Plant species characteristics and vegetation dynamics in the tropics

This paper attempts a differentiation of forest and savanna and an assessment of changes in these vegetation types based on their characteristic plant species. Farming activities are recognised as a main factor influencing the dynamics of the vegetations. The occurrences of plant species on selected fallow communities at various stages of development, along the regional boundary between forest and savanna, were therefore analysed. The analyses show that plant species not only differentiate between the two, but also suggest changing trends in their character. They show that forest and savanna are to a large extent, species specific, and that over a short term period, farming activities are capable of extending the present limit of savanna towards the forest areas.     

A new thermal performance index for dwelling roofs in the warm humid tropics

This research aims to find a scientific rating scheme for roof system for the warm humid tropics. The overall air-to-air thermal transmittance (U-value) or thermal resistance (R-value) of roof are most widely used properties, but these are based on steady-state heat conduction and do not respond to changing conditions of climate, design and comfort needs. The paper presents a new thermal performance index, which is based on thermal comfort and actual thermal performance of a roof design option. It provides a basis for identifying the optimum roof design for unconditioned and acclimatised regimes. A review of the acceptable limits of ceiling surface temperature is presented. The mathematical modelling for predicting performance of roof based on admittance procedure and derivation of thermal performance index is described. In the proposed scheme the galvanized iron roof is given 0% rating and the roof satisfying the comfort needs for the given climate is rated as 100%. Illustrative examples of built roofs or design options are taken from India and Australia. It clearly shows that the roofs with the highest thermal resistance are not necessarily optimum solutions.     

热带、亚热带近海设施生物污损特点与研究展望

生物污损现象会严重影响海洋设施的安全与使用寿命,对涉海经济活动产生极大危害。在热带和亚热带海区,引发生物污损的种类主要为牡蛎和藤壶,其次是珊瑚和水螅。今后的研究应着重于弄清大型污损生物对腐蚀的影响,建立污损生物数学生态模型,开展海洋恢复生态学研究工作。     

Solid waste management in the tropics — a case study of the Nigerian urban environment

A study of solid municipal waste management in five conjested cities in the Eastern states of Nigeria was carried out. Random sampling of waste piles show that the percentage composition by weight of garbage range between 32–56%, rubbish 8–30%, Ash/Dust 15–35% and Miscellaneous wastes 4–12%. The wastes were of peculiar nature but varied only in quantity with each city. Interviews and questionnaire reports show that the Environmental Protection Agencies are still in an infant stage of operation and require improved funding by government and also private sector participation. A public enlightenment campaigns is recommended for proper education of the public on modern ways of garbage disposal. Poor composting of solid wastes in landfills located near highways is discouraged. Solid waste recycling and reclamation using an advanced tropical composter equipped with solar collectors or a continous flow digester are recommended.     

Ontogenic variation of biologically active metabolites ofPteridium aquilinum (L. Kuhn) pterosins A and B,and ptaquiloside in a bracken population of the tropical andes

A negative correlation has been found between the amounts of pterosins A and B and ptaquiloside per biomass unit, and the growth stage of the blade of bracken. Their concentration decreased progressively from the crozierto the mature frond, where it attained less than 5% of the initial value. The growth was measured following the total blade length, its height, moisture content, and time of emergence from the soil surface. Quantitation of these compounds was achieved by HPLC using a water extraction, methylene chloride treatment, and silica gel microcolumn cleanup sequence. Pterosins were unevenly distributed in the blade, whereas ptaquiloside maintained a constant concentration throughout. Rhizomes contained only minor amounts of these compounds. Their possible role as semiochemicals in bracken is discussed.     

Role of manures and crop residue in alleviating soil fertility constraints to crop production: With special reference to the Sahelian and Sudanian zones of West Africa

In the West African semi-arid tropics (WASAT), continuous cultivation leads to drastically reduced levels of soil organic matter. Such reductions in the level of soil organic matter have resulted in decreased soil productivity. The addition of organic materials either in the form of manures or crop residue has beneficial effects on the soils' chemical and physical properties. For many of the countries in this region, the amounts of nutrients in crops and crop residue are often several orders of magnitude higher than the quantity of the same nutrients applied as fertilizers. The return of the crop residue for soil fertility improvement cannot be overstressed. It is essential that more information on the rates of organic matter decomposition as well as the many reactions between products of organic matter decomposition and the soil under WASAT conditions be made available.