Ecoregional Assessment of Biological Diversity in East Kalimantan

East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems
Lowland Rainforests are also often subdivided floristically into three altitudinal groupings of
dipterocarp forest. Faunal studies by CIFOR (Center for International Forestry) in the
Bulungan Kabupaten, near Kayan Mentarang National Park, have not elucidated clear trends
in biological diversity or gradients in lowland dipterocarp forests on different substrate types
or topography (D. Sheil, pers.com.; O’Brien 1997); they do show, however, that vegetation
diversity in these Lowland Rainforests is very high- with 60% of the tree families and 36% of
tree genera known for all of Kalimantan being recorded in just a single hectare plot (O’Brien
1997).
The Lowland Rainforest has close ecological connections to all the other lowland ecological
systems embedded in it (Mangroves, Freshwater Swamp Forest, Peat Swamp Forest, Heath
Forest and Karst Forest). In general, these other forest types have a poorer representation of
the biological diversity present in the Lowland Rainforest. Perhaps the Karst Forest is the
exception, because it has a mollusk fauna that has elements not represented in the matrix
community and is likely to have other unique species, both vertebrate and invertebrate, when
further surveys are carried out*. The interface between the Lowland Rainforest and the
Lower Montane Rainforest is not sharp either faunally or floristically.
The phenology of Lowland Rainforest flowering and leaf growth is very complex and not
necessarily closely tied to season. It can also be irregular, as is the case with dipterocarps,
most species of which flower every four to five years in response to dry periods (Ashton
1988).
Insects pollinate many trees in Lowland Rainforest. MacKinnon et al. (1996) examined the
information available on a range of fauna and demonstrated that the population peaks of
these insects (and fauna that feed on them) correspond frequently with the peaks of leaf and
flower production, usually just after the driest parts of the year. These authors showed that
availability of fruits affected animal feeding and reproductive behavior of frugivores. These
seasonal trends in phenology of flowering and fruiting in Lowland Rainforests can be
expected to impact the local movements of many faunal species throughout the Lowlands.
Likewise, the number and movement of the fauna such as wild boar can dramatically impact
the reproduction and recruitment of this forest type. Concerns now are that there are not
enough wild boars in these forests to maintain the natural recruitment of large dipterocarps
(Leighton and Cannon 1999 and Lisa Curren 2000).
Rainfall data indicate clear gradients of increasing aridity from the inland Lowland
Rainforests (mean annual rainfall as high as 4000 mm) to those nearer to the coast rainfall
less than 2000 mm). Presumably, these environmental gradients affect the periodicity of
flowering and fruiting - encouraging the more vagile species of animals to move in a
patterned way along the major inland-to-coastal axis, within the major watersheds. This has
implications for the need for restoration and/or conservation of faunal corridors linking the
inland and coastal Lowland Rainforest in each major watershed. This concept formed the
process of Portfolio assembly and the conservation strategy referred to as the “Ridges to
Reefs” approach.
* See Karst section for results of recent (2004) surveys
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