Tina Parkhurst

Globally, vegetation clearing for agriculture continues to cause biodiversity loss and land degradation. Restoration efforts to increase biodiversity and remediate land degradation are often constrained by legacies of agricultural land-use. Active restoration is often needed to overcome abiotic and biotic thresholds to assist re-assembly towards a reference ecosystem.

My thesis explores the effects of active restoration on soil condition and re-assembly of plant and invertebrate communities. I coupled a global meta-analysis with a field survey and experimentation in the Western Australian wheatbelt to examine effects of active woody plantings on various ecosystem components.

In a field survey of 30 plots, I characterised soil chemical properties, vegetation and ant assemblages in three vegetation states: fallow croplands, 10-year-old planted old fields and reference woodlands. In addition, I experimentally tested whether the addition of woody debris to planted old fields can accelerate restoration outcomes, using a multi-site Before-After Control-Impact design.

Results show that at a global scale, restoration has positive effects on soil condition, but inconsistent trends for invertebrate species. Overall, recovery remains incomplete. These results were mirrored at a local scale. Whilst concentrations of some soil nutrients in planted old fields were more similar to woodland reference system than fallow croplands, key abiotic thresholds, in particular elevated phosphorus concentrations, persisted. Woody species richness and cover on planted old fields were also similar to reference woodlands, but herbaceous species richness and cover, and large woody debris amounts, remained similar to the fallow cropland. Ant assemblages responded positively to changes in habitat, with increases of species richness and abundance of key functional groups, however full convergence to reference conditions was not observed. Addition of woody debris to planted old fields had few significant effects on soil chemical and biophysical properties and community re-assembly.

Overall, results show that soil condition, vegetation and invertebrate assemblages on planted old fields responded positively to restoration efforts, however, recovery remains incomplete. Future research should test the efficacy of additional restoration practices beyond tree planting and focus on identifying suitable functional groups of invertebrates to assess restoration outcomes.