Vitality variation and population structure of a riparian forest in the lower reaches of the Tarim River,NW China

Since 2000, the Chinese government has implemented emergency water diversion measures to restore the damaged riparian forest ecosystem with dominant tree species Euphrat poplar(Populus euphratica Oliv.)at the lower reaches of the Tarim River. In the present study, comparative analysis of variations in the vitality of P. euphratica trees were made using 2005 and 2010 data to illustrate the revitalization process of riparian forest. Poplar trees within 300 m of the riverbed were positively revitalized, while the vitality of trees farther than 300 m from the river decreased. Population structure was studied to demonstrate the development of poplar community. In the first belt, the class structure for the diameter at breast height(DBH) of P. euphratica fit a logistic model, and the 2nd, 3rd and 4th belt curve fittings were close to a Gaussian model; in other plots they were bimodal. Cluster analysis of the composition of the DBH class of poplar trees demonstrated that those within 16–36 cm DBH were the most abundant(58.49% of total) in study area, under 16 cm of DBH were second(31.36%), and trees >40 cm DBH were the least abundant(10.15%). More than 80% of the trees were young and medium-sized, which means that the poplar forest community in the vicinity of the lower Tarim River is at a stable developmental stage. The abundance of juvenile trees of P. euphratica in the first and second measuring belts was 12.13% in 2005 and increased to 25.52% in 2010, which means that the emergency water transfer had a positive impact on the generation of young P. euphratica trees in the vicinity of the river.

Comparable water use of two contrasting riparian forests in the lower Heihe River basin, Northwest China

Understanding forest ecosystem evapotranspiration（ET） is crucial for water-limited environments,particularly those that lack adequate quantified data such as the lower Heihe River basin of northwest China which is primarily dominated by Tamarix ramosissima Ledeb.and Populus euphratica Oliv.forests.Accordingly,we selected the growing season for 2 years （2012 and 2014） of two such forests under similar meteorological conditions to compare ET using the eddy covariance（EC） technique.During the growing seasons,daily ET of T.ramosissima ranged from 0.3 to 8.0 mm day^（-1） with a mean of 3.6 mm day^（-1）,and daily ET of P.euphratica ranged from 0.9 to 7.9 mm day^（-1） with a mean of 4.6 mm day^（-1） for a total of 548 and 707 mm,respectively.The significantly higher ET of the P.euphratica stand was directly linked to high soil evaporation rates under sufficient water availability from irrigation.When the soil evaporation was disregarded,water use was comparable to two contrasting riparian forests,a P.euphratica forest with a total transpiration of 465 mm and a T.ramosissima forest with 473 mm.Regression analysis demonstrated that climate factors accounted for at least 80% of ET variation in both forest types.In conclusion,water use of the riparian forests was low and comparable in this arid region,that suggest the long-term plant adaptation to the local climate and conditions of water availability.

Nighttime sap flow and its driving forces for Populus euphratica in a desert riparian forest, Northwest China

Nighttime sap flow is a potentially important factor that affects whole-plant water balance and water-use efficiency （WUE）. Its functions include predawn disequilibrium between plant and soil water potentials as well as between the increments of oxygen supply and nutrient uptake. However, main factors that drive nighttime sap flow remain unclear, and researches related to the relationship between nighttime sap flow velocity and environmental factors are limited. Accordingly, we investigated the variations in the nighttime sap flow of Populus euphratica in a desert riparian forest of an extremely arid region, Northwest China. Results indicated that P. euphratica sap flow occurred throughout the night during the growing season because of the partial stomata opening. Nighttime sap flow for the P. euphratica forest accounted for 31%-47% of its daily sap flow during the growing season. The high value of nighttime sap flow could be the result of high stomatal conductance and could have significant implications for water budgets. Throughout the whole growing season, nighttime sap flow velocity of P. euphratica was positively correlated with the vapor pressure deficit （VPD）, air temperature and soil water content. We found that VPD and soil water content were the main driving factors for nighttime sap flow of P. euphratica.

