During the period immediately after collection from the tree, seeds are particularly susceptible to damage. At the same time the environment in which they are placed, which is fairly easy to control in the seed centre or seed processing depot, is difficult to control in the forest and during transport from forest to seed depot. Fluctuations of climate cannot be predicted or prevented and transport may involve persons who do not have the same personal interest in the welfare of the seeds as the collector, processor or user. During this period there are serious dangers of loss of the identity as well as of the viability of the material. The risks are especially high in many tropical countries, where temperature and humidity are high and where transport may be difficult, slow and uncertain (Kemp 1975 a). Investigations into the problems of storing “difficult” species have sometimes revealed that the real trouble occurs between collection and processing/storing. If seeds have already lost some of their viability before storage, even the best storage treatment will give poor results. Careful advance planning is therefore essential in order to provide the closest possible control over the identity and health of the seed at all stages in its movement (Kemp 1975 a).
Almost invariably it is fruits, not seeds, which are picked from trees. Sundrying of fruits and extraction of seeds is carried out in the field in some countries where the climate is suitable (see pp. 80–81). In others it is considered preferable to transport the fruits as quickly as possible to the seed processing depot, where the conditions of extraction can be controlled much more closely than in the field.
If seeds are not extracted in the field, great care must be taken of the fruits both in the forest and during transport. Bulk quantities of fruits in high temperature and humidity are very susceptible to deterioration through the action of moulds and other fungi and through overheating due to a high rate of respiration. The importance of good ventilation in reducing these dangers cannot be overemphasized. If fruits are stored temporarily in separate containers, they should not be filled to the top. In particular, sacks containing fresh cones should be only half-filled; in this way space is left for expansion of scales as cones dry. Otherwise, scales may acquire a set which severely impairs subsequent seed extraction (Stein et al. 1974). To facilitate air circulation within sacks, as well as for easy handling during transport, it is advisable to put only 10 – 20 kg of fruits in each sack (Goor and Barney 1976). Loose-weave hessian sacks or nylon-mesh laundry bags (Yeatman and Nieman 1978) allow good air circulation through the side of the container. In the case of eucalypt capsules and fruits of other species with very small seeds, however, close-weave cotton bags should be used if there is any chance of the fruits opening during transit (Turnbull 1975 c). Large open-mesh baskets are ideal for promoting free air circulation in cones and other large fruits and may be constructed from locally available materials, whether metal, willow, bamboo or rattan. Aeration in loose-piled fruits can be improved by inserting loosely-constructed “chimneys” of wooden slats in the middle of the piles. Daily turning of loose-piled fruits or of sacks can do much to improve access of air to the less exposed fruits.
5.1 Interim cone storage racks in common use in North America. (Canadian/British Columbia Forestry Services)
5.2 Wire baskets used for temporary storage of cones in Denmark. (DANIDA Forest Seed Centre)
5.3 Temporary cone storage of Pinus taeda cones in 20 bushel (7.2 hl) boxes in southern USA. (USDA Forest Service)
5.4 Temporary frame for field drying eucalypt capsules in Australia. (Division of Forest Research, CSIRO Canberra)
If fruits cannot be transported at once to the seed processing depot, temporary field storage must be arranged, in sheds or under some kind of shelter (Morandini 1962). Shelter is needed against rain and, for some species, against too high insolation. Sheds should be open-sided or otherwise well ventilated and sacks well spaced on racks or hung from hooks to allow free air circulation. Hanging from hooks has the added advantage of giving protection against rodents. If storage is in the open, overhead shelter may be provided by canvas tarpaulins or polyethylene sheeting. If the collecting season coincides with a period of reliably dry but not too hot weather, no overhead shelter is necessary. Sacks should never be piled on top of each other in large heaps (Aldhous 1972, Stein et al. 1974).
For most orthodox seeds (see p. 130–131) some degree of advance drying of the fruits in the field is a good thing. Drying of orthodox seeds to under 12 % before shipment by air has been recommended (IBPGR 1981). Drying can be facilitated by the use of open-weave sacks. Polyethylene bags are not suitable for temporary storage of fruits of these species, since they prevent drying and may encourage fungal moulds and overheating. However, fruits of recalcitrant species (see chapter 7) must be kept cool and moist to maintain viability of their seeds. Polyethylene bags, which prevent drying, are suitable as containers for species of this type (Stein et al. 1974).
