DIGITALNA ARHIVA ŠUMARSKOG LISTA
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|ŠUMARSKI LIST 1-2/1966 str. 93 <-- 93 --> PDF|
correspond to the time when the trees have reached a period of steady increment
in growth, and therefore the future performance is predictable.
From the juvenile/mature correlations established so far it appears that
at the time corresponding to 1/3 of the rotation age the quality and growth of
trees can be predicted for the rest of the rotation. This is the criterion used
in Sweden for the evaluation of the genetic value of different progenies
Thus it would apear that not earlier than at the respective ages of about
30 and 35 years for pine and spruce it is possible to obtain information about
the quality and productivity of the different provenances.
Question 3. What is the minimum number of trees needed to reconstruct a population
for production purposes?
The most obvious way of reconstructing a population is by means of
establishing a seed orchard from the available trees. All seed orchards already
in existance are too young to give reliable information on the optimum number
of clones for commercial seed production. To provide sufficient genetic
variability in the resultant population the number of clones should not be
Andersson (1963) suggests that there should be 36—60 clones per
Matthews (1964) considers 20 or 30 trees as an acceptable minimum
number of trees in a seed orchard composed of plus trees. These are only
estimates and they may be too optimistic. The more clones in a seed orchard,
the greater the variability in the resultant population.
Since seed orchards established from plus trees are likely to yield more
elite seed than those established from trees remaining on the experimental plots
of the best provenance, there must be some scope left for the thinning of clones
in the seed orchard.
Thus I would suggest that 40 is the minimum number of trees that have
to remain per provenance at the time of establishment of a seed orchard from
the provenance trial.
Question 4. What is the maximum forest area that can be assigned to a provenance
The two basic criteria that have to be considered before answering such
a question are site uniformity and conformance with sound silvicultural
In Polish forestry regulations (Ministerstwo Lesnictwa 1961) it is specified
that clear fellings should cover no more than 6 ha in one belt with a maximum
width of 80 m.
Generally, compartments in Polish forestry are of the order of 25 ha.
These are divided into sub-compartments on the basis of site conditions. As far
as possible every difference in site requiring a different silvicultural treatment
or a different species composition is delimited into a sub-compartment. A
provenance experiment should be located within one sub-compartment, and it
should be rectangular in shape.
Thus it is not likely that more than 5 ha. could be found for one trial area,
but usually less.