共查询到20条相似文献，搜索用时 15 毫秒
1.
The first ecosystem mimic hypothesis suggests clear advantages if man-made land use systems do not deviate greatly in their
resource use patterns from natural ecosystems typical of a given climatic zone. The second hypothesis claims that additional
advantages will accrue if agroecosystems also maintain a substantial part of the diversity of natural systems. We test these
hypotheses for the savannah zone of sub-Saharan Africa, with its low soil fertility and variable rainfall. Where annual food
crops replace the natural grass understorey of savannah systems, water use will decrease and stream and groundwater flow change,
unless tree density increases relative to the natural situation. Increasing tree density, however, will decrease crop yields,
unless the trees meet specific criteria. Food crop production in the parkland systems may benefit from lower temperatures
under tree canopies, but water use by trees providing this shade will prevent crops from benefiting. In old parkland trees
that farmers have traditionally retained when opening fields for crops, water use per unit shade is less than in most fast
growing trees introduced for agroforestry trials. Strong competition between plants adapted to years with different rainfall
patterns may stabilise total system productivity -- but this will be appreciated by a farmer only if the components are of
comparable value. The best precondition for farmers to maintain diversity in their agroecosystem hinges on the availability
of a broad basket of choices, without clear winners or 'best bets'.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
2.
为了缓解水资源短缺,再生水回用于农田灌溉、工业用水、景观补水、生活杂用、地下水补给等方面.文章总结了再生水回用过程中,对其直接作用的土壤、植物、微生物等的影响.由于再生水质的差异,再生水对人居环境的影响尚未有定论,仍需采用新技术进行长期观察. 相似文献
3.
The relationships between hydraulic and photosynthetic properties in plants have been widely studied, but much less is known about how these properties are linked to water-source partitioning, the spatial and temporal separation of water sources in ecosystems. Plant water-source partitioning is often influenced by the proximity of groundwater from the natural surface. We studied the water acquisition strategy and hydraulic and photosynthetic properties of Tuart (Eucalyptus gomphocephala D.C.), a large coastal tree species that occupies seasonally dry habitats underlain by superficial aquifers. Our goal was to quantify water-source partitioning as the proportion of xylem water derived from the vadose and saturated zones with respect to stage of development and proximity of groundwater. We then sought to associate the proportional contribution of a given water source with xylem hydraulic and photosynthetic properties, thus conferring a linkage. Seedlings were more inclined to use surface soil water when rainfall recharge of the upper profile occurred, suggesting that they maintained or rapidly developed a proportionally high amount of functional roots in the upper, seasonally dry, soil profile. This strategy was associated with a lower xylem-area-specific hydraulic conductivity (K(S)), leaf-area-specific hydraulic conductivity (K(L)) and maximum photon yield of photosystem II (F(V)/F(M)). In contrast, trees acquired water from a variety of sources in different seasons and had a higher K(S), K(L) and F(V)/F(M). Despite the higher K(S) and K(L) in trees, the midday hydrodynamic water potential gradient from soil to leaves, ΔΨ, was similar. We conclude that there was a linkage between hydraulic and photosynthetic properties with the partitioning of water sources and that this adaptation to long-term hydrological regimes accommodated the different hydraulic characteristics and hydrological environments of trees versus seedlings. 相似文献
4.
At sites in the Sahel where windbreaks are used to control wind erosion, management strategies are required to minimise competition for water between trees and crops. Uptake of water by windbreak trees was therefore studied in experiments designed to compare water use among tree species, assess which variables exert most control over transpiration and determine the source of water transpired by windbreak trees. Transpiration and soil-water extraction by Acacia nilotica, Acacia holosericea and Azadirachta indica trees in windbreaks were measured at the ICRISAT Sahelian Centre, Niger. Coupling of windbreaks to the atmosphere was evaluated and a stable isotope technique was used to compare utilisation of groundwater by windbreaks and crops at two sites in Niger with different water table levels. Azadirachta indica used least water, probably as a result of lower stomatal conductances, since windbreaks exhibited good physiological control over transpiration. The potential for competition for water was most severe with Acacia nilotica and Acacia holosericea, as they extracted large quantities of water through lateral roots, and at the location where trees could not access groundwater. At such sites, the effects of competition on crop productivity should be minimised by planting tree species with low water requirements and by using pruning to limit tree transpiration.This revised version was published online in November 2005 with corrections to the Cover Date. 相似文献
5.
