A review of dipterocarps - Center for International Forestry Research

Seed Handling
B. Krishnapillay and P.B. Tompsett
In considering seed handling, it is important to be aware
of the sources of seed quality. Many benefits flow from
the use of better quality seeds, selected and handled
optimally; advantages include the improved survival of
seedlings and greater overall commercial returns.
However, methods to ensure high quality of seed
supply are not as advanced for dipterocarps as for other
forest species such as pines and eucalypts. The primary
problem is seed supply and this factor is a major
constraint in dipterocarp forest management. Thus, the
lack of seeds in sufficient quantity and quality has
discouraged the raising of seedlings in the nursery and
direct sowing of seeds in the field.
The majority of dipterocarps do not flower regularly.
In the aseasonal zones flowering occurs at intervals of
two to five years and its accurate prediction is impossible.
Consequently, it is difficult to plan major planting
activities. Even in flowering years, interference by
drought can cause premature fruit drop. On the other
hand, flowering is generally on an annual basis in the
seasonal climatic zones so that planning seed collection
in these areas is easier. Although seed production can
vary between years in any particular place, foresters can
make more secure plans by widening the area monitored
for seed supply.
A second problem in practice is the life span of
dipterocarp fruits; most species have short-lived
‘recalcitrant’ seed. If seed collectors do not harvest
mature seed and sow it immediately, a proportion will
soon become inviable. A few species, however, have longlived
seed. Early descriptions of the short-lived nature
of dipterocarp seeds include those of Troup (1921), Sen
Gupta (1939) and Dent (1948). The period between
collection and sowing should thus generally be as short
as possible. In practice, reports of fruiting are often
received at short notice; thus, in order to produce
dipterocarp seedlings, a collection team has to be hastily
prepared for collection, transport and sowing in the
nursery. Few agencies can liaise these activities
efficiently. Schaffalitzky de Muckadell and Malim
(1983) considered some relevant factors.
Chapter 4
In seasonal forests, on the other hand, the scope for
forestry operations with dipterocarp species is wider,
flowering being more regular and seed being longer-lived.
Even in this climatic zone, however, most species are
recalcitrant. Much work has been carried out on the factors
controlling the longevity of dipterocarp seeds (see
Chapter 3). Researchers have achieved success for
species from both seasonal and aseasonal zones but have
made relatively more progress with species that do not
possess recalcitrant seed. Alternative means of raising
planting material have been investigated as a
complementary approach.
Several handbooks have been produced on the
handling of tropical tree seed, a notable example being
that of Willan (1985). In this chapter, wider aspects of
seed handling, including biology and ontogeny, are
described. In addition, seed collection, seed storage,
seedling storage and cryopreservation are covered and
future research priorities and prospects for successful
forest seed programmes are considered.
Factors Affecting Seed Viability
When seeds (more correctly fruits) reach maturity on
the mother plant, they begin to deteriorate; the rate of
deterioration depends on the environmental conditions
they experience. Progressively, germination rate is
reduced, the number of abnormal seedlings is increased
and field emergence is lowered. Cumulative damage
occurs until the seed is incapable of germinating.
Preferably, foresters should use seed before its viability
has dropped significantly. Various factors operating
before seeds arrive at the seed centre can influence initial
germination percentage. These factors in relation to seed
handling considerations are summarised below and more
detail is given in Chapter 3.
The effect of climate and pest infestation
Climatic conditions prior to seed harvest and the
physiological state of the mother tree may influence