J. D. MATTHEWS
J. D. MATTHEWS is Professor of Forestry, University of Aberdeen, Old Aberdeen, Scotland. Other members of the drafting team were H. Kriebel (United states), H. Barner (Denmark) and O. Fugalli (FAO).
Seed stands or seed production areas are formed to produce seed of the best provenances of forest trees; seed orchards are planted to produce seed of new improved cultivars. It is shown that forest trees flower and fruit most regularly and profusely when given favorable climatic conditions, sufficient growing space and adequate nutrition. Periodicity in flowering and fruiting can be further reduced by adequate protection from animals, insects and fungi which damage or destroy flowers, fruits and seeds.
Seed stands are formed by selecting vigorous, healthy and well-formed trees as seed trees and releasing their crowns by removal of all other trees in the crop. Fertilizers are applied to increase seed production and the ground cover is carefully managed.
Seed orchards may consist of clones of grafts, cuttings or layers derived from selected (plus) trees, or selected seedlings, derived from open or controlled pollination. Rapid early growth is essential for early onset of flowering. Thereafter production of well-filled viable seed is maintained by the use of fertilizers and careful treatment of the ground cover. Choice of rootstock and treatment with plant growth substances should eventually provide additional increases in flowering and seed production.
In both seed stands and seed orchards the degree of genetic improvement depends on effective isolation of the seed trees from inferior sources of pollen and on the intensity of selection practiced.
The object of seed certification procedures is to make available to the forester seed and plants that are true-to-name and satisfy certain minimum requirements of quality.
Four categories of seed and plants are moving in national and international trade: unclassified, source-identified, selected and certified. The first two categories of seed and plants are being discarded as rapidly as possible and are being replaced by selected and certified seed and plants.
Twelve national comprehensive certification schemes for forest seed and plants are analyzed to bring out the essential features of national schemes for forest seed and plants. The present lack of quick growing-on tests and the difficulties of separating provenances and cultivars of some species make essential adequate field inspection and records.
Six international bodies are active in matters affecting trading in forest tree seed. Nationally acceptable seed certification standards are being framed for forest tree seed and plants.
Consideration of the facts presented during the earlier chapters of this report leads to the conclusion that the use of well-filled viable seed of good inherent quality provides a sound basis for the raising of vigorous and healthy forests capable of producing wood of good quality. The efforts of forest geneticists and tree breeders to introduce superior provenances and improved cultivars into forest practice depend on the organization of an adequate supply of seed for which special seed producing units are required. Seed of the best provenances is produced in selected parts of natural forests or selected plantations which have been converted into seed stands or seed production areas; while seed of new improved cultivars is produced in seed orchards which consist of grafted plants or plants of seedling origin, derived from selected parent trees.
Besides being of a superior provenance or cultivar, the seed which reaches the forester for sowing in the nursery or in the forest must be clean, viable and healthy if wastefully low yields of plants or crop failures are to be avoided. In more precise terms, the seed must be free from impurities, possess high germinative capacity and be free from seed-borne pests and diseases. Thus, if the productivity of the forest is to be raised through the use of the products of selection and breeding, the supply of seed and plants must be so organized and regulated that it is possible to obtain seed and plants that are both true-to-name and satisfy certain minimum requirements of quality.
Seed production areas and seed orchards exist to produce the greatest possible yield of well-filled viable seed. Their successful management depends on a thorough knowledge of the genetics and physiology of flowering and seed production, and it is therefore necessary to summarize the present state of knowledge on these subjects. For the sake of brevity, this summary is largely derived from a recent review by Matthews (1963) of some of the factors affecting the production of seed by forest trees. The reader is also referred to Chapter 6 of this report and to the paper by Kozlowski (1963).
Initiation of flower buds
The juvenile phase of growth has already been discussed in Chapter 6 and it is convenient to begin here at the adult phase of growth when the flowering condition has been attained.
In many temperate tree species flower primordia are formed early in the growing season preceding the spring in which the flowers appear. The critical period appears to lie between early May and the end of July. A certain minimum degree of heat is apparently necessary for flower bud initiation. Trees grown in sunny positions come into flower earlier in life and flower more regularly and prolifically than those grown in a close stand or in shade. A reduction in water supply in summer is frequently associated with flower bud formation but lack of moisture evidently can become a limiting factor and cases are known where irrigation resulted in an increased seed crop. Sarvas (1962, 1963) has provided ample evidence for Pinus sylvestris that flowering and seed production are better on the more fertile sites. Although similar detailed studies of the relationship between flowering, seed production and high soil nutrient status are lacking for other species, it is now generally accepted that a relatively high soil nutrient status is essential for the regular initiation of flower buds and that vegetative vigor per se does not necessarily preclude flower bud initiation (Priestley, 1962).
There is no doubt that on many forest sites the application of fertilizers will stimulate flowering and seed production but the results obtained so far have been very variable. Responses in flowering and fruiting have been obtained from the application of nitrogen, phosphorus and potassium applied singly; from combinations of nitrogen and phosphorus, and phosphorus and potassium; and from complete NPK fertilizers. In at cases where the fertilizer was applied in combination with crown release by thinnings, the combined treat meets produced better results than were obtained with fertilizer alone, and the same obtains where fertilizes has been applied in combination with irrigation.
Little is known of the role of plant growth substances and the internal changes in forest trees associated with flowering, but the success of Japanese workers in using gibberellic acid to induce flowering in a number of coniferous tree species encourages further research into the role of plant growth substances in flower initiation.
Flowering and pollination
The importance of adequate pollination for the development of viable seed by forest trees has been well demonstrated for several species. Cross pollination is the general but by no means universal rule in many tree species of economic importance, and a considerable number are more or less self-sterile.
