Effects of sand-fixing and windbreak forests on wind flow:a synthesis of results from field experiments and numerical simulations

Sand-fixing and windbreak forests are widely used to protect or/and improve the ecological environments in arid and semi-arid regions. A full understanding of wind flow characteristics is essential to arranging the patterns of these protective forests for enhancing the effectiveness. In this study, the wind velocity over the underlying surface with sand-fixing forests and windbreak forests at the heights of 1–49 m was monitored from two 50-m high observation towers in an oasis of Minqin, Gansu Province of China. The wind velocities were simulated at different locations over these protective forests between those two towers by a two-dimensional Computational Fluid Dynamics（CFD） model. The results showed that at the heights of 1–49 m, the wind velocity profiles followed a classical logarithm law at the edge of the oasis and a multilayer structure inside the oasis. With increasing number of sand-fixing forest and windbreak forest arrays, the wind velocity at the heights of 1–49 m generally decreased along the downstream direction of the prevailing wind. Specifically, below the height of windbreak forests, the wind velocity decelerates as the airflow approaches to the windbreak forests and then accelerates as the airflow passes over the windbreak forests. In contrast, above the height of windbreak forests, the wind velocity accelerates as the airflow approaches to the windbreak forests and then generally decelerates as the airflow passes over the windbreak forests. Both the array number and array spacing of sand-fixing and windbreak forests could influence the wind velocity. The wind protection effects of sand-fixing forests were closely related to the array spacing of windbreak forests and increased with the addition of sand-fixing forests when the array of the forests was adequately spaced. However, if the array spacing of windbreak forests was smaller than seven times of the heights of windbreak forests, the effects were reduced or completely masked by the effects of windbreak forests. The results could offer theoretical guidelines on how to systematically arrange the patterns of sand-fixing and windbreak forests for preventing wind erosion in the most convenient and the cheapest ways.

Wind-proof and sand-fixing effects of Artemisia ordosica with different coverages in the Mu Us Sandy Land,northern China

Wind erosion is a key global environmental problem and has many adverse effects.The Mu Us Sandy Land of northern China is characterized by an arid climate,where vegetation patches and bare sand patches are usually distributed mosaically,and aeolian activities occur frequently.Vegetation plays a significant role in controlling wind erosion.Artemisia ordosica is the most dominant native plant species in the Mu Us Sandy Land.It is urgent to study the wind-proof and sand-fixing effects of Artemisia ordosica in the Mu Us Sandy Land.This study analyzed the wind-proof and sand-fixing effects of Artemisia ordosica based on the field data of wind regimes,aeolian sediment transport,and surface change of Artemisia ordosica plots with four coverages(denoted as site A,site B,site C,and site D)in the Mu Us Sandy Land during the period from 1 June 2018 to 29 June 2019.The coverages of Artemisia ordosica at site A,site B,site C,and site D were 2%,16%,29%,and 69%,respectively.The annual average wind speeds at 2.0 m height above the ground for site A,site B,site C,and site D were 3.47,2.77,2.21,and 1.97 m/s,respectively.The annual drift potentials were 193.80,69.72,15.05,and 6.73 VU at site A,site B,site C,and site D,respectively.The total horizontal aeolian sediment fluxes during the period from 2-3 June 2018 to 6 June 2019 at site A,site B,site C,and site D were 4633.61,896.80,10.54,and 6.14 kg/m,respectively.Site A had the largest surface changes,and the surface changes at site B were significantly weaker than those at site A,whereas the surface changes at site C and site D were minimal.The results indicated that Artemisia ordosica significantly reduced the wind speed,drift potential,aeolian sediment transport,and surface changes.The higher the coverage of Artemisia ordosica is,the more obvious the effects of wind-proof and sand-fixing.Wind erosion would be effectively controlled in the Mu Us Sandy Land if the coverage of Artemisia ordosica is greater than 29%.These results provide a scientific basis for evaluating the ecosystem service function of Artemisia ordosica and the vegetation protection and construction projects in the Mu Us Sandy Land.

