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Na Hang Nature Reserve, Tat Ke Sector 1997 Figure 13. Graph showing the percentage of the total number of individuals caught in pitfall traps at each site, in major invertebrate orders. PF1 PF3 Site PF2 PF4 PF5 others Aranae Orthoptera Hemiptera Diptera Coleoptera Hymenoptera 0% 20% 40% 60% 80% 100% 6.4 Discussion 6.4.1 Sweep-netting Although sample sizes were too small to allow statistical analysis of results, general trends in sample size and diversity can be explained, at least in part, by the vegetation of each forest site. The highest diversity of insects are in Forest Transects FT4 and FT1, and these are the sites with the most diverse ground flora. Forest Transect 4 gave a large sample with high diversity, and this is probably a result of its highly diverse herb and shrub layers. In forest Transect 2, where the ground layer was densely shaded by the canopy of young, regenerating trees above, and was itself dominanted by a small number of tree seedlings, the catch was small (although, since most of the individuals caught represented different taxa, the overall diversity index α for this site is relatively high). On the basis of so few samples, it is impossible to conclude whether the altitude of sites had any effect on invertebrate communities, although previous studies suggest that this would be the case; Holloway (1984) found that the overall diversity of moth communities in Sarawak (sampled by light-trapping) was highest in Lower Montane forests, at around 1000m. In Costa Rica, Janzen (1973b) found that the diversity of sweep-net samples reached a peak at altitudes of around 1,100m. However, these samples were taken from open habitats, and Wolda (1987), who sampled insects of several orders using light-traps in forest habitats of Panama, found a decrease in diversity with altitude, and suggested that the relationship between diversity and altitude differered between different habitat types. Frontier-Vietnam Environment Research Report 9 24
Na Hang Nature Reserve, Tat Ke Sector 1997 Compared to the sweep-net samples taken in the Ban Bung sector of the Na Hang reserve (Hill and Kemp, 1996), the values of α were all very small. This could be a result of the smaller samples (due to differential sampling effort), but α should be relatively robust to changes in sample size (Magurran, 1988), so the decrease in diversity is likely to be a real effect, caused by the differences in forest structure between the northern and southern sectors of the reserve (and, possibly, by seasonal effects). However, without much more extensive sampling it would be impossible to ascertain the cause of this difference. 6.4.2 Pitfall-trapping Pitfall trapping gave mixed results, largely because of environmental conditions. During particularly heavy monsoon rains, traps at PF5 and PF6 were flooded. Those at PF5 were re-set, but this was not possible for PF6. Also, due to the constraints of time, it was not possible to attempt pitfall trapping at FT4. However, a complete set of pitfall data were obtained for sites PF1-PF5. All the samples were relatively large, when compared to the samples taken by sweepnetting. The smallest pitfall samples were at PF5, which contained only 270 individuals, and PF2, with 463 individuals. Both PF5 and PF2 also had relatively low diversity index values α; in the case of the latter site, this is probably because the sample was heavily dominated by its most abundant taxon (a Collembolan species). There was no clear progression, as might be expected, from less diverse earlysuccessional faunas to more diverse forest faunas (indeed, the sample with the lowest α diversity is the forest PF5). This may be because even the early-successional sites PF1 and PF3 were relatively close to forest or scrub which supported relatively diverse invertebrate faunas. Figures 12 and 13 show that, although the taxa present vary little in importance between sites, there are major differences in the numbers of individuals, particularly in three groups; Hymenoptera, Orthoptera, and 'Others'. In part, these differences can be explained by successional change; thus, the site PF1 had a particularly large proportion of Orthoptera (grasshoppers and crickets). In particular, one cricket species (which was found in all of the sites studied) was extremely abundant here (271 individuals were found). Orthoptera were less abundant in the grassland site PF3 and the forested sites. Although the Orthoptera were found in large numbers at PF1, species diversity was low throughout all the sites. The social nature of many of the Hymenoptera accounts for the variation of this group; if the traps were located near an ant nest, a large catch was guaranteed. The 'Others' group included the insect orders Collembola, Thysanura, Isoptera, Psocoptera, Blattoidea, Dermaptera, Lepidoptera, Mantoidea, the Isopoda (Crustacea), Oligochaetes, Myriapoda, Chilopoda and Arachnids (excluding spiders). These taxa made up a very small proportion of the total number of RTUs recognised, but were Frontier-Vietnam Environment Research Report 9 25
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Page 70 and 71: Appendix 1. Habitat; Plants Plant s
Page 72 and 73: Species Habitat Fertile Uses/Status
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Species Habitat Fertile Uses/Status
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stages SONNERATIACEAE 638. Duabanga
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FOREST TRANSECT 1 Key: Ac Ao Ar Cl
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FOREST TRANSECT 3 Key: Cl Clusiacea
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Appendix 3. Forest plot data
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Myrtaceae 4 1.081 3.60 8 1.250 4.66
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Nymphalidae 32. Cethosia biblis Dru
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Appendix 4b. Butterflies recorded a
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1 2 3 4 5 25 Opsarichthys uncirostr
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Appendix 6. Amphibians and Reptiles
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A B C Upupipae: Hoopoe 14. Hoopoe (
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A B C Subfamily Muscicapinae: Flyca
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7b. Formulation used for the assess
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Appendix 8. Key; A Identified from:
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Appendix 9. List of specimens Insec
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