Both light quantity and quality affect the development and autoecology of plants under shade conditions, as in the understorey of tropical forests. However, little research has been directed towards the relative contributions of lowered photosynthetic photon flux density (PPFD) versus altered spectral distributions (as indicated by quantum ratios of 660 to 730 nm, or R:FR) of radiation underneath vegetation canopies. A method for constructing shade enclosures to study the contribution of these two variables is described. Three tropical leguminous vine species (Abrus precatonus L., Caesalpinia bondicela Fleming and Mucuna prunens (L.) DC) were grown in two shade enclosures with 3–4% of solar PPFD with either the R:FR of sunlight (1.10) or foliage shade (0.33), and compared to plants grown in sunlight. Most species treated with low R:FR differed from those treated with high R:FR in (1) percent allocation to dry leaf weight, (2) internode length, (3) dry stem weight/length, (4) specific leaf weight, (5) leaf size, and (6) chlorophyll a/b ratios. However, these plants did not differ in chlorophyll content per leaf dry weight or area. In most cases the effects of low R:FR and PPFD were additional to those of high R:FR and low PPFD. Growth patterns varied among the three species, but both low PPFD and diminished R:FR were important cues in their developmental responses to light environments. This shadehouse system should be useful in studying the effects of light on the developmental ecology of other tropical forest plants.

Earthworm populations in grassland and plantations in the area of Bulolo, Papua New Guinea were compared with populations in nearby undisturbed rain forest. The grasslands had been maintained by burning for many years. The Pinus plantation had been developed on a burned grassland site and the Araucaria plantation on a site which had been cleared of secondary forest.

The grasslands and the Pinus plantation supported moderate populations of exotic earthworms including Pontoscolex corethrurus, but no indigenous species. The Araucaria site supported a native species, Amynthas zebrus only, which was also found together with two other native species at very low density in rain forest.

Exotic earthworm species widespread throughout the tropics, were present in disturbed soils and formed moderately high density populations in burned grasslands. There was no evidence that they displaced native Megascolecidae in rain forest.

An investigation of seasonal changes in litterfall in a dense stand of the invasive tropical shrub Mimosa pigra was carried out in northern Australia between October 1984 and December 1986. Total annual litterfall averaged 758 g m−2, close to the value predicted for the latitude and altitude of the site. Leaf litter formed 56.6% of this total, woody material 22.7%, and reproductive material 20.7%. Total litterfall was strongly seasonal, at a maximum in the late wet season or early dry season, and at a minimum late in the dry season. A broadly similar pattern was shown by the various components of the litter, except for woody litterfall, which followed no strong seasonal trend. Variation in the amount of available soil moisture, as calculated from a simple water balance model, accounted for much of the variation in the components of litterfall.

The proportion of all initiated flower heads which produce seeds was estimated to be between 2.1 and 4.5%. The mean annual seed fall was 9103 m−2, nearly two orders of magnitude higher than most native shrub populations, and it is argued that this is partly a result of the absence of natural enemies in the introduced range.

Soil water potentials were measured weekly by psychrometers at 20 cm depth during the dry season in a tropical moist forest on Barro Colorado Island, Panama. There was a persistent gradient of decreasing soil moisture from gap centre to gap edge to adjacent understorey at both a large and a small gap. On both a north-south and an east-west transect, the soil was drier (water potentials were more negative) on an upland surface than on moderate slopes. This trend was reflected in the predawn, total water potentials of shallow-rooted Psychotria horizontalis and deep-rooted Trichilia tuberculata measured in the understorey during the last two months of the dry season. P. horizontalis from the wettest sites on the transects had higher osmotic potentials at full hydration and at zero turgor, indicating less drought resistance than for conspecifics from the driest sites.