For large collections it has been contended by Isaacs (1972) that large wirebound pallet boxes, with a capacity of 7.3 hectolitres, are much more efficient for the physical handling of cones prior to processing. These boxes, used as a single container for handling, shipping and storing, are delivered as components which can be assembled in less than three minutes as needed. But, because of their weight of around half a ton when filled, they need the use of a forklift truck for loading and unloading and are therefore only suitable for large and highly mechanized operations.
Special measures may be needed to prevent damage from pests and diseases. The use of insecticidal or fungicidal dusts may be advisable in some circumstances, if there is a high risk of severe damage, but great care is needed in treating fresh and relatively moist seed, to avoid damage from the chemicals themselves (Kemp 1975 a). Maintaining fruit hygiene, particularly through good ventilation, is usually preferable to reliance on chemicals. Storage of sacks off the ground will itself give some protection against rodents. The incidence of pests and diseases is often worst on the forest floor and prompt collection of fallen fruits can do much to minimize subsequent losses.
The decision whether to extract the seed from the fruit at a central seed processing depot or close to the site of, and soon after, collection must be made in the light of local conditions. As stated by Kemp (1975 a), reduction in bulk and weight of the collected material greatly facilitates transport and for this reason the extraction of the seed from relatively bulky fruits may be desirable at an early stage, even if the more critical operations of dewinging, cleaning and final drying are better done at the central depot. In some cases it has also been found that early extraction of the seed is essential to maintain maximum viability. Fleshy fruits such as the syncarp of Chlorophora ferment if stored in bulk for any length of time and the fermentation impairs seed viability. The use of the sun to speed extraction and drying of the seed is common in the tropics, particularly for many conifers and trees with woody, dehiscent fruits e.g. eucalypts, and is generally beneficial. However, too rapid drying of fruits may sometimes cause them to remain closed and prevent later extraction, a condition analogous to the “case-hardening” of timber. This is true of the cones of some pines if they are collected before peak maturity. In such cases it is necessary to keep the fruits under cover, with a good circulation of air, for one or two weeks before more rapid drying is attempted. Some seeds, particularly of species from the ever-wet tropical forests, are easily killed by rapid drying of the fruits. For these species sun drying of the fruits is inappropriate and they should instead be kept moist during transit (Kemp 1975 a). Factors to be considered when deciding whether to extract locally or centrally include:
Distance to central seed processing depot and efficiency of the transport system. The longer the period to be spent in transit, the greater the risk of deterioration, the greater the saving in cost from transporting seeds instead of fruits, and the stronger the argument for local extraction.
The characteristics of the species in question. For example, in fleshy fruits with a high risk of fermentation, seed should be extracted by maceration locally and soon after collection while dry, resistant fruits and seeds of some leguminous species can withstand a lengthy transit period under poor conditions without serious loss of viability.
The suitability of the species for extraction by sun. Species which need kiln treatment for full extraction of the seeds will usually be sent to the central kiln-drying facilities without any attempt at local drying, but use of portable kilns or artificial heat from sawmills is sometimes feasible. Recalcitrant species which will not withstand drying are best despatched moist to the central seed depot as soon as possible.
The reliability of sunshine during the collection season. Dry season collection in Mediterranean or dry tropical climates should ensure ideal conditions. Thus in Greece the present practice of field drying and extraction has proved successful for most species (Cooling 1971). In the ever-wet tropics, in cool-temperate conditions and for collections during the rainy season, sundrying is not practicable.
Even where seed extraction is done locally, it is preferable to do it where there are some facilities in buildings and communications rather than in the forest itself. In a country with a well-developed forest service, the local Forest District HQ is often the best place. Seed collecting in inaccessible and sparsely inhabited forests will have no such facilities and will need to improvise a seed extracting depot in the forest.
Techniques of seed extraction are described on pp. 92–111.