H. -J. Von Maydell 《Agroforestry Systems》1995,31(2):133-142
Integrated management of natural resources and the multiple use of trees and forests have prevailed in most European societies since prehistoric times. In the Middle Ages, expanding and intensified agriculture resulted in the separation of trees from agricultural fields. During the last century, with the introduction of sustainable and highly productive forest management, the goal of increased wood production has been achieved in most parts of central, northern, and eastern Europe. Today, agroforestry is not considered to be an important land-use option within the region; however, there are many practices that could rightfully be classified as agroforestry. These include tree/crop systems in which trees provide products and/or environmental benefits, and tree/animal systems in which animals are grazed in forests or open woodlands.The future seems to offer some prospects for agroforestry. Large areas, hitherto used for food production, are either marginally suited to agriculture, or will probably be taken out of production due to agricultural policy considerations. Agroforestry may, at least in part, offer alternatives for the use of such lands. The availability of (surplus) fertile soils, capital, and labor may provide incentives for site-adapted forms of agroforestry, including improved fallow management. The focus of such systems would be on maintenance of biodiversity in the landscape, environmental protection, recreation, and product diversification.There are numerous expectations as to what agroforestry might provide for the land holder and for society as a whole. These expectations should be carefully analyzed and evaluated prior to political decisions on future land use. The promotion of agroforestry requires overall investment; agroforestry does not happen by itself. A set of integrated actions — not isolated efforts — must be implemented if agroforestry is to become a successful land-use option. 相似文献
6.
7.
Water balance information at locations across southern Australia is analysed to identify mechanistic causes for higher water
tables under agricultural systems compared to natural vegetation. Contrasting patterns of water use indicate pronounced physiological
activity in summer by natural ecosystems ensuring the persistence of the dominant perennial species. A strategy of tempered
water use during periods of rainfall excess in winter/spring enables seasonal carryover of soil water to be withdrawn by deep
roots for summer functioning. Characteristic patterns of water use by agricultural systems, comprised mainly of determinant
annual species, are truncated in time but feature elevated peak rates coinciding with periods of maximum soil water availability
during the cooler months. Low seasonal vapour pressure deficit explains the observed benefits of enhanced biomass production
due to high water use efficiency. The associated limited scope for soil water uptake carries the penalty of increased frequency
of drainage and the subsequent resource degradation currently associated with farmland. Inclusion of a perennial lucerne phase
in rotation with crops confers environmental benefit through summer uptake from a rooting depth double that of crops. An effective
buffer is thus provided to restrict drainage under an ensuing cropping phase in a manner that more closely emulates natural
systems. Simulations of phase farming point to a halving in long term drainage. They suggest adoption over a range of arable
land units could cause local retreat of water tables by 0.3 m y−1 initially, leading to a new equilibrium level which would still remain elevated with respect to that under natural vegetation.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
8.
9.
介绍国内外对水资源的利用情况,总结我国水资源开发利用的主要问题,从水资源良性循环的角度提出,将再生水回用于景观用水和地下水回灌有机地结合在一起作为我国再生水利用的短期目标和长期目标,以实现水生态的良性循环,保证经济、社会的可持续发展. 相似文献
10.
Agroforestry has been advocated as a means of managing excess water that has accumulated in the agricultural landscape of
southern Australia since clearing of native vegetation. This article examines the feasibility and profitability of agroforestry
systems designed to manage rising, saline watertables. A framework for Australian conditions is described that considers the
interactions between trees, crops and their below ground environment and how they influence water use, crop yield and profitability.
Data is presented from a study of a commercial scale agroforestry system under ideal conditions where trees have access to
a shallow fresh water table. The discussion is then broadened to encompass soil, relief and ground water conditions more typical
of the southern Australian cropping zone. The relative merits of segregating, integrating and rotating trees with crops are
then examined. It is concluded that, in most cases, trees would need to be widely dispersed over a significant proportion
of the landscape to manage deep drainage and salinity. Agroforestry is therefore only likely to be an effective solution to
water management where trees can compete directly on commercial terms with conventional agriculture. Given the generally low
rates of biomass accumulation in semi-arid woody species, this presents a significant challenge for agroforestry in the cropping
zone of southern Australia.
This revised version was published online in June 2006 with corrections to the Cover Date. 相似文献
11.
