Application of age-structured production models to assess oyster Striostrea margaritacea populations managed by rotational harvesting in KwaZulu-Natal, South Africa     

de Bruyn  Paul A.; Moloney  Coleen L.; Schleyer  Michael H. 《ICES Journal of Marine Science》2009,66(2):408-419

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Growth performance of exotic and indigenous tree species in saline soils in Turkana, Kenya     

Gufu Oba  Inger Nordal  Nils C. Stenseth  Jrn Stave  Charlotte S. Bjor  Josphat K. Muthondeki  William K. A. Bii 《Journal of Arid Environments》2001,47(4):499

In the arid zone of central Turkana, north-western Kenya, where soil salinity affects 15–20% of the rangelands, growth performances of trees planted in saline soil rehabilitation trials have not been evaluated. Tree-planting trials have emphasised exotic species over indigenous ones. However, advantages and disadvantages of promoting exotic tree species have not been examined. The current study was aimed at evaluating growth performance of seven exotic and nine indigenous tree species used in saline soil rehabilitation trials. The tree species were established from 6-month-old saplings using microcatchments (FT1) from 1988 through 1990 and pitting treatment (FT2) from 1989 through 1992. The soils in FT1 and FT2 treatments were moderately to highly saline. The exotic tree species produced greater cover and volume during the first year (FT1) but by the second year, production was not sustained due to greater mortality (FT1 & FT2). The indigenous species in general had higher survival rates. Relative growth rates (RGR) of exotic and indigenous species did not differ (FT1 & FT2). Tree mortality was negatively correlated with RGR for exotic species in FT1 but not for indigenous ones. However, changes in plant performance were not in response to salinity alone. Rather, water scarcity superimposed on soil salinity might have influenced plant growth performance. Greater water and salinity stress and subsequently greater mortality in exotic species provided a more convincing reason for promotion of indigenous tree species. In the future, knowledge of salinity distribution and selection of indigenous species to match this will be a better way of rehabilitating sites affected by soil salinity in the arid zone of central Turkana, north-western Kenya.  相似文献   

The impact of small-scale wood harvesting on neem Azadirachta indica A. Juss stands in the coastal savanna of Ghana     

Michael O'Neal Campbell 《Area》2005,37(1):8-16

Although the introduced neem tree Azadirachta indica A. Juss is a very important energy source in the coastal savanna of Ghana, the sustainability of small-scale wood harvesting (SSWH) has not been investigated with regard to this species. This paper assesses the sustainability of SSWH on neem stands in the coastal savanna, using a socio-economic and ecological survey. The results show that SSWH, incorporating coppicing, stand tolerance, balanced with total bole cutting and root removal, and based on socio-cultural supports, has created a modified yet sustainable system of SSWH. It is concluded that these systems may contribute to tree stand conservation.  相似文献   

The Effects of Annual Harvesting on the Subsequent Phytomass and Species Composition of Grassland and Fernland: A Hong Kong Case   总被引：1，自引：0，他引：1  

R.D. Hill  M.R. Peart  Guan Dong-Sheng 《Singapore journal of tropical geography》2004,25(1):77-91

Anthropogenic grasslands mixed with fern and shrubland, on scales from metres to kilometres, are widespread in tropical Southeast Asia, and especially in southern China and adjoining regions where harvesting for domestic fuel is a major factor in their maintenance. Baseline surveys in grassland and fernland in 1989–90 and resurveys in 2001 of three 6 × 20 m plots in Wong Chuk Yuen, Hong Kong, showed substantial change in species composition and total aboveground phytomass as a result of annual harvesting, with more pronounced change in the fernland. Under harvesting pressure, the species composition of the grassland changed considerably, though the proportions of the various life‐forms did not. Ischaemum spp. and Miscanthus floridulus increased whereas Themeda gigantea died out while the proportion of other grass species remained much the same. Under the same regime the species composition and life‐forms of the fernland changed markedly. The proportion of Dicranopteris fern dropped substantially, though still comprising a third of the phytomass by 2001. The shrub Melastoma survived harvesting. A firebreak cut in the fernland became grassy under annual harvesting and remained grassy six years after cutting ceased. The annual harvests from the growth‐years 1991–2000 showed a substantial though variable increase in total phytomass. Analyses relating harvested phytomass with various climatic parameters showed no significant correlations. Some possible reasons for this are suggested. Although annual harvesting was clearly sustainable over the ten years of observation, the question of continued sustainability on sites harvested for centuries, the situation in much of southern China and parts of upland mainland Southeast Asia, remains unresolved.  相似文献   