To ensure maintenance of seed lot identity, each container of fruit must be labelled correctly when it is filled. As an additional insurance against accidental loss of the exterior label, identical labels should be placed both inside and outside the container (Stein et al. 1974, Robbins et al. 1981). Weatherproof labels should be used and the minimum information recorded should include species, seed lot number, geographic location or name of seed source and weight of seed contained, date of collection and collector's name (Stein et al. 1974). Information on seed lot number and species is the key for seed documentation. If detailed information is given on seed collection data sheets (see Appendix 1) the information given on the labels can be limited to seed lot number, species, seed source and weight of seed contained. A copy of the seed collection data sheet or certificate of origin with reference to seed lot number must be attached to the documents accompanying the seed - or preferably be mailed before the seed is despatched. When one seed lot is divided between several containers for despatch, each label should state also the number of containers involved (e.g. 1 of 4) (Kemp 1975 a). In large-scale operations, information may be coded (Aldhous 1972, Dobbs et al. 1976). In the case of small collections for research purposes, e.g. provenance collections or single-tree collections for progeny trials, additional information is recorded on a separate certificate of seed origin or collection data sheet. Reference to seed lot number is important. Labelling is more time-consuming, but also it is even more important, in numerous small research seed lots than in bulk collection, since it is essential to keep each seed lot separate and clearly identified at all stages between collection and sowing in the nursery. Small nylon bags are ideal containers for small lots of cones and seeds which need to be kept separate. They allow good ventilation and many of the stages of seed handling (transport, sun or kiln drying manual dewinging) can be carried out without removal of the cones or seeds from the bag.
Additional information, apart from that on the label, often needs to be recorded, especially for research seed collections. As noted by Kemp (1975 a) there are three main purposes for documentation of seed, (i) to record the location of the collection, so that good sources can be revisited if necessary at any time in the future and, equally important, bad sources avoided, (ii) to provide information on the ecological conditions, the actual populations sampled and the methods of collection and handling of the seed, to assist with interpretation of research results or the planning and conduct of other collections and (iii) to comply with requirements for safe and rapid transport and acceptance of the seed. Examples of seed collection recording forms are included in Appendix 1. Special documentation which may need to accompany seeds in transit, especially if movement is between countries, includes collecting licences, seed movement orders, export and import permits, phytosanitary certificates and certificates of origin or of genetic value under national or international schemes of seed certification.
It is important to ensure that the minimum possible time should elapse between the despatch of fruits or extracted seed from the collecting site or local seed collecting depot and its arrival at the central seed processing depot. Part of the planning operation must be to provide transport which is adequate in quantity and quality to avoid delays in despatch and breakdowns en route. Even short stop-overs add to the heat build-up in fruit and cone sacks during transit. Vehicle drivers should be informed of the nature of their loads and the need for proper care and prompt delivery (Dobbs et al. 1976). Road transport is commonly used for at least the first part of the journey. Railway transport may be more economical over long distances (Morandini 1962) and air transport quicker, but both involve some loss of control over storage conditions in transit and any trans-shipment means extra handling and delay. Road transport is likely to be the preferred method in most conditions.
In large-scale seed collection operations in Gmelina arborea plantations in the Jari project in Brazil, great emphasis is placed on reducing the period in transit in sacks to the minimum. The average period is 1.2 days (Woessner and McNabb 1979). Germination of fruits may drop by 22 percentage points after a day and nearly to zero after a week. In some areas seed maturity and weather conditions affect the safe period in transit. In Zimbabwe pine cones collected early in the season, at the height of the rains and when seed moisture content is high, should not remain in sacks longer than 2 – 3 days; drier cones collected towards the end of the rains may remain up to 10 days without deterioration (Seward 1980).
If transport distances are short and large quantities of a single species and provenance are to be transported, fruits may be loaded into vehicles without containers (Morandini 1962, Goor and Barney 1976). The vehicle must be cleaned of all seed carried on previous trips before a new lot is loaded. For longer journeys or smaller seed lots individual containers should be used. Sacks should be carefully arranged in the vehicle to allow as much air circulation as possible between them. Open-mesh baskets are excellent for promoting free air circulation during transport as well as during temporary storage.
