A vegetation carbon isoscape for Australia built by combining continental-scale field surveys with remote sensing

Context Maps of C 3 and C 4 plant abundance and stable carbon isotope values (δ 13 C) across terrestrial landscapes are valuable tools in ecology to investigate species distribution and carbon exchange. Australia has a predominance of C 4 -plants, thus monitoring change in C 3 :C 4 cover and δ 13 C is essential to national management priorities. Objectives We applied a novel combination of field surveys and remote sensing data to create maps of C 3 and C 4 abundance in Australia, and a vegetation δ 13 C isoscape for the continent. Methods We used vegetation and land-use rasters to categorize grid-cells (1 ha) into woody (C 3 ), native herbaceous, and herbaceous cropland (C 3 and C 4 ) cover. Field surveys and environmental factors were regressed to predict native C 4 herbaceous cover. These layers were combined and a δ 13 C mixing model was used to calculate site-averaged δ 13 C values. Results Seasonal rainfall, maximum summer temperature, and soil pH were the best predictors of C 4 herbaceous cover. Comparisons between predicted and observed values at field sites indicated our approach reliably predicted generalised C 3 :C 4 abundance. Southern Australia, which has cooler temperatures and winter rainfall, was dominated by C 3 vegetation and low δ 13 C values. C 4 -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 C 3 :C 4 abundance under climate change, which is expected to substantially alter current C 3 :C 4 abundance patterns.