TREE DIVERSITY IN THE RAIN FORESTS OF KALIMANTAN
Kalimantan, which has large areas of forest, encompasses a variety of forest types comprising
mangrove forest, coastal forest, swamp forest, evergreen tropical rainforest, forest over
limestone and heath forest, and stretching from sea level up to 2556 m altitude. The mixed
dipterocarp forests are situated mostly in lowland areas, below 600 m altitude. Very few
Dipterocarp species occur at high altitudes, i.e., Hopea mengerawan, Shorea curtisii ssp.
found only at an altitude of 1450-1600 m, where it mainly grows together with some species of
Lithocarpus dominate vegetations on the mountain peaks of Mt. Lunjut and Mt. Mencah (Kayan
Mentarang National Park). A typical highland species, Weinmannia borneesis is also found
here. Tristaniopsis sp. can be dominant on very steep and rocky slopes. Shorea balangeran and
Detailed information on the vegetation (trees) of Sungai Wain Protected Forest in East
Kalimantan is presented. In a plot area of 3.6 ha, divided into 9 subplots, 385 tree species with
the dbh of 10 cm or more were recorded. These species belong all to 143 genera and 49
families. The species composition in the different subplots sometimes varies greatly. Ranked by
importance of species, Shorea laevis, Madhuca kingiana, Eusideroxylon zwageri, Shorea
The forests of the Malaysian region are very species-rich in all groups of biological organisms.
Of the estimated 42,000 vascular plant species (Roos, 1993) or from the 25,000 species of
flowering plants according to Whitmore (1990), the vast majority occur in forest ecosystems,
and a very high proportion of these plant species are trees and large shrubs. Kalimantan, which
has large area of forest, is believed to be one of the islands that still harbours numerous
unknown and endemic species that have not yet been described. This is a reasonable assumption
because, in the area of flora, most of the biologists (especially botanists) agree that the
Indonesian provinces of Kalimantan area are still under-collected. Relatively few botanical
explorations have been made in the past. In the period 1989–1999, collections by the staff of the
Wanariset Herbarium added more than 11000 items to the collection of Kalimantan (Sidiyasa et
al., 1999). These collections comprise mainly trees from the East Kalimantan area.
Borneo, including the Indonesian provinces of Kalimantan and the Malaysian states of Sarawak,
Sabah and Brunei, is the largest island in the Sundanic biogeographical subregion. It is a centre
for many genera and species of the Malaysian flora. It is said that Borneo is also the home of the
South East Asian Dipterocarps. According to Newman et al. (1998), there are 273 species and
20 subspecies of Dipterocarpaceae in this area. Most of the island comprises undulating hilly
The highest peak is unnamed and is located above the headwaters of the Bahau River in East
Kalimantan. The climate is humid, with a rainfall varying between 2000 and 4000 mm/year.
The FAO (1981) described Borneo as an island covered by a continuous carpet of evergreen
rain forest dissected by swirling brown rivers. Today, a lot of forest areas have been cleared for
timber, agricultural land, industries and resettlement. Forest fires in 1982/1983 and 1997/1998
had a disastrous impact on remaining forest conservation areas. Soon, after the forest cover had
been removed, people who live nearby, automatically extended their ladang area into the
conserved forest lands.
Kartawinata et al. (1981), Bratawinata (1986), Sidiyasa (1987, 1995) and Riswan (1987),
among others, have already published information and detailed studies on the structure and the
species composition of forests at some places in Kalimantan. However, much more research is
still needed. The present paper elaborates on the results of the research on tree species diversity
in primary forests carried out by the MOFEC-Tropenbos-Kalimantan Project during its
existence in this area (since 1987). Literature study is also incorporated in order to provide more
The area where lowland forest occurs refers usually to the area below 700 m above sea level,
and does not include specific habitats like kerangas forest, swamp forest, coastal forest and
mangrove forest. Most of the Kalimantan forests are in this category, where the Dipterocarp
species may be dominant. In many cases, the dominance of the Dipterocarpaceae in the area is
related to their trunk or bole sizes, which is usually very large. It is different from the family of
Euphorbiaceae, which is also very often dominant, but the dominance is related to the higher
number of genera and species found.
Nine genera of Dipterocarpaceae are found in Kalimantan. They are Shorea, Anisoptera,
Parashorea, Dipterocarpus, Cotylelobium, Dryobalanops, Hopea, Vatica and Upuna. From the
10 genera of the Malaysian Dipterocarps, only Neobalanocarpus has not been recorded from
Borneo so far. This species occurs in Thailand and in Peninsular Malaysia.
