Yu Xinxiao

Ways to improve low-benefit black locust forests in Loess Plateau

This paper presents a general standard for the low-benefit black locust (Robinia pseudoacacia L.) forests in Loess Plateau based on defining the concept of “tri-low forest”, and emphasizes the major factors which result in low-benefit black locust, such as, lack of soil moisture of forest and nutrient, breaching the principle of matching tree species to sites, and high density of forests. Based on different characteristics of low-benefit forests, following the principle of “adjusting measures to local conditions, giving priority to ecological benefits, assisting with economic benefits”, the authors put forward some technical ways to reform low-benefit black locust forests, for example, taking measurements of collecting runoff and storing water, lowering the forest density, introducing mixed forests and transforming species, directive breeding and so on.

Effects of closing mountain for forest restoration in the watershed of Miyun reservoir, Beijing

The paper provides a systematical analysis of ecological restoration effects of natural secondary forest of closure area in Chao Guanxi Gou, Miyun County, Beijing. The results indicate that through more than twenty years of hillclosing afforestation since 1983, canopy closure has improved almost by 0.2; forest cover rate has raised from 7.2% to 93.8%; biodiversity, tree biomass and vegetation community have increased to a great extent. Compared with the average canopy closure before hillclosing afforestation in this area, it has improved to over 0.4 in average and increased by 0.1-0.2. The forest coverage degree has reached more than 90%. Consequently, the forest plays more important roles in intercepting precipitation, improving water storage capacity of soil, decreasing the surface runoff, and preventing soil and water loss.

Effects of forest vegetation on runoff and sediment transport of watershed in Loess area, west China

This paper aims to study the effects of vegetation on runoff and sediment transport at the watershed scale, and to provide a theoretical basis for afforestation in the Loess area, in the nested Caijiachuan watershed, Jixian County, Shanxi Province of west China. Forest watersheds and farmland watersheds with similar terrain features were selected through cluster analysis to study their runoff and sediment transport characteristics. Results showed that compared with farmland watersheds, runoff generation time in forest watersheds was delayed remarkably, and peak flow was reduced greatly, which indicates that vegetation played an important role in holding and absorbing rainfall. Besides, with the increase of forest coverage, the runoff amount, runoff depth and runoff coefficient decreased during the rainy seasons. The runoff depth and runoff coefficient of farmland watersheds in the rainy season were 5–20-fold as much as that of forest watersheds, and runoff and sediment yield of watersheds with low forest coverage were 2.7–2.9-fold and 3–6-fold as great as those with high coverage during rainstorms, and low forest coverage had larger variation in sediment hydrograph. For the complexity and scale dependence of the influence of forest vegetation on runoff, forest hydrological functions based on regional scale or watershed scale were worthy of further studies.

Soil preferential flow in the dark coniferous forest of Gongga Mountain based on the kinetic wave model with dispersion wave (KDW preferential flow model)

Abstract Based on the law of soil water movement in unsaturated zones, the study discusses the effect of preferential flow on the movement of the researched soil through a soil column experiment using homemade experimental apparatus in four successive stages—young, middle-aged, mature and over-mature and combining dye-tracer analyses of the field process. The study proves that the preferential flow occurs in the area, and as indicated by the Reynolds numerical calculation of the preferential flow path in the 4 different successive stages, the preferential flow in the Gongga Mountain forest ecosystem is a transition flow between the laminar flow and the turbulent flow. By applying the kinetic wave model with dispersion wave (KDW preferential flow model) and comparing this model with the field experiment, the study finds that the preferential flow model has good practicability and high credibility. Verifying the KDW preferential flow model through statistic analysis indicates that the model can simulate the water movement in columns very well and the results are better in low rainfall than in high rainfall.

Effect of forest vegetation on runoff and sediment production in sloping lands of Loess area

According to fixed-position data for 1985–2003 from nine runoff plots of Caijiachuan watershed which lies in Jixian County of Shanxi Province in Loess area, this paper studied the relationship between vegetation and runoff and sediment production in sloping lands in detail, which helps to provide scientific basis for vegetation re-construction and studies on environmental transformation of water and sediment in watersheds of Loess area. Although, many study results testify that forest vegetation has an important function in soil and water conservation and cutting runoff, the effect of vegetation on runoff and sediment transmission is complicated, and this needs to be studied in depth. The results of the paper showed the following. Firstly, the natural secondary forest performs better function of soil and water conservation than artificial Robinia pseudoacacia forest, and runoff and sediment produced in the former in individual rainfall were 65%–82% and 23%–92% of those produced in the latter. At the same time, better correlative relationship between runoff and sediment production and rainfall and rainfall intensity were testified by multiple regression, but the correlation decreased gradually with the increase of canopy density of forest. Secondly, the difference of runoff and sediment production in several land use types was very distinct, and the amount of runoff and sediment produced from Ostryopsis davidiana forest and natural secondary forest were the least, and runoff and sediment produced from in artificial Robinia pseudoacacia forest and Pinus tabulaeformis forest were 5-fold as much as those from O. davidiana forest. Besides, runoff and sediment produced in mixed planting of apple trees and crops were 16.14-fold and 2.96-fold than those of O. davidiana forest, respectively, but the amount decreased obviously after high-standard soil preparation in the case of the former. Thirdly, based on gray cognate analyses of factors affecting runoff and sediment production in sloping land, the factors of stand canopy density and herb and litter biomass were the most significant ones, whose gray incidence degree exceeded 0.6. Therefore, mixed forest with multi-layer stand structure and shrub forest should be developed in vegetation re-construction of Loess area, which will help to increase coverage and litter thickness in order to cut down the runoff and sediment dramatically in sloping land.

