Paddock trees promote pasture biomass accumulation and improve soil properties in grazing systems

Background and aims Pasture systems occupy approximately three billion hectares and contribute almost $21 trillion to the global economy. They are important for food production, carbon storage, water catchment reserves, biodiversity maintenance and cultural and recreational needs. However, pasture systems sustainability and productivity may be reduced with increasing climate hazards, such as heat stress and drought, due to global warming. Strategically integrating trees into pastoral landscapes may improve pasture system resilience and productivity by benefting pasture leaf function and enhancing soil fertility.

Methods To evaluate if trees in pasture systems are favourable for pasture performance and sustainability, we conducted feld experiments in the New England Tablelands of New South Wales and assessed soil properties and measured leaf functional traits of pasture species, under tree canopies, at tree canopy edges and beyond tree canopies (i.e. in open felds). Functional traits measured were net carbon assimilation, photosynthetic heat tolerance, specific leaf area and leaf nitrogen content.

Results Aboveground and belowground pasture biomass were significantly higher under paddock tree canopies compared with canopy edges and in open fields. Similarly, concentrations of measured soil elements (organic carbon, nitrogen, phosphorus and potassium) were all significantly higher under tree canopies compared with canopy edges and in open fields. Leaf functional traits did not vary with proximity from paddock tree canopies, and higher undercanopy pasture biomass was not associated with leaf functional traits. Leaf trait-trait relationships were mixed and varied with proximity from paddock tree canopies.

Conclusions This study demonstrates the significant role of paddock trees within tree-pasture systems in driving pasture productivity, particularly through improved soil fertility. The results emphasize that paddock trees can contribute to climate change resilience of pastures in grazing systems by facilitating greater resource capture.