Hailiang Xu

How to Regenerate and Protect Desert Riparian Populus euphratica Forest in Arid Areas

We found that the most suitable flooding disturbance model for regenerating Populus euphratica forest was two to three times per year with a duration of 15–20 days and an intensity of 25–30 m3/s. The flooding should take place during the seed emergence to young tree growth stages, and should be based on flooding experiments and data from vegetation quadrats and ecological water conveyance. Furthermore, we found that tree-ring width index for P. euphratica declined as the groundwater depth increased, and ascertained that the minimum groundwater depths for young trees, near-mature trees, mature trees and over-mature trees were 4.0 m, 5.0–5.4 m, 6.9 m and 7.8 m, respectively. These were derived from a quantitative relationship model between groundwater depth and tree-ring width index. The range for ecological water conveyance volume was 311–320 million m3 in the lower reaches of the Tarim River. This study not only provides a technical basis for sustainable ecological water conveyance in the Tarim River Basin, but also offers a theoretical guide and scientific information that could be used in similar areas to regenerate and protect Populus euphratica around the world.

Impact of long-term zero-flow and ecological water conveyance on the radial increment of Populus euphratica in the lower reaches of the Tarim River, Xinjiang, China

Based on the dendro-hydrology theory, we studied the impacts of two significant environmental occurrences (long-term zero-flow and ecological water conveyance) on the radial increment of Populus euphratica in the lower reaches of the Tarim River, Xinjiang, China. We also studied the relationships between radial increment and groundwater table as a function of the distance from the river channel. We found that the radial increment of P. euphratica respond significantly to both zero-flow and water conveyance, and these responses differed among four transects and they weakened with increasing distance from the Daxihaizi Reservoir. The depth to the groundwater table is a key factor that restricts P. euphratica growth in extremely arid regions, and the relationship between radial increment and the groundwater table was significant. The radial increment decreased remarkably with increasing duration of the zero-flow period. The influence of long-term zero-flows on P. euphratica growth was a long-term and slow process. The response of P. euphratica showed a delayed response to the groundwater changes after ecological water conveyance. This lag response differed among the monitoring transects and different distances away from river channel.

Impact of Implementation of Large-Scale Drip Irrigation in Arid and Semi-arid Areas: Case Study of Manas River Valley

With the large-scale application of drip irrigation under mulching, drip-irrigated areas have experienced significant changes in the past 10 years in the Manas River valley. Based on long-term monitoring data of soil salt content and groundwater depth and the investigation of shelter forest growth and seedling emergence, this article analyzed the distribution characteristics of soil salt content in different drip-irrigated soil layers and their effect on the environment. The main conclusions are as follows: (1) Two obvious soil layers of salt accumulation are 40–80 cm deep after drip irrigation and 0–5 cm deep before drip irrigation. (2) Salt accumulated in different soil layers after drip irrigation for several years: 0–40 cm and 40–100 cm deep after drip irrigation for 3 and 7 years respectively. (3) Extension of the drip-irrigated area has caused a number of environmental problems in the study area, and countermeasures for agricultural development in arid and semi-arid areas are proposed.

Negative feedback adjustment challenges reconstruction study from tree rings: A study case of response of Populus euphratica to river discontinuous flow and ecological water conveyance.

Drought stress changes the relationship between the growth of tree rings and variations in ambient temperature. However, it is not clear how the growth of trees changes in response to drought of varying intensities, especially in arid areas. Therefore, Tree rings were studied for 6years in Populus euphratica to assess the impacts of abrupt changes in environment on tree rings using the theories and methods in dendrohydrology, ecology and phytophysiology. The width of tree rings increased by 8.7% after ecological water conveyance downstream of Tarim River compared to that when the river water had been cut off. However, during intermediate drought, as the depth of the groundwater increases, the downward trend in the tree rings was reversed because of changes in the physiology of the tree. Therefore, the growth of tree rings shows a negative feedback to intermediate drought stress, an observation that challenges the homogenization theory of tree ring reconstruction based on the traditional methods. Owing to the time lag, the cumulative effect and the negative feedback between the growth of tree rings and drought stress, the reconstruction of past environment by studying the patterns of tree rings is often inaccurate. Our research sets out to verify the hypothesis that intermediate drought stress results in a negative feedback adjustment and thus to answers two scientific questions: (1) How does the negative feedback adjustment promote the growth of tree rings as a result of intermediate drought stress? (2) How does the negative feedback adjustment lower the accuracy with which the past is reconstructed based on tree rings? This research not only enriches the connotations of intermediate disturbance hypothesis and reconstruction theory of tree rings, but also provides a scientific basis for the conservation of desert riparian forests worldwide.

The oasis soil type change and its fractal in Manasi River Basin between 1987–2006, arid Northwestern China

Abstract During the past 20 years, great landscape changes took place in the northwest of China. Landscape change resulted in soil type transformations. This paper discusses the changes and fractal of soil types in oasis. In order to do it, the soil type maps of Manasi River Basin in 1987 and 2006 were used. 13 types of soil and 2 types of land-use were classified and analyzed in the study area. Results indicated many variations in characteristics. Firstly, all soil types underwent remarkable changes from 1987 to 2006 in the study area: the identified changed area was about 30% or 6506.33 km2. Secondly, in comparison with 1987, in 2006 2/3 of the areas soil types increased, while 1/3 decreased. Rapid expansion of Aquicambids (415.28 km2), and rapid decrease of Petrocambids (797.05 km2) and Aquisalids (415.93 km2) were the noticeable findings. Furthermore, Haplocambids obtained largest gains from other soil types, while Petrocambids lost largest area to other types. Additionally, the fractal relationship ...

Role of Water Management in Ecological Restoration and Economic Development in Arid Regions: Taken the Lower Reaches of Tarim River as an Example

Water resource is a crucial factor in social and economic development and ecological protection in arid and semi-arid areas. The unbridled development and use of water resources in the lower reaches of the Tarim River over the last 50 years have led to a serious ecological degradation: (1) groundwater level drop. (2) water quality deterioration. (3) land desertification and frequent natural disasters occurrence. Meanwhile, the environmental degradation caused some negative effects on local agricultural development: (1) soil salinization declines agricultural areas. (2) deterioration water quality declines agricultural production. (3) natural disasters cause high economic loss. However, after watering, the degraded ecology is becoming obviously reversible. The natural vegetation has a favorable response in certain range of the water channel. The areas arable land increased greatly; furthermore, the total value of agricultural production is 1293.13×104 Dollars, increased by 128% after adoption of new management of water. Livestock population has experienced a growth trend as a result of watering. The results indicate that favorable eco-environment has an obvious positive function in the local economic development. Based on those facts, this paper analyzed the relationship between eco-environment and economic development. Some issues are pointed out in water resource management. Scientific water management countermeasures are discussed in Tarim River.