Livestock grazing and forest structure regulate the assembly of ecological clusters within plant networks in eastern Australia

Questions: How do changes in grazing intensity by different herbivores and differences in forest structure affect the assembly of ecological clusters within plant ecological networks in dryland plant communities?. Location: Eastern Australia across an area of 0.4 million km2. Methods: We used correlation network analysis and structural equation modelling to examine how changes in grazing intensity, by different herbivores, and differences in forest structure (tree canopy cover, basal area and density) and soil fertility influenced the assembly of ecological clusters of plant communities (i.e. relative abundance of ecological clusters formed by co-occurring plant species within an ecological network) in three forested communities from eastern Australia. Results: Livestock grazing and forest structure regulated the relative abundance of ecological clusters within plant networks, but their effects on these plant assemblies were highly dependent on the ecological cluster and forest community type, with no single winner or loser across forest types, conditions or grazing intensities. Thus, the relative abundance of some ecological clusters increased under grazing while others declined, a response that was maintained across different forest structures. The relative importance of grazing, forest structure and soil fertility varied across forest community type. The two eucalypt communities exhibited mixed effects of grazing and forest structure (Eucalyptus largiflorens) or forest structure only (Eucalyptus camaldulensis). In the third (Callitris glaucophylla) community, grazing played a larger role in controlling the plant community assembly. Soil fertility (soil C and P) effects were of a similar magnitude to grazing and forest structure, but the effects differed among clusters. Conclusions: Livestock grazing and forest structure regulated the relative abundance of ecological clusters within networks of plant communities in forests in eastern Australia. Our study uses a novel approach of ecological clusters to show that differences in grazing and forest structure will always disadvantage some plant ecological clusters. Furthermore, changes in one cluster will ultimately affect other clusters. Any changes in management therefore will have varied effects on different ecological plant clusters. © 2018 International Association for Vegetation Science