It now appears that the dispersal of pollen in wind-pollinated species is not so dependent on the weather prevailing during the period of flowering as was once thought; the reason appears to lie in the great speed and quantity of pollen dispersal as soon as conditions are right. Extensive observations on the flowering of Betula verrucosa, B. pubescens, Picea abies and Pinus sylvestris in Finland led Sarvas to conclude that the start of flowering, the duration, and the occurrence of the peak of flowering are all closely dependent on temperature. Strong winds may accelerate pollen release and rain may interrupt it, though rain seems to have less effect on pollination and seed set than has often been assumed. In the case of insect-pollinated species, such as Acer pseudoplatanus and Tilia, good flying weather for insects is required for pollination, that is bright, dry and fairly calm weather. The reader is referred to the paper by Sarvas (1963) for information on the design of pollen catching equipment.
There are many records of small amounts of airborne tree pollen traveling great distances from the source (" foreign pollen ") but several workers have shown that the bulk of airborne pollen falls fairly close to its source (" local pollen "). The results suggest that pollination is mainly effected by trees in the immediate vicinity of the seed tree. However, the behavior of pollen produced by stands of trees must also be considered as well as factors affecting the distance of dispersal including the size and shape of the stand, and the quantity and nature of the pollen produced (Andersson, 1955, 1963). Pollination conditions are best in extensive stands containing trees with well-developed crowns.
Fertilization and seed formation
Pollination is normally followed by fertilization. The process of pollen formation, pollen shedding and sub sequent germination on the tip of the nucellus in Larix and Pseudotsuga is described in detail by Barner and Christianson (1960, 1962). The lapse of time between pollination and fertilization is usually quite short, but in Pinus the interval is about one year.
The comprehensive study made by Sarvas (1962) can again be referred to for a good account of the normal course of fertilization in Pinus sylvestris. The pollen grains are normally very viable, they develop sperm nuclei with great regularity and these are carried with great accuracy to the eggs by the pollen. The eggs are generally fertile and there appear to be no genetic barriers that significantly prevent fertilization. However, the competition between developing embryos is often decided by genetic factors as, for example, when the union of semi-lethal genes to form homozygotes at fertilization leads to the defeat of the embryo during the competition in the embryo cavity.
Nonpollinated ovules gradually collapse, mostly during the first growing season and in Pinus poorly-pollinated cones soon drop. High embryo mortality in Pinus sylvestris is attributed by Sarvas (1962) to self-fertilization, and Ehrenberg et al. (1955) also showed that self-fertilization often results in poor germination of full seeds and inferior progenies.
The size of the seed crop
Trees that bear heavily one year and then sparsely or not at all for several years are said to show periodicity in seed-bearing. In many species the seed crop of one year affects the seed crop of the following year, both through the reduction of potential foliage-producing or vegetative buds and the reduction of carbohydrate resources (Kozlowski, 1962; Priestley, 1962). The flowering and seed production of young trees is commonly sparse and sporadic but increases rapidly with increasing age and size. Within a forest stand it is the larger, dominant trees that bear the most seed but there are also inherent differences between trees in flowering, fruiting and the production of viable seed that make necessary careful selection for fertility and fruitfulness.
Good flower years occur much more frequently than good seed years. There may be several reasons why a spate of flowers often fails to produce a spate of seed, but deficient pollination, the effects of self-fertilization, the activities of seed-destroying and cone and fruit-damaging insects, animals and birds and unfavorable weather are usually to blame for this. Periodicity in flowering and seed production depends to a large extent on external factors and protection from climatic dangers and the animals, birds, insects and fungi that damage or destroy flowers, fruit and seed should do much to mitigate, but not prevent irregular seed production. For many species the gap between good seed years can be bridged by the use of refrigerated seed storage.
The quality of the seed crop
The spells of warm, dry sunny weather which appear to favor the initiation of flower buds and the accumulation of carbohydrate resources also favor the maturing of the fruit and seed. Considerable variation in seed quality and time of maturation has been found between individual trees and stands of the same species.
In northern latitudes a greater part of the cone or fruit crop is borne on the south than on the north side of the crowns of seed trees. This distribution affects the methods used to assess the size of seed crops. In many species the best cones, fruits and seeds are generally found on the middle and upper parts of the crowns. There is also a variation in seed quality within the cones of many coniferous species, the middle portion being the most productive of well-fired viable seed.
Two general recommendations for the improvement of seed supplies can be made.
1. Full advantage should be taken of good seed years in all species, because the highest proportion of well-filled viable seed is produced in such years.2. Much can be gained by improving seed collection methods both from standing trees and from the ground as in Fagus, Quercus and Tectona.
Objects and choice of seed stands
The objects of forming seed stands or seed production areas are to:
1. produce seed of improved inherent quality by selecting and favoring seed trees which are vigorous, straight-stemmed and healthy and produce wood of good quality;2. concentrate seed collection into a few specially treated parts of the forest, thus making seed collection easier to organize and control;
3. improve the germinative energy and germinative capacity of the seed collected.
All three objects can be achieved by one simple treatment, that is, the careful selection of seed trees and the complete isolation of the crowns of these seed trees by thinnings.
A necessary preliminary to the formation of seed stands is a survey of the region (Figure 20) to locate suitable natural stands or plantations (Jensen and Broekhuizen, 1952; Arnborg and Åkebrand, 1955; Matyas, 1960; Morandini, 1956). A seed source is a crop of fast-growing and healthy trees with good growth habit suitable for seed production. Plus seed sources are suitable for regular and intensive seed collection; normal seed sources are suitable provided careful selection is made of the seed trees; minus stands are unsuitable for seed collection. A seed source becomes a seed stand or seed production area when all defective trees have been removed, leaving the best trees isolated to develop big crowns and so produce more seed. The ground and the seed trees may also be treated to increase the seed crops and make collection easier.
