Forest gain across tropical and subtropical Asia masks widespread loss of complex forests

<title>Abstract</title> <p>Forest cover has expanded across tropical and subtropical Asia in recent decades, but area alone is an inadequate metric because it does not capture forest structure, which is critical for supporting key ecosystem functions and services, including biodiversity. Here, we apply sub-meter resolution satellite imagery to characterize the complexity of forests from a horizontal perspective by quantifying the diversity of tree crown sizes and their spatial arrangement across India, Southeast Asia, and southern China. We reveal large mismatches between reported forest area and the complexity of the forests. While overall, the majority of the forests still have a relatively high complexity, a recent change towards low complexity forests is observed. India, despite its large forest extent, shows a particularly low forest complexity, with more than half of its forests classified as low-complexity. Analysing forests affected by gain or loss in area between 2000 and 2024, we find that approximately three quarters of newly established forests are of low structural complexity, while high-complexity forests, concentrated in Myanmar, Laos, Cambodia, and Indonesia, continue to disappear. Our results highlight the need to move beyond forest cover statistics toward quality-based indicators for monitoring in the support of conservation policy.</p>