Summary1 Leaf demography was examined for trees of various heights over a 3.7-year period in a Malaysian rain forest. We compared demography between upper and lower parts of the crown and its relation to height. The results were analysed at the stand level by pooling several trees of various shade-tolerant species, as well as three species for which multiple individuals were sampled. 2 Photon flux density was generally higher in the upper than in the lower crowns. Leaf production rate and leaf loss rate were faster, and number of leaf cohorts and median leaf life span were therefore lower, in the upper crowns of most trees. Faster rates of leaf loss and shorter life spans were associated with increasing height, although leaf production rate was unaffected. 3 Leaf life span and specific leaf area were plastic traits which decreased with height within several shade-tolerant tree species, indicating functional convergence. 4 Vertical distribution of leaf biomass was almost even in the stand. Because leaf life span was shorter in the upper canopy, these leaves contributed most to litter production. The vertical structure of the forest stand was therefore maintained through dynamic processes in trees of various heights over short time-scales.

The general air quality of Malaysia since 1970 has deteriorated. Studies have shown that should no effective countermeasures be introduced, the emissions of sulfur dioxide, nitrogen oxides, particulate matter, hydrocarbons and carbon monoxide in the year 2005 would increase by 1.4, 2.12, 1.47 and 2.27 times, respectively, from the 1992 levels.

On a monoaxial erect stem of trees with continuous leafing, the older leaves would be quickly shaded by newer (upper) leaves if the trees did not have any compensating mechanisms to avoid self-shading. We hypothesized that the dynamic adjustment of leaf deployment, by regulating the patterns of leaf growth and by changing leaf orientation as leaves age, is a compensating mechanism. To verify this hypothesis, we analyzed leaf development and crown structure of a Far Eastern tropical pioneer tree species, Macaranga gigantea (Rub. f. et Toll.) M.A., which unfolds huge leaves directly on a monoaxial stem with a short leafing interval. Petioles required more than 90 days for full elongation and the petiole angle (the angle between the petiole axis and the vertical) increased over time. Thus, a series of leaves on a stem progressively increased in petiole length and petiole angle from the youngest to the oldest leaves. This is beneficial because it decreases the degree of self-shading within a crown. A simulation suggested that an average crown for the M. gigantea seedlings, which was constructed using empirically determined morphometric data cannot entirely eliminate self-shading within the crown. But an average crown had a lower degree of self-shading, with less dry mass allocation to the petiole than simulated crowns that were identical to the average crown in all but one respect: they had constant petiole lengths or petiole angles. We conclude that M. gigantea seedlings reduce self-shading by regulating elongation of the petiole and changes in the petiole angle with increasing leaf age.

Allometry of shoot extension units (hereafter termed "current shoots") was analyzed in a Malaysian canopy species, Elateriospermum tapos Bl. (Euphorbiaceae). Changes in current shoot allometry with increasing tree height were related to growth and maintenance of tree crowns. Total biomass, biomass allocation ratio of non-photosynthetic to photosynthetic organs, and wood density of current shoots were unrelated to tree height. However, shoot structure changed with tree height. Compared with short trees, tall trees produced current shoots of the same mass but with thicker and shorter stems. Current shoots with thin and long stems enhanced height growth in short trees, whereas in tall trees, thick and short current shoots may reduce mechanical and hydraulic stresses. Furthermore, compared with short trees, tall trees produced current shoots with more leaves of lower dry mass, smaller area, and smaller specific leaf area (SLA). Short trees adapted to low light flux density by reducing mutual shading with large leaves having a large SLA. In contrast, tall trees reduced mutual shading within a shoot by producing more small leaves in distal than in proximal parts of the shoot stem. The production of a large number of small leaves promoted light penetration into the dense crowns of tall trees. All of these characteristics suggest that the change in current shoot structure with increasing tree height is adaptive in E. tapos, enabling short trees to maximize height growth and tall trees to maximize light capture.

Recycling of solid wastes should be integrated into the existing and future waste management plans so as to yield the benefits of conservation of natural resources, saving of fossil fuels and prolonging lifespan times of disposal sites. This paper discusses the current status of waste recycling in Malaysia and its future prospects. Although a large amount of Malaysian wastes could be recycled, less than 5% of the total (almost 10 000 t d‐1) is actually separated and recycled. There is a good demand for waste plastics, paper and glass, with resale prices of about US$60 t‐1, US$44 t‐1 and US$32 t‐1, respectively. Recovery of only 5% of the available waste plastics, paper and glass is estimated to yield a total of about US$3.4 million y‐1. Recommendations to increase recycling are discussed in the paper.