2003年新疆地质矿产勘查主要成果及今后工作建议     

董连慧 《新疆地质》2004,22(1):1-3

2003年我区地质勘查工作上了一个新台阶，提交了可供开发的资源量，延长了矿山的服务年限．发现了一大批有进一步工作价值的矿产地和矿化线索，基础地质研究也取得许多新认识．今后地质勘查工作要继续坚持“主攻天山，深化阿尔泰山．开拓昆仑、阿尔金山”的总体部署思路，遵循“区划、区调、矿产普查、物化探和科研五统一”的工作原则，针对铜、金、富铁、富铅锌、富锑等国家和自治区急需的矿产及相应的重要矿床成因类型，以寻找大型-超大型矿床为突破口．兼顾可开发的中小型矿床．  相似文献   

柴达木盆地油气资源战略调查成果与下步工作重点     

甘贵元  尹成明  张冰清  孟丽  赵明君  韩秦鹏 《地质通报》2006,(Z2)

柴达木盆地是中国七大含油气陆相盆地之一,油气资源总量丰富,勘探潜力巨大。柴达木盆地油气资源战略调查及评价项目研究工作开展2年以来,取得了重要的成果和认识:德令哈断陷内大面积分布中—下侏罗统烃源岩;盆地东部石炭系具有生烃能力;盆地北缘东段红山地区地震勘探采集到较好品质的资料;狮子沟地区天然地震勘探得到初步成果;综合应用地震、钻井等资料,确定了狮子沟构造的深层构造。下一步工作的重点是进一步加强盆地东部石炭系评价的力度,深化狮子沟、红山、德令哈等地区深层构造的研究及圈闭资源量评价工作。  相似文献   

Contrasting water management techniques in Tunisia: towards sustainable agricultural use     

Jennifer Hill  Wendy Woodland 《The Geographical journal》2003,169(4):342-357

Tunisia is a marginal country hydrologically and it has adopted a number of distinctive methods of water management for agriculture. The central region supports modern dam irrigation, whilst traditional rainwater harvesting is practiced in the south. These contrasting techniques are described and evaluated in terms of sustainability using empirical field data and secondary literature for two study sites. Research focuses primarily on the physical environment, but socio-cultural and economic viability are also examined. Analysis indicates that traditional water management advantageously partitions the continuum dividing hazards and resources through subtle manipulation of the environment. A potentially hazardous environment is rendered secure by resourceful water management based on community action and cumulative knowledge. This practice minimizes community dependency and local economic imbalance. With dam irrigation, carrying capacity is established more forcibly by centralized control in order to place society within world markets. An almost total break from environmental variability is made in the short term, but this can lead to disequilibrium over longer durations. Additionally, the spatial and social distributions of development are uneven. In Tunisia, maintenance of traditional methods can reduce the negative impacts caused by modern programmes and support their positive characteristics. A mix of both methods offers a foundation to sustainable water supply in the new millennium.  相似文献   