Tree mortality and regeneration of Euphrates poplar riparian forests along the Tarim River,Northwest China

Background:Tree mortality and regeneration(seedling and sapling recruitment)are essential components of forest dynamics in arid regions,especially where subjected to serious eco-hydrological problems.In recent decades,the mortality of the Euphrates poplar(Populus euphratica)along the Tarim River in Northwest China has increased.However,few studies have quantified the causes of mortality and regeneration in this azonal riparian forest type.Methods:The present study describes the annual hydrological response of tree mortality and regeneration in forest gaps.A total of 60 canopy gaps were investigated in six replicate grid plots(50m×50 m)and the annual runoff and water consumption data during the period of 1955–2016 were collected from hydrological stations in the middle reaches of the Tarim River.We compared the regeneration density of seedlings and saplings within the canopy gap areas(CGAs),undercanopy areas(UCAs),and uncovered riverbank areas(RBAs)through detailed field investigation.Results:Our study found that the mortality of young and middle-aged gap makers has increased remarkably over recent decades,particularly since the year 1996.The main results indicated that regional water scarcity was the primary limiting factor for long-term changes in tree mortality,as shown by a significant correlation between the diameter at breast height(DBH)of dead trees and the annual surface water.The average density(or regeneration rate)of seedlings and saplings was highest in the RBAs,intermediate in the CGAs,and lowest in the UCAs.Compared with the UCAs,the CGAs promote tree regeneration to some extent by providing favorable conditions for the survival and growth of seedlings and saplings,which would otherwise be suppressed in the understory.Furthermore,although the density of seedlings and saplings in the CGAs was not as high as in the RBAs,the survival rate was higher in the CGAs than in the RBAs.Conclusion:Forest canopy gaps in floodplain areas can play a decisive role in the long-term germination and regeneration of plant species.However,as a typical phreatophyte in this hyper-arid region,the ecosystem structure,functions and services of this fragile P.euphratica floodplain forests are threatened by a continuous decrease of water resources,due to excessive water use for agricultural irrigation,which has resulted in a severe reduction of intact poplar forests.Furthermore,the survival of seedlings and saplings is influenced by light availability and soil water at the regional scale.Our findings suggest that policymakers may need to reconsider the restoration and regeneration measures implemented in riparian P.euphratica forests to improve flood water efficiency and create canopy gaps.Our results provide with valuable reference information for the conservation and sustainable development of floodplain forest ecosystems.

Tree Species Composition and Diversity in the Riparian Forest of Lake Barombi Kotto, Cameroon

Tree species composition and diversity were investigated in the riparian forest around Lake Barombi Kotto, Cameroon. This study aimed at determining the tree species composition, population structure, and providing evidence of anthropogenic disturbances in the riparian forest of Lake Barombi Kotto. The objectives were to determine the tree species composition and diversity in the riparian forest around Lake Barombi Kotto, to elucidate the forest structure and to document the anthropogenic disturbances in this forest. Five plots were laid within which the tree enumeration and measurement of dbh were carried out. Trees were identified using scientific identification keys in the Flora of West Africa. Disturbance scores were given to each site by qualitatively assessing various disturbances. A total of 340 trees belonging to 70 plant species, 63 genera and 28 plant families were enumerated. Shannon-Wiener diversity varied across sites, with the highest value (H = 3.45) recorded in Tung and the lowest (H = 2.21) in Malenda. Population structure differed across sites, the largest stand basal area of 43.78 m2/ha was recorded in Bondokombo while the smallest (2.15 m2/ha) was recorded in the Sacred Island. Cecropia peltata L., Pseudospondias macrocarpa Oliv. Pierre and Ceiba pentandra (L.) Gaertn had the largest basal areas across the different sites. Species rich families were Malvaceae (9 species), Fabaceae (9 species), Annonaceae (4 species), and Anacardiaceae (4). This study shows that, there is a high tree species diversity in the protected forest (Tung) but the other unprotected sites are highly disturbed by anthropogenic activities. There is need to develop and enhance existing management policies for this riparian forest, especially by replanting the cut trees and creating a protected riparian buffer to conserve its floristic diversity and ecological functions.

Sand mining disturbances and their effects on the diversity of arbuscular mycorrhizal fungi in a riparian forest of Iran

