Dissecting forest transition: Contribution of mature forests, second-growth forests and tree plantations to tree cover dynamics in the tropics

Forest Transition (FT) is a theoretical framework for understanding tree cover changes but often overlooks differences within countries, across forest types (e.g., second-growth forests, tree plantations replacing natural forests), regions, and climates. We quantified tropical tree cover dynamics across eight regions in four tropical countries, examining how these patterns relate to FT and how they vary between climates and forest types. Each country represented a different stage in the FT trajectory. We combined Landsat-derived time-series from 1990 to 2020 with Sentinel-2-based land cover classification to distinguish between mature natural forests (MF), second-growth forests (SF), tree plantations (TP), and their dynamics. During this period, 50 % of MF was lost, while tree cover gains averaged 16 % across regions; SF contributed 23 % and TP 12 % of total tree cover by 2020. SF steadily increased, yet its average lifespan was only 10 years, limiting its ecological contributions compared to MF. The studied regions followed the theoretical FT trajectory: the Ghanaian regions were in early transition (pre-inflection), Mexican regions were in late transition (pre-inflection), and the Australian and Brazilian (São Paulo state) regions were in post-transition (post-inflection). Evaluating FT while including or excluding TP results in different conclusions about the FT trajectory of a region or country. MF was lower in dry (from 55 % in the 1990s to 23 % in 2020) than in wet (from 73 % in the 1990s to 35 % in 2020) forest regions. SF gains were higher in dry (31 %) than in wet (23 %) regions, though SF increases did not compensate for MF loss, resulting in reduced biodiversity and ecological functioning. Hence, halting deforestation and protecting young forests are equally crucial. Evaluating FT excluding TP and quantifying SF persistence may have far-reaching consequences for how to evaluate tree cover by not only evaluating tree cover quantity, but also tree cover quality. Our findings can inform policymakers to design smart policy mixes that sequence the right policy instruments at the right time. Local people must participate in forest restoration strategies and issues of equity, justice and power imbalances must be addressed to facilitate FT. Dissecting FT increases our understanding of the underlying forest cover dynamics, which can lead to better policies for protecting local people`s livelihoods, halt deforestation, and facilitate FT to restore the natural world upon which people`s lives and society depend.