Ümüt Halik

Stand structure and height-diameter relationship of a degraded Populus euphratica forest in the lower reaches of the Tarim River, Northwest China

Understanding stand structure and height-diameter relationship of trees provides very useful information to establish appropriate countermeasures for sustainable management of endangered forests. Populus euphratica, a dominant tree species along the Tarim River watershed, plays an irreplaceable role in the sustainable development of regional ecology, economy and society. However, as the result of climate changes and human activities, the natural riparian ecosystems within the whole river basin were degraded enormously, particularly in the lower reaches of the river where about 320 km of the riparian forests were either highly degraded or dead. In this study, we presented one of the main criteria for the assessment of vitality of P. euphratica forests by estimating the defoliation level, and analyzed forest structure and determined the height-diameter (height means the height of a tree and diameter means the diameter at breast height (DBH) of a tree) relationship of trees in different vitality classes (i.e. healthy, good, medium, senesced, dying, dead and fallen). Trees classified as healthy and good accounted for approximately 40% of all sample trees, while slightly and highly degraded trees took up nearly 60% of total sample trees. The values of TH (tree height) and DBH ranged from 0–19 m and 0–125 cm, respectively. Trees more than 15 m in TH and 60 cm in DBH appeared sporadically. Trees in different vitality classes had different distribution patterns. Healthy trees were mainly composed more of relatively younger trees than of degraded tress. The height-diameter relationships differed greatly among tress in different vitality classes, with the coefficients ranging from 0.1653 to 0.6942. Correlation coefficients of TH and DBH in healthy and good trees were higher than those in trees of other vitality classes. The correlation between TH and DBH decreased with the decline of tree vitality. Our results suggested that it might be able to differentiate degraded P. euphratica trees from healthy trees by determining the height-diameter correlation coefficient, and the coefficient would be a new parameter for detecting degradation and assessing sustainable management of floodplain forests in arid regions. In addition, tree vitality should be taken into account to make an accurate height-diameter model for tree height prediction.

Spatio-temporal Variability of Soil Water at Three Seasonal Floodplain Sites: A Case Study in Tarim Basin, Northwest China

The floodplain vegetation of the Tarim River in Northwest China is strongly influenced by irrigated agriculture. The abstraction of river water disturbs the natural dynamics of the floodplain ecosystem. The human impact on the hydrological system by bank dams and the irrigation of cotton plantings have caused adverse changes of the Tarim River and its floodplains, so the current stocks of the typical Tugai vegetation show significant signs of degradation. Field studies of soils and statistical analysis of soil moisture data have shown that the vitality of the Tugai vegetation is primarily determined by its position to the riverbank and the groundwater. There exist complex interactions between soil hydrological conditions and the vitality of the vegetation. But the availability of water is not only influenced by the groundwater level and seasonal flood events. The spatial distribution of stocks at different states of vitality seems also to be decisively influenced by physical soil properties. Our results show that the water supply of plant communities is strongly influenced by the soil texture. Spatial differences of soil moisture and corresponding soil water tensions may be the decisive factors for the zonation of vegetation. Physical soil properties control the water retention and rising of capillary water from deeper soil layers and the phreatic zone and may supply the root systems of the phreatophytic vegetation with water.

Patterns of dust retention by five common tree species for urban greening in Aksu City, Northwest China

南部典型绿洲城市——阿克苏市不同功能区的绿化树种, 用多重比较法对比分析了二球悬铃木(Platanus × acerifolia)、新疆杨 (Populus alba var. pyramidalis)、圆冠榆(Ulmus densa)、天山梣(Fraxinus sogdiana)和垂柳(Salix babylonica) 5个树种叶片平均滞 尘量随时间变化及不同高度叶片的滞尘能力, 探讨了阿克苏市主要绿化树种的滞尘规律, 得出以下结论: 不同绿化树种单位 叶面积滞尘量差异显著, 差距在1.15–2.17倍之间, 绿化树种滞尘量随着时间延长而增加; 同一树种在城市不同功能区的滞尘 能力不同: 工业区>交通枢纽区>居民区>清洁区; 不同高度的叶片, 其滞尘量在工业区和交通枢纽区差异显著: 高度1 m的叶 片滞尘量>高度2 m的叶片滞尘量>高度4 m的叶片滞尘量。 关键词 阿克苏市, 不同功能区, 滞尘, 多重比较, 绿化树种

A WFS-SVM Model for Soil Salinity Mapping in Keriya Oasis, Northwestern China Using Polarimetric Decomposition and Fully PolSAR Data

Timely monitoring and mapping of salt-affected areas are essential for the prevention of land degradation and sustainable soil management in arid and semi-arid regions. The main objective of this study was to develop Synthetic Aperture Radar (SAR) polarimetry techniques for improved soil salinity mapping in the Keriya Oasis in the Xinjiang Uyghur Autonomous Region (Xinjiang), China, where salinized soil appears to be a major threat to local agricultural productivity. Multiple polarimetric target decomposition, optimal feature subset selection (wrapper feature selector, WFS), and support vector machine (SVM) algorithms were used for optimal soil salinization classification using quad-polarized PALSAR-2 data. A threefold exercise was conducted. First, 16 polarimetric decomposition methods were implemented and a wide range of polarimetric parameters and SAR discriminators were derived in order to mine hidden information in PolSAR data. Second, the optimal polarimetric feature subset that constitutes 19 polarimetric elements was selected adopting the WFS approach; optimum classification parameters were identified, and the optimal SVM classification model was obtained by employing a cross-validation method. Third, the WFS-SVM classification model was constructed, optimized, and implemented based on the optimal match of polarimetric features and optimum classification parameters. Soils with different salinization degrees (i.e., highly, moderately and slightly salinized soils) were extracted. Finally, classification results were compared with the Wishart supervised classification and conventional SVM classification to examine the performance of the proposed method for salinity mapping. Detailed field investigations and ground data were used for the validation of the adopted methods. The overall accuracy and kappa coefficient of the proposed WFS-SVM model were 87.57% and 0.85, respectively that were much higher than those obtained by the Wishart supervised classification with values of 73.87% and 0.68, as well as those of the commonly applied SVM classification of 83.61% and 0.80. Accuracy of different salinized soil mapping was also enhanced with the proposed methodology. The results showed that the proposed method outperformed the Wishart and SVM classification, and demonstrated the advantages offered by the WFS-SVM classification and potentials of PolSAR data in the monitoring soil salinization.

Providing Urban Ecosystem Services for Human Well-Being: A Comparison of Exemplary Institutional Arrangements in China and Germany

Urbanization is a worldwide phenomenon and a major driver of global environmental change. For example, 75 % of the annual CO2 emissions are produced in cities and towns. Currently, more than half of the world’s population lives in cities. By 2050, this proportion is predicted to increase to 66 % (UN World Urbanization Prospects 2014).