Seed stands are usually formed in natural forests or plantations that are sufficiently old or sufficiently well-developed to provide reasonable assurance that they are well adapted to the site and will continue to show rapid and healthy growth. A suitable lower limit is a top height of 11 to 12 meters (36 to 39 feet) (Faulkner, 1962) and a good upper limit is half the rotation age (Rudolf, 1960). Clearly it is desirable to convert relatively young stands because the response of younger trees to thinnings and fertilizers is greatest and there will be opportunity as the trees develop in later years to make further selection among the seed trees. Nevertheless, many outstanding or plus stands approaching or at the age of maturity for timber purposes can form valuable seed stands. The area of seed stand required can be fixed by observing the average seed production of well-grown trees and setting this against the future planting or regeneration program.
FIGURE 20. - Seed collection map for Picea abies in the Province of Alvsborg, Sweden. Districts with good stands are indicated by cross hatching; minus district are blank. Stands chosen for seed collection are marked by dots.
Isolation from foreign pollen
An additional criterion in choosing seed stands is the absence of neighboring natural stands or plantations of the same or closely related species which are of poor or minus quality. Such isolation from inferior sources of pollen is very important. It has already been shown in this chapter that dispersal distance is affected by very many factors and it is easy to oversimplify a complex situation. Nevertheless, when fixing the size of isolation strips around the seed stand and isolation distances from large sources of undesired foreign pollen, it should be remembered that the degree of contamination by foreign pollen is roughly proportional to the size of its source, and that contamination is least when the size of the seed stand and the local pollen cloud are large in relation to the cloud of foreign pollen. These considerations are the basis for the recommendation that seed stands should be at least 3 and preferably 5 hectares (7.5 to 12 acres) in extent (Andersson, 1963).
Selection of seed trees
The first step in forming a seed stand is to select and mark the seed trees. These should be fast-grown healthy dominants capable of producing wood of good quality. The stems should be persistent and straight, and also free from defects such as fluting, spiral grain and epicormic shoots. The branches should be smart in relation to the stem at the point of origin, the branch angle should be flattened to moderately ascending, and good natural pruning is also a desirable feature. The crowns should be compact and well-provided with foliage and the trees should show signs of having borne seed in the past. Where wood characters such as specific gravity or tracheid and fiber dimensions can be clearly specified, it may also be possible to select seed trees for these characters.
The number and relative superiority of the seed trees marked have an important effect on the genetic improvement of the progeny raised from the seed collected in the seed stand. More precisely, the genetic gain or change in the average genotype of the population produced by the selection of seed trees depends on the heritability of the characters for which selection is made, the variability of these characters and the proportion of the population selected. The genetic gain from seed stands is greater when the proportion selected is low, but the number of seed trees per hectare must be sufficient to ensure adequate cross-pollination between the seed trees, thus avoiding the effects of self-pollination or inbreeding.
Thinning seed stands
The second stage in forming a seed stand is the removal of the phenotypically inferior trees to free completely the crowns of the seed trees. Sometimes seed stands are formed from groups or avenues and such trees often have long, well-developed crowns. In most cases, however, the seed stands will previously have been managed for wood production so that the crowns of the seed trees are relatively small. This is particularly the case in the light-demanding species of Pinus and Larix and also holds for Tectona grandis, Eucalyptus species and Casuarina. The frequency and intensity of thinnings to achieve full crown release must depend on local conditions, and particularly the danger of windthrow, but the sooner the seed trees are isolated the better for future seed production. The first thinnings should be in the nature of heavy crown thinnings to free the crowns of the seed trees, and to remove large, rough dominants from the seed stand and isolation strip. Thereafter the remaining trees are removed as soon as convenient or safe.
Fertilizer treatments
The next step is to consider what other treatments should be applied to increase flowering and seed production still further and to make their occurrence more regular. Root pruning and stem girdling or strangulation are likely to be more harmful then helpful, but the application of fertilizers stands out as a beneficial and worthwhile treatment, especially where soil fertility is relatively low.
The quantities and relative proportions of the various major elements which are necessary to stimulate flowering and seed production obviously vary with the nature of the crop, especially the age and size of the trees and the site conditions. It is, however, clear that the fertilizer should correct existing deficiencies and supplement the major nutrients and for this a general prescription such as 2N: 1P: 2K at the rate per hectare of 112 kilograms of nitrogen, 56 kilograms of phosphorus and 112 kilograms of potassium (or about 100 pounds of nitrogen, 50 pounds of phosphorus and 100 pounds of potassium per acre) would appear to be a good starting point for fertilizer treatments. Usually the fertilizer is applied over the whole area but where the seed trees are scattered it is preferable to apply it below each seed tree to an area of ground one-and-a-half times the diameter of the crown.
In general the best time to apply compound fertilizers is in early spring before the new flower buds are differentiated: the period February to May is suitable in the temperate regions. But the most effective time of application does vary somewhat with the major elements, and it appears that nitrogen should be applied in late spring but not later than May (Devitt, 1960). Potassium can also be applied in spring but phosphorus may best be applied in autumn (Ozawa and Matsukai, 1958). Finally, it appears certain that fertilizer application will in most cases have to be repeated if high seed production is to be sustained. Irrigation cannot be dealt with in detail here but it may have an important part to play in areas where water supply can become limiting to flowering and seed production.
Other treatments of trees and ground
The stems of seed trees in older seed stands should be high-pruned to the base of the living crown to facilitate the use of the Swiss tree bicycle or special ladders for climbing to collect the seed (Seal, 1959; Carlborg, 1961; Hagner and Bergman, 1961), but no live branches should be removed from the base of the crown because this is the region of pollen production in many species. If truck-mounted ladders are used (FAO, 1958), any undergrowth and lop and top will either have to be removed from the site or stacked in heaps so that the truck can be maneuvered.
Strong weed growth often develops on the forest floor following the application of fertilizers and heavy thinnings; if allowed to grow unchecked, shrubs and weeds will be a serious barrier to the collection of the fruits and nuts of Quercus, Fagus and other species which are picked from the ground. Such weed growth can be suppressed by regular cutting and clearing or by the use of complete weedkillers such as "Simazine" or "Monuron" which have given promising results in apple orchards (Anon, 1960). Another possibility worth serious consideration is the use of leguminous ground crops; this has been the subject of much investigation for maintaining the health and yield of Hevea plantations in Malaya (Watson, 1963).