采用实地调查的方法对麓湖公园的水生植物资源进行系统分析,结果表明,麓湖公园目前应
用的水生植物共 28 种,隶属于 18 科,其中挺水植物 14 种、浮叶植物 3 种、沉水植物 3 种、耐水湿生
木本植物 8 种;根据观赏部位划分,观花类水生植物有 11 种,花色主要集中在白色、粉色、紫红色、黄
色,多数为顶端花序,花形各异,全年有花可赏;观叶类水生植物有 10 种,叶色不同,叶形各异;观姿
类水生植物有 4 种;麓湖公园的驳岸方式有硬质直立式驳岸和自然斜坡驳岸两种,硬质直立式驳岸以单
一水生植物列植为主,通过水生植物的种类和株高变化丰富景观效果,自然斜坡驳岸以风景林、多种植
物组合配置形式为主,通过耐水湿生木本植物和地被植物种类的变化增加景观的多样性。麓湖公园的水
生植物景观展现出季相变化、色彩搭配和层次效果,若要维持优美的水生植物景观效果,后期的养护管
理非常重要,建议在少游客的游览区域营造以耐水湿生木本植物为主的持久、低养护的水体景观。 相似文献
12.
南京主要滨河绿地植物群落的调查 总被引：8，自引：0，他引：8
应用群落生态学方法,对南京紫霞湖、前湖、护城河与玄武湖滨河绿地植物群落的外貌、组成与结构等进行了调查。结果表明,5个绿地主要以阔叶落叶树种为主,缺少常绿树种的运用;群落结构不甚合理,乔木层相对丰富,而低矮灌木及地被层种类和数量相对缺少;人工绿地过于注重观赏品种的运用,而忽视耐水湿性种。作者认为,应结合地形和环境,合理地把握植物耐水湿性与观赏性,创造有地域特色的滨河植物景观,达到自然景观与人工景观的统一;可适当增补一些观赏性好的适生树种,提高植物景观多样性,营造城市滨河生态廊道,使其成为城市绿地系统中的组成部分。 相似文献
13.
Enrique MurgueitioZoraida Calle Fernando UribeAlicia Calle Baldomero Solorio 《Forest Ecology and Management》2011,261(10):1654-1663
Extensive cattle production currently occupies more than 27% of the rural landscapes in Latin America, and continues to expand. This activity, deeply rooted in the culture and rural economy of the region, requires an urgent transformation if it is to become both more efficient and environmentally friendly. Silvopastoral systems that incorporate native trees and shrubs are instrumental for the productive rehabilitation of cattle production and for biodiversity conservation in agricultural landscapes. We discuss research progress and adoption of intensive silvopastoral systems in Colombia and Mexico. Intensive silvopastoral systems (ISS) are a sustainable form of agroforestry for livestock production that combines fodder shrubs planted at high densities (more than 10,000 plants ha−1), trees and palms, and improved pastures. High stocking and the natural production of milk and meat in these systems are achieved through rotational grazing with electric fencing and a permanent supply of water for the cattle. While milk and meat production and cattle reproduction are enhanced, production costs decline as external inputs are replaced by natural processes related to fertility and biological control. We also discuss the importance of the ISS with native trees for climate change adaptation and mitigation, the barriers for their adoption, and how these have been successfully addressed using payment for environmental services, special credits and technical assistance. Finally, we highlight the need for enhancing landscape connectivity by integrating SPS to conservation corridors with native species to promote biodiversity conservation and other environmental services demanded by society. 相似文献
14.
湖南省中隆国际·御玺景观工程是广州施工团队针对湖南长沙的环境条件,采用野生乡土树种大树全冠移植、树皮回收利用和植物水体净化等多项施工技术而建成的自然生态的楼盘绿地景观,并在此基础上进行高质量的园林绿化施工管理,具有较好的示范作用。 相似文献
15.
在人们日益向往乡村田园风光、渴望回归自然的当代社会,乡村作为人与自然接触最为密切的地理区域,如何在景观建设过程中,保持其原有人文特色和自然生态,同时实现一定的经济效益具有重要意义。本文以广东省广州增城北部三镇乡村景观生态建设为例,分析乡村景观的生态特征,探讨乡村景观生态规划建设的原则与方法。 相似文献
16.
Agroforestry and its application in amelioration of saline soils in eastern China coastal region 总被引：2，自引：0，他引：2
Some environmental problems, especially soil salinity hinder the regional sustainable development of eastern China coastal region. Salinity mainly comes from tide weave, seawater flooding and seawater intrusion. Over exploitation of groundwater,which is the result of unfitful land use systems, leads to seawater intrusion and salt concentration increase. Agroforestry systems can enrich soil fertility and prevent soil salinization, furthermore help maintain biodiversity and enhance productivity. For the intergrated multiple ecosystems the most critical issue is to select optimum tree species and rationally arrange these plants. The basics of this multiple ecosystem is that different plants will occupy variable ecological niches within an area, both in space and in soil depth.Shelterbelts and trees intercropping with agricultural crops are major types of the multiple ecosystem. Shelterbelts can reduce wind speed and consequently lessen evaporation and erosion of the soil, increase pasture growth by up to 60% on exposed sites, increase crop yields by up to 25%. Besides intercropping with jujube, other agroforestry multiple ecosystem such as forestry plus agriculture,forestry plus agriculture plus fishery, and forestry plus animal husbandry are the most appropriate ways to utilise land resource in this region. 相似文献
17.
