Fragmentation increased in over half of global forests from 2000 to 2020.

Habitat fragmentation, in which contiguous forests are broken into smaller, isolated patches, threatens biodiversity by disrupting species movement, shrinking populations, and altering ecosystem dynamics. Past assessments suggested declining global fragmentation, but they relied on structure-based metrics that overlook ecological connectivity. We analyzed global forest fragmentation from 2000 to 2020 using complementary metrics that captured patch connectivity, aggregation, and structure. Connectivity-based metrics revealed that 51 to 67% of forests globally—and 58 to 80% of tropical forests—became more fragmented, which is nearly twice the rate suggested by traditional structure-focused methods (30 to 35%). Aggregation-focused metrics confirmed increases in 57 to 83% of forests. Human activities such as agriculture and logging drive this change. Yet protected tropical areas saw up to an 82% reduction in fragmentation, underscoring the potential of targeted conservation. Editor's summary: Land conversion not only reduces the total habitat available to other species, but it also fragments habitat into smaller and less-connected patches, thus supporting smaller and less-connected populations. Ecologists have developed various metrics capturing different aspects of habitat fragmentation, such as the number and size of habitat patches and their distribution across space. Zou et al. used remotely sensed data to quantify the degree of fragmentation of global forests from 2000 to 2020, comparing metrics focused on patch connectivity, aggregation, and structure. Measures incorporating habitat connectivity and aggregation suggested that more than half of global forests have become more fragmented over the past two decades. These changes suggest widespread forest degradation beyond the direct effects of habitat loss. —Bianca Lopez [ABSTRACT FROM AUTHOR]