Preparation and Water Retention Properties of Clay-based Sand-fixing and Grass-planting Materials

Targeting the problem of available water conservation in sand fixation, the sand-fixing and grass-planting materials were prepared with clay modified by emulsifying vegetable waxes and octylphenol polyoxyethylene ether （OP4）. The water retention property was studied in simulating desertification environmental climate and the materials were characterized by means of UV-Vis, SEM, FTIR, XRD and TGA measurements. The experimental result showed that the materials had excellent water retention properties, due to that vegetable waxes adhered evenly to clay particle surfaces, made the clay pores changing from hydrophilic to hydrophobic and so inhibited the water evaporation. Grass-planting experiment showed that, with reasonable mass ratio of clay, vegetable waxes and surfactant, the materials not only inhibited water evaporation but also maintained sound air permeability so shat the germination rate and survival rate of grass were significantly improved.

Sand-fixing characteristics of Carex brunnescens and its application with straw checkerboard technique in restoration of degraded alpine meadows

Carex brunnescens（Pers.）, a typical clonal species, is considered to be the only herb found to date that can develop on sand dunes in Maqu alpine region of northwestern China. However, the characteristics that C. brunnescens resists to harsh alpine environment have not been documented. In this study, we conducted a field investigation to determine the morphological, reproductive, and sand-fixing characteristics of C. brunnescens. Concomitantly, we transplanted the belowground rhizomes of C. brunnescens to sand dunes and compared the abilities to restore degraded alpine meadows among sand dunes that had no further treatment（SD＋N）, sand dunes that had straw checkerboard technique but no transplanted rhizomes of C. brunnescens（SD＋SCT）, and sand dunes that had both SCT and transplanted rhizomes of C. brunnescens（SD＋SCT＋P）. We found that belowground vertical rhizomes and horizontal rhizomes（including branching rhizomes and main rhizomes） of C. brunnescens were highly developed and that population reproduction was dominated by horizontal rhizomes. C. brunnescens exhibited a significant sand-fixation effect under following conditions： population density was 145–156 ramets/m^2, vegetation cover was 31.2%–39.3%, total length of belowground rhizomes was 11,223 cm/m^2, total length of belowground first-order roots was 9161–10,524 cm/m^2, fresh weight of aboveground part was 198.5–212.6 g/m^2, and fresh weight of belowground part was 578.8–612.4 g/m^2. It should be particularly noted that SD＋SCT＋P treatment（sand dunes that had both straw checkerboard technique and transplanted rhizomes of C. brunnescens） was the best and SD＋N（sand dunes that had no further treatment） was the worst in terms of following biotic indicators： total number of reproductive ramets, total number of belowground rhizomes, and fresh weight of aboveground and belowground parts of C. brunnescens, contents of soil organic carbon, available nitrogen, microbial biomass carbon, and microbial biomass nitrogen. It implies that applying SCT in sand dunes and transplanting belowground rhizomes to sand dunes with SCT could improve both soil fertility and growth of C. brunnescens. These results suggest that the SCT-promoted high reproductive abilities of belowground rhizomes of C. brunnescens can successfully facilitate the establishment of ramets and can thus be an effective strategy to restore degraded vegetation in Maqu alpine region of northwestern China.

