Tropical forests vary in structure, function, and composition in ways that influence their ecological value. This variability is caused by anthropogenic and natural disturbance regimes which influence forests’ ability to support biodiversity, store carbon, mediate water yield, and facilitate human wellbeing. While international environmental agreements mandate protecting and restoring forests, only forest extent is considered, while forest quality is ignored. Accordingly, the locations and loss rates of forests of high ecological value are not known and coordinated strategies for conserving these forests remain undeveloped. Here, we apply recent advances in remote sensing and the latest human footprint data to produce, for the first time across the humid tropics, fine-resolution maps of three-dimensional forest structure, integrated with human pressure.
Our Forest Structural Condition Index (SCI) spans from short, open-canopy, recently disturbed forests to tall, closed canopy stands that have not been disturbed during 2000 to 2018. Our Forest Structural Integrity Index (FSII) is derived from overlaying an index of human pressure on the SCI. Higher values of FSII represent forests high in structural complexity and low in human pressure. Such forests are most likely to not be compromised in either the compositional or functional components of ecological integrity.
Results/Conclusions
We discovered that only 47% of the tropical forest estate is high in FSII. The majority (76%) of the remaining high FSII forest is in the Americas, particularly in the Amazon Basin. Some 86% of the global high FSII forests are not under strict legal protection. High FSII forest loss rates during 2013-2018 were substantial, but lower than for other forest classes: 1.3% for high FSII forests; 4.0% for high SCI forests; and 7.5% for other forests. The proportion of remaining forest meeting the criteria for each conservation strategy were: maintain protections (6.5%); new protections (40.5%); restore forest structure (6.8%); and restore forest integrity (19.0%).
There is urgent need to identify and conserve the remaining high FSII forests before they are further lost to deforestation and other human disturbances. Managing forests wisely in these regions is critical to avoiding dramatic shifts in climate, vegetation, and loss of ecosystem services. Forest structural integrity can be used in conservation planning to spatially design measures to best maintain and restore ‘best of the last’ forests of high ecological value and low human pressure.