Malaysia is establishing large-scale plantations for reforestation and the production of wood for pulp and paper as well as for light construction. The main species used currently is the exotic legume Acacia mangium. The above-ground biomass, litter production and litter accumulation in a four-year-old stand in Peninsular Malaysia were studied. The mean diameter at breast height (dbh) was 12 cm. The mean annual increment (MAI) in dbh of individual trees ranged from 0.9 to 5.1 cm while MAI in height of sample trees ranged from 2.9 to 5.5 m. The total above-ground biomass of the stand was 90.4 t ha−1, consisting of 57.6 t stem, 14.1 t branch and 5.4 t leaf. Litter production averaged 10.23 t ha−1 yr−1 with leaf litter making up 87.4% of the total. Leaf litter accumulation amounted to 6.64 t ha−1 and the turnover constant of leaf litter was estimated at 1.35. The high productivity is discussed in relation to the high turnover of foliage and the low turnover of litter.

Fish communities of a fourth order stream impounded by a weir were studied in Southern Nigeria. Fifty-eight species were recorded of which 90% occurred upstream while reservoir and downstream accounted for 48% and 43% respectively. The distribution of some fish families indicated the effects of habitat alterations caused by reservoir and downstream conditions. The fauna upstream was different from that of reservoir and downstream. Relative abundance of non-cichlids common to reservoir and downstream showed 42% similarity. The longitudinal distribution of three non-cichlid populations was different in reservoir and downstream. Non-cichlid species richness was almost similar in reservoir and downstream, but its general diversity and evenness were higher in reservoir than its downstream. Fish community changes in this stream are discussed.

Dormancy and germination ecology of two Harpagophytum species (Pedaliaceae) from an open Acacia savanna in Botswana were investigated. The maintenance of dormancy is governed partly by the seed coat but mainly by the endosperm and the embryo itself, as demonstrated by removal of the endosperm. Dissemination of the seed from the fruit can be delayed for several years without affecting the viability of the embryo, due to very low respiration rates.

Germination can be enhanced slightly by high temperatures under natural conditions, and by gibberellic acid or removal of the endosperm under laboratory conditions. Relative growth rates for both Harpagophytum species are lower than for subtropical grasses and legumes, due to a strong investment in root and tuber biomass. Germination and seedling growth is discussed in relation to the drought avoidance syndrome and the animal disperser syndrome.

Tubificid worms that live in the paddy mud increase in numbers when an organic fertilizer is applied. They mix the soil by passing it through their gut as well as by their burrowing and respiratory movements, thereby checking the sprouting of paddy weeds. Tubificids inhabiting the pond's mud also serve as fish food. It is suggested that such a pond might be appropriate for aquaculture.

This study considers a method to control paddy field ecosystems based on the above to produce rice and freshwater fish, with organic fertilizers but without the use of herbicides and insecticides.

An investigation into the causes of massive destruction of the vegetation around Tsekelewu Oil Field in the Niger Delta was carried out. The 200 km2 area suffering varying degrees of damage was mapped and the damage quantified by photo interpretation of black and white aerial photographs. Soil, surface and ground water samples were taken from the various zones for chemical analyses which included the determination of pH, electrical conductivity and soluble salt analysis.

The results showed that salt accumulation decreased from the sea inland-wards, with some upsurge in the saline-fresh water transitional zone where the greatest damage occurred. The electrical conductivity of the ground water varied from 45 dS m−1 in the area of greatest damage to less than 4 dS m−1 in the fresh water zone where there was no apparent damage. The salt-tolerant species along the coast were not affected, but in the transitional saline-fresh water zone in which the electrical conductivity of ground water was greater than 30 dS m−1, all the vegetation including the relatively salt-tolerant white mangrove (Avicennia africana) were killed. This destruction is attributed to high salinity caused by salt water incursion from the sea.

Aechmea magdalenae is a terrestrial bromeliad that dominates areas of forest understorey on Barro Colorado Island, Panama. Nocturnal CO2 uptake via crassulacean acid metabolism was the primary means of carbon gain under well-watered conditions and all light regimes. The ability to maintain a positive carbon balance under conditions of very low light was demonstrated by laboratory measurements of photosynthesis and forest measurements of growth. Low-light-grown juvenile rosettes had the same daily net assimilation whether tested at photon flux densities of 15 or 300 μmol m−2 s−1 Growth rates of rosettes in treefall gaps were similar to those of plants in closed canopy forest. Growth rates of forest plants were increasingly correlated with canopy openness as the wet season progressed due to increased growth by gap plants, suggesting that water availability rather than light may limit growth during the annual dry season.