A bibliometric analysis using machine learning to track paradigm shifts and analytical advances in forest ecology and forestry journal publications from 2010 to 2022

Forest habitats are critical for biodiversity,ecosystem services,human livelihoods,and well-being.Capacity to conduct theoretical and applied forest ecology research addressing direct(e.g.,deforestation)and indirect(e.g.,climate change)anthropogenic pressures has benefited considerably from new field-and statistical-techniques.We used machine learning and bibliometric structural topic modelling to identify 20 latent topics comprising four principal fields from a corpus of 16,952 forest ecology/forestry articles published in eight ecology and five forestry journals between 2010 and 2022.Articles published per year increased from 820 in 2010 to 2,354 in 2021,shifting toward more applied topics.Publications from China and some countries in North America and Europe dominated,with relatively fewer articles from some countries in West and Central Africa and West Asia,despite globally important forest resources.Most study sites were in some countries in North America,Central Asia,and South America,and Australia.Articles utilizing R statistical software predominated,increasing from 29.5%in 2010 to 71.4%in 2022.The most frequently used packages included lme4,vegan,nlme,MuMIn,ggplot2,car,MASS,mgcv,multcomp and raster.R was more often used in forest ecology than applied forestry articles.R software offers advantages in script and workflow-sharing compared to other statistical packages.Our findings demonstrate that the disciplines of forest ecology/forestry are expanding both in number and scope,aided by more sophisticated statistical tools,to tackle the challenges of redressing forest habitat loss and the socio-economic impacts of deforestation.

Livelihood Vulnerability and Adaptation for Households Engaged in Forestry in Ecological Restoration Areas of the Chinese Loess Plateau

Chinese Loess Plateau has achieved a win-win situation concerning ecological restoration and socio-economic development.However,synergistic development may not be realized at the local scale.In areas undergoing ecological restoration,livelihood vulner-ability may be more pronounced due to the inflexibility,policy protection,and susceptibility to climate and market changes in forestry production.Although this issue has attracted academic interest,empirical studies are relatively scarce.This study,centered on Jiaxian County,Shaanxi Province of China explored the households’livelihood vulnerability and coping strategies and group heterogeneity con-cerned with livelihood structures or forestry resources through field investigation,comprehensive index assessment,and nonparametric tests.Findings showed that:1)the percentage of households with high livelihood vulnerability indicator(LVI)(>0.491)reached 46.34%.2)Eight groups in livelihood structures formed by forestry,traditional agriculture,and non-farm activities were significantly different in LVI,land resources(LR),social networks(SN),livelihood strategies(LS),housing characteristics(HC),and socio-demo-graphic profile(SDP).3)The livelihood vulnerability of the groups with highly engaged/reliance on jujube(Ziziphus jujuba)forest demonstrated more prominent livelihood vulnerability due to the increased precipitation and cold market,where the low-engaged with reliance type were significantly more vulnerable in LVI,SDP,LR,and HC.4)The threshold of behavioral triggers widely varied,and farmers dependent on forestry livelihoods showed negative coping behavior.Specifically,the cutting behavior was strongly associated with lagged years and government subsidies,guidance,and high returns of crops.Finally,the findings can provide guidance on the dir-ection of livelihood vulnerability mitigation and adaptive government management in ecologically restored areas.The issue of farmers’livelihood sustainability in the context of ecological conservation calls for immediate attention,and eco-compensations or other forms of assistance in ecologically functional areas are expected to be enhanced and diversified.

Advancing climate resilience through a geo-design framework: strengthening urban and community forestry for sustainable environmental design

Urban and community forestry is a specialized discipline focused on the meticulous management of trees and forests within urban,suburban,and town environments.This field often entails extensive civic involvement and collaborative partnerships with institutions.Its overarching objectives span a spectrum from preserving water quality,habitat,and biodiversity to mitigating the Urban Heat Island(UHI)effect.The UHI phenomenon,characterized by notably higher temperatures in urban areas compared to rural counterparts due to heat absorption by urban infrastructure and limited urban forest coverage,serves as a focal point in this study.The study focuses on developing a methodological framework that integrates Geographically Weighted Regression(GWR),Random Forest(RF),and Suitability Analysis to assess the Urban Heat Island(UHI)effect across different urban zones,aiming to identify areas with varying levels of UHI impact.The framework is designed to assist urban planners and designers in understanding the spatial distribution of UHI and identifying areas where urban forestry initiatives can be strategically implemented to mitigate its effect.Conducted in various London areas,the research provides a comprehensive analysis of the intricate relationship between urban and community forestry and UHI.By mapping the spatial variability of UHI,the framework offers a novel approach to enhancing urban environmental design and advancing urban forestry studies.The study’s findings are expected to provide valuable insights for urban planners and policymakers,aiding in creating healthier and more livable urban environments through informed decision-making in urban forestry management.

