Effects of Ecological Water Conveyance on the Ring Increments of Populus euphratica in the Lower Reaches of Tarim River

Groundwater is an important source of water for the growth of natural vegetation in arid and semi-arid areas. Previous studies indicated that the natural vegetation in arid and semi-arid areas is vulnerable, and can be affected by the groundwater level.

The Tarim River, located in a remote part of the Taklimakan Desert, is a continental river in a region where the ecological environment is vulnerable. During the past 50 years, the groundwater level continuously dropped in the Tarim River, which affects the stability of the ecosystem in this area.

Populus euphratica, the dominant species in the Tarim River, is sensitive to water changes in arid regions. It is important to understand the ecological restoration in this region by investigating and analyzing the response of P. euphratica ring increment to ecological water conveyance. As a regional environment proxy, ring width increment data have the advantages of high temporal resolution, widespread distribution, long time series and precise dating.

Based on the ring increment data from the past 40 years in the lower reaches of the Tarim River, YU PuJia et al. studied the effects of ecological water conveyance on the ring width increments of P. euphratica by using the trend analysis method, the moving t test technique and a regression equation. 

The results showed that the ring increments of P. euphratica in four monitoring transects (Yinsu, Kardayii, Alagan, and Yiganbjma) along the river can be divided into two parts, 1970–2001 and 2002–2008. This division implies that the ecological water conveyance had a positive effect on the increase of ring increments.

The ring increments of P. euphratica in Yinsu, Kardayii, Alagan and Yiganbjma increased by 79.37%, 174.5%, 75.61% and 71.81% after ecological water conveyance, respectively. 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 mm, 0.987 mm, 0.265 mm and 0.671 mm, respectively. The main cause of the changes in ring width increments was the rising of groundwater level. The results from this study should contribute to improved management of the ecosystems in the lower reaches of the Tarim River.

The result was published in Journal of Forest Research on October 2012, 17(5): 413-420. The paper can be downloaded from http://link.springer.com/article/10.1007%2Fs10310-011-0312-3#.