Altitudinal analyses of dipterocarps of limestone vegetation in Sarawak

September 29, 2006 by

Julaihi Abdullah

Forest Research Centre

Sarawak Forestry Corporation

Fax: 082-617953

julaihi@tm.net.my




ABSTRACT


The study on floristic composition, total above ground biomass and species dominance of trees with d.b.h. ≥ 5 cm was conducted at 100 m intervals from 130 m to 1130 m a.s.l. at Gunung Api, Gunung Mulu National Park, Sarawak, Malaysia. A total of 1103 trees with d.b.h. ≥ 5 cm were enumerated in an accumulative area of 1.04 ha, belonging to 195 species from 108 genera and 45 families. The mean density of trees with d.b.h.≥ 5 cm is 940 trees ha-1 with a total above ground biomass of 264 ton ha-1, basal area (BA) of 31.37 m2 ha-1 and leaf area index (LAI) of 3.93 ha ha-1. Within all studied plots, Euphorbiaceae has the most number of trees recorded followed by Dipterocarpaceae and Myrtaceae. 12.51% of the trees are dipterocarps which are common from 130 m to 730 m a.s.l.. Hopea andersonii is the most dominant tree species with importance value (IV) of 20.49, relative density (Rd) of 5.17, relative frequency (Rf) of 4.28 and relative basal coverage (RD) of 11.05. Dipterocarps contributed 36.20% of TAGB, 29.99% of BA and 27.66% of LAI. The endemic species of dipterocarps in limestone forest will be discussed. Results of the study show that limestone forest of Gunung Api is indeed very rich in species especially dipterocarps and many species are confined to limestone habitats. Conservation status of the limestone flora in general and dipterocaps species recorded will be presented. The result of the study will contribute to the conservation and sustainable management of the dipterocarps in Sarawak.


1.0 Introduction


Sarawak is the largest state in Malaysia and 70% is still covered by forests. It is situated at latitude between 0°75’ N and 5° 00’ S. The climate is hot and humid with an average annual rainfall of 423 cm. Sabah and Sarawak is the richest area in the world for dipterocarp species. A total of 267 species in 9 genera was reported from sea level to 1800 m a.s.l. 140 species are endemic to Borneo (Ashton, 2004).


Limestone forest is one of the eight major forest types. However, the floristic composition and ecology of limestone forest is the least understood. In the past years, emphasis has been on other forest types which are timber production areas such as dipterocarp forest, heath forest and peat swamp forest. Limestone forest covers about 520 m2 or 0.4% of Sarawak (total area 124,000 km2). Although the area cover by limestone forest is relatively small, it is of wide occurrence forming only shallow lenses outcropping between non-calcareous rocks. Many of the limestone hills are found from Bau to Tebakang, Niah and the Melinau massif in Mulu. The higher hills in West Sarawak range from 300 m and 600 m a.s.l. Bukit Bra’ang (750 m) is the only hill that exceeds 600 m in west Sarawak. The large limestone massif in the Melinau, on the boundary between Miri and Limbang divisions, reaches a much higher altitude. The twin peaks of Gunung Api and Benarat exceed 1600 m.


It is a known fact that the limestone flora is exceptionally rich and many species are endemics or are species that are not found away from limestone. The richness of the flora is in part due to the variety of the microhabitats that limestone hills provide within a very confined area. The limestone flora is particularly vulnerable because it occupies a relatively small area compared to other types of forests. The vegetation on limestone hills particularly those in Bau has been seriously disturbed in the past years. Gold and antimony deposits, associated with intrusive rocks have been mined for at least a hundred years. Due to fast pace of development, many limestone hills have been threatened or destroyed by quarrying and other land development. Many species of limestone flora are threatened due to their potential in horticulture industry.


Gunung Api is located in the centre of Gunung Mulu National Park, in Northern Sarawak, Malaysia approximately 110 km from Miri. It lies between the altitudes of 4º05’N and 4º08’N and longitudes of 114º52’E and 114ºE55’E. Gunung Mulu National Park was gazetted as National Park on 3rd October 1974 with an area of 52,864 ha. The Park is inscribed as World Heritage Sites on 29th November 2000.



2.0 Materials and methods

2.1 Sampling methods


Sampling plots were established from the foot of the Gunung Api at 130 m a.s.l. to the viewing point of the pinnacles at 1130 m a.s.l. Although the summit of Gunung Api has an elevation of c. 1600 m, no plots were established beyond 1130 m as the site is inaccessible. Three plots of 0.04 ha (20 m x 20 m) each following the methods of Ashton (1964) and Kochummen (1982) were established at 100 m intervals from 130 m a.s.l. to 930 m a.s.l. only. Each plot was then divided into four subplots of 10 m x 10 m so that 12 subplots occurred at each elevation from 130 m to 930 m. Due to inaccessibility and the steep formation of the limestone outcrops, only three plots each of 10 m x 10 m were established at 1030 m and 1130 m a.s.l. The plot sizes from 1030 m to 1130 m a.s.l. were reduced to 10 m x 10 m as the sites were too small for establishment of larger plots. The plots were visually selected at 2 m away from the trail going up to the pinnacles.


In each plot, all trees with ³ 5 cm d.b.h (diameter at breast height) were identified to family, genus or species level. All plants encountered in the plots were identified as far as possible to families, genera, species and vernacular names. Voucher specimens were collected to confirm the species at the Sarawak Herbarium, Forest Research Centre, Forest Department Sarawak. Tree heights were estimated and diameters were measured at breast height…

Sources: 8th Round-Table Conference on Dipterocarps

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