Coupling and Long-term Change Characteristics of Forest Carbon Sink and Forestry Economic Development in China

[Objectives]To analyze the changes in of forest carbon sink and forestry economic development,provide reference for relevant management decisions,ecological governance and resource and environment management,and promote the development of green low-carbon economy in China.[Methods]Based on the data of six forest resource inventories from 1989 to 2018 and related studies,the comprehensive evaluation model of forest carbon sink and forestry economic development,the coupling degree model of forest carbon sink and forestry economic development,and the coupling coordination degree model of forest carbon sink and forestry economic development were adopted.The coupling degree of forest carbon sink and forestry economic development from 1992 to 2018 was analyzed.Stepwise regression and ARIMA model were used to analyze the influencing factors and lagging characteristics of forest carbon sink.The coupling degree between forest carbon sink and forestry economic development in China from 2019 to 2030 was predicted by autoregression and ADF test.The coupling between forest carbon sink and forestry economic development in China and its long-term change characteristics were also discussed in this study.[Results](i)The investment of ecological construction and protection,the actual investment of forestry key ecological projects,GDP and the import of forest products had a significant impact on forest resources carbon stock.The total output value of forestry industry,the actually completed investment of forestry key ecological projects and the export volume of forest products had a significant impact on the forest carbon sink,and the actually completed investment of forestry key ecological projects has the greatest impact on the two.(ii)The impact of actually completed investment of forestry key ecological projects had a lag of 2 years on the forest resources carbon stock and a lag of 1 year on the forest carbon sink.When investing in forest carbon sink,it is necessary to make a good plan in advance,and do a good job in forest resources management and time optimization.(iii)From 1992 to 2018,the coupling degree of forest resources carbon stock,forest carbon sink and long-term development of forestry economy in China was gradually increasing.Although there were some fluctuations in the middle time,the coupling degree of forest resources carbon stock and the long-term development of forestry economy increased by 9.24%annually,and the degree of coupling coordination increased from"serious imbalance"in 1992 to"high-quality coordination"in 2018.From 1993 to 2018,the coupling degree of forest carbon sink and long-term development of forestry economy increased by 9.63%annually,slightly faster than the coupling coordination degree of forest resources carbon stock and long-term development of forestry economy.The coordination level also rose from level 2 in 1993 to level 10 in 2018.(iv)The prediction shows that the coupling coordination degree of forest resources carbon stock,forest carbon sink and the long-term development of forestry economy would increase from 2019 to 2030.The coupling coordination degree(D)values of both were close to 1,the coordination level was also 10 for a long time,and the degree of coupling coordination was also maintained at the"high-quality coordination"level for a long time.[Conclusions]Forest has multiple benefits of society,economy and ecology,and forest carbon sink is only a benefit output.The long-term coupling analysis of forest carbon sink and forestry economic development is a key point to multiple benefit analysis.The analysis shows that the spillover effect and co-evolution effect of forest carbon sink in China are significant.From 1992 to 2018,the coupling coordination degree of forest carbon sink and forestry economic development was gradually rising.The prediction analysis also indicate that the coupling coordination degree between the forest carbon sink and the long-term development of forestry economy will remain at the level of"high-quality coordination"for a long time from 2019 to 2030.Therefore,improving the level of forest management and maintaining the current trend of increasing forest resources are the key to achieving the goal of carbon peaking and carbon neutrality in China.