As the most suitable habitat, it is well known that the lowland forests consist of the highest
diversity of plants, especially trees. The most durable timber species “iron wood”
(Eusideroxylon zwageri) is mostly adapted to flat lands along rivers, sometimes dominant, and it
is extremely slow growing. Sidiyasa (1995) found this species was also growing well on
undulating areas in Sintang, West Kalimantan.
Other common and important tree species in lowland primary forests in Kalimantan are
Koompassia excelsa, Pometia pinnata, Dracontomelon dao, Durio spp., Artocarpus spp., and
Dialium spp., These species, except Koompassia excelsa, are important and well known
because of their fruits, which are edible. Sindora spp. and Palaquium spp. are known for their
timber quality. Pometia pinnata and Dracontomelon dao are some of the trees which usually
grow along the rivers and small tributarys. Pometia pinnata especially is very easy to
distinguish in the field because of its young leaves, which are dark red.
It is already well known that, in most places at higher altitudes, the diameter of trees tends to be
smaller than that of trees growing at lower altitudes. This characteristic is very obvious when
the habitats are rocky or are higher than 1600 m altitude. Very few Dipterocarp species occur at
this level. During our botanical exploration in the Kayan Mentarang National Park (Mt. Lunjut
and Mt. Mencah), four species of Dipterocarpaceae were collected. They are Hopea
mengerawan, Shorea curtisii ssp. curtisii, Shorea sp. and Vatica oblongifolia. Shorea curtisii
ssp. Curtisii, in particular. is found at the altitude of 1000 - 1600 m. The high quality timber
species Agathis endertii is found only at an altitude of 1450-1600 m. It grows mainly together
with some species of Lithocarpus, Nageia wallichiana and Podocarpus neriifolius. At the top
of Mt. Lunjut (1900 m), Eugenia spp. are very dominant, while on Mt. Mencah (1980 m) the
vegetation is dominated by Adinandra spp. and Lithocarpus. A typical highland species,
filling and red-orange outer bark can be dominant on very steep and rocky slopes.
In Kalimantan and the other parts of Borneo, this forest formation is called ‘kerangas’. The
forest grows on very acid soils, that usually consist of white sand.Nutrients are therefore very
low and rice will not grow. The most common tree species that occur in kerangas forests are
Depending on the type of the habitat of its occurrence, this forest is may be called ‘peat swamp
forest’, if it occurs in a wet area with waterlogged condition, or ‘freshwater swamp forest’, if it
occurs in an area where flooding is periodic, either daily, monthly or seasonally. In peat swamp
forest, some tree species such as Gonystylus bancanus, Alstonia pneumatophora, Alstonia
spatulata, Cobretocarpus rotundatus (Anisophylleaceae), Dactylocladus and Lophopetalum
javanicum grow particularly well. In freshwater swamp forest many more species are usually
adapted to the habitat conditions. Calophyllum spp., Eugenia, Vatica venulosa, Horsfieldia spp.
are common here.
STRUCTURE AND SPECIES COMPOSITION OF SUNGAI WAIN FOREST
The forest of the Sungai Wain Protected Forest (SWPF) is the remaining tract of primary
lowland forest nearest to the large cities in East Kalimantan. The forest is located only 15 km
north of the Balikpapan city, along the Balikpapan - Samarinda main road. The total area is
about 10,000 ha. Unfortunately, local communities occupy part of the area, especially along the
Balikpapan - Samarinda main road. According to Sukmajaya et al. (1999), about 360 ha have
been already converted into agricultural land by 147 families. In addition, more than 50 percent
was affected by forest fires in 1997/1998.
As the only primary forest remaining near a big city like Balikpapan, the Sungai Wain forest has
a very important function, economically as well as ecologically. Much research on flora or
fauna, including their ecosystems, has been or still is being done here. This area supports
populations of sun bear (Helarctos malayanus), red monkey (Presbytis rubicunda), orang-utan
(Pongo pygmaeous) (Orang-utan Reintroduction Project) and a wide range of other rare
endemic fauna and flora species. The forest also provides non-timber forest products for the
supplying the immense oil refinery industry in Balikpapan.
The aim of this study is to obtain detailed information on forest structure and tree species
composition (diversity) and to compare these characteristics with other forest sites, mainly in
Kalimantan, Sarawak, Sabah and Peninsular Malaysia.
