DIGITALNA ARHIVA ŠUMARSKOG LISTA
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| ŠUMARSKI LIST 1-2/1966 str. 75 <-- 75 --> PDF |
mother trees were well scattered throughout the population, but not scattered too sparsely, we could then transfer nearly completely the gene pool of the population into the seed lot. The new platnations should include a large number of individuals. Since some of the useful genes may show very low frequencies such as 10~2 per cent or less, it is evident that a large number of individuals is desirable. But the productivity of such stands are not as large as those of the stands established with the seeds of elite seed orchards, because the former have not passed through selections as intensive as the latter. Therefore, the establishment of too large plantations of such purpose is not desirable from the viewpoint of commercial forestry. Ten to twenty hectares must be the maximum on which several ten thousand individuals can be grown. The plantations should be divided into two or three plots and be located apart from each other, to avoid total destruction by accidents. Individual plots should be no smaller than two or three hectares. If the preservation of specific genes is the objective in the plantation, smaller size plots may be acceptable, but, on the other hand, the conservation of the total gene pool requires larger plots because the peripheral members of the stands cannot be used as seed trees for the next generation because of contamination from foreign pollen. In Kyusyu, the south-western most major island of Japan, we have been making efforts to establish gene preservation stands since 1958. The efforts have been concentrated on the four main conifers, Cryptomeria japonica, Chamaecyparis obtusa, Pinus thunbergii and Pinus densiflora, which constitute the bulk of all plantations in this area. Cryptomeria and Chamaecyparis are not naturally distributed in Kyusyu, with rare exceptions. Populations were selected, such as (1) ones exhibiting very good performance, (2) fairly old plantations, (3) plantations famous for some special characteristic, and (4) undisturbed natural stands. As for the two pines, on the other hand, there are many natural stands and naturally regenerated second growth, so the effort was concentrated in natural populations of nice growth and gcod tree from. However, nice plantations were also sampled as well. Seeds have been harvested from six stands of Cryptomeria, two of Chamaecyparis, five of P. thunbergii and two of P. densiflora. These seeds were sown in the nursery of Kyusyu Forest Tree Breeding Station at Kumamoto. The seedlings were divided into two lots for each population, one being sent back to the original Forest Districts and the second to some other Districts. They were planted by the State Forest agents in a manner similar to usual commercial plantations. Unfortunately, the total area for each population has been too small, five to eight hectares. Sometimes, mistakes occurred, for instance, when two lots of seedlings of different origin were sent to one District, they were planted together in the same plot, making it impossible to get second generation seeds of the characteristic gene pool for the two populations separately. These plantings are not yet enough for Kyusyu and must be expanded. In the other parts of Japan, similar work has been started more recently. The »gene pool« plantations are registered and their development is observed periodically. The stands will be harvested when they have reached commercial maturity. The time for collecting second generation seeds needs special considerations. In general, young stands do not supply suitable seed, |