A review of dipterocarps - Center for International Forestry Research

Seedling Ecology of
Mixed-Dipterocarp Forest
M.S. Ashton
Introduction
Successful reproduction depends on the completion of a
sequence of events starting with flower bud initiation and
ending with the establishment of a young seedling (Smith
1986); failure of any single stage in this sequence can
have catastrophic consequences for the regeneration of a
new stand. Several stages of the sequence considered in
this chapter are i) the dispersal of fruits; ii) germination
of seed; iii) early survival; and iv) the establishment of
seedlings. These stages comprise a period of
reorganisation and initiation of a new forest stand after
which composition and structure depends mainly upon
competition and self-thinning. These stages provide an
opportunity in silviculture for promoting the desired
composition and stocking of the future stand. To quote
from Smith (1986) ‘Many of the successes or failures of
silvicultural treatment are preordained during stand
establishment. Physicians bury their worst mistakes but
those of foresters can occupy the landscape in public view
for decades’.
South and southeast Asia boast a rich history of forest
research. The mixed-dipterocarp forest 1 of this region has
been studied more than any other tropical forest type
primarily because of its importance for producing timber.
This chapter reviews the state of knowledge on the
seedling ecology of regenerating mixed-dipterocarp forest
and suggests future avenues of research. However, it is
not an exhaustive review of the literature and in most
cases cites widely available papers. There is much
information on seedling dipterocarp ecology that remains
unpublished or is only available at local research institutes,
or university and government departments. This
information in its own right deserves documentation,
compilation and synthesis. Also, though this account
concentrates on a review of the literature of the seedling
ecology of dipterocarp species it emphasises the need to
obtain information about the seedling ecology of non-
Chapter 5
dipterocarp species in mixed-dipterocarp forests. Often
silvicultural management of mixed-dipterocarp forests has
concentrated on the regeneration autecology of a few
commercial dipterocarp species without an understanding
of their interaction with other species, and their role in
the successional dynamic of the whole forest. This has
led to a silviculture that has focused on only the current
commercial species and has tended to simplify, and in
many instances degrade, the dynamic and structure of
mixed-dipterocarp forests (Ashton et al. 1993).
Dispersal and Germination
Early studies on mixed-dipterocarp forests were done on
seed phenology and dispersal mechanisms and the
categorisation of tree species by dispersal agent (Ridley
1930). Subsequent work has been done in more detail on
the role of seed dispersal by animals (Medway 1969,
Leighton 1983, unpublished data); and on dipterocarps
in particular (Fox 1972, Kochumen 1978, Dayanandan
et al. 1990). However, these studies are few and much
more long-term phenological information on seed
dispersal needs to be gathered on representative guilds
of species within mixed-dipterocarp forest. Future studies
should also focus on the amount and distribution patterns
of seed dispersed from parent trees and germination. This
will lead to a better understanding of the spacing and
period of time required for the retention of a residual
overstorey to ensure satisfactory stocking of seedlings.
This kind of information is essential for the development
of natural regeneration methods.
1 Mixed-dipterocarp forest is defined here as that lowland and hill
rain forest where the Dipterocarpaceae are predominant amongst
the canopy and emergent trees of mature forest. The majority of
tree species are non-dipterocarp. The soils are weathered in situ
and would be classified as belonging to either oxisols or ultisols
(USDA 1975). The climate is warm and humid with high rainfall
that has little seasonality.