The Role of Mangroves in Retaining Penaeid Prawn Larvae in Klang Strait,Malaysia

The mangrove-fringed Klang Strait, Malaysia, retains approximately 65 billion penaeid prawn larvae annually prior to their settlement in coastal nursery grounds. This phenomenon appears to be due principally to tidal currents and lateral trapping in mangrove-fringed channels, the wind playing an insignificant role.     

迎面火与主地表火相互作用的实验研究

为了研究地表火卷吸作用的范围和迎面火与主火相互作用的机理 ,在大空间室内实验室进行了实验研究 .在该实验室实验可以避免环境风和环境温度变化的影响 .研究结果表明 :(1)在火头前方有明显的逆风区存在 .在逆风区下部的逆风风速要比上部的大 ,而且当高度达到某一数值时 ,逆风就不明显了 ;(2 )迎面火与主火之间即使相距较远也存在相互作用 .当它们相互接近到一定程度时 ,彼此相互吸引 .这使得火的蔓延速度显著升高 .对于火线火强度为 16 0kW·m-1地表火来说 ,蔓延速度增加2 7% .     

生物措施治理水土流失项目管理信息系统研发浅议

研制开发生物措施治理水土流失项目管理信息系统,可以利用现代技术提升项目管理工作,对项目建设和推广有着十分重要的意义。本文介绍了生物措施治理水土流失项目管理信息系统研发的目的任务、技术思路、运行环境及系统的主要功能。     

不同植被恢复模式土壤结构特征与健康评价

对湘西女儿寨流域不同植被恢复类型的土壤结构特征研究和健康评价的结果表明:荒草灌丛容重最高,人工林土壤容重高于天然林及混交林;对土壤孔隙状况的改善作用表现为林分类型优于荒草灌丛类型,天然林优于人工林,0~20 cm土层优于20~40 cm土层;土壤团聚体平均重量直径以油桐人工林、杜仲人工林最高,马尾松天然林、毛竹杉木混交林其次,而润楠次生林、荒草灌丛、杉木人工林较低;各层土壤团聚体分形维数值大小排序为:毛竹杉木混交林>马尾松天然林>荒草灌丛、润楠次生林>杜仲人工林>油桐人工林>杉木人工林;土壤结构健康综合评价的灰色关联分析结果表明,土壤结构以荒草灌丛最差,油桐人工林最好,其余类型介于两者之间.研究结果可为女儿寨流域及我国类似生态脆弱区的植被恢复与重建提供一定依据和参考.     

The role of shelter in Australia for protecting soils,plants and livestock

The purpose of this review is to examine the current knowledge of the role of trees in providing shelter for pastures, crops, and livestock, for controlling erosion of soils and improving productivity and sustainability of agricultural production in Australia — and the extent to which this knowledge has been applied.Land degradation — tree loss and associated soil salinity, water and wind erosion, soil acidification, soil structural decline and nutrient degradation — is evidence that our primary production systems are not sustainable. We have sought increased production without proper consideration of the ecological context of that system. About half of Victoria's crop and pasture lands are affected or at risk, and in Western Australia about 25% of the cleared agricultural land is wind-eroded and 60% is potentially susceptible, salinity affects 0.43 m ha and half of the divertible surface water is affected by salinity. Similar problems occur in other States. At least 43 m ha or 13% of our rangelands are seriously degraded by wind erosion caused by overgrazing, often coinciding with drought or a run of drier years.Minimum tillage and stubble management for erosion control in cropping has been a major extension and research activity in Australian agriculture. Severe weather, combined with imperfect adoption of appropriate grazing and crop management systems, shows the weakness of complete reliance on these methods of erosion control. An effective system must accommodate the impact of extreme events, which are the most damaging. However, the complementary use of windbreaks to reduce soil erosion is rare, and their establishment has not been promoted, despite the wide-spread adoption of this technology by other countries.In the cropping and higher rainfall grazing areas, the systematic planting of 10% of the land in a net of shelterbelts/timberbelts/clusters could achieve a 50% windspeed reduction; this would substantially improve livestock and pasture production in the short and long-term. Wind erosion could be dramatically reduced and crop production probably increased by the use of windbreaks. Wheat and oat yield at Rutherglen (Victoria), and lupin yield at Esperance (Western Australia), were increased in the sheltered zone by 22% and 47%, and 30%, respectively.In semi-arid and dry temperate areas, planting of 5% of the land to shelter could reduce windspeed by 30–50% and soil loss by up to 80%. This planting would also contribute substantially to achieving other objectives of sustainable agriculture. Agroforestry — particularly timberbelts applications — will be important in the long-term strategy for achieving revegetation. If some of the trees yield a marketable product then the adoption of the system will be more readily achieved.In the arid (pastoral) areas there is an urgent need to promote the ethic that preservation and improvement of the perennial grass and shrub vegetation is critical for the protection of the soil and maintenance of land capability. Control of animal grazing remains the sole means of preventing erosion in much of this zone. While satellite imagery allows us to assess the condition of leasehold lands, we have failed to achieve stocking policies that will halt the degradation of our rangelands.     