Where there is little or no ground cover, the fallen seed can be easily seen and taken by birds and the use of bird-scaring devices may become necessary.
Protection against fungi, insects and animals
The effects of these agencies in reducing flower, cone and fruit crops have already been stressed. The immediate application of creosote or other recommended chemical to the freshly cut stumps of felled trees in coniferous seed stands will reduce the spread of infection by Fomes annosus (Low and Gladman, 1960). Hardwood stumps which show signs of attack by Armillaria mellea should be grubbed up and burned where this is practicable.
When crown feeding insects assume epidemic proportions, as, for example, Bupalus piniarius on Pinus sylvestris, control should generally be achieved by applications of DDT, using ground fogging machines; aerial sprays are not normally economically justified. For tall trees in seed stands and smaller seed trees in seed orchards, systemic insecticides may eventually provide a suitable means of protection against the attacks of shoot borers and Adelges species, but this method is still at an early stage of development. Of the insects which attack flowers and seeds, Megastigmus species are among the most important at present.
The gray squirrel (Sciurus carolinensis) is a serious pest feeding on nuts, buds and bark. It can be controlled by poking out drays and shooting or trapping (United Kingdom Forestry Commission, 1960). Wide metal bands placed round the stems of widely spaced seed trees have been used in the United States of America to prevent red squirrels climbing (Tackle, 1957).
Many species of both wild and game birds eat fallen seeds and some, for example the crossbill (Loxia curvirostra), extract seeds from cones. Control measures may be necessary and will depend on the wild life laws of the country concerned.
Zobel et al. (1958) have defined a seed orchard as a plantation of genetically improved trees, isolated to reduce pollination from genetically inferior outside sources and intensively managed to produce frequent, abundant and easily harvested seed crops. It is established by setting out clones or seedling progeny of trees selected for the desired characters. Seed orchards are often established while genetic evaluation of the parent material is still under way. In such cases components shown by progeny testing to be genetically undesirable will subsequently be removed from the seed orchards.
FIGURE 21. - The procedure used to form clonal seed orchards in Sweden. A. Twenty-five high elevation plus trees between latitudes 62 and 64° North are selected and grafted. The grafts are planted in a seed orchard on the coast. The seeds from the orchard give seedlings for planting in the interior.
B. Plus tree of Pinus sylvestris No. Z4007 at latitude 62° 48' North and 590 meters above sea level.
C. A sketch showing the arrangement of the grafts in one part of an orchard containing 25 clones. At the first thinning every other tree is removed.
D. Part of a newly established clonal seed orchard of 25 hectares.
Kinds of seed orchard
There are several kinds of seed orchard. Clonal seed orchards consist of grafts, rooted cuttings or layers; while seedling seed orchards are composed of selected progenies derived from open-pollination or controlled crosses. Clonal seed orchards may be subdivided into those in which the clones are from plus or untested parent trees; and those composed of clones from elite or tested parent trees.
Concentrating first on clonal seed orchards based on plus trees, three kinds may be recognized on the basis of the origin of the clones:
1. Plus trees are selected from a specified geographic or climatic region; or from a group of stands; or, more rarely, from a single stand. All the plus trees are of the same species. This is a very common kind of seed orchard, and the procedure employed is illustrated in Figure 21.2. Plus trees are of the same species but originate from different geographic regions. These are called "provenance seed orchards" by Andersson (1960) who described one such seed orchard containing Swedish and Polish clones of Picea abies.
3. Plus trees are of different species and the object is to produce interspecific hybrids. Examples are
the seed orchards planted to produce seed of the F1 hybrid Larix decidua x L. leptolepis = Larix x eurolepis. Andersson (1963) calls these "species crossing seed orchards."
Clonal seed orchards composed of elite or tested clones will form the next generation of seed orchards. Their formation is dependent on systematic test crosses made in the seed orchards composed of plus or untested clones.
Seedling seed orchards have been advocated by Wright (1963) who bases his argument on a theoretical comparison of the response to selection or genetic gain to be expected from several alternative selection procedures.
Test crosses in seed orchards
The design of test crosses and the associated progeny testing have already been discussed in Chapter 2. To repeat the main point, the object is to identify clones showing low combining ability so that they may be removed from the seed orchard. The minimum number of clones in seed orchards composed of plus trees is now generally accepted to be 20 or 30, and a common maximum number is 60 clones. When elite or tested clones are available 2-clone orchards are envisaged by Andersson (1963).
Choice of site and ground treatments
Seed orchards are planted on sites well isolated from large areas of plantations of the same or related species, the distances recommended being up to 1,000 meters (1,100 yards), and favorable to the regular initiation of flower buds and the regular production of large crops of well-filled viable seed. The local climatic requirements are shelter from strong wind and adequate air drainage to reduce the damage done to flowers and fruits by frosts. Soils with a good nutrient status are preferred; the evidence presented in the first part of this chapter suggests that is it generally a mistake to site seed orchards on soils of low nutrient status.
There are three possible ground treatments during the early growth of seed orchards: clean cultivation (this being the treatment favored in Sweden at the present time), cover crops and sward (see Figures 21, 22, and 23; see also Figure 25 on page 123). Once the seed trees are well established, the sward appears to be a convenient treatment for many temperate tree species because of the relatively simple management and, by analogy with fruit trees, beneficial effects on the potassium and phosphorus status of the seed trees. On the three main types of sward used in fruit orchards, that is, the "tumble down," white clover sward and grass-white clover sward, the last appears to satisfy the three conditions of contributing soil humus, supplying some nitrogen (through the clover) and providing good ground cover. It should be noted, however, that drought effects can develop under uncut sward conditions so regular grass cutting or grazing is essential. Again, as with seed stands, grass swards are not suitable for all species and leguminous cover crops are worth consideration (Watson, 1963).
