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