The role of different agroforestry systems in the conservation of plant diversity and forest structure has not been directly
compared in many agricultural dominated landscapes. In this study, we investigated tree diversity and forest structure in
a complex agroforestry landscape traditionally grown for cocoa and mixed food crops and compared these to the natural forest
in southeastern Ghana. The study was carried out using 36 25 m × 25 m plots. There was significant difference [95% Confidence
Interval (95% CI)] in the native forest/non-crop tree species richness between the natural forest and the agroforest farmlands
but species richness was similar between the cocoa and mixed food crops agroforests. The density of native forest/non-crop
trees was significantly higher (P < 0.05) in the natural forest but similar between cocoa and mixed food crops agroforest. Similarly, the basal area of native
forest/non-crop trees was significantly higher (P < 0.05) in the natural forest but comparable between cocoa and food crops agroforest. Of the 20 most abundant native forest/non-crop
trees recorded, 12 of them showed significant responses (P < 0.05) to land use change with nine of the species significantly abundant in the natural forest relative to the agroforest
systems. Eighteen native forest/non-crop trees species in the agroforestry systems were commonly recorded as being used; 100%
of them being used as fuel wood with 83.3 and 77.8%, respectively, used as medicines and materials. The findings of this study
suggests that although complex agroforestry systems are a poor substitute for the natural forest the heterogeneous mosaic
landscape in which complex agroforestry forms part can be strategically managed to maximize the benefits of both sustainable
agriculture production and conservation of plant diversity by acting as buffer between protected areas and intensively managed
areas. 相似文献
18.
Quantifying plant response to ozone: a unifying theory 总被引：36，自引：0，他引：36
Reich PB 《Tree physiology》1987,3(1):63-91
Published information about the effects of ozone on plants and ecosystems is synthesized into a conceptual model to explain the response of evergreen conifers, deciduous hardwoods and agricultural crops to ambient levels of ozone pollution. The effects of ozone on carbon balance and growth of individual plants can be quantified on the basis of concentration, external dose (concentration x duration of exposure), or uptake. For an equivalent dose within a single growing season, agricultural crops are the most sensitive to ozone, with hardwoods intermediate and conifers least sensitive. In contrast, all species display a similar decline in photosynthesis and growth in response to equivalent total uptake or uptake per leaf life span, with trees somewhat less sensitive than agricultural crops on a calendar time scale, but slightly more sensitive on a relative (leaf life span) time scale. Among species, differences in ozone uptake and response can be predicted from differences in the inherent leaf diffusive conductance. 相似文献
19.
《中国林业科技(英文版)》2009,(1)
Salt-affected soils extensively distribute on the earth.Although the causes are various,generally speaking salinization occurrence results from the accumulation of free salts to an extent that causes degradation of vegetation and soils.Besides,irrational human practices have increased soil salinity by allowing excess recharging of groundwater to change the natural balance of the water cycle in the landscape. This reduces the suitability to plant growth and increases the potential for other forms of land ... 相似文献
20.
The widespread removal of native trees from the agricultural zone and replacement with annual crops and pastures is a major cause of dryland salinity in Australia. It has been recognised that a large proportion of the landscape needs to be replanted to trees to prevent further salinisation. However, for much of the agricultural zone, agroforestry is not an option due to lack of species that can viably generate the products currently demanded by the market. The emerging carbon market may provide a new agroforestry option for landholders, through carbon sequestration. This analysis assesses the viability of growing trees for the purpose of selling carbon credits, from a landholder’s perspective. Benefits of trees in preventing the onset of dryland salinity are accounted for. Two regions in Western Australia; a low rainfall (330 mm/year) region and a medium rainfall (550 mm/year) region, are analysed. At the expected carbon price of A$15/tCO2-e, growing trees for carbon is not a viable alternative for landholders in the low rainfall region, due to low sequestration rates. In the medium rainfall region, growing trees for carbon and timber is a viable alternative; however the opportunity costs of land mean the carbon price would still need to be higher than expected for growers to choose this alternative. Accounting for the salinity prevention benefits makes growing trees a more attractive investment for landholders in both regions. However in both regions, even after accounting for salinity benefits, the price of carbon would need to be A$25–A$46/tCO2-e higher than expected to make growing trees a worthwhile investment. 相似文献