Occurrence of Australian woody species is driven by soil moisture and available phosphorus across a climatic gradient

Prepared by Jingyi Ding, Samantha K. Travers & David J. Eldridge

When you are walking in the bush or hiking in a forest in Australia, you can find a diverse range of woody plants, with some species more often growing in dense forests but other species only occurring on open woodlands. Have you ever wondered what factors drive species distribution across different environmental conditions?

Woody species are a major component of terrestrial plants, and their long-lived nature allows them to exist in different regions across the globe. Climate has a major effect on the distribution of plant species, largely by affecting the availability of water resources. For example, from coasts to deserts, woody plants change from fast-growing rainfall forest species to dwarf shrubs that are highly tolerant to drought. Soil also plays an important role in regulating species distribution by affecting resource distribution such as soil moisture and nutrients essential for the germination and growth of woody plants. However, global climate change that leads to warmer temperatures, and more extreme and prolonged droughts and flooding are causing drastic environmental shifts. This will affect the chances of woody species persisting in some regions and impact the fauna that depends on these species for habitat.

To understand more about how the distribution of woody species would shift under changing climates, we conducted a field survey along a 1500 km rainfall gradient at 150 sites from the humid coast to arid shrublands across eastern Australia. In each site, we recorded the presence of woody species in a 100m by 20m plot, and we also sampled soil under the most common woody species to test the soil nutrient levels in laboratory. Finally, we built a model to understand how rainfall season, soil phosphorus, soil moisture and soil texture affect the chances of woody species occurring in a site.

We found that Australian woody species were more likely to occur on soils with low phosphorus levels, and the effect of other factors changed with climatic conditions. For example, greater soil moisture in the topsoil layers enhanced the chance of woody species occurring in mesic sites but not in more arid sites. Similarly, fine-textured soil can increase the chance of woody species occurring in subhumid sites, but coarser soil supports more woody species in the arid zone. Our results suggest that forecasted hotter and drier climates may restrict the distribution of woody species preferring particular soils (e.g., Callitris spp. Eucalyptus largiflorens), but expand the range of woody species (e.g., Eucalyptus populnea) that are already resilient to drought, giving them a competitive advantage under changing climates.

This is a plain language summary for the paper of Ding et al. published in the Journal of Vegetation Science (https://doi.org/10.1111/jvs.13095).