JAPANESE JOURNAL OF ECOLOGY

A major forest fire occurred in Daxinganling, China, on May 6th, 1987 and kept burning for over one month, causing great damage to the forest (1,330,000 ha). Images of the entire burnt area were extracted from data provided by the American satellite NOAA/AVHRR taken in 1988 and 1996. Using the maximum likelihood method, the vegetation types in the burnt area, called Tahe, were classified with an accuracy of over 94% and 100% in 1988 and 1996, respectively. Based on the satellite information and ground surveys, the pixels in the study area (13.3×10⁵ ha) were classified into the following types : conifers (6.0×10⁵ ha), hardwood (1.3×10⁵ ha), shrubs (1.9×10⁵ ha), mixed forest (1.8×10⁵ ha), grass (1.1×10⁵ ha), others (1.2×10⁵ ha). Correlating the volume of timber and the vegetation index (NDVI) calculated from the satellite data, the volume of timber in each pixel was estimated and mapped for each forest type (conifer and hardwood) and for each level of damage. The average timber volumes of conifer and hardwood were 166 and 37 m³ha^-1 in 1988, and 469 and 179 m³ha^-1 in 1996, respectively, for all burnt areas covered by ground survey. The satellite data for the same month in different years (1986 and 1996) and the results from ground surveys suggested that the vegetation coverage had almost fully recovered. Therefore, it was indicated that a healthy forest ecosystem would be regained even after a large scale fire.

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Ant-aphid interactions have often been regarded as mutualism. However, the effects of ants on aphids depend on the situation, and many species of aphids are not myrmecophilous despite the fact that aphid excretion is a desirable food for ants. In this paper, I discuss the factors that influence the mutualism of these insects. First, I review the background of ant foraging strategy and the mechanism regulating their foraging behavior. Decision-making by ants to tend or attack aphids and selection of more appropriate food sources are considered to have important effects on the ecology and evolution of aphid myrmecophily. Second, I give an outline of the mechanism by which the foraging strategy of ants makes their relationships unstable and causes interference among sympatric sugar sources. Ant predation according to the supply-demand balance of honeydew can alter the effects of ants on the population growth of aphids from positive to negative, as the supply of sugary food increases. In addition, ant predation is directed to aphids that are less desirable as a honeydew source. In this way, the existence of a more desirable sugar source creates a negative effect of ants on aphids of lower value. Therefore, in order to be myrmecophilous, aphids must be more attractive to ants than other sugar sources. Otherwise, repelling of ants is considered to be an alternative strategy. This potential antagonism among sugar sources should restrict the mutualism between ants and aphids.

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General flowering (GF) is a phenomenon unique to lowland dipterocarp forests in Southeast Asia. During GF, which occurs at irregular intervals of 3-10 years, most dipterocarp species, together with species of other families, come heavily into flower sequentially for several months with high intraspecific synchronization. A series of studies conducted in Lambir Hills National Park, Sarawak, Malaysia, by the Canopy Biology Program in Sarawak (CBPS) have described the phenomenon and plant-animal interactions of GF in detail. They showed that fluctuations of available flower and fruit resources caused by GF had great effects on animals, and possibly contribute maintenance of species diversity in the forests. In the light of these findings, it was suggested that predator satiation proposed by JANZEN (1974) alone could not explain GF, and that two other factors-promotion of pollination and paucity of climatic cues suitable for flowering trigger-might be involved. GF also has some implications for phenological studies in tropical forests. The supra-annual seasonality of GF indicates that the complicated nature of phenology in tropical forests requires suitable methods of description. One of the most useful indices may be the flowering frequency of an individual plant. In addition, integrative studies at a particular field site and comparison of phenology and other biotic and abiotic factors among tropical forests are essential. Although phenology comparisons among different forests are often difficult due to differences in methodology, are now underway to integrate different phenological studies.

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The author reviewed the ecological roles of heterotrophic nanoflagellates (HNF) and ciliates in freshwater pelagic environments, focusing especially on their roles as consumers of microbial plankton, food resources for zooplankton, and regenerators of inorganic nutrients. HNF and ciliates are important consumers of heterotrophic and autotrophic picoplankton, and are subsequently consumed by rotifer and crustaceans. Since the nutrient content of these protists is relatively high among other planktonic organisms, they serve as nutritious food for zooplankton. Nutrient release from the protists can be explained using stoichiometry. Nutrient regeneration by the protists is substantial in the nitrogen and phsphorus cycles of aquatic ecosystems. However, there is still some controversy over the relative importance of protists as food for zooplankton or regenerators of nutrients. This depends on prey selection by zooplankton and the vulnerability of coexisting phytoplankton to zooplankton grazing.

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