Effect of Slope on Growth of Three Hard Broadleaved TreeSpecies in Northeast China

Analysis on tree hegiht and diameter(DBH) growth of the belt-mixed plantations of Fraxinus mandshurica,Phellodendron amurense and Juglans mandshurica(panted in 1986) were conducted by using the methods of variance analysis and multiple comparison. The results show that the position of slope is a significant physical factor to affect height growth and DBH growth. Fraxinus mandshurica grew best at meddle hill. Juglans mandshurica grew best at mid-down slope, and Phellodendron amurense grew best at down slope. The analysis of the positive edge effect was also made for belt-mixed plantation of Juglans mandshurica and Larix dahurica. The result indicated that Larix dahurica presented positive edge effect to growth of Juglans mandshurica present.

Using multi-source remote sensing data to classify larch plantations in Northeast China and support the development of multi-purpose silviculture

Due to increasing timber demands, large areas of secondary forests have been converted to larch plantations （LPs） in Northeast China because the secondary forests could not produce timber as much as LPs. However, there are a series of ecological problems such as lower soil fertility, reduced water-holding capacity and acidification of surface runoff water occurring in LPs because of the single-species composition of LPs. Therefore, a guidance on how to transform LPs into larch-broadleaf mixed forests （LBMFs） at a large spatial scale is needed for local foresters. First, Landsat time series data set and SPOT-5 images were combined to map the spatial-temporal distribution of LPs in Northeast China. Then, the topographical characteristics of LPs in 2010s were determined. Furthermore, three sub-regions of LPs were divided closely linking to their ecosystem services and forest management aims. Finally, detailed information on how to transform the LPs into LBMFs was given according to the three sub-regions. The results showed that the area of LPs increased during 1980s and 2010s, and reached 2.61 million ha in 2010s. Of which, 0.72 million ha （27.6%） and 1.89 million ha （72.4%） LPs distributed in slopes less than 5° and greater than 5°, respectively. Of the LPs （72.4%） in slopes greater than 5°, 48.7 and 23.7% located in downslope （LPs locating at the down slope of adjacent secondary forests in the same aspect） and upslope （LPs locating at the up slope of adjacent secondary forests in the same aspect）, respectively; 0.10 million ha （3.8%） located in slopes greater than 25°. The LPs were divided into Sub-Regions-I, II, III according to slopes. For Sub-region-I （top role is to produce timber）, self-fertilizing shrub species can be intro- duced after clean cutting for young-aged LPs, and release thinning can be applied for middle-aged LPs, fast growth thinning for near-matured LPs, and clear cutting for matured LPs. For Sub-Region-II （the priority is to provide water conservation combined with timber production）, the LPs should be induced into LBMFs. The LPs located the downslope positions in Sub-Region-II can be transformed to LBMFs by natural regeneration of broadleaved tree species after thinning because of enough seed sources of broadleaved tree species from the secondary forests locating the upslope positions. The LPs located the upslope positions or the region where seed sources of broadleaved tree species are unavailable in Sub-Region-II must be induced to LBMFs by al＇tificial regeneration. For Sub-Re- gion-III （the preference is only for water conservation because the slope is greater than 25°）, the LPs should be particularly protected from intensive disturbances, and induced into LBMFs by natural regeneration.

Experimental Study of the Pressure Fluctuations in a Pump Turbine at Large Partial Flow Conditions

Frequent shifts of output and operating mode require a pump turbine with excellent stability. Current researches show that large partial flow conditions in pump mode experience positive-slope phenomena with a large head drop. The pressure fluctuation at the positive slope is crucial to the pump turbine unit safety. The operating instabilities at large partial flow conditions for a pump turbine are analyzed. The hydraulic performance of a model pump turbine is tested with the pressure fluctuations measured at unstable operating points near a positive slope in the performance curve. The hydraulic performance tests show that there are two separated positive-slope regions for the pump turbine, with the flow discharge for the first positive slope from 0.85 to 0.91 times that at the maximum efficiency point. The amplitudes of the pressure fluctuations at these unstable large partial flow conditions near the first positive slope are much larger than those at stable operating condtions. A dominant frequency is measured at 0.2 times the impeller rotational frequency in the flow passage near the impeller exit, which is believed to be induced by the rotating stall in the flow passage of the wicket gates. The test results also show hysteresis with pressure fluctuations when the pump turbine is operated near the first positive slope. The hysteresis creates different pressure fluctuations for those operation points even though their flow rates and heads are similar respectively. The pressure fluctuation characteristics at large partial flow conditions obtained by the present study will be helpful for the safe operation of pumped storage units.

