The Positive Response of Some Ecological Indices of Populus Euphratica to the Emergency Water Transfer in the Lower Reaches of the Tarim River

The Tarim River is about 1 320 km long and is also one of the longest continental inland waterways in the world. In an undisturbed state, it is accompanied on both sides by floodplain forests of Euphrat poplars (Populus euphratica Oliv.). The rising water consumption in the upper and middle reaches, and massive hydro-technical interventions in the development of uncultivated land use (cotton growing), especially in the past decades, have led to widespread destructions of the natural ecosystems, particularly in the lower reaches of the river, where 320 km of the floodplain forests are either highly degraded or dead. Since 2000, the Chinese government has made efforts to restore these ecosystems and conducted ecological water transportation. The starting process of the recovering measures needs an efficient and extensive long-term monitoring. A combined approach of remote sensing and terrestrial samples can meet the demands. The study is based on the data from a small-scale ecological monitoring for the past 5 years and QuickBird image information of the floodplain forests along the lower reaches of the Tarim River, which is accompanied by the ecological water diversion. The effects of the emergency water transfer (so-called ecological water diversion) on the restoration of the groundwater layer and Populus euphratica forests are studied in the region of Argan. The results are as follows: with the continuance and expansion of the ecological water transport, the groundwater level rises from 10-12 m to 5.5-6.2 m below the surface in the vicinity of the river beds. Some ecological indicators of the Populus euphratica forests have different levels of response to the ecological water transfer. To specify, in the vertical direction, the farther the coverage is from the river, the weak response the ecological indicators are. These indicators include the canopy density, crown size, crown loss as well as the initiation sticks of Populus euphratica seedlings and the frequency of delivery. Generally, the Populus euphratica forests within 200 m to the river bed have recovered remarkably, and those between 200 m and 800 m from the rivers have shown a medium response to the ecological water transfer, while forests further than 800 m from the river bed have shown no sign of recovery.