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Studies in Malaysian Rain Forest: I. The Forest on Triassic Sediments in Jengka Forest Reserve

M. E. D. Poore
Journal of Ecology
Vol. 56, No. 1 (Mar., 1968), pp. 143-196
DOI: 10.2307/2258073
Stable URL: http://www.jstor.org/stable/2258073
Page Count: 56
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Studies in Malaysian Rain Forest: I. The Forest on Triassic Sediments in Jengka Forest Reserve
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Abstract

1. This paper describes an extensive survey of the composition of the canopy in two sample areas taken from 1 mile2 (2.5 km2) of relatively uniform, undisturbed Lowland Dipterocarp forest in the Malay Peninsula. This survey was designed to find out what factors control the distribution of species within such a forest. 2. A brief introduction is given to Malayan forest types based mainly on the work of Wyatt-Smith; this shows that a number of types of forest are already recognized and that the distribution of these, even within the complex of Lowland Dipterocarp forest, is related broadly to habitat. 3. Jengka Forest Reserve is situated to the east of the main watershed of the Malay Peninsula between 150 and 250 ft (45 and 75 m) above sea level. The survey area lies on Triassic shales and sandstones which form a yellow latosol. The climate is typically equatorial with a well-distributed rainfall, though there is evidence that evaporation exceeds precipitation for some months in dry years. The forest is typical in structure of Malayan Lowland Dipterocarp forest and is, as far as can be ascertained, undisturbed by human interference past or present. 4. Two surveys were made. `A' was a grid sample amounting to 20 ha in which all trees reaching the canopy (mainly those over 3 ft (91 cm) girth) were enumerated and mapped. `B' was a block of 24 ha in which all individuals reaching the canopy of the nineteen commonest species were enumerated and mapped. 5. A total species list and an analysis of the basal area and number of trees per family was prepared for `A'. This shows that the Dipterocarpaceae is the most important family by any criterion. The sample contained 2773 trees of 375 species, 139 genera and fifty-two families. The average basal area was 24.2 m2/ha. 6. The network of narrow swamps which traverse the area (amounting to 4.6% of the total) have a significantly different flora from the rest. 7. The eighteen commonest trees in `B' were mapped and thirteen of these were analysed by the partition of variance to detect pattern. Some species were found to be randomly distributed while others showed significant aggregations of various dimensions. The most marked pattern for several species measured approximately 200 m across. The degree of aggregation seemed to be related to means of dispersal and size of fruit. 8. The distribution maps of the same thirteen species showed that smaller trees were generally grouped round larger trees but occasionally occurred in isolated positions, presumably forming foci for new aggregation. 9. Covariance analysis of the thirteen commonest species for pattern showed no groups or pairs of species which were consistently positively or negatively associated with one another at all sizes of aggregation. The degree and the sign of the association between any pair of species frequently changed as the size of the aggregations changed. 10. Normal and inverse association analysis were applied to the distribution of 184 species in 192 plots each of 20 × 60 m. Normal association analysis revealed those species which were known to have indicator value for swamp conditions. In the inverse analysis there appeared a number of groups of species which could be interpreted from present knowledge of the ecology of Malayan Lowland forest. These groups contained mainly the rarer species of the survey area. The groups containing the commoner species did not correspond with the results of the covariance analysis. 11. Further analysis of the data show that a plot of at least 2 ha is necessary to obtain a coefficient of similarity of 50% for canopy tree species between two samples of this forest and that Williams' Index of Diversity (α) increases with increasing size of plot. Calculations made from the proportion of gap in the forest and from the distribution of girth classes both lead to the view that any piece of forest may persist, between gap phases, for an average of 200-400 years. 12. An hypothesis is advanced to account for the kinds of distribution of species that were found. The `rarer' species are thought to occur in associated groups, the distribution of which depends on changes of soil and micro-environment. These occur within a matrix of commoner species whose distribution is determined more by the relations between flowering, fruiting, agency of dispersal and the formation of gaps (i.e. by chance) than by their relation to small changes of environment. 13. The evidence of the behaviour of Dipterocarpus, Koompassia and Shorea leprosula suggest that the forest is not in equilibrium and that the balance of some of the more important species in it has changed within the last 100 years.

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