Manurial regimes for seed orchards are unlikely to differ much from those already suggested for seed stands, with the possible exception of methods of application. In top-fruit orchards (that is, apples, pears, etc.) certain fertilizers, in particular nitrogen and magnesium, are often more readily absorbed by the leaves of trees than through the roots. Olroyd (1957) made special reference to foliar applications of urea to top fruits.
Distance between seed trees
The most suitable distance between seed trees varies with species and methods of management, but initial planting distances should not be too wide because pollen production will be sparse and consequently the yield of viable seed will be rather low in the early years. Moreover, at a later stage, clones or seedlings shown by test crosses and progeny tests to be genetically inferior are also removed from the seed orchard, thus giving more growing space for the trees which remain.
Layouts designed to allow one or two "mechanical" thinnings are now general. The distances recommended range from initial spacings of 3 meters (10 feet) for Pinus sylvestris and Fagus sylvatica (Jensen, 1954; Matthews, 1960) to final spacings of 6 to 9 meters (20 to 30 feet) for species of southern American pines Zobel et al., 1958). The arrangement of the clones of grafted plants or seedling progenies must meet the requirements of adequate cross-pollination and reduced self-pollination and so a randomized distribution of single seed trees is general (see especially Andersson and Andersson, 1962, and also Figure 21c). The value of clone or tree banks as a means of preliminary screening of clones for time and pattern of flowering, self compatibility and other related characters is worth stressing here.
Treatment of seed trees
In seed orchards the seedlings, grafts or cuttings should be encouraged by careful choice of site and favorable treatment at planting to grow rapidly from the beginning; this should lead to an early onset of flowering and fruiting. Thereafter, everything should be done to favor rapid growth and the best treatments appear to be regular crown release, the application of organic and inorganic fertilizers, control of the ground cover, pruning and geotropic treatments and, in some areas, irrigation. It may also be necessary to stimulate flowering by excessive applications of fertilizers, restricting water supply, stem girdling or root pruning, but in general these should be regarded as emergency or experimental, rather than regular, treatments. In the long term, choice of rootstock and treatment with plant growth substances will play their part.
Shoot bending, pruning and other crown treatments
The literature on these subjects has recently been reviewed by Matthews (1963). The orientation of the shoot has a marked effect on flower initiation in apple and species of Larix. The geotropic or branch bending treatment developed for Larix by Longman and Wareing (1958) can be applied in larch seed orchards by tying branches of the seed trees into a downward pointing position during the dormant season. Goddard et al. (1962) report favorable flowering responses from bending over grafts of Pinus elliottii in Florida. Disbudding to induce or increase flowering has proved useful in Pinus sylvestris, and pinching off the shoot tips before meiosis takes place has been used in Japan in experiments on the artificial control of sex differentiation in Pinus densiflora and P. thunbergii (see Matthews, 1963. There is also scope for much more work on the effects of foliar application of growth regulators and nutrients on the initiation and differentiation of flower buds. Finally, it is clear that attention should in general be focused on the use of shoot bending, pruning (Figures 22 and 23), nutrients and growth substances to increase pollen production, which is often insufficient in young seed orchards of Pinus species.
Use of selected rootstocks in grafting
It is now commonplace to find that grafted plants, formed by grafting scions taken from adult flowering trees on to seedling rootstocks in the juvenile nonflowering condition, soon begin to flower and bear seed. This is the basis of seed production in clonal seed orchards. In fruit orchards, selected clonal rootstocks are used to control the size of the grafted tree and the nature of the fruit bearing, and it would appear that the use of selected clonal rootstocks will also lead to similar benefits or uniformity and control of tree behavior in tree seed orchards. The idea is not new, Johnsson and others having grafted Pinus sylvestris scions on to seedling rootstocks of Pinus mugo and two origins of Pinus sylvestris. Analysis of the cone and seed harvest of 1959 and 1960 from these trees (Johnsson, 1961) failed to reveal any influence of the rootstocks on the seed production of the scions, so the only evidence so far is negative. Nevertheless, an additional problem associated with the interaction of rootstock and scion is that of incompatibility of the graft union and this has been reported for Pseudotsuga taxifolia and Fagus sylvatica and may make necessary increased attention to selection of rootstocks.
Protection against fungi, insects and animals
A factor which may have to be considered in the siting and subsequent treatment of Pinus seed orchards is the damage done by cone rusts. An example is provided by Cronartium strobilinum which damages the cones of Pinus elliottii and P. palustris. Quercus virginiana appears to be the most important alternate host, and Maloy and Matthews (1960) have recommended the siting of Pinus elliottii seed orchards away from Quercus virginiana and rust control measures in established seed orchards. In young seed orchards of Larix, Pinus and Pseudotsuga taxifolia the Adelges species which commonly appear on the grafted plants can be controlled by "Malathion" sprays. As in seed stands, systemic insecticides may also prove useful as a control measure in the future.
The future for seed orchards
In conclusion, it may be said that the early development of seed orchards in Europe and America has been very promising, but the problem of mass-controlled pollination requires attention and more must be learned about the variation in self-incompatibility of the different clones and the role and nature of inbreeding. The early estimates of annual seed yields for Pinus sylvestris, which ranged from 11 to 16 kilograms of seed per hectare (10 to 15 pounds per acre), now appear, after 10 years' experience, to be sound (Johnsson, 1961), and the estimates for other species - for Larix 17 to 22 kilograms per hectare (16 to 20 pounds per acre) and for Pinus taeda 22 to 45 kilograms per hectare (20 to 41 pounds per acre) - also appear to be reasonable. There are now very considerable areas of seed orchard and, although most of them have been planted during the past 10 years, there is no doubt that they form a valuable and essential part of forest genetics and tree breeding work.
