Ice age survivors in the cloud forest
The town of Pyin Oo Lwin, a former British hill station, sits at an elevation of 1,070 meters (3,510 feet) in the Shan Highlands. This altitude provides a cooler, temperate climate, different from the heat of the Mandalay basin below. The average temperature varies from about 9°C to 33°C (48°F to 92°F) throughout the year. This specific climate, combined with the region's unique geological history, has created isolated pockets of habitat where unusual plant species have evolved. Among these are numerous endemic orchids, some of which are considered "Pleistocene relicts."
These particular orchids are living remnants of ancient lineages. During the Pleistocene epoch, which ended about 11,700 years ago, global climate fluctuated dramatically. Glacial periods, or ice ages, caused cooler and drier conditions to spread across Southeast Asia. Montane forests, like those around Pyin Oo Lwin, became refuges for species adapted to these cooler temperatures. When the climate warmed again, these populations became genetically isolated from relatives in other mountain ranges. Genetic studies on some local orchid species have confirmed this long-term isolation, revealing deep evolutionary divergence from their closest relatives. This makes them unique species that show a past ecosystem. Myanmar hosts a significant diversity of orchids, with estimates suggesting more than 800 different species. The forests of the Indo-Burma Biodiversity Hotspot, which includes this region, are exceptionally rich, containing over 13,500 plant species, more than half of which are endemic. However, less than 5% of this hotspot's original vegetation remains intact due to deforestation and agriculture. This habitat loss poses a direct threat to the survival of Pyin Oo Lwin's endemic orchids.