Plot establishment and site description
Following an extensive field orientation, nine permanent subplots, each 200 x 20 m (0.4 ha),
totalling 3.6 ha, were established in the Sungai Wain PF. In order to facilitate the inventory, the
subplots were divided into 10 x 10 m units. Ironwood poles of 5 x 5 x 130 cm were used as the
corner (border) markers of each subplot. Slope corrections were made for horizontal distances.
The main terrain characteristics of the subplots were:
- subplot 1: consists mostly of flat land, which is located on a small tributary of the Wain river;
- subplot 3: on lower and middle slope, a small part on a small tributary of the Wain river;
- subplot 5 undulating area on a small tributary of the Wain river;
- subplot 7, upper slope, ridge and a little part in a swampy area;
- subplot 9, slope and flat land on a small tributary of the Bugis river;
- subplot 11, undulating;
- subplot 13, undulating, partly swampy and small tributaryof the Bugis river;
- subplot 15, slope and a small part in the swampy area;
- subplot 17, ridge, slope and small tributary of the Bugis river.
The forest in the plots was considered primary forest, but there has probably been some illegal
logging and damage by storm in the past. Many big trees had fallen, probably because of the
loose soils, which are mostly sandy.
All trees with a dbh 10 cm or more (dbh = diameter at breast height, 130 cm above ground
level) or if buttresses present, about 30 cm above buttresses, were measured in all nine subplots.
The position where the measurement was made was marked by red paint (a horizontal ring
around the tree bole). All trees in the subplots were numbered permanently, using aluminium
tags. Preliminary tree identification was made in the field, but later a detailed identification was
made in the herbarium at the Wanariset station. All specimens (plant samples) which could not
be identified with certainty to the species level were collected. These (paucher) specimens were
also important for identifying the total number of species, even if the plants were not fully
identified to species level; in which case, a numeric coding system was used, e.g. Baccaurea
sp.1, Baccaurea sp.2, Garcinia sp.2, etc.
The Important Value index (I.V.) of Cottam and Curtis (1956) is used to describe and compare
the species dominance of the subplots. The I.V. of the taxon of each subplot is defined as the
sum of its relative density and relative dominance; while, in order to describe the dominance of
species in the whole plot, the I.V. is defined for the whole plot (all 9 subplots) - - by adding its
relative frequency. The following equations are used:
Number of individuals of a taxon
------------------------------------------ x 100
Total number of individuals
Basal area of a taxon
----------------------------------------- x 100
Total basal area of the subplot
Frequency of a taxon
---------------------------------------- x 100
Total frequencies of all taxa
Based on the data collected in the whole plot area of 3.6 ha, the forest in the Sungai Wain FR
has a density of 535 trees/ha and a basal area of 23.5 m2/ha (Table 1 shows the tree density and
basal area of each subplot). The tree density is more or less similar in most subplots, with a
variation between 470 trees/ha in subplot 5 and 712 trees/ha in subplot 17. There is no distinct
correlation between the tree density and basal area found in the subplots. As shown in Table 1,
the forest in subplot 7 has the largest basal area of 30.2 m2/ha, with a density of only 500
trees/ha. In subplot 17 the density of 712 trees/ha is much higher than that in the other subplots,
but here the basal area is only 23.1 m2/ha (lower than those found in subplots 5, 7 and 11).
Flat, small stream
Slope, small stream
Slightly undulating, small stream
Slope, ridge and swampy
Slope, flat and small stream
Undulating, small stream and swamp
Slope and a little swamp
Ridge, slope and small stream
is in very good condition. The number of trees with a diameter of more than 60 cm in this
subplot is higher than in the other subplots (except subplot 1), which have only one or two trees
of more than 60 cm in diameter.
Comparison with some other forest areas in Kalimantan, Sarawak, Sabah and Peninsular
Malaysia shows that the forest in Sungai Wain has the lowest basal area (see Table 2). This low
basal area is probably due to the small diameter of the trees in the Sungai Wain PF. In the whole
plot area of 3.6 ha, only 18 trees with the diameter of more than 60 cm were recorded. In the
“Matthijs” permanent plot in the Wanariset Forest with a plot area of 0.51 ha, 10 trees with a
dbh of more than 60 cm were recorded, and in a plot of 1.12 ha in the Apo Kayan forest 19 such
trees were found (van Valkenburg, 1997).
Wanariset (plot Matthijs)
van Valkenburg (1997)
Proctor et al. (1983)
Newbery et al. (1992)
Wyatt Smith (1966)
*) As cited in Newbery et al. (1992).
