Predicting ecological change in tussock grasslands of Aotearoa New Zealand

Natural grasslands are among the most threatened biomes on Earth. They are under pressure from land cover change including afforestation, farming intensification, invasive species, altered fire regimes, and soil amendments, all of which impact native biodiversity and ecosystem functioning. In Aotearoa New Zealand, tussock-dominated native grasslands expanded due to increased fire activity during waves of human settlement. These areas have subsequently been maintained as modified grasslands by agricultural pastoral land management practices and effects of introduced feral mammals. Despite many decades of research on biodiversity in tussock grasslands, we need greater fundamental understanding of many processes causing change in their biodiversity and ecosystem functioning in order to predict how future global change will impact this important and increasingly threatened biome. In this perspective forum article, we present five key research questions that, if answered, would greatly enhance our understanding of connections between tussock grassland biodiversity, ecosystem functioning, and associated ecosystem services: (1) What are the relative impacts of domesticated and non-domesticated mammals on indigenous biodiversity in grasslands? (2) Where will invasive plants undergo range expansion? (3) Will future fires tip tussock grasslands into alternative vegetation states? (4) What are the implications of woody thickening by native or non-native species? (5) What are the impacts of global change, and vegetation change in particular, on soil processes and ecosystem functioning? We provide recommendations for research to address and integrate across these questions using both existing and new data. This work would build on our current knowledge and lead to a framework to better understand the ecological impacts of ongoing global change in tussock grasslands.