Effects of ecological water conveyance on the ring increments of Populus euphratica in the lower reaches of Tarim River

Because of long-term drying of the lower reaches of the Tarim River, oasis ecosystems are facing serious threats and have started to degenerate. An ecological water conveyance project has been started in the lower reaches of the Tarim River to save the degenerated ecosystem. The effects of ecological water conveyance on the ring width increments of Populus euphratica were studied by use of the trend analysis method, the moving t test technique, and a regression equation based on ring increment data from the past 40 years in the lower reaches of the Tarim River. Results showed that the ring increments of Populus euphratica in four monitoring transects along the river can be divided into two parts, 1970–2001 and 2002–2008. This division implies that ecological water conveyance had a positive effect on the increase of ring increments. The ring increments of Populus euphratica in Yinsu, Kardayii, Alagan, and Yiganbjma increased by 79.37, 174.5, 75.61, and 71.81% after ecological water conveyance. The years 2002, 2001, 2001, and 2002 were the transition years in the Yinsu, Alagan, Kardayi, and Yiganbjma transects, respectively. The ring width increments in Yinsu, Kardayi, Alagan, and Yiganbjma as a result of ecological water conveyance were 1.41, 0.987, 0.265, and 0.671 mm, respectively. The main cause of the changes in ring width increments was the rise of groundwater level. The results from this study should contribute to improved management of the ecosystems in the lower reaches of the Tarim River, and can also provide a scientific basis for implementing similar projects in other arid and semiarid areas.