For most species open trucks and trailers should be used in preference to closed vans in order to promote air circulation (Dobbs et al. 1976). But for species which need to maintain a high moisture content if they are to retain viability, care must be taken to prevent excessive drying; use of polythene bags and provision of shade against insolation are necessary. Rapid transport direct to the final destination and immediately after collection may be essential for some species which either germinate naturally or lose their viability soon after seed fall at normal temperatures. Provision of special insulated containers, to control temperature and humidity in transit, may also be needed (Kemp 1975 a). Styrofoam containers or metal thermos flasks are recommended as a precaution against temporary exposure of recalcitrant seeds to cold or freezing conditions in aircraft holds (IBPGR 1981). This situation may be found among some trees of the ever-wet tropical high forest but is rare among species which have evolved under conditions which include a severe cold season or dry season each year. Many of the species most widely used in plantation forestry fall into the latter category.
With valuable collections it may be advisable to split each lot of seed or fruits into at least two parts, to travel separately, in order to guard against losing an entire collection through accidents en route. It may also be desirable to insure the contents against loss or damage, for a sum that will cover at least a proportion of the cost of repeating the collection (Kemp 1975 a).
Information on the estimated time of arrival of a shipment of fruits must be sent in advance to the seed processing depot. This enables the receiving station to provide staff for prompt unloading of fruits (Dobbs et al. 1976). Similar information should be sent to intermediate recipients responsible for transshipping or forwarding consignments of fruits.
Most of the problems in maintaining seed viability which are outlined in this chapter are accentuated in the case of recalcitrant species in the humid tropics. They have short life spans, and can neither tolerate low temperatures (not much below 20°C) nor reduction in their moisture content below a relatively high value. The majority of seeds in the humid tropics are recalcitrant, and as a result of high rates of seed spoilage in transit, such species are seldom used in reforestation except within their countries of origin. Even for seeds collected and used locally, deterioration can be serious within a matter of days unless special precautions are taken. Collectors have to work within relatively narrow limits of tolerance. The main precautions to note are as follows (Ng 1983):
Ventilation: Recalcitrant seeds (and their fruits) respire actively, hence require good ventilation. If large quantities are closely packed, suffocation, physiological breakdown, fungal growth, and overheating will occur resulting in rapid death of the seeds. If plastic bags are used as containers, their tops should be left open or small holes should be made in their sides. Baskets or cloth bags are suitable although usually more bulky or expensive. It is not easy to strike the right balance between adequate ventilation and adequate moisture conservation (see below).
Temperature: Temperatures below 20°C or above 35°C should be avoided. Low temperatures are likely to be experienced in air transportation unless the seeds are kept in the pressurized cabin. High temperatures may be due to respiration or to direct heating by the sun. Good ventilation will reduce heat build-up from respiration. Recalcitrant seeds should be kept shaded from direct sun at all times.
Moisture content: Recalcitrant seeds deteriorate if their moisture content is reduced too much or too rapidly. This is likely to happen during transportation in open vehicles because of air movement. The size and number of ventilation holes in the containers should be reduced under such circumstances. Open containers should be covered with newsprint or cloth to reduce the dessicating effect of air movement.
Organization of nursery: Before the collection is made, the recipient nurseries should be forewarned to have their germination beds ready. Recalcitrant seeds should be sown as soon as possible after collection.
Long trips: Collection trips for recalcitrant seed should not exceed a few days in duration. If a long trip cannot be avoided, a lot of extra work has to be done in daily inspection and processing of the collections already made. If decay and fungal growth set in, the seeds will have to be spread out for better ventilation. Decaying pulpy fruits will have to be separated from the healthy fruits and depulped immediately. Capsules must be discarded as soon as they have opened sufficiently for their seeds to be extracted. If seeds begin to germinate during the trip, the germinants may be saved by storing in rigid containers or baskets lined with newsprint or other absorbent material and kept moist. Some seeds deteriorate so rapidly that the best way to transport them may be in a germinating condition in a moist medium.