Tree Species Diversity and Carbon Storage Potential across Urban Green Open Spaces in Yogyakarta, Indonesia

Quantitative characterization of urban forest structures remains under-researched in rapidly expanding Indonesian cities. The research assesses taxonomic diversity and carbon capture in 87 sampling plots in Yogyakarta. Sixty-five species were recorded, and total carbon stock was 87.95 Mg-C ha−1 (322.77 Mg-CO2 ha−1). There was strong spatial inequality in carbon distribution; although there were strong centers of biomass carbon distribution in public green belts and heritage zones, the private sector controlled a substantial proportion of the total biomass. The abundance of aboveground biomass (AGB) was highly right-skewed, and the sequestration capacity of the city was dominated by a small group of species referred to as foundation species, namely Samanea saman (357.67 Mg-CO2 ha−1). We demonstrate that there is clear decoupling between diversity and productivity, with the Shannon index (H′) and Simpson index (D) showing weak and non-significant relationships with AGB, while basal area proved to be a strong predictor (R2 = 0.936). According to these outcomes, the structural maturity and the size of individual trees in Yogyakarta are the primary determinants of carbon storage capacity rather than species richness. Large-diameter tree cohorts should therefore be prioritized in urban mitigation strategies compared to mere horizontal expansion of green cover.