The efficiency of clonal seed orchards in producing regular crops of well-filled viable seed will depend to a large extent on the knowledge gained about the flowering and fruiting behavior of the present clones.
Need for certification
The object of the certification of tree seed and plants is to maintain and make available to the practicing forester sources of seeds, plants and other propagating materials of superior provenances and cultivars so grown and distributed as to insure the genetic identity and high quality of the seed and plants.
Superior provenances are identified by means of provenance tests (see Chapter 4). The duration of these tests depends on the rate of growth and the length of the economic rotation for each species but, in general, it must be accepted that provenance tests are essentially long-term experiments. The need to provide safe prescriptions for the movement of seed and plants so that expensive losses in wood production can be avoided has led foresters in countries with large variations of site and climate to devise zoning schemes defined in terms of latitude or distance and elevation (see Rudolf, 1963). Thus in Austria (Tschermak, 1953), Czechoslovakia (Vincent, 1958), Norway (Austin, 1959), Sweden (Langlet, 1936, 1945, 1957) and the Federal Republic of Germany (Hermann and Astinet, 1961) to name a few such countries, seed is collected and the plants are utilized within the same zone. Countries with smaller ranges of site and climate tend, when importing seed, to look for seed sources growing in places with similar features of site and climate, although as the results of provenance tests accrue the specification can sometimes be made less strict and the search for superior provenances tends to range farther afield.
The state forest services of many countries maintain registers of seed sources which list classified seed sources for home use and export, and acceptable provenances that can be imported. General lists of acceptable provenances covering a wide range of species have been published in the United Kingdom (Macdonald, 1957), Denmark (Barner, 1958, and Gøhrn, 1962) and Belgium (Reginster, 1954) and more restricted lists are available in other countries. Even if the best provenances are not yet known, foresters are often clear about what they should not use.
The rapid progress made with selection and breeding in the genus Populus has been largely due to the easy propagation of many species and hybrids by means of stem cuttings. There is a very wide range of distinct and stable cultivars in use, and control of genetic identity is exercized in most western European countries, partly by control of the sales of planting stock (as in Belgium, the Netherlands and Spain) and partly by the distribution of cuttings from registered stool beds (as in Belgium, France, Italy, the Netherlands and the United Kingdom).
The production of cultivars of those species of forest trees that are reproduced through seed is now developing rapidly and, as the seed production areas and seed orchards described earlier in this chapter become more productive, an increasing quantity of seed and plants of superior provenances and improved cultivars will be available for general use. The efforts of forest geneticists and tree breeders will be largely nullified unless certification procedures are available to maintain the genetic purity and quality of the seed and plants.
Categories of seed and plants
Four broad categories of tree seed and plants are moving in national and international trade (Isaac, 1960; Sweden, 1951) and these categories are distinguished by the precision with which origin is described; the degree of selection of the seed trees and their isolation from foreign pollen; whether the offspring of the seed trees have been tested or not; the amount of supervision and independent inspection of seed collection, processing and storage, and plant production; and the standards of record keeping and labeling. It is convenient to describe these four categories of seed and plants in ascending order of genetic value.
1. Unclassified seed and plants. The origin of this category is unknown or inadequately described, or the seed has been collected in stands not classed as seed sources by a recognized agency because of poor quality of the trees or lack of isolation from inferior trees of the same or closely related species. Unclassified seed is largely collected from felled or stunted trees and the seed, and plants are collected, raised and marketed with little or no supervision. The object of every country is to discard this category of seed and plants as rapidly as possible.2. Source-identified seed and plants. This category is derived from good natural stands and plantations registered as seed sources by a competent service. The place or region where the seed is collected is clearly defined; the seed is harvested, processed and stored and the plants are raised under supervision and independent inspection; the labeling is adequate and records are available for inspection.
3. Selected seed and plants. The seed is collected from carefully selected seed trees growing in natural stands and plantations classified as better than average and registered by a competent service. Trees that do not conform to stated standards of growth rate, stem and crown form, branching habit, health and other characters are removed as rapidly as possible from within the stand and from an isolation surround of prescribed width. These seed stands or seed production areas are also treated to increase seed production by means of fertilizer applications and protective measures against the animals, insects and fungi that damage seed. The statements made for source-identified seed about supervision, independent inspection, labeling and records also apply to selected seed.
4. Certified seed and plants. This category is derived mainly from clonal seed trees in seed orchards (and also from elite trees and stands) whose genetic superiority has been proved by progeny testing to standards defined by a competent service: Certified seed and plants are produced in a manner that insures genetic identity and proved interspecific hybrids may be included in this category. Clonal seed orchards contain highly selected clones arranged to favor cross-pollination. The site is well isolated from pollen of inferior trees of the same or closely related species. Certified seed is harvested, processed and stored, and certified plants are raised under supervision and independent inspection. The labeling is adequate and records are available for inspection. In particular, the exact sources of the individual components of the seed orchards and the results of progeny testing must be readily available (Wakeley, 1960). Seed collected from seed orchards before progeny testing is completed is sometimes sold as plus or selected seed.