Forestry ecological footprint in China during 1973–2003

The ecological footprint （EF） model has received much attention as an assessment indicator for sustainable development in recent years. Firstly, the temporal changes of domestic timber production, imports and exports in China were analyzed from 1973 to 2003, the analysis results showed an apparent fluctuation in timber production during 1973-1995 but a decreasing trend during 1995-2002, an increasing trend in timber imports since 1995 especially after the implementation of the Natural Forest Protection Project （NFPP）, an decreasing trend year by year in timber exports since 1995. Secondly, this paper presented a time series analysis of actual forest area demand in the sustainable yield and production approach in China from 1973 to 2003, which includes both import and export forest area demand. The results showed the actual forest area demand simulated from the sustainable yield approach was slightly higher than that from the production approach during 1978-1988 and a little lower during 1989-2003; however, the actual forest area demands simulated by these two model approaches were larger than calculations that expressed in conventional forest EF. Meanwhile, the results indicated the forestry development in China during 1978-1988 was unsustainable due to overexploitation of forest stocking volumes, and China＇s forestry moved toward sustainable development since 1989 because forest resources are exploited at lower rates than they are regenerated. However, compared to forestry developed countries, the forestry development capacity in China is still lower. Finally, based on the model results we analyzed the relationships between forestry EF and the key policies, including trade policy, economic policy and forest conservation programs. In addition, several suggestions about reducing forestry EF and enhancing sustainable forestry development in China are given.

Prevention and Utilization of Invasive Plants of Agriculture and Forestry in Guangdong Province

Guangdong has become a major＂window＂ for invasive plants, and the largest zone, where cross-border and intercontinental migration frequencies reach the peak. The invasive plants in Guangdong are dominated by Mikania micrantha, Eichhornia crassipes, Alternanthera philoxeroides, Eupatorium odoratum, and Wedelia trilobata. It is an important way for treating the invasive plants by exploring the prevention methods and making ful use of the characteristics of the invasive plants, and it is of great significance to prevent and utilize alien species in a scientific and effective way in order to control the invasive plants with minimal cost.

Current situation of Chinese forestry tactics and strategy of sustainable development

Based on the analysis of the current situation of Chinese forestry and a series of ecological, environmental, eco-nomic, and social problems, this paper emphasized on the importance of forests in social and economic development in China The author pointed out that sustainable development, particularly the sustainable development of forestry, is the inevitable choice to solve the problems of ecological environment and social economics. The objectives, criteria, and strategies of sus-taining forestry were also demonstrated and expounded, from the viewpoints of ecology, economics, and sociology.

Analysis of Textbook "Garden Plant Protection" Construction in Agricultural and Forestry Universities or Higher Vocational Colleges

The survey of textbook 'Garden Plant Protection' was introduced in this study,and the necessity of textbook 'Garden Plant Protection' construction in agricultural and forestry universities or higher vocational colleges was also analyzed.Aimed at the status of textbook 'Garden Plant Protection' construction in agricultural and forestry universities or higher vocational colleges,the corresponding ideas for its construction were put forward.

A Needs-analysis Approach to Postgraduate English Curriculum Design in Chinese Agriculture and Forestry Universities——A Case Study of Shandong Agricultural University

In order to investigate the curriculum design for postgraduate English in Agriculture and Forestry Colleges, this papermakes great attempts to probe into the target needs and learning needs of English in SDAU. Both quantitative and qualitative re-search methods were employed in the survey. The final conclusion of this study is that the current English curriculum design forpostgraduate in SDAU can not satisfy the needs of students and workplace completely. On the basis of such major findings and re-sults, this paper makes attempts to develop an English curriculum design and implementing model for postgraduate English teach-ing in SDAU, hoping to offer implications on curriculum design of postgraduate English in Agriculture and Forestry Colleges and of-fer suggestions on personalized teaching reform of postgraduate English.

