Paola Pisetta Raupp (PhD student, Hawkesbury Institute for the Environment, Western Sydney University) 

Motivated by a passion for contributing to real-life bush regeneration efforts through research, I am investigating how to restore native ecosystems, focusing on the critically endangered Cumberland Plain Woodland (CPW) in western Sydney as part of my PhD. The understorey of these ecosystems, comprising grasses, herbs, and shrubs, accounts for about 90% of the CPW plant diversity. These plants play a crucial role in ecosystem processes through their interactions with soil organisms and their functions. Despite this, the CPW understorey is often overlooked and a challenge to recover in restoration efforts.  

Exotic plant species, whose seeds can be widely dispersed and persist in the topsoil waiting for future emergence, outcompete natives and further complicate restoration outcomes. To address these and other challenges, including soil legacies like excessive nutrient content in the topsoil, many techniques involve removing the topsoil to give native plants a competitive edge. However, the impact of this technique on the balance between native and exotic species establishment and on soil properties remains unclear. Moreover, predicted changes in precipitation regimes may pose further challenges to establishing native plant communities.   

My project focuses on exploring how topsoil removal, planting diversity, and water availability influence the establishment of native and exotic plant species and the soil properties and functions associated with these responses. 

To explore these questions, I have set up a mesocosm experiment using topsoil (0-10 cm) and, separately, subsoil (15-25 cm) collected from a partially degraded CPW site. In October 2023, I planted native understorey species in three treatments: a monoculture of Themeda triandra (kangaroo grass), a medium-diversity mix of four species, and a high-diversity mix of 12 species. After the planted and regenerating (from the seed bank) plants were established, these treatments were combined with low, medium, and high watering regimes based on local climate predictions for 2070.   

So far, I have completed aboveground plant composition, abundance, and cover assessments. Belowground, my soil analyses include pH, moisture, nutrient content, and microbial composition, diversity, and structure, assessed through DNA extraction/sequencing and phospholipid fatty acid (PLFA) analysis. The next steps include analysing soil microbial enzymatic activity to provide deeper insight into soil functioning and assessing the final plant community growth, root and shoot biomass. Ultimately, this will provide valuable insights into the role of soil physicochemical and biological properties in restoration. 

This project is one chapter of my PhD thesis, and the Ecological Society of Australia (ESA) ‘Student Research Award’ provided funding to purchase DNA kits, which were essential for sequencing the DNA of my soil samples. This work will allow me to identify the fungal and bacterial microbiota in these soils and understand how they influence and are influenced by aboveground plant dynamics. Sharing my initial findings at the VCN Sydney Region Autumn Meeting was an exciting opportunity to contribute to the ongoing conversation about improving restoration practices for the CPW. 

I hope this research will enhance our understanding of the ecological factors driving native and exotic species’ establishment in degraded ecosystems. While my findings primarily aim to inform local restoration efforts in the CPW, they also have broader implications. Insights into plant diversity, plant species selection, future water regimes, and the impacts of seed banks and soil properties on restoration outcomes can help restore ecosystems more widely, enabling them to recover and flourish.  

I acknowledge the Traditional Custodians of the Cumberland Plain, where my research takes place, along with the many Aboriginal and Torres Strait Islander peoples connected to the Country today. I pay my respect to the Elders of the Dharug, Gundungurra and Dharawal nations, both past and present, and recognise their enduring connection to this land. I also gratefully acknowledge the contributions of many people from my research groups, including PhD’s and master’s students, post-docs, and my supervisors. This project is supported by the Cumberland Plain Research Program, the Hawkesbury Institute for the Environment at Western Sydney University, the NSW Department, Greater Sydney Local Land Services, and ESA.