TABLE 9. - PROGRESS OF THIRTY COUNTRIES TOWARD NATIONAL CERTIFICATION SCHEMES
|
Country |
Provenance research |
Classified list of provenances |
Zoning scheme |
Register of seed resources |
Seed production areas |
Seed orchards |
Full certification schemes |
|
Australia |
X |
X |
X |
X |
X |
X |
|
|
Austria |
X |
X |
X |
X |
X |
X |
|
|
Belgium |
X |
X |
X |
X |
X |
|
X |
|
Canada 1 |
X |
X |
X |
X |
X |
X |
|
|
Czechoslovakia |
X |
X |
X |
X |
X |
|
X |
|
Denmark |
X |
X |
|
X |
X |
X |
X |
|
Finland |
X |
X |
X |
X |
X |
X |
X |
|
France |
X |
X |
|
X |
X |
X |
|
|
Germany, East |
X |
|
X |
X |
X |
X |
X |
|
Germany, Fed. Rep. of |
X |
X |
X |
X |
X |
X |
X |
|
Hungary |
X |
|
X |
|
X |
X |
|
|
Ireland ² |
X |
X |
|
X |
X |
|
|
|
Italy |
X |
X |
X |
X |
X |
|
|
|
Japan |
X |
X |
X |
X |
X |
|
X |
|
Mexico |
|
|
|
X |
X |
|
|
|
Netherlands |
X |
X |
|
X |
X |
X |
X |
|
New Zealand |
X |
X |
|
X |
X |
X |
|
|
Norway |
X |
X |
X |
X |
X |
X |
X |
|
Poland |
X |
|
X |
X |
X |
|
X |
|
Portugal |
|
|
|
|
|
|
|
|
Romania |
X |
|
|
X |
X |
|
|
|
South Korea |
X |
X |
|
X |
X |
X |
|
|
Spain |
|
|
|
X |
|
|
|
|
Sweden |
X |
X |
X |
X |
X |
X |
X |
|
Switzerland |
X |
X |
X |
X |
X |
|
X |
|
Turkey |
|
|
|
|
|
|
|
|
United Kingdom |
X |
X |
X |
X |
X |
X |
X |
|
United States ³ |
X |
X |
X |
X |
X |
X |
X |
|
U.S.S.R. |
X |
X |
X |
X |
X |
|
X |
|
Yugoslavia |
X |
|
|
X |
X |
|
|
1 The information for Canada refers to eastern Canada, particularly Ontario.
² Provenances suitable for use in the United Kingdom generally succeed also in Ireland.
³ The information for the United States of America refers to eastern and southern states, particularly New York, Georgia, South Carolina, Alabama.
NOTE: A blank in this table indicates that information was not available to the author on 31 December 1963.
Administrative control of seed and plant production
It is believed that there are 12 comprehensive national certification schemes (Table 9) and these can be grouped into 3 classes: voluntary schemes operated by independent seed associations; voluntary schemes operated by state forest services; and compulsory schemes operated by state forest services. The Czechoslovakian and Polish procedures (Koospol, 1961; Paged, 1962; Tyzkiewicz, 1950) are based on virtual state monopoly of tree seed and plant production, both for internal use and export. In the other countries with certification schemes, particularly the United States and central and northern Europe, there is a strong private seed and nursery trade. In the Federal Republic of Germany the Federal Seed Act of 1957 provides legal backing for a full official certification service (Langner, 1963; Hermann and Astinet, 1961; Astinet, 1961; Rossmässler, 1961). The scheme used in Georgia, U.S.A., is backed by two state laws but is voluntary (Barber and Darby, 1959; Georgia Crop Improvement Association, 1958); it is based on widely accepted procedures sponsored in the United States by the International Crop Improvement Association (ICIA, 1959; Society of American Foresters, 1961; Rudolf, 1963). In Finland (Kärki, 1961) and the Netherlands (van Vloten, 1957), there are private tree breeding associations that gain a good part of their revenue from the sale of certified seed and plants.
Those certifying agencies operated by independent associations (as, for example, those in Denmark and the United Kingdom) are directed by a seed board or management committee elected by and representing the seed and nursery trade, forest owners, the state forest service and forest research institutes (including the seed testing agency). An important principle is that the purchasers of seed and plants should be represented. The management committee decides policy, sets up rules governing the certification program and has a professional forester as executive secretary or manager (Larsen, 1960).
The voluntary certification agencies operated by state forest services usually have an officially-appointed supervisor who is responsible for the certification program under the direction of an appointed board that determines policy and sets up rules. Compulsory certification schemes are based on seed laws and are operated by the state agencies named under the seed laws.
Most certification schemes are nonprofit-making and largely financed by fees paid by the seed producers and nursery trade. These fees usually include a forest or nursery charge and an area inspection fee. Additional charges may be levied by means of official stamps or labels provided to the merchant by the certifying agency at a predetermined unit cost. The selling price of seed and plants of the superior categories is increased, often considerably, but the cost of seed is a very small fraction of total establishment costs and it can be shown (see Faulkner, 1962) that small increases in yield justify large increases in seed prices.
An outline national certification
The elements of a comprehensive national certification scheme for forest seed and plants are as follows:
1. Inspection of the seed source by a qualified professional forester before pollination of the seed crop. At this time (which is from 6 to 21 months before seed collection) the quality of the seed trees, incidence of inferior trees and effectiveness of the isolation can be checked. Many forest trees do not produce seed every year and, after the first inspection, subsequent re-inspections are made only in years when seed is to be collected (the longest interval being about 5 years).2. Assessment, if possible, of the cone or fruit crop by a qualified professional forester at a stated time (about 90 days) before collection begins.
3. Collection of the cones of fruits by a registered seed collector; extraction, cleaning and packaging of the seed at a registered seed extraction plant; and storage of the seed at a registered seed store. The records of collection, processing and storage are made available for inspection and the labels must conform to minimum requirements.
4. Testing, under the rules of the International Seed Testing Association, of an adequate sample of the seed at an official seed testing station.
5. Sowing of the seed in a registered nursery where labels and records satisfy minimum requirements. Inspection of the seedlings and transplants should be made by a qualified professional forester before they are lifted and dispatched.
Although growing-on tests are not yet widely used, the progress of research in several countries holds promise of their eventual use on a wide scale.
Minimum requirements for certification of seed and plants
The prescriptions that follow have been derived from the published accounts of national certification schemes in 12 countries. The prescriptions also incorporate relevant details from the scheme for the varietal certification of herbage seed sponsored by the Organization for Economic Co-operation and Development (OECD, 1961).