The implementation of fog water collection systems in South Africa     

J. Olivier  C. J. de Rautenbach   《Atmospheric Research》2002,64(1-4)

Two fog water collection systems (FWCS) have been implemented in South Africa. Both are located in areas where communities experience acute water shortages but which are prone to frequent fog episodes. The first was located at a high elevation site at the Tshanowa Junior Primary (JP) School in the Soutpansberg located in the Northern Province and the other near a small rural community at Lepelfontein along the West Coast. The former represents a mountainous site, while the latter is located on a low level coastal plain. The principal aim of the projects was to implement operational FWCSs to supply the communities with water. During the period 1999 to 2001 the total recorded cloud water yields at the Tshanowa JP School and Lepelfontein water collection sites were in the region of 72 422 and 148 691 l, respectively. This is equivalent to just over 2 l m⁻² day⁻¹ at the Tshanowa JP School and 4.6 l m⁻² day⁻¹ at the Lepelfontein site. Despite the relatively low average daily yields recorded, the total water volume collected on a particular day may be considerable. In fact, at both sites the maximum daily yield exceeded 3800 l. Fog deposition accounted for around 25% and 88% of the total water yield measured at the Tshanowa JP School and Lepelfontein sites, respectively. Both experiments indicated that fog water collection holds considerable potential as an alternative water source in the mountainous regions and along the West Coast of South Africa.  相似文献   

情景分析法在工业用地置换中的应用 ——-以福建省长汀腾飞经济开发区为例     

宗跃光  徐建刚  尹海伟 《地理学报》2007,62(8):887-896

从土地综合价值出发, 将一般用于宏观研究的情景分析法引入微观领域, 根据社会、经济、环境效益的最佳、最差和最可能情景模式, 确定工业用地和居住用地开发的情景过程及其对比特征。研究表明, 福建省长汀腾飞经济开发区最可能情景下的工业收支比经过16 年才能达到平衡, 居住和商业用地最可能情景下收支比可以维持在3~5 左右的稳定发展水平, 在前5 年, 居住用地的收支比8~10 倍于工业用地, 然后差距逐步缩小, 降低到20 年期2 倍的水平。这一情景表明, 腾飞经济开发区要缩小规模, 分步、分阶段地把没有进行开发的闲置土地和3 年左右依然处于亏损的企业用地置换出来, 工业用地应该由目前的2.5 km² 缩减 到1~1.5 km²。  相似文献   

Agricultural management impacts on groundwater: simulations of existing and alternative management options in Peninsular India          下载免费PDF全文

Daniel R. Dourte  Sanjay Shukla  Dorota Z. Haman  M. Devender Reddy  M. Uma Devi  Adusumilli Mani 《水文研究》2014,28(19):5021-5033

Understanding the principal causes and possible solutions for groundwater depletion in India is important for its water security, especially as it relates to agriculture. A study was conducted in an agricultural watershed in Andhra Pradesh, India to assess the impacts on groundwater of current and alternative agricultural management. Hydrological simulations were used as follows: (1) to evaluate the recharge benefits of water‐harvesting tillage through a modified Soil and Water Assessment Tool (SWAT) model and (2) to predict the groundwater response to changing extent and irrigation management of rice growing areas. The Green–Ampt infiltration routine was modified in SWAT was modified to represent water‐harvesting tillage using maximum depression storage parameter. Water‐harvesting tillage in rainfed croplands was shown to increase basin‐scale groundwater recharge by 3% and decrease run‐off by 43% compared with existing conventional tillage. The groundwater balance (recharge minus irrigation withdrawals), negative 11 mm/year under existing management changed to positive (18–45 mm/year) when rice growing areas or irrigation depths were reduced. Groundwater balance was sensitive to changes in rice cropland management, meaning even small changes in rice cropland management had large impacts on groundwater availability. The modified SWAT was capable of representing tillage management of varying maximum depression storage, and tillage for water‐harvesting was shown to be a potentially important strategy for producers to enhance infiltration and groundwater recharge, especially in semi‐arid regions where rainfall may be becoming increasingly variable. This enhanced SWAT could be used to evaluate the landscape‐scale impacts of alternative tillage management in other regions that are working to develop strategies for reducing groundwater depletion. Copyright © 2013 John Wiley & Sons, Ltd.  相似文献