Responses of Intrinsic Water-use Efficiency and Tree Growth to Climate Change in Semi-Arid Areas of North China

Tree-level intrinsic water-use efficiency (iWUE) is derived from the tree-ring 13C isotope composition (δ13C) and is an important indicator of the adaptability for trees to climate change. However, there is still uncertainty regarding the relationship between long-term forest ecosystem carbon sequestration capacity and iWUE. To determine whether elevated atmospheric CO2 concentration (Ca) increase iWUE and tree growth (basal area increment, BAI), dendrochronological methods and stable isotope analyses were used to examine annual changes in the tree-ring width and carbon isotope composition (δ13C) of Platycladus orientalis in northern China. The iWUE derived from δ13C has increased significantly (p < 0.01). Long-term iWUE trend was largely and positively driven by the elevated atmospheric CO2 concentration and temperature. We observed a general increase in averaged BAI, which had significant positive correlation with iWUE (R2 = 0.3186, p < 0.01). Increases in iWUE indeed translated into enhanced P. orientalis growth in semi-arid areas of northern China. Elevated atmospheric CO2 concentration significantly (p < 0.01) stimulated P. orientalis biomass accumulation when Ca was less than approximately 320 ppm in the early phase; however, this effect was not pronounced when Ca exceeded 320 ppm.

密云山区油松树轮 δ 13 C对气温和降水量变化的响应

目的探究北京市密云山区油松树轮δ13C对气温和降水量变化的响应，重建1947-2014年密云山区气候资料，以期为揭示该地区的气候变化规律提供依据。 方法测定密云山区红门川流域油松树轮δ13C值，建立1947-2014年的树轮δ13C序列，并剔除序列值中受大气CO2碳同位素值影响产生的下降趋势，之后获得油松树轮δ13C去趋势序列（DS），然后结合当地气象站资料分析油松树轮δ13C值对降水和气温变化的响应，构建δ13C与降水和气温的关系方程，进而重建1947-2014年的降水和气温资料。 结果1947-2014年，密云山区油松树轮δ13C呈下降趋势，其中，1995-2014年波动较大，剔除大气CO2背景值的DS序列呈现二次曲线的走势，拐点出现在1980年附近；油松树轮δ13C值DS序列与7月平均气温等极显著正相关（r=0.719 7，P 结论油松树轮δ13C对7月份气温和夏季降水量响应极为显著；1947-2014年密云山区气候变化呈现波动性变暖变干趋势。

Research on changes of dynamic characteristics of rainfall though Platycladus Orientalis plantation canopy in Beijing Mountain Area

Due to forest canopy layer redistributes the energy of rainfall,the size distribution,terminal velocity and kinetic energy of raindrops change through the canopy. These changes are important part of the ecological hydrology functions of forest. However,at home and abroad,there is less studies on forest affecting the dynamic characteristic of rainfall is less, and the research methods are always imperfect. This study,performed at the Miaofeng Mountain forest farm in Beijing,used two laser raindrop spectrometers to synchronously monitor precipitation both inside and outside a Platycladus orientalis plantation,and analyzed the size,amount,velocity,kinetic energy and other dynamic characteristics of raindrops outside and inside forest for the typical rainfall events. The results show the amount of raindrops outside forest was 37. 8% above inside forest,the amount of small and big diameter raindrops increased inside forest,but the middle diameter raindrops decreased. The rainfall volume contribution outside forest showed unimodal curve with the increase of raindrop diameter change,but that showed polymodal curve inside forest. The terminal velocity reduced inside forest,especially for the raindrops with diameter in the range of 0. 75—4. 5 mm. Compared with outside forest,the correlation between the diameter and terminal velocity of raindrops inside forest was reduced,and the raindrop spectrum distribution was more scattered. The rainfall kinetic energy contribution outside forest showed unimodal curve with the increase of raindrop diameter change,but that showed polymodal curve inside forest. When the raindrops terminal velocity was in the range of 4—9m / s,the kinetic energy contribution of the raindrops outside forest was obviously higher than inside forest. The total kinetic energy of the raindrop fallen on the ground inside the Platycladus orientalis plantation was 27. 0% less than outside forest,and the main reason of that is the forest canopy cut down the precipitation inside forest.

Sediment and Water Quality Response to Climate Change in Bai River Basin

Geographic informational system (GIS) and the Soil and Water Assessment Tool (SWAT) was used to simulate the transport of runoff, sediment, total nitrogen and total phosphorus into the Zhangjiafen stations. The main objective was to discuss climate change affecting on sediment and water quality. The results showed: The SWAT generally performs well and could accurately simulate monthly runoff, sediment, total nitrogen and total phosphorus yield with a Nash-Sutcliffe coefficient and a coefficient of determination of greater than0.7 during calibration and validation. Climate change had large effect on runoff, followed by sediment, total nitrogen and total phosphorus.