Mountain social‐ecological systems (MtSES) are vital to humanity, providing ecosystem services to over half the planet's human population. Despite their importance, there has been no global assessment of threats to MtSES, even as they face unprecedented challenges to their sustainability. With survey data from 57 MtSES sites worldwide, we test a conceptual model of the types and scales of stressors and ecosystem services in MtSES and explore their distinct configurations according to their primary economic orientation and land use. We find that MtSES worldwide are experiencing both gradual and abrupt climatic, economic, and governance changes, with policies made by outsiders as the most ubiquitous challenge. Mountains that support primarily subsistence‐oriented livelihoods, especially agropastoral systems, deliver abundant services but are also most at risk. Moreover, transitions from subsistence‐ to market‐oriented economies are often accompanied by increased physical connectedness, reduced diversity of cross‐scale ecosystem services, lowered importance of local knowledge, and shifting vulnerabilities to threats. Addressing the complex challenges facing MtSES and catalyzing transformations to MtSES sustainability will require cross‐scale partnerships among researchers, stakeholders, and decision makers to jointly identify desired futures and adaptation pathways, assess trade‐offs in prioritizing ecosystem services, and share best practices for sustainability. These transdisciplinary approaches will allow local stakeholders, researchers, and practitioners to jointly address MtSES knowledge gaps while simultaneously focusing on critical issues of poverty and food security.

The relationship between trajectories of forest-cover change and the biophysical and social characteristics of the landscape in the mountains of Western Honduras is addressed. Metrics of land-cover change were used to infer patterns of land-use change, using Landsat TM imagery from 1987, 1991 and 1996. With 15-20% of the land cover changing across each two-date period, the study landscape was very dynamic. Areas of reforestation were significantly larger than areas of deforestation, across all dates. Patch size was a good indicator of economic activity. Stable patches of forest and agriculture were fewer and larger, compared to forest regrowth and clearing. Small patches of swidden agriculture were found close to roads, at lower elevations and on more gradual slopes between 1987 and 1991. Between 1991 and 1996, expansion of export coffee production resulted in forest clearings on steeper slopes and at higher elevations. Results highlight the importance of landscape metrics in monitoring land-cover change over time.