Comparing genetic diversity in agroforestry systems with natural forest: a case study of the important timber tree Vitex fischeri in central Kenya

It is possible that current tree domestication practices undertaken by farmers reduce the genetic base of tree resources on farms, raising concerns regarding the productivity, sustainability and conservation value of agroforestry ecosystems. Here, we assessed possible changes in genetic variation during domestication in the important and heavily utilised timber species, Vitex fischeri Gürke (syn. Vitex keniensis), by comparing geographically proximate forest and farm material in central Kenya. Employing RAPD analysis, a total of 104 polymorphic markers revealed by five arbitrary primers were scored in a total of 65 individuals, 32 from forest and 33 from farmland. Despite concerns of possible genetic erosion, forest and farm stands did not differ significantly in levels of genetic variation, with H values of 0.278 and 0.269, respectively. However, Mantel tests did reveal greater geographically related associative genetic structure among individuals in farm rather than forest material, with r _M values of 0.217 and 0.114, respectively. A more detailed analysis of structure suggested this could be due to local variation in origin of some on-farm trees. Implications of data for the genetic management of V. fischeri stands during farmer-led tree domestication activities are discussed. At present, there appears little reason to reject on-farm V. fischeri as a source of germplasm for future on-farm planting or for conservation purposes, although this situation may change and will require monitoring.     

Ecological Benefit of Reforestation in a Severely Degraded Red Soil Region

Guifeng, Yiyang County, belongs to a seriously degraded red soil region. In 1991, Pinus elliottii and Lespedaza spp. were the species selected for the establishment of a mixed forest in the area. The results of an investigation of the soil system in a 12-year-old forest indicated the following: (1) Organic matter and total nitrogen of the forest soil to a depth of 40 cm were 88.0 and 36.0% higher, respectively, than those of a control plot; total phosphorus and available phosphorus were 40.9 and 22.3% higher than those of the control; available potassium contents were 8.13% lower than those of the control. (2) Soil aeration and the soil air regime improved. (3) Proteinase, catalase, and urease in the forest soil to a depth of 40 cm were usually higher than those in the control plot and decreased with soil depth. Translated from Acta Agriculturae Universitatis Jiangxiensis, 2005, 27(1) (in Chinese)     

Protective effect of floor cover against soil erosion on steep slopes forested with <Emphasis Type="Italic">Chamaecyparis obtusa</Emphasis> (hinoki) and other species

