Ecoregional Assessment of Biological Diversity in East Kalimantan

East Kalimantan Ecoregional Assessment: Chapter 2 – Target Ecological Systems
In order to achieve an ecoregional scale-appropriate identification for this system type, we
modified existing vegetation maps, which lacked coverage for a large part to the west of East
Kalimantan (and also which did not differentiate between Lower Montane Rainforests and
Upper Montane Rainforest/Cloud Forest), by drawing the upper boundary of Lowland
Rainforests at the altitude of 1000 m a.s.l. There is, though, the awareness that some parts of
the map designated as Lowland Rainforest may in fact be Montane Rainforest or Cloud
Forest. Such anomalies can be sorted out in the more detailed analysis of Conservation Area
Planning once sites are identified for conservation action. This potential for discrepancy
should be kept in mind at the results reporting section.
Lowland Rainforests in Borneo are dominated by dipterocarp trees (named because of their
winged seeds) and are frequently referred to as Lowland Dipterocarp Forests. Dipterocarps
are extremely tall trees and frequently reach heights of 45m. In the richest forests, 10% of all
trees and 80% of all emergents are dipterocarps, usually belonging to the genera
Dipterocarpus, Dryobalanops and Shorea. The other dipterocarp emergents are commonly
the legumes Dialium, Koompassia and Sindora (Ashton 1982).
One of the characteristics of these forests is that they are considered to be stratified into three
or more vertical layers. However, this stratification is frequently not readily apparent, as
different growth stages of plants tend to confuse the simple classical view of stratification.
These forests also have flowers and fruits that are commonly borne on their trunks – referred
to as cauliflory- the extent of which diminish with their altitudinal occurrence.
Lowland Rainforests also have dense tree crown epiphytes, including many ferns and orchids
in the upper strata as well as abundant large woody climbers and bole climbers. Many of the
enormous trees in this forest have very shallow root systems designed to utilize the soil
nutrients limited to the surface soil resulting from the decomposition of leaf litter. Because
many of these trees generally lack stabilizing taproots, they have evolved huge buttress roots
to support their tall straight trunks. The ground layers are frequently sparse because the
continuous upper canopy layer allows little light through.
Evidence suggests that if naturally disturbed, through formation of tree-fall gaps, these
Lowland Rainforests take 120-140 years to regenerate to their original mature structure,
although floristically they may contain the dominant trees after 60 - 70 years (Riswan et al.
1985). MacKinnon et al. (1996) estimate that it may take 200 years for a logged-over
lowland forest to completely regenerate to its pre-logging structure and composition.
The predominant ecological formation type, or matrix formation, in the East Kalimantan
assessment area is Lowland Rainforest. It blankets most of the lowlands up to an altitude of
1,000m. It is far from a homogeneous formation: its topography ranges from
alluvial/colluvial plains, both flat, gently sloping, and gently undulating, to hilly areas,
usually lower than 300 m a.s.l., and foothills. The formation occurs on volcanic, sedimentary
and sedimentary substrates, and has a variety of soil types. This soil variety is represented in
the land system types that the ECA team used at a later stage in this process to subdivide the
Lowland Rainforest ecological system into discrete occurrences.
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