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Biotic Interactions in Tropical Rain Forest (BITRF) - First Year's Progress on the Overseas Research Programme (February 2001)
Our research programme in the Sepilok Forest Reserve in Sabah, Malaysia got off to a great start with the successful initiation of a suite of experiments (see figures below) aimed at testing the hypothesis that biotic factors, such as competing plant species, herbivores, mycorrhizas, seed predators, and fungal pathogens, interact with the abiotic environment to determine the performance and survival of juvenile life stages of Dipterocarpaceae, the dominant tree family in the lowland rain forests of Southeast Asia (see May 2000 bulletin (31: 2) for project description).
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Permanent plots established in sandstone ridge forest and alluvial forest serve to provide descriptive data on the tree and liana floras in the two forest types. Our manipulative studies will test hypotheses of the importance of biotic factors in species distributions across the two forest and soil types. Other forest-based plots were established for examining seedling demography in relation to adult tree densities (Richard Thewlis, Imperial College)
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A reciprocal transplant experiment will be used to examine the relative importance of soil type, light environment, and nutrient addition to seedling growth, survival, nutrient use efficiency, incidence of foliar herbivory and symptoms of pathogen attack. Robert Bagchi, an undergraduate ecology student from York University, is studying leaf demography.
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Working in Sepilok has been very rewarding. Although initially the project focused on the distinctive tree floras of the alluvial and sandstone ridge soils, Kalan Ickes (U Aberdeen) and Saara De Walt's (Louisiana State University, USA) preliminary work on the liana flora suggests that the liana communities are also distinct. And heath forest (locally known as 'kerangas'), found in the eastern edge of the reserve, is being included in several of the comparative experiments as it represents a more extreme contrast to the alluvial forest than the sandstone ridge forest, in terms of drainage and soil nutrient status.
While it is still early to draw conclusions from the preliminary findings, rates of foliar herbivory on seedlings appear to vary by soil type and light environment. Our poster at the Winter Meeting in Birmingham will provide a further update on progress.
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Seedling resistance to fungal pathogens is determined by passive (e.g., bark thickness) and active (e.g., wound response) resistance. Jamilah Mohd. Salim (University of Aberdeen) is conducting a nursery experiment to determine how bark defences and wound responses are affected by light and soil conditions. With Markus Eichhorn (University of Leeds), she will examine how investment in foliar defences against herbivores relates to investment in bark defences. She is inoculating seedlings of Dryobalanops lanceolata with a canker-causing fungus (Phoma).
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Reuben Nilus (Unviersity of Aberdeen) is using a bioassay experiment to identify nutrients and mineral elements limiting growth in a group of dipterocarp species that are more frequently found in one of the two forest types. Dipterocarps all possess ectomycorrhizas that are thought to improve their uptake of limiting nutrients, particularly. P. Francis Brearley (University of Sheffield) is investigating the relationship between mycorrhizas and dipterocarp seedling nutrition under controlled conditions and in the field.
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Michelle A Pinard 
University of Aberdeen
(m.a.pinard@abdn.ac.uk)
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Introduction to the project