There are three very big trees (with a dbh more 100 cm) in Sungai Wain PF sample plot. One of
these trees is Dipterocarpus cornutus and the other two are Shorea laevis. The largest diameter,
122.6 cm, is a Shorea laevis. All of these species belong to the heavy Dipterocarps group. The
largest size for ironwood (Eusideroxylon zwageri) was 75.2 cm in diameter in subplot 5, where
this species is also the dominant species.
In terms of tree density (see Table 2), the Sungai Wain plot as well as the forest plots in the
Wanariset area (Kartawinata et al., 1981and van Valkenburg, 1997), and the plot in Lempake
(Riswan , 1987) may be considered as representative for the Balikpapan-Samarinda area. The
very high density for the forest plot in Apo Kayan described by Bratawinata (1986) in a
Fagaceae forest may be the highest one in Kalimantan so far.
In the plot area of 3.6 ha, 385 tree species (dbh 10 cm or more) were recorded. They belong to
143 genera and 49 families. Based on number of species of each family, Euphorbiaceae is the
most dominant family (consist of 47 species), followed by Lauraceae (28 species),
Myristicaceae (27 species) and Myrtaceae (24 species). The ten most common families in the
present study in Sungai Wain PF as well as in studies in primary forest plots in some other
places in East Kalimantan, are presented in Table 3.
In the family Euphorbiaceae, Baccaurea is the most common genus (with 10 species) followed
by Aporosa (9 species) and Cleistanthus (8 species). In the family of Lauraceae, 10 genera were
recorded, led by Litsea consisting of 11 species. The family of Myristicaceae was dominated by
subplot 1, where only one tree of Eugenia was recorded. In the other subplots the genus
occurred usually more, with up to 18 trees belonging to 9 species in subplot 9. Depending on the
species, some tend to grow on flat land and along streams and some others on slopes or ridges.
number of species, except for ITCI plots and the Apo Kayan plot, which are based on Importance Value
Also included in the top ten in Wanariset, Lempake, Apo Kayan and ITCI
* = present study; ¹ = Kartawinata et al. (1981); ² = Riswan (1987); ³ = van Valkenburg (1990)
The sweet edible (pulp) fruit of Baccaurea macrocarpa is found in subplots 1, 5, 7, 11, 13 and
17. Some other common fruit tree species were found in the area, such as Artocarpus
The dominance of species in each subplot was determined on the basis of the I.V. of each
species (see Table 4). Shorea laevis and Madhuca kingiana appeared to be the most common
species in the plot area. Each was found to be dominant in three subplots. Shorea laevis was
always dominant in areas with relatively dry soils and on upper slopes and ridges; while
Madhuca kingiana prefers the slightly wet habitat, on lower slopes and flat land.
Eusideroxylon zwageri, which is now said to be becoming rare, is dominant in subplot 5, in a
slightly undulated flat stretch along a small tributary of the Wain river. This species grows
mainly in the company of Dipterocarpus tempehes, Madhuca kingiana and Shorea johorensis.
Compared with other forests in other sites in Kalimantan, Sarawak, Sabah and Peninsular
Malaysia, as shown in Table 5, its seems that the species composition of the Sungai Wain forest
is rather rich. Probably, only the Apo Kayan plot is richer than the Sungai Wain plot. The much
smaller Apo Kayan plot of 1.12 ha, contains as many as 58 families with 136 genera and 264
species. The ITCI plot 76-4, which is located in the middle slope and in a valley, is a poor plot,
with only 198 species being recorded in an area of 1.65 ha.
Number of families, genera and tree species (dbh 10 cm or more) at various sites in Kalimantan, Sabah,
Sekadau, West Kalimantan
Kartawinata et al. (1981)
PT. ITCI (upper slope,
PT. ITCI (middle slope/
Valley, plot 76-4)
Apo Kayan, Fagaceae plot
Gunung Mulu, alluvial plot
Proctor et al. (1983)
Gunung Mulu, diptero. plot
Kochummen et al. (1990)
* = Trees >12 in. (30.5 cm) girth at breast height.
Tree species that are common in montane forests in East Kalimantan include Shorea
Shorea balangeran and Cratoxylum glaucum are the most common tree species found in
density of 535 trees/ha (representative for the Balikpapan-Samarinda area) and a basal area
of 23.5 m2/ha, which is the lowest value compared to other forest sites that have been
studied in Kalimantan.
The Sungai Wain forest is rather rich in tree species. In the sample plot of 3.6 ha, 385 tree
species (dbh 10 cm or more) were recorded, belonging to 143 genera and 49 families.
with 47 species, followed by Lauraceae with 28 species, Myristicaceae with 27 species and
Myrtaceae with 24 species.
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