Forest fire risk zone mapping from satellite images and GIS for Baihe Forestry Bureau, Jilin, China

A forest fire can be a real ecological disaster regardless of whether it is caused by natural forces or human activities, it is possible to map forest fire risk zones to minimize the frequency of fires, avert damage, etc. A method integrating remote sensing and GIS was developed and applied to forest fire risk zone mapping for Baihe forestry bureau in this paper. Satellite images were interpreted and classified to generate vegetation type layer and land use layers （roads, settlements and farmlands）. Topographic layers （slope, aspect and altitude） were derived from DEM. The thematic and topographic information was analyzed by using ARC/INFO GIS software. Forest fire risk zones were delineated by assigning subjective weights to the classes of all the layers （vegetation type, slope, aspect, altitude and distance from r3ads, farmlands and settlements） according to their sensitivity to fire or their fire-inducing capability. Five categories of forest fire risk ranging from very high to very low were derived automatically. The mapping result of the study area was found to be in strong agreement with actual fire-affected sites.

Developing a quantitative index system for assessing sustainable forestry management in Heilongjiang Province,China： a case study

In this study, we developed a comprehensive index system for forestry sustainability of Heilongjiang Province, which includes forest resources sustainability,sustainable economic development, sustainable social development and sustainable advancement in science and technology. Based on this system and the regional forest development, we further evaluated the sustainability of Heilongjiang Province for year 2008-2013. The results show that even though the regional forestry has been preliminarily on the track of sustainable development, it is fragile. Four indicators, e.g. soil and water retention rate,forest stand growth（per unit area）, the proportion of national investment and the annual carbon sequestration have important impact on the sustainability, with a weight of 39.0 % in all the indicators. We also analyzed the factors hindering the sustainable development. It turns out that soil and water retention rate, forest stand growth（per unit area）,the proportion of science and technology funds, per capita GDP and the proportion of the tertiary industry production are the main factors hindering regional sustainable development, which accounts for 50.94 % of the total obstacle degrees in the system. At last, we discussed how to promote the regional sustainable development from the perspectives of forest resources sustainability, economic development sustainability, society development sustainability and the sustainable advancement of science and technology.

Over-mature beech trees (Fagus orientalis Lipsky) and close-to-nature forestry in northern Iran

Oriental Beech is the most important commercial tree species in northern Iran. In recent years wood production companies interested in felling large beech trees for profit have challenged advocates of close-to-nature silviculture who favor conservation. Our study objective was to assess the economic value of over-mature beech trees by relating tree diameter （DBH） to amount of decay. Based on the location of onset of decay, we categorized three types of decay as stump, stem, and crown decay. Trees of greater diameter （age） typically showed greater decay in the stem. Percent of decayed volume, diameter of decayed tissue, and length of decay in tree stems varied between 0.5%-64.3%, 15 cm-75 cm, and 2.0-19.5 m, respectively. With increasing trunk diameter, the propor- tion of truck decay increased. Red heart and dark red heart constituted 25% and 14.3% of sampled trees, respectively. However, we found no correlation between intensity of stem decay and morphological charac- teristics of trees. Seedlings were not abundant around the bases of over-mature trees, suggesting that the trees did not contribute to regeneration of the stand. Beech trees of diameter 〉1 m do not provide valu- able round wood for industries and cause to raise wood production costs. We recommend that these trees 〉1 m DBH should be retained in forest stands because of their low commercial value but high ecological and conservational values such as maintaining biodiversity in forest ecosystems.

Economic dependence of rural people on homestead forestry in Mymensingh, Bangladesh

