biogeochemical cycling and carbon sequestration. Here we evaluated the effects of elevated CO₂ (400 vs. 550 ppm) on the spatial distribution of understorey plant communities from a mature eucalypt woodland in Eastern Australia (EucFACE experiment). Three years of elevated CO₂ resulted in a loss of the characteristic aggregated and segregated spatial pattern of species richness at both short and long distances (20 cm–227 cm), respectively. Changes in spatial patterns emerged over time, indicating that these results are due to a relatively slow reordering of the understorey plant community. In contrast, when analysed from a multivariate perspective, changes in terms of community composition were not as clear as changes in the spatial rearrangement of plant communities. Synthesis. Given that the spatial patterns of communities are likely a reflection of the way in which multiple species interact and how energy and matter flow throw ecosystems, community reordering due to global change may have far-reaching implications in terms of ecosystem functioning. Moreover, subtle early changes in the spatial pattern of understorey plant communities may represent an early-warning indicator of global change impacts in forest ecosystems.