Woodland structure and function in response to increasing aridity

Abstract

Woodlands, characterised by a matrix of trees, shrubs and open interspaces, are important biomes on Earth. Woodlands support a number of important ecosystem functions such as primary production, carbon fixation and nutrient cycling, and provide multiple ecosystem services that are essential for human livelihoods. Woodland structure and function are regulated by both large-scale shifts in climate, and smaller-scale variation in species interactions, resource availability and land management. Predicted changes in climate are expected to increase dryness and intensify management activities (e.g., grazing, plant removal), imposing substantial challenges on the functioning of woodlands and their dependent biota. Exploring how woodlands change across a climatic (aridity) gradient and among different management practices is essential for understanding how they adapt to drier climates and intensified woodland management, and to predict the ecological consequences of increasing aridity on their functions. This thesis examines the response of woodland structure and function to increasing aridity and woody plant removal, and the impact of biotic (e.g., plant traits, competition, grazing) and abiotic (e.g., climate, soil) drivers at both microsite and sub-continental scales, based on meta-analysis and field survey. Chapter 1 provides an overview of woodland structure and function, and their biotic and abiotic driving factors, highlighting important findings on the impact of increasing dryness on woodland structure (e.g., trees, shrubs, and open interspaces) and function (e.g., fertile islands). Chapter 2 examines the allometric response of different Australian woody plant genera to increasing dryness. Chapters 3 and 4 describe variation in biocrust cover and the fertile island effect beneath perennial vegetation across different patch types at the microsite scale, and with increasing aridity at the sub-continental scale. Chapters 5 and 6 synthesise the ecosystem outcomes of removing woody plants and the impact of woody plant traits, climatic regimes, and removal practices on the effectiveness of woody plant removal across the globe. Chapter 7 provides a synopsis of previous chapters, highlighting the adaptation strategies of woodlands to predicted drier climates, suggesting alternative woodland management under changing climates, and providing direction for future work in this field.