The major objective of this study was to evaluate the effects of sand mining disturbances on the diversity of arbuscular mycorrhizal fungi（AMF）. In addition, the proportional changes in the diversity of AMF to the distances from riverbanks were assessed. For this purpose, the riparian forest of the Maroon River, Iran was divided into three locations with a 200-meter wide zone in between. Thus, the locations studied were named Distance I（riverbank）, Distance II（intermediate）, and Distance III（farthest from riverbank）. In each of these distances, 10 Tamarix arceuthoides and Populus euphratica of each species were randomly selected. At the same time, soil and root samples were collected from the rhizosphere of the tree species studied. Results indicated that totally 13 AMF species were observed in T. arceuthoides and 19 AMF species were recorded in P. euphratica rhizosphere belonging to 6 genera and 6 families. In these AMF species, Glomus segmentatum, G. geosporum, G. rubiforme, G. nanolumen, G. spinuliferum, Claroideoglomus drummondii, Gigaspora gigantea and Acaulospora paulinae appeared only in P. euphratica rhizosphere, while G. multiforum and Claroideoglomus claroideum were observed only in T. arceuthoides rhizosphere. Moreover, Distance II had the least AMF species both in T. arceuthoides and in P. euphratica rhizospheres, and also the least spore density and root colonization rate. Our results are important in that they provide a list of resistant AMF species that could be used in the conservation of biodiversity.

Installation of a Riparian Forest by Means of Soil Bio Engineering Techniques—Monitoring Results from a River Restoration Work in Southern Brazil

Soil bioengineering has been applied more and more in different regions of Brazil in recent years. The study in hand presents the installation of “new” riparian forest based on soil bioengineering techniques. This riverbank restoration work was implemented in the year 2010 and two onsite vegetation surveys, one shortly after the construction, and one in 2013. Besides that, the structures of reinforcement work, and its effectiveness were evaluated. By means of the vegetation survey, the applied species were examined for their ability to establish the riverbank in an environmentally sustainable way. Most notably, the species Calliandra brevipes Benth. (Fabaceae, Mimosoideae), Phyllanthus sellowianus Müller Arg. (Euphorbiaceae), Salix humboldtiana Willd. (Salicaceae), Bauhinia forficate Link (Leguminosae), Inga marginata Willd. (Mimosoideae) and Ateleia glazioveana Baill. (Leguminosae, Papilionoideae) showed a good growth development. The proportion of spontaneous vegetation increased significantly, with Pennisetum purpureum Schumach. becoming a dominating species. Resulting from that, the intervention can be assessed as functional and safe, but the strong increase of spontaneous vegetation is undesirable due to less flood resistance. The vegetated riprap could be the best to meet the expectations of the construction elements. Partly, the anchored willows showed as well a good growth development whereas the species used for the hedge brush layer could not develop as expected in large parts of the construction.

Nutrient status of Populus euphratica growing in desert riparian forests of northwestern China

Seasonal and microhabitat variations of chemical constituents of foliar organic carbon （C）, total nitrogen （N）, total phosphorus （P）, and total potassium （K）, in Populus euphratica growing in desert riparian forests in northwestern China and their correlations were studied. Results show that ranges of C, N, P and K contents in the leaves ofP. euphratica were 39.08%-46.16%, 0.28%-2.81%, 0.05%-0.18% and 0.35%-2.03%, with means of 43.51%, 1.49%, 0.102% and 1.17%, respectively. The ratio of C/N, C/P and N/P changed from 16.26 to 146.61, from 258.08 to 908.67 and from 2.89 to 26.67; the mean was 37.24, 466.27 and 15.14, respectively. The mean N content was significantly lower than of deciduous trees in China, but the mean P content was nearly equivalent. The ratio of C/N was remarkably higher than of global land plants. The ratio of N/P indicated that growth ofP. euphratica was jointly limited by N and P nutrient deficiency. During the growth season, total trends of leaf C, N, P and K contents decreased. The max- imum appeared in May, and the minimum in September. Among microhabitats, C, N and K contents gradually increased from ri- parian lowland, flatland, sandpile, Gobi and dune, but C/N ratio was opposite, and P content was not apparent. Foliar C content was extremely, significantly and positively correlated with N and K contents, respectively. The relationships of N-K and P-K were both significantly positive.

How changes of groundwater level affect the desert riparian forest ecosystem in the Ejina Oasis,Northwest China

