Biodiversity conservation programs rely on accurate knowledge about past rates of ecological change and patterns of human use. In remote areas of the world, empirical data on historical trends rarely exist to inform conservation planning. Such is the case in the mountains of Yunnan, where there are many perceptions about historical drivers of environmental change, but little direct evidence. Since 2001, The Nature Conservancy has employed repeat photography to develop a historical profile for northwestern Yunnan. This 100-year profile allows us to assess the true magnitude of threats to bio-diversity and the long-term contributions made by indigenous cultures to biodiversity maintenance. We found that many assumptions, often stated as fact, are wrong or do not apply universally. The magnitude and drivers of forest cover loss, arid shrubland dynamics, crop field expansion, and glacier retreat fall into this group. We also found that some threats have been ignored, such as a rapidly warming climate. The direct evidence of landscape change provided by repeat photographs has a range of conservation policy, investment, and management implications.