Homestead forests contribute substantially to the rural econ- omy of Bangladesh. Rural people depend on trees and plants for their energy usage, housing, food and other forms of subsistence livelihood. In order to identify the potential role of forests on homestead dwellers, an empirical field investigation was conducted in the four Upazilas of My- mensingh district of Bangladesh. It was found that land holdings of the respondents within the four sites are the highest in Mymensingh. The study made an important observation that among all homestead vegeta- tion between 5-6 years old, tree species are generally preferred over plants. This is perhaps due to the efforts of the social forestry extension service to demonstrate that planting trees is an important long-term in- vestment. In all four Upazilas, there was a significant correlation between household annual income and homestead forestry, agriculture and fisher- ies practice, suggesting that higher income families tend to have larger holdings of homesteads, farms and pond areas. Three Upazilas displayed a strong positive relationship （nearly 45%） between homestead forest areas and annual family income; however, the Fulbaria Upazila showed a very poor relationship （0.2%） in this regard. The results of this study suggest that homestead forests play a positive role in the rural economy, in addition to helping mitigate the increasing problem of deforestation in Bangladesh.

Reliability of GPS/GNSS-based positioning in a forestry environment

The critical environment is one of the main insufficient to positioning. Geodetic observing systems such as the global positioning system （GPS） and the global navigation satellite systems （GNSS） are routinely used to estimate the contaminating effects by critical environment. In an effort to define the accuracy and reliability of GPS/ GNSS positioning, we investigated the data having con- taminating effects due to forestry environment. Some reliability criteria and geometric concepts were defined and then examined by them. Two sets of data were collected in open sky and closed canopy separately. The analysis of the observed data was performed using the reliability criteria and geometric concepts. The accuracy and reliability of positioning strongly depended on the canopy ratio and satellite availability. The minimum detectable error on baseline was estimated about 2.5 mm under closed canopy. The number of observable satellites and minimal detectable errors were computed for each epoch. The minimal biases on estimated baselines, bias-to-noise ratios for estimating baseline components and probability of success of the integer ambiguity solution were defined in case of forest canopy. Finally, geometric quality could be achieved using the factors of dilution of precision. Thus, the presented accuracy and reliability concepts fulfill the requirement proposed by the global geodetic observing system in forest environment.

Plant water use strategies in the Shapotou artificial sand-fixed vegetation of the southeastern margin of the Tengger Desert, northwestern China

Stable oxygen and hydrogen isotopic compositions(δ^(18)O and δD) of plant xylem water and its potential water sources can provide new information for studying water sources, competitive interactions and water use patterns of plants. The contributions of different water sources to three plants, Hedysarum scoparium(HS), Caragana Korshinskii(CK) and Artemisia ordosica(AO), were investigated in the artificial sand-fixed vegetation of Shapotou, the southeastern margin of the Tengger Desert of northwestern China, based on meteorological data and δ^(18)O and δD values of precipitation, groundwater, soil water and xylem water of HS, CK and AO. Our results indicated that soil water infiltration through precipitation was the main water source of the artificial sand-fixed vegetation. Obvious differences in soil water content and in δ^(18)O of soil water and xylem water were found among different seasons. No relationship was found between the δ^(18)O in plant xylem water and in soil water in January. The same water use patterns were found in CK, HS and AO in May, suggesting they have the same water sources. The different water sources of CK, HS and AO in August indicate that water competition occurred. In addition, the main water sources of CK, HS and AO in August mainly come from shallow soil water, while they use relatively deep soil water in May. This phenomenon is related to the differences of soil water content throughout soil profile, precipitation, transpiration and water competition under different growth periods. The water use patterns of CK, HS and AO respond to soil water content throughout the soil profile and their competition balance for water uptake during different growth season. The results indicate that these sandfixed plants have developed into a relatively stable stage and they are able to regulate their water use behavior as a response to the environmental conditions, which reinforces the effectiveness of plantation of native shrubs without irrigation in degraded areas.

Introduction to Urban and Community Forestry in the United States of America: History, Accomplishments, Issues and Trends

The urban and community forestry movement in the United States has matured over the last 20 years from managing street trees, to understanding the benefits of trees in urban ecosystems, and now to managing urban green infrastructure. This paper introduced the history, development, and major accomplishments of the urban and community forestry movement, highlighted the economic, ecological, environmental, and social values of forests and trees to communities, and discussed issues and trends of the urban and community forestry program in the United States.