Groundwater is a key factor controlling the growth of vegetation in desert riparian systems. It is important to recognise how groundwater changes affect the riparian forest ecosystem. This information will not only help us to understand the ecological and hydrological process of the riparian forest but also provide support for ecological recovery of riparian forests and water-resources management of arid inland river basins. This study aims to estimate the suitability of the Water Vegetation Energy and Solute Modelling(WAVES) model to simulate the Ejina Desert riparian forest ecosystem changes,China, to assess effects of groundwater-depth change on the canopy leaf area index(LAI) and water budgets, and to ascertain the suitable groundwater depth for preserving the stability and structure of desert riparian forest. Results demonstrated that the WAVES model can simulate changes to ecological and hydrological processes. The annual mean water consumption of a Tamarix chinensis riparian forest was less than that of a Populus euphratica riparian forest, and the canopy LAI of the desert riparian forest should increase as groundwater depth decreases. Groundwater changes could significantly influence water budgets for T. chinensis and P. euphratica riparian forests and show the positive and negative effects on vegetation growth and water budgets of riparian forests. Maintaining the annual mean groundwater depth at around 1.7-2.7 m is critical for healthy riparian forest growth. This study highlights the importance of considering groundwater-change impacts on desert riparian vegetation and water-balance applications in ecological restoration and efficient water-resource management in the Heihe River Basin.

Evapotranspiration and its main controlling mechanism over the desert riparian forests in the lower Tarim River Basin

Evapotranspiration(ET) and its controlling mechanism over the desert riparian forests in arid regions are the important scientific basis for the water resources managements of the lower reaches of the inland rivers of China. Nearly three years of continuous measurements of surface ET, soil water content at different depths and groundwater table over a typical Tamarix spp. stand and a typical Populus euphratica stand were conducted in the lower reach of the Tarim River. The ET seasonal trends in the growing season were controlled by plant phenology, and ET in non-growing season was weak. The diurnal variations of ET resulting from the comprehensive effects of all atmospheric factors were significantly related with reference ET. The spatial pattern of ET was determined by vegetation LAI, more vegetation coverage, more ET amount. Groundwater is the water source of surface ET, and the soil water in shallow layers hardly took part in the water exchange in the groundwatersoil-plant-air system. The temporal processes of ET over the Tamarix stand and the Populus stand were similar, but the water consumption of the well-grown Populus euphratica was higher than that of the well-grown Tamarix spp. Further analysis indicates that plant transpiration accounts for most of the surface ET, with soil evaporation weak and negligible; groundwater table is a crucial factor influencing ET over the desert riparian forests, groundwater influences the processes and amounts of ET by controlling the growth and spatial distribution of desert riparian forests; quantifying the water stress of desert riparian forests using groundwater table is more appropriate, rather than soil water content. Based on the understanding of ET and water movements in the groundwater-soil-plant-air system, a generalized framework expressing the water cycling and its key controlling mechanism in the lower reaches of the inland rivers of China is described, and a simple model to estimate water requirements of the desert riparian forests is presented.

Water use strategies of the desert riparian forest plant community in the lower reaches of Heihe River Basin, China

The object of this paper is the different plant communities in the Ejina desert riparian forest. Groundwater depth, soil moisture, plant water potential, relative leaf moisture content and water use efficiency was monitored, and the response of soil moisture and plant ecology to the groundwater depth and the water use efficiency of the different plant communities was analyzed. The results showed that：（1） Along with the groundwater depth increasing, predawn and midday water potential of the plants, with the exception of Reaumuria soongorica, did not decrease significantly, indicating that when the groundwater depth is less than 3 m, the plant communities in the range of 4 km from the river way did not suffer or slightly suffer from water stress;（2） The distribution of higher soil moisture content within 0–3 m soil layer is suitable with the plants’ root system, as indicated in the communities of coexisting overripe Populus euphratica or Taramrix chinensis, both of which can release excessive water into soil for shallow rooted shrubs or herbaceous plants when there is water shortage;（3） R. soongorica can absorb deep soil moisture through deep roots for their own survival;（4） The community consisting of Sophora alopecuroides, Karelinia caspica, T. chinensis, and overripe P. euphratica has the best species combination for restoring the damaged eco-environment in the lower reaches of Heihe River;（5） The order of plants’ relative leaf water contents is K. caspica ＆gt; S. alopecuroides ＆gt; young P. euphratica ＆gt; overripe P. euphratica ＆gt; mature P. euphratica = T. chinensis coexisting with other species ＆gt; single R. soongorica ＆gt; single T. chinensis and the order of WUE is single T. chinensis ＆gt; single R. soongorica ＆gt; T. chinensis living in symbiosis with other species ＆gt; S. alopecuroides = young P. euphratica ＆gt; mature P. euphratica ＆gt; overripe P. euphratica ＆gt; K. caspica. Therefore, with ample soil moisture, the plant community helps rapid growth of T. chinensis, young P. euphratica and R. soongorica plants of less moisture content. Despite this they do not have much water storage capability, but have strong drought resistance, and higher moisture contents of S. alopecuroides and K. caspica, thus leaving them with poor drought resistance. Overall, the desert riparian forest plant community in the lower reaches of Heihe River helps the species of higher WUE live on it.

