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 impa...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.展开更多
Modeling height–diameter relationships is an important component in estimating and predicting forest development under different forest management scenarios. In this paper, ten widely used candidate height–diameter ...Modeling height–diameter relationships is an important component in estimating and predicting forest development under different forest management scenarios. In this paper, ten widely used candidate height–diameter models were fitted to tree height and diameter at breast height(DBH)data for Populus euphratica Oliv. within a 100 ha permanent plots at Arghan Village in the lower reaches of the Tarim River, Xinjiang Uyghur Autonomous Region of China. Data from 4781 trees were used and split randomly into two sets:75 % of the data were used to estimate model parameters(model calibration), and the remaining data(25 %) were reserved for model validation. All model performances were evaluated and compared by means of multiple model performance criteria such as asymptotic t-statistics of model parameters, standardized residuals against predicted height,root mean square error(RMSE), Akaike’s informationcriterion(AIC), mean prediction error(ME) and mean absolute error(MAE). The estimated parameter a for model(6) was not statistically significant at a level of a = 0.05. RMSE and AIC test result for all models showed that exponential models(1),(2),(3) and(4) performed significantly better than others. All ten models had very small MEs and MAEs. Nearly all models underestimated tree heights except for model(6). Comparing the MEs and MAEs of models, model(1) produced smaller MEs(0.0059) and MAEs(1.3754) than other models. To assess the predictive performance of models, we also calculated MEs by dividing the model validation data set into 10-cm DBH classes. This suggested that all models were likely to create higher mean prediction errors for tree DBH classes[20 cm. However, no clear trend was found among models.Model(6) generated significantly smaller mean prediction errors across all tree DBH classes. Considering all the aforementioned criteria, model(1): TH ? 1:3 t a= e1 t b?eàc?DBHT and model(6): TH ? 1:3 t DBH2= ea t b?DBH t c ? DBH2T are recommended as suitable models for describing the height–diameter relationship of P. euphratica. The limitations of other models showing poor performance in predicting tree height are discussed. We provide explanations for these shortcomings.展开更多
Central Asia(CA)occupies the hinterland of the Eurasian continent,containing the countries of Uzbekistan,Kyrgyzstan,Turkmenistan,Tajikistan,and Kazakhstan[1,2].Being isolated by the Pamir Mountains in Tajikistan,the T...Central Asia(CA)occupies the hinterland of the Eurasian continent,containing the countries of Uzbekistan,Kyrgyzstan,Turkmenistan,Tajikistan,and Kazakhstan[1,2].Being isolated by the Pamir Mountains in Tajikistan,the Tibetan Plateau and the Tian Shan Mountains on the border between China and Kyrgyzstan.展开更多
基金新疆维吾尔自治区自然科学基金项目"塔里木河下游生态输水过程中荒漠河岸林恢复监测"(2010211A05)德国Robert-Bosch基金会项目"Vegetation and soil response to water diversion on the lower Tarim RiverXinjiang/China"(32.5.8003.0063.0)
基金Under the auspices of Federal Ministry of Education and Research of Germany Project-Sustainable Management of River Oases along the Tarim River(No.01LL0918D)National Natural Science Foundation of China(No.31270742,31360200)
文摘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.
基金supported by the National Natural Science Foundation of China(Grant No:31360200,31270742)German Federal Ministry of Education and Research(BMBF)within the framework of the SuMaRiO project(01LL0918D)the Volkswagen Stiftung(Eco CAR project,Az.88497)
文摘Modeling height–diameter relationships is an important component in estimating and predicting forest development under different forest management scenarios. In this paper, ten widely used candidate height–diameter models were fitted to tree height and diameter at breast height(DBH)data for Populus euphratica Oliv. within a 100 ha permanent plots at Arghan Village in the lower reaches of the Tarim River, Xinjiang Uyghur Autonomous Region of China. Data from 4781 trees were used and split randomly into two sets:75 % of the data were used to estimate model parameters(model calibration), and the remaining data(25 %) were reserved for model validation. All model performances were evaluated and compared by means of multiple model performance criteria such as asymptotic t-statistics of model parameters, standardized residuals against predicted height,root mean square error(RMSE), Akaike’s informationcriterion(AIC), mean prediction error(ME) and mean absolute error(MAE). The estimated parameter a for model(6) was not statistically significant at a level of a = 0.05. RMSE and AIC test result for all models showed that exponential models(1),(2),(3) and(4) performed significantly better than others. All ten models had very small MEs and MAEs. Nearly all models underestimated tree heights except for model(6). Comparing the MEs and MAEs of models, model(1) produced smaller MEs(0.0059) and MAEs(1.3754) than other models. To assess the predictive performance of models, we also calculated MEs by dividing the model validation data set into 10-cm DBH classes. This suggested that all models were likely to create higher mean prediction errors for tree DBH classes[20 cm. However, no clear trend was found among models.Model(6) generated significantly smaller mean prediction errors across all tree DBH classes. Considering all the aforementioned criteria, model(1): TH ? 1:3 t a= e1 t b?eàc?DBHT and model(6): TH ? 1:3 t DBH2= ea t b?DBH t c ? DBH2T are recommended as suitable models for describing the height–diameter relationship of P. euphratica. The limitations of other models showing poor performance in predicting tree height are discussed. We provide explanations for these shortcomings.
基金supported by the Strategic Priority Research Program of the Chinese Academy of Sciences(XDA20060303)the Fund“Light of West China”Program of Chinese Academy of Sciences(2018-XBQNXZ-B-017)+1 种基金the High-level Talents Project in Xinjiang(Y942171)“One Hundred Person Project of Chinese Academy of Sciences”(Y931201)。
文摘Central Asia(CA)occupies the hinterland of the Eurasian continent,containing the countries of Uzbekistan,Kyrgyzstan,Turkmenistan,Tajikistan,and Kazakhstan[1,2].Being isolated by the Pamir Mountains in Tajikistan,the Tibetan Plateau and the Tian Shan Mountains on the border between China and Kyrgyzstan.