Legacies of <i>Pinus contorta</i> Invasions Drive Ecosystem Change in Short Tussock Grasslands

Abstract

Biological invasions are expanding worldwide, causing negative ecological impacts and economic costs. Plant invasions can alter ecosystem properties as well as biotic interactions, these effects may persist long after the invasive species has been removed, influencing ecosystem recovery. While the impacts of biological invasions and short-term outcomes following their management are widely understood, few studies have considered the long-term outcomes for plant communities. This thesis investigates how short tussock grassland communities in Te Manahuna / the Mackenzie Basin, New Zealand change following extensive invasion and management of the non-native tree species <i>Pinus contorta</i>. By combining space-for-time field observations with statistical modelling I show that soil and plant community legacies persist for at least 16 years following management. Native plant communities are influenced both directly by past invasion and indirectly through altered soil biogeochemistry and competition from non-native grasses. Trajectories are strongly shaped by the original invasion stage, with late-stage invasions resulting in simplified communities dominated by non-native species. By integrating plot-scale data with four decades of aerial imagery to assess invasion and legacy patterns across landscapes, I demonstrate that early management is critical for preserving native biodiversity, that invasion dynamics reflect propagule pressure, and that management outcomes vary with property-level management decisions. These findings provide useful insights for conservation management, informing decisions about the timing of invader removal and the need for additional management to achieve specific conservation goals.