Land Use and Environmental Gradients Influence on Riparian Woody Plant Diversity and Structure in Lake Manyara Watershed Ecosystem, Tanzania

Riparian vegetations are important in supporting ecological connectivity between aquatic and terrestrial ecosystems. The structure and species composition of riparian woody plants have been subjected to multiple forces with varying degree of influences. This study examined the influence of land use and environmental gradient to the structure and composition of the riparian woody plants in northern Tanzania. A total of 270 plots were surveyed for woody plant species in the riparian ecosystems and later analysed to determine the influence of land use categories (homegarden, crop field, woodlot, open canopy forest, and closed canopy forest) and environmental variables (temperature, precipitation, elevation and slope) to the species richness, abundance, and stand parameters. Basal area was higher in woodlots, homegardens and crop fields than in the open and closed canopy forests;and as expected the reverse was true for the number of stocking density. Correlation among stand parameters with environmental variables varied significantly. Species richness and species abundance were negatively correlated to precipitation, temperature and elevation, while stocking density and basal area were positively correlated to precipitation. The study recommends continual retentions of trees on farm, further promoting of agroforestry interventions and sustainable utilization of woody plants in open and close canopy forests.

Responses of distribution pattern of desert riparian forests to hydrologic process in Ejina oasis

By using the theories and methods of landscape ecology and the technology of GIS and RS, a study has been carried out on the responses of distribution pattern of desert riparian forest to hydrologic process on the basis of the hydrologic data from 1990 to 2000 and the TM image of 2001 year. The results showed that: (1) there appears an even distribution pattern for the relative forest area in oasis, however, the degenerated forest diaplays an increasing tendency from west to east; (2) the desert riparian forest in Ejina is in completely degenerated process at the patch scale; (3) the number of patch is influenced not only by hydrologic process,but also by agricultural activity such as cultivation. The severe deterioration of the degraded vegetation in whole oasis initiates from lower reaches, and gradually impels to upstream; the fragmentation of landscape in the terminal site is more obvious, which is influenced by river shape and decreasing flux of water. It is found that the influence of surface hydrologic process to the ground hydrologic process of desert riparian forest in Ejina oasis is little for the recent ten years. The relative area of the degenerated forest increased with increasing ground water depth in the direction of parallel to river channel. On the contrary, in the direction perpendicular to river channel, there is a decreasing tendency for the average patch area of the forest and the degenerated forest with increasing ground water depth.

Assessment of water-recharging based on ecological features of riparian forest in the lower reaches of Tarim River

被 mesophytes 种类主要统治的河边的森林的出现和发展与表面水仔细联系。因为到过去的 5 十年年里的 Tarim 河的更低的活动范围没有水分泌物，河边的森林严重地降级。在 2002 和 2003 的 Yingsu， Argan 和 Luobuzhuang 的监视数据的基于的在分析，效果再装 ofwater 被讨论。再装水的工程忽视事实控制在露面，而是对植被的地下水影响的焦点上开拓殖民地于的 Populus euphratica 的过程，这正在泛滥。泛滥的控制背离河边的森林开发的固有的法律，河边的森林的自然新生因此被检查。地下水上的河边的植物的反应范围高举极其狭窄、很河边的社区没被优化。因为 theirphysio 生态的特征被忽略，主导的种类的幼苗都没在充满区域被发现。然而，在溪流的附近的植被变化仅仅在浅地下水上反映 mesophytes 种类的需求为河边的植物的幼苗建立提供合适的产地的 water-re-chargingfails。再装 presentwater 计划是困难的认识到植被恢复。

Influence of Land Use Activities on Riparian Vegetation, Soil and Water Quality: An Indicator of Biodiversity Loss, South West Mau Forest, Kenya

