The mountainous forests in arid regions, being sensitive to climate change, are one of the key research topics related to the mechanism of interaction between climate and the terrestrial ecosystem. In this study, the spatial distribution of a mid-mountain forest and its environmental factors were investigated by using a combination of remote sensing technology, field survey, climate indices and soil nutrient analysis in the Sangong River watershed of the northern Tianshan Mountains. The forest(Picea schrenkiana) was distributed between 1,510 and 2,720 m asl. Tree height and diameter at breast height(DBH) exhibited a bi-modal pattern with increasing elevation, and rested at 2,450 and 2,250 m asl, respectively. The two maxima of DBH appeared at 2,000 and 2,550 m asl, and the taller trees were observed at 2,100 and 2,600 m asl. For the annual mean temperature, the difference was approximately 5.8°C between the lowest and the highest limits of the forest, and the average decreasing rates per hundred meters were 0.49°C and 0.55°C with increasing altitude between 1,500 and 2,000 m asl and above 2,000 m asl, respectively. The annual precipitation in the forest zone first increased and then decreased with the increase of altitude, and the maximum value was at 2,000 m asl. For per hundred meters, the annual precipitation increased with the rate of 31 mm between 1,500 and 2,000 m asl and decreased by 7.8 mm above 2,000 m asl. The SOM, TN and TP were high between 2,000 and 2,700 m asl and low at the lower and upper forest limits. The minimum Ca CO3 concentration, p H value and EC coincided with the maximum precipitation belt at 2,000 m asl. The SOM, TN and TP were high in the topsoil(0–10 cm) and differed significantly from the values observed in the deep soil layers(>10 cm). The soil nutrients exhibited spatial heterogeneity and higher aggregation in the topsoil. In conclusion, soil and climate are closely related to each other, working synergistically to determine the development and spatial distribution of the mid-m
Mountainous ecosystems are considered highly sensitive and vulnerable to natural disasters and climatic changes.Therefore,quantifying the effects of elevation on grassland productivity to understand ecosystem-climate interactions is vital for mountainous ecosystems.Water-use efficiency(WUE)provides a useful index for understanding the metabolism of terrestrial ecosystems as well as for evaluating the degradation of grasslands.This paper explored net primary productivity(NPP)and WUE in grasslands along an elevational gradient ranging from 400 to 3,400 m asl in the northern Tianshan Mountains-southern Junggar Basin(TMJB),Xinjiang of China,using the Biome-BGC model.The results showed that:1)the NPP increased by 0.05 g C/(m2·a)with every increase of 1-m elevation,reached the maximum at the mid-high elevation(1,600 m asl),and then decreased by 0.06 g C/(m2·a)per 1-m increase in elevation;2)the grassland NPP was positively correlated with temperature in alpine meadow(AM,2,700-3,500 m asl),mid-mountain forest meadow(MMFM,1,650-2,700 m asl)and low-mountain dry grassland(LMDG,650-1,650 m asl),while positive correlations were found between NPP and annual precipitation in plain desert grassland(PDG,lower than 650 m asl);3)an increase(from 0.08 to 1.09 g C/(m2·a))in mean NPP for the grassland in TMJB under a real climate change scenario was observed from 1959 to 2009;and 4)remarkable differences in WUE were found among different elevations.In general,WUE increased with decreasing elevation,because water availability is lower at lower elevations;however,at elevations lower than 540 m asl,we did observe a decreasing trend of WUE with decreasing elevation,which may be due to the sharp changes in canopy cover over this gradient.Our research suggests that the NPP simulated by Biome-BGC is consistent with field data,and the modeling provides an opportunity to further evaluate interactions between environmental factors and ecosystem productivity.
Grazing is a main human activity in the grasslands of Xinjiang, China. It is vital to identify the effects of grazing on the sustainable utilization of local grasslands. However, the effects of grazing on net primary productivity(NPP), evapotranspiration(ET) and water use efficiency(WUE) in this region remain unclear. Using the spatial Biome-BGC grazing model, we explored the effects of grazing on NPP, ET and WUE across the different regions and grassland types in Xinjiang during 1979–2012. NPP, ET and WUE under the grazed scenario were generally lower than those under the ungrazed scenario, and the differences showed increasing trends over time. The decreases in NPP, ET and WUE varied significantly among the regions and grassland types. NPP decreased as follows: among the regions, Northern Xinjiang(16.60 g C/(m^2·a)), Tianshan Mountains(15.94 g C/(m^2·a)) and Southern Xinjiang(-3.54 g C/(m^2·a)); and among the grassland types, typical grasslands(25.70 g C/(m^2·a)), swamp meadows(25.26 g C/(m^2·a)), mid-mountain meadows(23.39 g C/(m^2·a)), alpine meadows(6.33 g C/(m^2·a)), desert grasslands(5.82 g C/(m^2·a)) and saline meadows(2.90 g C/(m^2·a)). ET decreased as follows: among the regions, Tianshan Mountains(28.95 mm/a), Northern Xinjiang(8.11 mm/a) and Southern Xinjiang(7.57 mm/a); and among the grassland types, mid-mountain meadows(29.30 mm/a), swamp meadows(25.07 mm/a), typical grasslands(24.56 mm/a), alpine meadows(20.69 mm/a), desert grasslands(11.06 mm/a) and saline meadows(3.44 mm/a). WUE decreased as follows: among the regions, Northern Xinjiang(0.053 g C/kg H_2O), Tianshan Mountains(0.034 g C/kg H_2O) and Southern Xinjiang(0.012 g C/kg H_2O); and among the grassland types, typical grasslands(0.0609 g C/kg H_2O), swamp meadows(0.0548 g C/kg H_2O), mid-mountain meadows(0.0501 g C/kg H_2O), desert grasslands(0.0172 g C/kg H_2O), alpine meadows(0.0121 g C/kg H_2O) and saline meadows(0.0067 g C/kg H_2O). In general, the decreases in NPP and WUE were more significant in the regions with relatively hi
