Fig. 3: Precipitation, tree carbon and crown area.

a, The tree carbon probability density function computed along the rainfall gradient of the study from the hyper-arid (0–150 mm year⁻¹), arid (150–300 mm year⁻¹), semi-arid (300–600 mm year⁻¹) and dry sub-humid (600–1,000 mm year⁻¹) rainfall zones. The percentage area of each semi-arid zone is shown in blue and the percentage of total carbon in red. The increasing tree carbon probability function shows the importance of precipitation for tree carbon in semi-arid regions. Most tree carbon is found in the semi-arid (26%) and dry sub-humid zones (64%), which represent only 30% of the area in our study. The per cent carbon density contribution by rainfall zones is linearly related to the tree carbon density (Mg C ha⁻¹) reported in Fig. 1c by a factor of 2.5. b, A total of 88.4% of our mapped trees had crown areas <50 m². The average tree crown area in the 0–150 mm year⁻¹ zone was 15.1 m², for the 150–300 mm year⁻¹ zone it was 18.4 m², for the 300–600 mm year⁻¹ zone it was 20.9 m² and for the 600–1,000 mm year⁻¹ zone it was 28.1 m². Only 11.6% of our mapped trees had crown areas >50 m² and less than 0.6% had crown areas >200 m².