A forest of glacial survivors
In the Nuratau Mountains of Uzbekistan, a unique forest of Persian walnuts (Juglans regia) holds a remarkable genetic history. These trees are considered a relict population, meaning they are survivors from an earlier geological period. Genetic studies suggest that these groves are part of a larger glacial refugium—a pocket of habitat where species persisted during the last ice age, when glaciers covered much of Eurasia. While many walnut populations were wiped out by advancing ice, these isolated mountain valleys provided the necessary conditions for their survival.
The forests are a core component of the Nuratau State Nature Reserve, established in 1975. The reserve covers the central part of the Nuratau ridge, at elevations from 500 to 2,169 meters. Some of the individual walnut trees within these groves are estimated to be several hundred years old, with trunks reaching up to two meters in diameter. The trees thrive in the xerophylic, or dry, conditions typical of the region, which receives only 300-400 mm of precipitation annually in the mountainous zones.
The genetic makeup of the Nuratau walnuts shows a high degree of diversity, which is characteristic of a center of origin for a species. This genetic variation is a direct link to the ancestral populations that existed before widespread human cultivation began around 7,000 years ago. Analysis of the trees' DNA shows scientists how the species adapted to past climate fluctuations and is a valuable resource for developing more resilient walnut cultivars today.
A biodiversity hotspot
The Nuratau Mountains are recognized as a Key Biodiversity Area within the Mountains of Central Asia Global Biodiversity Hotspot. The region's unique geological history, having existed as a chain of islands during the Cretaceous-Paleogene transgressions of the Tethys Sea, has promoted a high degree of endemism. The flora of the mountains includes 1,283 species of vascular plants, with 32 species being endemic to the area.
Beyond the ancient walnuts, the reserve protects a wide array of life. The forests host 34 mammal species, including about 90% of the world's population of Severtzov's argali sheep (Ovis ammon severtzovi), a rare and endemic subspecies. The avifauna is also notable, with 196 bird species recorded. The area provides critical nesting sites for large birds of prey like the Lammergeier (Gypaetus barbatus), Eurasian griffon (Gyps fulvus), and the endangered Cinereous vulture (Aegypius monachus).
The entire ecosystem is interconnected. The walnut trees create a canopy that supports a specific undergrowth, which in turn provides a habitat for a diverse range of insects and animals. The preservation of these groves is about more than a single species, but about maintaining the integrity of a complex and ancient biological system. The combination of relict walnut genetics and high endemism makes the Nuratau region a living laboratory for studying evolutionary processes.