Spatial distributions of soil nutrients affected by land use,topography and their interactions,in the Loess Plateau of China

Soil nutrient availability and their spatial distributions are strongly related to land use and landscape morphology.This study aims to address the knowledge gap regarding the interaction between these factors and the underlying mechanisms.We selected five land uses(grassland with Artemisia gmelinii,woodland with Robinia pseudoacacia,shrubland with Caragana korshinskii and Hippophae rhamnoides,and apple orchard with Malus pumila)and nine slope positions across hillslopes in the Loess Plateau,China,to investigate their combined effects on the contents and stocks of soil organic carbon(SOC),total nitrogen(TN)and total phosphorus(TP).Parametric and non-parametric statistical tests were conducted to determine the significant differences in the means or the medians of the soil nutrient variables.Results showed that the SOC and TN contents of shrubland with Caragana korshinskii were statistically significantly greater than those of the grassland(p<0.05).SOC and TN contents generally decreased from the upper slope to the middle slope,and to the foot slope for the grassland,woodland and shrublands,and on the contrary,an increasing trend from the upper slope,to the middle slope,and to the foot slope was identified for the apple orchard.This study highlights that land use,slope position and their interaction have significant effects on the spatial distributions of soil nutrients.It provides essential empirical evidence for the identification of the optimal vegetation type and slope positions in land management and vegetation restoration activities.

Effects of crop residue managements and tillage practices on variations of soil penetration resistance in sloping farmland of Mollisols

Soil penetration resistance(SPR)is one of the major indicators of soil physical properties.Crop residue managements,tillage practices and their interactions exert significant effects on the SPR.However,rare information is available in the sloping farmland of Mollisols.Field experiments were conducted to investigate the variations of the SPR as affected by crop residue managements and tillage practices on the sloping land in Northeast China from 2015 to 2019.The split-plot experiment was arranged with two crop residue managements(removed,REM and retained,RET),and three tillage practices(no tillage,NT;rotary tillage,RT;plow tillage,PT).SPR data in 0-80 cm soil depth was measured at the end of harvest of maize monoculture.Results showed that the two crop residue managements induced significant variations in the SPR at 0-15 cm,15-30 cm and 0-80 cm soil depths under NT,RT,and PT treatments,respectively.In comparison with RET treatment,the average values of the SPR under REM treatment were 10.9%and 8.9%higher in 45-60 cm and 60-80 cm soil depths,respectively.The average values of the SPR under PT treatment were 12.4%and 14.1%lower in 0-15 cm soil depth,and 23.9%and 10.4%lower in 15-30 cm soil depth than those under NT and RT treatments.However,the average value of the SPR under PT treatment was 11.2%and 22.0%higher in 60-80 cm soil depth than those under NT and RT treatments,respectively.The SPR generally decreased with the slope position declined in the deeper soil depth(except for the NT+RET treatment).The findings from this research can provide a scientific reference for the establishment of rational cultivation and the sustainable development of productivity on the sloping land of Mollisols in cold regions.

Exclosures restored the density and root colonization of arbuscular mycorrhizal fungi in Tigray, Northern Ethiopia

Introduction:Exclusion of grazing animals and tree plantations were among the methods used for the restoration of degraded lands in tropical semiarid areas.Exclosures can foster secondary forest succession by improving soil conditions and modifying microclimate for understory growth.This paper compared the arbuscular mycorrhizal fungi(AMF)spore density,root colonization of woody plants and soil chemical properties under exclosure with increasing age,and grazing land at different slope positions.Methods:The study was conducted in northern Ethiopia from 12 exclosure sites paired each with adjacent grazing land in total from 24 sites with four treatments replicated three times.In the entire study,216 plots were examined of which 108 were in exclosures and 108 in communal grazing lands.There were four age classes and three slope positions in each of the land uses.Composite soil and root samples were collected using nested plots measuring 100m2 from four sides of 1763 plants for spore enumeration and root colonization.Soils for chemical properties were collected from the four corners and center of 5 m×5 m plots.Results:All the 61 woody plant species that belong to 41 families were colonized by AMF.Spore density and root colonization were significantly higher in exclosures as compared to grazing land and increased with increasing ages of exclosures.Foot slope had significantly higher spore density and root colonization than middle and upper slopes.Soil chemical properties were significantly higher in the exclosure,oldest age of exclosure,and foot slope position(except P).AMF spore density and root colonization were significantly positively correlated with soil chemical properties.Conclusions:Exclosures are helpful to restore the AMF spore density and root colonization of woody species and soil fertility.