Previous history of the seed source. A seed stand or seed production area may be formed in a natural stand (established by natural regeneration) or plantation (established by planting or sowing) of indigenous, introduced or unknown origin. In some countries, such as Czechoslovakia, France, the Federal Republic of Germany, Poland and Switzerland, determined efforts are being made to preserve and use the indigenous growing stock (Bouvarel, 1958; Schmidt, 1954; Stern, 1956). In other countries the replacement of the indigenous growing stock by introduced species and provenances is very advanced and the exotic material must be accepted. Finally, some countries exclude from their certification schemes any stands of unknown origin, but although this is desirable it is not always practicable.
Isolation from foreign pollen. The requirements for isolation of seed production areas and seed orchards from large stands of inferior trees of the same or closely related species and for the width of isolation strips vary somewhat with species and country, but a generalized prescription for seed production areas and seed orchards is: 1,000 meters (1,100 yards) from a large stand of inferior trees and 100 to 150 meters (110 to 165 yards) from the nearest inferior tree - thus fixing the width of the isolation strip.
Field inspection of seed trees, seed crop and plants: Inspection of seed sources, seed production areas and seed orchards is most often made by the state forest service or by qualified professional foresters nominated by the certifying agency. The standards for seed production areas are based on the number of vigorous, well-formed and healthy seed trees per hectare and removal of inferior trees. Inferior trees are marked by the inspector and if possible felled while he is in the area, but the rate at which inferior trees are removed is often determined by local silvicultural requirements and re-inspection may be necessary when the fellings are completed.
During seed collection and processing, the cones, fruit and seed must be handled so as to prevent mixture and maintain identity. Similarly, mixture must be prevented and identity maintained in the seed store and when raising plants in the nursery.
Standards for germination and purity. The methods of determining purity, germination and moisture content and the standards of health supervision with regard to seed-borne pests and diseases are generally based on those set by the Forest Tree Seeds Committee of the International Seed Testing Association (ISTA) Standards of germination and purity for purposes of sowing the seed and getting a good yield of plants are available for a very wide range of species (ISTA, 1959, 1962).
Labels and certificates. It is generally agreed that the amount of information required on labels should be kept within reasonable bounds, and a number of distinctive yet simple labels are in use. Most of these bear the following items of information:
Species (Latin name)
Subspecies variety or cultivar name
Category (source-identified, selected, certified)
Provenance (reference number, place or region, elevation)
Supplier (name and address)
Seed (month and year of crop, quantity)
Plants (age or size, quantity).
In 1950, FAO and IUFRO (FAO, 1952) jointly prepared an international certificate of origin and quality for tree seed and plants and this carries a large amount of information. This certificate has great value in exchanges of small quantities of seed for provenance research, but something simpler is needed for bulk trading in tree seed and plants. Such a certificate would bear the following items:
Certifying agency
Consignee (name and address)
Sender (name and address)
Species (latin name)
Subspecies variety or cultivar name
Category (source-identified, selected, certified)
Provenance (reference number, place or region, elevation)
Gross weight of packages
Contents (seed or plants, quantity)
Disinfection treatment (date, place, method).
Reference numbers. Comprehensive yet simple methods of identifying the origin of seed and plants by means of reference numbers or letters are of great assistance in administering a comprehensive certification scheme. FAO has adopted the universal decimal classification system by which each country is identified by a permanent number consisting of three digits (FAO, 1961).
Certification of forest tree seed and plants moving in international trade
Rohmeder (1960) points out that tree seed moves in national or international trade for three main reasons:
1. in large quantities for large-scale cultivation of a species, provenance or cultivar, as, for example, in Pseudotsuga taxifolia, Pinus radiata, Tectona grandis and Eucalyptus;2. in small quantities for research purposes, such as species trials, provenance tests, progeny tests and tests of cultivars produced by selection and breeding;
3. as an item of food, such as chestnuts (Castanea sativa) walnuts (Juglans regia) or olives (Olea europaea).
The discussion that follows deals entirely with the first situation and is intended to refer to both seed and plants.
In Europe there has been regular and extensive international trade in seed and plants of Pinus sylvestris, Picea babies, Larix decidua and Abies alba for a very long time. Now there is extensive trading in tree seed between North America and Europe in the coniferous and broadleaved trees of the northern temperate zone, important examples being Pinus contorta, Pinus nigra, Picea sitchensis and Pseudotsuga taxifolia. Looking further afield, the Eucalyptus species and subtropical pines are playing a rapidly increasing part in afforestation in the Mediterranean region, central and southern Africa, South America, and the Asia and Pacific region. Finally, two tropical species deserve mention, namely the Honduras mahogany (Swietenia macrophylla) and teak (Tectona grandis), seed of which is moving extensively between tropical countries of Africa and Asia. A summary of the movement of seed and plants of 22 important species is given in Table 6. For phytosanitary reasons, the movement of tree seed is more extensive than the movement of plants.
Six international bodies are active in matters affecting trading in forest tree seed and plants:
1. The Forest Seeds Committee of the International Seed Testing Association have developed rules for testing the quality of tree seed (ISTA, 1959, 1962).2. Section 22 of the International Union of Forest Research Organizations continues to sponsor international provenance research.
3. FAO has consistently sponsored improved records for use in the international exchange of tree seed, and organized the World Consultation on Forest Genetics and Tree Improvement to foster the use of genetically superior tree seed and plants.
4. The International Crop Improvement Association in the United States has supported specific standards for certifying the origin of forest tree seed, drawn up by the Society of American Foresters (SAF, 1961; Rudolf, 1963).
5. Foresters of countries in the European Economic Community have agreed rules for trading in forest tree seed and plants.
6. The Organization for Economic Co-operation and Development (OECD) has sponsored schemes for the certification of agricultural seeds.
The work of these international organizations suggests that the time is coming when internationally acceptable seed certification standards can be framed for forest tree seed and plants. The first steps have recently been taken by OECD which has provided funds to enable a working group to prepare the necessary draft rules and directives for consideration by all member countries.
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