DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 1-2/1966 str. 74 <-- 74 --> PDF|
PRESERVATION OF GENE POOL IN FOREST TREE POPULATIONS
Government Forest Experiment Station, Kyusyu Branch, Kumamoto, Japan.
It is not necessary to say much about the importance of the protection
against loss of useful genes under the influence of tree breeding programs and
intensive forest management. Breeding always involves selection which results
in the loss of some genes. By selection, we intend, of course, to retain favorable
genes and to discard unfavorable ones, but it is inevitable that many useful
but still unknown genes may be lost in the process. Favorable genes are also
lost through the negative selection which is rather commonly practiced in
commercial forestry. It is, therefore, urgently needed that some action be taken
to prevent the extinction of the hidden genes and to keep the gene pool large
enough for future improvements.
There are two ways to obtain this goal: one is the conservation of mature
stands, either natural or artificial, and the other is establishing special new
stands for the preservation of a broad gene pool.
The first could be said to be a static method. It does not require any
actual operation other than preserving nice stands in virgin forests or excellent
plantations. Each reserve stand should desirably be made up of more than ten
thousand individuals, which must be excluded from commercial utilization.
Because of the large numbers of trees needed, there is considerable opposition
against such reservation, and it is very difficult to designate such stands solely
for use in forest genetics. Therefore, any stand reserves must be connected
with natural protection promoted from the view point of public health,
recreation, protection of wild life and natural monuments.
The second method involving establishment of special stands is a dynamic
one. Here, there is no need to reserve stands from a commercial forest, but
it is only necessary to collect seeds from superior stands and to establish new
stands from these. The newly established stands can then be commercially
utilized when they become mature after the next generation has been established
from their seeds. It is not difficult, therefore, to get support of the commercial
forest management organizations for this approach.
In a population for which the gene pool is to be preserved, seeds must
be collected in a rich seed year on scattered seed trees. There should be forty,
fifty or more such trees, each better than average in vigor and quality. Trees
not selected as seed trees contribute their genes to the next generation through
their pollen. Selecting this many mother trees in every generation should
involve little risk of inbreeding in later generations (Stern , 1959). If the
|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
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,
|ŠUMARSKI LIST 1-2/1966 str. 76 <-- 76 --> PDF|
because (1) the performances expected at older ages are still not known, (2)
inferior individuals have not yet been rogued and they contribute inferior
genes to the population. However, in the case of gene preservation plantations,
these points do not apply. Here the objective is to collect seeds from the
registered plantations with the minimum loss of genes. Therefore, the seeds
should be collected as soon as the stands reach full sexual maturity.
Besides the four major conifers, we have several tree species which are
harvested in natural forests and are desired in the market but are not planted.
Some of them supply rather large quantities of timber, such as Abies firma,
Tsuga sieboldii, Castanopsis cuspidata, and Machilus thunbergii. Others, such
as Sciadopitis verticillata, Torreya nucifera, Betula grossa, Quercus gilva,
Zelkova serrata, Cercidiphyllum japonicum, Cinnamomum camphora, and
Fraxinus sieboldiana, are rather scarce but produce timber of good quality.
Natural stands usually show much smaller increments of standing crops than
artificial plantations, so they are being rapidly replaced with the latter.
Although there are still fairly large stands of naturally regenerated second
growth, it is quite seldom that superior specimens of these species are able
to establish their offspring. Because of this, the preservation of the gene pool
is urgently needed. In fact, it is already too late for some species such as
T°rreya nucifera, of which almost all of larger specimen has been felled
For those species such as Abies firma or Castanopsis cuspidata which appear
more commonly in the form of almost pure stand, the same method of
sampling as for planted stands can be employed. For the species of rare
occurrence, it is necessary to select a sufficient number of seed trees throughout
a wider region in order to avoid considerable inbreeding.
It is well known that an isolated group of a few individuals have a high
degree of inbreeding, which increases generation by generation, until little
genetic variation is shown within the group (Sewall Wright efect). In such
cases, only a small area is needed for the preservation of each small population,
but the desirable procedure is to obtain wide genetic variation by mixing
several populations into a single plantation.
The species which are not often planted are usually slow-growers and
require large dimensions for their commercial maturity. Therefore, they have
to be retained far longer than the usually planted conifers.Such slow growth
is the main reason why these valuable species have not been artificially
propagated, and it makes it difficult, at the same time, to get an area of forest
land to plant the seedlings for gene preservation. In the authors opinion, the
best place to grow them is on the protection belts which separate commercial
plantations and consist of natural vegetations. The belt is used as a safeguard
of the plantation against fire or pests and, in total, amounts to very large
areas. It is, therefore, favorable not only from the genetic point of view but
also from the commercial one that the seedlings of these valuable species are
planted mixed with natural second growth, because the operation will give
increased quality products.