Watershed and riparian areas of Mau Forest Complex in Kenya are experiencing increased threats due to unsustainable land use activities geared towards economic growth amidst growing population. This study was carried out to examine effects of land use activities on riparian vegetation, soil and water quality along two major rivers (Chemosit and Kipsonoi) of South West Mau Forest (SWMF). Land use activities adjacent to these rivers and biodiversity disturbance on the riparian zone were identified and underpinned to changes on Total Nitrogen, Total Phosphorous, Potassium, Sulphur, Cadmium, Copper, Lead, Total Suspended Solids and soil Organic Carbon. Three sampling sites designated(upstream, midstream and downstream) were identified and established along each river as guided by existing land use activities represented by forest, tea plantation and mixed agricultural farming respectively. At each sampling site, a 200 m × 50 m section was systematically marked on each side of the river bank;the longest side being parallel to the river flow and divided into three belts transects each 20 m × 50 m, spaced 70 m apart. Six distinct land use activities (indigenous forest, food crop, tree and tea farming, livestock keeping and urban settlement) were identified as the major land use activities in SWMF. Plant species richness decreased and overall riparian disturbance increased from upstream (intact canopy with native vegetation) to mid-stream and downstream as epitomized by the structure, biodiversity disturbance resulting from extensive and intensive farming, intrusion of exotic species to livestock grazing and urban settlement. Variation among sampling sites in Total Suspended Solids, pH, Total Nitrogen, Phosphorus and Potassium were associated to different land use activities along the riparian zone. Total Nitrogen and water pH showed significant sensitivity to land use changes (p < 0.05). Put together these results indicate loss of biodiversity, riparian disturbance hence a need to adopt environmental-friendly land use planning and sustainable farming systems in SWMF.

塔里木荒漠河岸林物种多样性沿地下水埋深梯度的分布格局

探讨荒漠河岸林土壤水分、物种多样性的空间变异性及其相互关系,可为干旱区天然林保护、可持续经营和生态恢复提供科学依据。以塔里木荒漠河岸林为研究对象,基于野外样带调查和采样测定,系统分析了地下水埋深(GWD)梯度下林地土壤水分与物种多样性的空间变异及其权衡关系。结果表明:随GWD增加和土壤水分减少,荒漠河岸林群落物种数减少、结构简化、群落发生退化,退化顺序为浅根系的中生草本植物和灌木,最后留存的是抗旱性较强的乔灌木或灌木;同时土壤水分和物种丰富度、物种多样性指数均呈显著的线性递减趋势,而物种均匀度指数降幅较小。GWD与土壤水分、物种多样性之间均呈极显著的相关(P<0.01),土壤水分与物种多样性的相对收益随GWD增加而逐渐降低,表明GWD是控制荒漠河岸林土壤水分和物种多样性空间变异的关键因素。荒漠河岸林土壤水分与物种多样性权衡关系的转折点为GWD 4.5m左右,转折点以下(GWD<4.5m)二者沿GWD以相同速率变化,呈协同关系;转折点以上(GWD>4.5m)土壤水分与物种多样性的权衡明显增大,土壤水分相对收益剧降,即维持当前相应的物种多样性以消耗土壤水分为代价,系统通过反馈调节使物种多样性降低。综上表明,维持塔里木荒漠河岸林物种多样性和生态系统功能的合理GWD在4.5m左右,这为塔里木河流域荒漠河岸林保育与生态输水工程实施提供科学依据。

洪水漫溢对林窗微环境时空差异的影响--以塔里木河中游荒漠河岸林为例

林窗是森林生态系统中普遍存在的干扰形式。探究洪水漫溢对林窗内部微环境时空异质性的影响,对揭示荒漠河岸林物种多样性变化及其更新特征具有重要意义。在塔里木河中游非洪水和洪水漫溢区各选取一个大小相似的林窗样地,并使用便携式气象监测仪对林窗内不同方位的空气温湿度进行监测,对比分析不同水淹条件下林窗内微环境的时空分布差异,为深入探索荒漠河岸林植被更新机制奠定基础。结果表明:(1)非洪水漫溢区和洪水漫溢区林窗内空气温度均呈现先上升后下降的变化趋势,空气湿度均呈现先下降后上升的变化趋势,且同一个样地中温度与湿度之间存在明显的负相关关系,而洪水漫溢改变了森林微环境,使林窗内湿度升高,温度下降。(2)非洪水漫溢区和洪水漫溢区林窗内不同方位温度分布差异较小,洪水漫溢对温度变化影响不大;两个样地林窗内湿度变化过程较为复杂,差异明显,洪水漫溢区湿度变化梯度更为密集。(3)非洪水漫溢区和洪水漫溢区林窗内温度差界限明显,西南方向温度差较小,中心位置温度差最大,洪水漫溢并未改变不同方位温度变化趋势;湿度差以中心偏北方向较大,其中非洪水漫溢区湿度差在西北方向较小,而洪水漫溢区湿度差最小值出现在西南方向。研究结果表示荒漠河岸林林窗微环境时空差异具有干旱区独特性,同时阐明了林窗微环境对洪水漫溢的响应,为深入研究林窗干扰对荒漠河岸林更新与演替提供了科学依据。

