Testing the importance of large-scale climate factors for Australian rainforest community assembly following land-use change

Background/Question/Methods

There is a pressing need to understand how communities reassemble following human land-use change and how they differ from unmodified communities. It is often assumed that land-use changes and habitat destruction lead to species loss and corresponding loss of functional trait diversity – a common proxy for ecosystem function. Recent research challenges this assumption, demonstrating that species and functional diversity can sometimes increase in response to land use-change, and that changes in species diversity can be decoupled from changes in functional diversity. However, it remains unclear whether changes in species and functional diversity resulting from land-use change occur predictably in response to key environmental factors for most plant communities. To better understand how climate factors influence species and functional diversity responses to land-use change, we examined differences in the diversity of species and trait values for seven plant functional trait categories between reference natural (remnant) forest and regrowth following clearing, occurring across large scale climate gradients (rainfall, temperature and solar irradiation) and vegetation strata (canopy or understory), in Australian rainforests. We focused on functional traits (SLA, wood density, maximum height, seed mass, fruit-type and dispersal mode) that represent well known plant environmental response strategies. This approach allowed us to examine the role of key climate factors on species and functional diversity relationships in reassembling plant communities while holding landscape type constant.

Results/Conclusions

In both canopy and understory strata, species diversity exhibited differences across climate gradients but did not differ between regrowth and remnant forest. In contrast, functional trait categories showed increases, decreases and no differences in diversity between regrowth and remnant patches in the canopy and understory, but did not respond predictably across climate gradients. Within climatic regions, the diversity of functional trait categories between regrowth and remnant rainforest also often exhibited distinctly different responses both within and between tree strata. Our results suggest that, even within the same landscape type and for traits that are well linked to environmental response strategies, large scale differences in rainfall, temperature and solar irradiation are not always strong predictors of species and functional diversity responses to land-use change. They also highlight that species diversity may be a poor surrogate for capturing changes in functional diversity in response to land use change in some landscapes.