Unfortunately, we have not yet been able to start such a program, but
there are good prospects to do so soon.
Finally, we have to discuss the analysis of the genetic variation of the
populations. From the view point of gene preservation only, it is not necessary
to distinguish seeds from individual seed trees, but it is not difficult to collect
|ŠUMARSKI LIST 1-2/1966 str. 77 <-- 77 --> PDF|
and sow the seeds separately. It has been proven that these single tree progenies
are very valuable as the materials for studying the genetic nature of populations.
Therefore, the author wishes to recommend the parallel establishment of
progeny trial for each population, so that the information about the genetic
nature of the population will be available along with the major function of
acting as a gene pool. However, for the purpose of simplifying the work, many
of our early plantations were not accompanied by such progeny trials.
The author wishes to express his thanks to Professor Bruce Zobel who
has kindly read and corrected the manuscript.
SAČUVANJE GENOFONDA U POPULACIJAMA ŠUMSKOG DRVEĆA
Postoje dva načina da se genofond šumskog drveća sačuva: 1. konzervacijom
/relih sastojina, bilo prirodnih ili umjetnih; 2. podizanjem specijalnih novih sastoiina.
Za prvu metodu može se reći da je statička. Kod nje se ne zahtijeva nikakva
druga operacija osim sačuvanje lijepih sastojina u prirodnim šumama ili izvrsnim
nasadima. Svaka takva sastojina, koja treba da se sačuva mora sadržavati više od
deset hiljada individua. Zbog velikog broja stabala vrlo je teško sačuvanje takvih
sastojina samo u genetske svrhe pa se to povezuje sa zaštitom prirode i divljači, rekreacijom
Druga metoda je po svojim osobinama dinamična. Kod nje nije potrebno da se
sastojine zaštite od komercijalnih zahvata, nego se samo sakupi sjeme iz najboljih
sastojina i od toga sjemena se podižu nove sastojine. Takve novopodignute sastojine
mogu se iskorišćavati kada dostignu svoju dob zrelosti, ali nakon toga što se prethodno
od njih pomoću sjemena uzgoji slijedeća generacija. Zbog toga nije teško
dobiti podršku šumarske operative za takav rad.
U populaciji čiji genofond treba sačuvati sjeme se sakuplja u godini bogatog
uroda sa stabala koja su raštrkana po čitavoj površini. U sastojini treba da se nalazi
po četrdeset, pedeset ili više takvih stabala od kojih je svako bolje i u rastu i
kvaliteti od prosjeka. Stabla s kojih se ne sabire sjeme prenose svoje gene na slijedeću
generaciju putem polena. Ako se odabiru majčinska stabla u svakoj generaciji,
postoji mali riziko inbridinga u kasnijim generacijama. Novi nasadi trebaju sadržavati
velik broj individua budući da neki korisni geni maju vrlo malu frekvenciju
npr. 0,01 posto ili manje. Površina na kojoj bi moglo rasti više desetina hiljada individua
treba imati maksimalno deset do dvadeset hektara. Nasadi trebaju biti podijeljeni
u dvije ili tri plohe koje su dovoljno udaljene jedna od druge. Pojedinačne
plohe ne smiju biti manje od dva ili tri hektara. Na otoku Kyusyu u Japanu radi se
od 1958. godine na podizanju nasada od Cryptomeria japonica, Charnaecyparis obtusa,
Pinus thunbergii i Pinus densiflora.
Ako postoje male izolirane grupe jedne vrste drveća, u tom slučaju dolazi u vi
sokom stepenu do inbridinga. Zbog toga se malene populacije ne mogu sačuvati od
inbridinga te je u takvim slučajevima potrebno podići nasade ne od pojedinačnih
populacija već od mješavine više populacija.
Na kraju je razmatrana mogućnost analiziranja genetskih varijacija unutar po
pulacija. Ukoliko se sjeme sabire odvojeno sa svakog stabla te tako uzgoji potom
stvo, ono će biti i veoma vrijedan materijal za izučavanje genetske prirode tih po
pulacija. Zbog toga autor preporučuje paralelno postavljanje test potomstva za svaku
Stern , K.: Der Inzuchtgrad in Nachkommenschaften von Samenplantagen. Silvae
Genetica 8(2): 37—42. 1959.