Vegetation history of the walnut forests in Kyrgyzstan (Central Asia): natural or anthropogenic origin?

Extensive forests of common walnut (Juglans regia L.) occur in the mountains of the Fergana and the Chatkal Ranges of Kyrgyzstan (Central Asia), where they form a rich cultural landscape with a mosaic of natural and planted forest stands, fields, pastures, and drier open areas. These remote forests are likely to be an important genetic resource for J. regia, not only for in situ conservation but also as a resource for tree breeding. Pollen and charcoal analyses of the sediments of four lakes and two peat bogs in the core regions of the walnut forests provide new data to infer the vegetation history of the last 6800 years in the Fergana and Chatkal Ranges in Kyrgyzstan. Our results suggest that the potential natural forests or woods in the modern walnut forest region were dominated by Juniperus together with trees of Betula, Fraxinus, Rosaceae, and possibly Acer. A special focus was put on the vegetation history of J regia, as it has been suggested that the walnut forests of Kyrgyzstan might be a refuge for this tree. However, our results suggest that the stands of J. regia are at the most 2000 years old, most of them even only about 1000 years old and probably of anthropogenic origin, confirming an old legend that is still orally transmitted in Kyrgyzstan. As with other old and widespread cultivated plants, it is not easy to reconstruct the original distribution and determine the borders of the past natural ranges. A review of paleoecological data points to refugia in southern Europe, Syria, Kyrgyzstan, China, and the Himalaya, where Juglans possibly outlived the last glaciation. (C) 2007 Elsevier Ltd. All rights reserved.