塔里木河中游不同生境胡杨林土壤有机碳及活性组分特征

以塔里木河中游不同生境典型胡杨河岸林为研究对象,分析旱生、中生和周期性水淹3种不同生境下0~100 cm土体中土壤有机碳及活性组分含量变化特征。结果表明,1)3种生境胡杨林SOC含量均值依次为中生(3.65 g/kg)>旱生(3.56 g/kg)>周期性水淹(3.35 g/kg);随土壤深度的增加,SOC含量均呈波动性下降趋势。2)3种生境土壤MBC含量均值依次为中生(408.93 mg/kg)>周期性水淹(289.80 mg/kg)>旱生(182.75 mg/kg),而EOC和DOC含量为周期性水淹(2.28 g/kg、104.39 mg/kg)>中生(1.92 g/kg、67.40 mg/kg)>旱生(1.89 g/kg、57.79 mg/kg);随土壤深度的增加,EOC含量总体增加后降低,DOC含量呈降低趋势;MBC在不同生境和土层间均差异显著(P<0.05);EOC仅表层(0~10 cm)与下层(60~100 cm)差异显著(P<0.05);中生生境DOC土层间差异显著(P<0.05)。3)40~100 cm土层MBC/SOC、20~60 cm土层EOC/SOC、10~100 cm土层DOC/SOC在3种生境间差异显著(P<0.05)。4)3种生境SOC与DOC均呈显著正相关(r>0.58,n=15),活性组分之间相关性在中生生境下最显著。综合以上分析,不同生境和土层对SOC及活性组分含量产生显著影响,旱生和周期性水淹生境SOC及活性组分含量在0~20 cm土层维持着较高水平,中生生境则在20~40 cm土层保持着较高的SOC活性组分分配比例,其土壤微生物活性最高,SOC转化速率较高。

干旱区荒漠河岸林引洪灌溉生态修复研究

选择典型荒漠河段引洪灌溉生态修复区域,利用遥感数据和地下水监测数据,结合实地调查等手段对和田河沙漠段典型荒漠河岸林引洪灌溉生态修复效果开展了研究,采用多波段水体指数MBWI和归一化差异植被指数NDVI分析评价研究区生态修复效果。结果表明:引洪灌溉对生态修复区地下水有抬升作用,缓解年内地下水持续降低趋势,同时提高植被覆盖水平,这导致植被覆盖度高地区面积增加,无植被覆盖地区面积减少。然而目前引洪灌溉生态修复存在积水面积较大,积水时间较长,区域分布不均等问题,引洪灌溉生态闸位置和合理的运行制度还需要进一步研究。研究成果可以为干旱区内陆河流域荒漠河岸林生态修复提供借鉴。

Discussion on Role of Forest to Control Agricultural Non-Point Source Pollution in Taihu Lake Basin-Based on Source-Sink Analysis

Taihu Lake is located at the center of Changjiang delta region, the Lake and its effluent rivers are important water sources for 40 million around inhabitants and rapidly increasing industrial factories in Shanghai, Ji-angsu and Zhejiang. The pollutants originate mainly from acidy rain, home sewage of the vast number of inhabitants, livestock manure, agricultural fertilizers & pesticides applied over fields in the drainage basin, and the industrial sewage. Due to the kinds of pollutants, the Lake water is getting highly eutrophic, with frequent blooms of blue-green algae. Compared with point-source pollutants, diffuse pollution is much com-plicated and difficult to control. Thus combating non-point pollution (NPP) is paid much great attention. Based on analysis on source-sink of NPP in Taihu Lake basin, it is concluded that the function of forests on NPP control is multiple and important by both source reduction and sink expansion. The primary objective of planting trees through constructing forested wetlands and establishing riparian forest buffers is to control soil & water erosion, decrease agrochemicals application, and improve farming conditions in the region of Taihu Lake basin. Moreover forests help to intercept acidy rain, protect streambanks, uptake nutrients, hold up pollutants and provide habitat for wildlife.