 We evaluated the protective effects of floor cover against soil erosion in three types of forest located on steep slopes under a humid climate: 22- and 34-year-old Chamaecyparis obtusa (hinoki), 34-year-old Cryptomeria japonica (sugi), and 62-year-old Pinus densiflora (red pine) stands. We measured sediment transport rates (sediment mass passing through one meter of contour width per millimeter of rainfall), using sediment traps, before and after removing floor cover. Raindrop splash erosion was dominant in the experimental stands. Floor cover percentage (FCP) during the preremoval stage varied from 50% to 100% among the four stands, and sediment transport rates ranged from 0.0079 to 1.7 g m⁻¹ mm⁻¹. The rates increased to 1.5–5.6 g m⁻¹ mm⁻¹ immediately after removing floor cover, and remained high throughout the experiment. The presence of physical cover near the ground has a crucial effect on sediment transport on forested slopes. The protective effect ratio (the ratio of the sediment transport rate in a control plot to that in the removal plot) in a young hinoki stand, in which the FCP decreased markedly, was 0.3 at most, which is close to the rate for bare ground. The protective effect ratio in the red pine stand was ≤0.003. We concluded that the protective effect of floor cover in undisturbed forests in Japan differs by over two orders of magnitude, based on comparisons with previous studies. Received: March 11, 2002 / Accepted: August 16, 2002 Present address: Department of Forest Site Environment, Forestry and Forest Products Research Institute, Ibaraki 305-8687 Japan Tel. +81-298-73-3211; Fax +81-298-74-3720 e-mail: miura@affrc.go.jp Present address: Department of Forest Site Environment, Forestry and Forest Products Research Institute, Ibaraki 305-8687 Japan Tel. +81-298-73-3211; Fax +81-298-74-3720 e-mail: miura@affrc.go.jp Acknowledgments This study was supported by the Research Council of the Ministry of Agriculture, Forestry, and Fisheries, of Japan. We thank H. Ujihara, S. Ujihara, and M. Ogasawara in Otoyo, Kochi, who provided the experimental stands used in this study. We also thank K. Hirai, S. Kuramoto, E. Kodani, and the rest of the staff at the Shikoku Research Center, Forestry and Forest Products Research Institute, for their help in conducting the experiments. Correspondence to:S. Miura     

Effect of alley cropping on soil aggregate stability of a tropical Alfisol

The beneficial effect of organic matter on soil aggregate stability is well documented. Alley cropping has been suggested as a possible alternative to maintain soil organic matter content in cropping systems without fallowing the land. The objective of this study was to asses the effect of alley cropping on dry and wet soil aggregate stability on land degraded by shifting cultivation. The aggregate size distribution by dry sieving, aggregate stability by wet sieving, soil organic Carbon content and soil bulk density were measured following two and three years of alley cropping with Gliricedia (Gliricidia sepium) and Pigeon pea (Cajanas cajan) in a tropical Rhodustalf. Alley cropping increased the mean aggregate diameter and water stability of soil aggregates. The mean aggregate diameter obtained from dry sieving increased from 1.3 mm of the control to 2.68 and 3.11 mm after three years in Pigeon pea and Gliricidia alley cropped plots, respectively. This is an indication of resistance to wind erosion in alley cropped plots. The wet aggregate stability which shows the resistance to erosion by water also increased in alley cropped plots. These increases were significant after three years of hedge row establishment. The increase in soil organic C in alley cropped plots contributed to the higher dry and wet aggregate stability, and decreased soil bulk density. The improvement was higher in plots alley cropped with Gliricidia than Pigeon pea. This study shows the importance of ally cropping in increasing aggregate stability of degraded sandy soils which in return reduce erosion by wind and water.     

灌木林对地表风况及空气动力学参数影响的野外调查研究——以丰宁满族自治县小坝子乡为例

通过野外实地调查和定位观测,系统研究了灌木林盖度和高度对地表风况及空气动力学参数的影响。结果表明:风速轮廓线受灌木林覆盖度和高度的影响显著;风蚀率随灌木林覆盖度的减少呈指数增加,灌木林高度对土壤风蚀影响相对较小。空气动力学粗糙度及零风速平面位移高度均与灌木林覆盖度之间呈幂函数关系。灌木林高度对空气动力学粗糙度的影响不明显。