Phenology of Australian temperate grasslands: linking near-surface phenology to C3/C4 community composition

Vegetation phenology is relatively well-studied in northern hemisphere temperate biomes, but limited research has been conducted on phenological drivers and responses in Australian temperate ecosystems. Australian temperate grasslands represent a broad range of plant communities from exotic pastures to native grasslands, but all are important for food security (livestock grazing) and biodiversity retention. Climate predictions for temperate Australia include higher temperatures, altered rainfall frequency/seasonality, increased drought severity and more regular wildfires. The ecosystem response to these climatic factors is unknown, and the need to improve the monitoring of these highly dynamic grassland systems at a landscape scale is acute. The aim of this research is to use high-frequency phenological data to improve the identification of grassland functional types and ultimately use this to improve the inter-annual monitoring of dynamic grassland systems. We use hourly repeat photography and the Green Chromatic Coordinate vegetation index to characterize the vegetative phenology of several native and exotic grassland communities. Monthly vegetation surveys allow us to correlate plant functional groups with indicator features on the phenology profile. C4-dominated grasslands are characterized by a consistent low greenness during winter, the commencement of greening in late spring/early summer and the retention of green vegetation throughout the summer. Exotic C4 grasslands can be distinguished from native ecosystems by their early-spring flush of annual grasses and forbs prior to the primary greening in late spring/early summer. Native C3 grasslands are more variable in response to rainfall and exhibit multiple greening/browning cycles within the year. They tend to green up earlier in the spring and brown off rapidly in response to high temperatures and low rainfall. Exotic C3 grasslands also green up in early spring but exhibit a more traditional unimodal phenology profile. We discuss the advantages and disadvantages of using this method for monitoring grassland vegetation dynamics, including considerations of time-of-day, shadowing and camera angle. Finally, we highlight the potential benefits and challenges for integrating these methods with satellite systems.