A vegetation carbon isoscape for Australia built by combining continental-scale field surveys with remote sensing
2022
Munroe, Samantha E. M. | Guerin, Greg R. | McInerney, Francesca A. | Martín-Forés, Irene | Welti, Nina | Farrell, Mark | Atkins, Rachel | Sparrow, Ben
CONTEXT: Maps of C₃ and C₄ plant abundance and stable carbon isotope values (δ¹³C) across terrestrial landscapes are valuable tools in ecology to investigate species distribution and carbon exchange. Australia has a predominance of C₄-plants, thus monitoring change in C₃:C₄ cover and δ¹³C is essential to national management priorities. OBJECTIVES: We applied a novel combination of field surveys and remote sensing data to create maps of C₃ and C₄ abundance in Australia, and a vegetation δ¹³C isoscape for the continent. METHODS: We used vegetation and land-use rasters to categorize grid-cells (1 ha) into woody (C₃), native herbaceous, and herbaceous cropland (C₃ and C₄) cover. Field surveys and environmental factors were regressed to predict native C₄ herbaceous cover. These layers were combined and a δ¹³C mixing model was used to calculate site-averaged δ¹³C values. RESULTS: Seasonal rainfall, maximum summer temperature, and soil pH were the best predictors of C₄ herbaceous cover. Comparisons between predicted and observed values at field sites indicated our approach reliably predicted generalised C₃:C₄ abundance. Southern Australia, which has cooler temperatures and winter rainfall, was dominated by C₃ vegetation and low δ¹³C values. C₄-dominated areas included northern savannahs and grasslands. CONCLUSIONS: Our isoscape approach is distinct because it incorporates remote sensing products that calculate cover beneath the canopy, the influence of local factors, and extensive validation, all of which are critical to accurate predictions. Our models can be used to predict C₃:C₄ abundance under climate change, which is expected to substantially alter current C₃:C₄ abundance patterns.
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